1:250 000 - IIS Windows Server - Northern Territory Government

NORTHERN TERRITORY GEOLOGICAL SURVEY
1:250 000
Geological
Map Series
Explanatory Notes
MOUNT DRUMMOND SE 53-12
DJ RAWLINGS, IP SWEET
and PD KRUSE
135°00'
17°00'
139°30'
17°00'
CALVERT
HILLS
WALHALLOW
SE 53-07
SE 53-11
SE 54-05
SE 53-08
BOXER
6261
BRUNETTE
DOWNS
WESTMORELAND
BENMARA CLEANSKIN
6361
6461
MOUNT
DRUMMOND
LAWN HILL
SE 54-09
SE 53-12
MITTIBAH MITCHIEBO CARRARA
6260
6360
6460
CAMOOWEAL
SE 54-13
NT
RANKEN
SE 53-16
20°00'
135°00'
QLD
ALROY
SE 53-15
20°00'
139°30'
DEPARTMENT OF PRIMARY INDUSTRY, FISHERIES AND MINES
MINISTER: Hon Chris Natt, MLA
CHIEF EXECUTIVE: John Carroll
NORTHERN TERRITORY GEOLOGICAL SURVEY
DIRECTOR: Ian Scrimgeour
Rawlings DJ1, Sweet IP2 and Kruse PD
Mount Drummond, Northern Territory. 1:250 000 geological map series explanatory notes, SE 53-12
BIBLIOGRAPHIC REFERENCE: Rawlings DJ, Sweet IP and Kruse PD, 2008. Mount Drummond, Northern Territory.
1:250 000 geological map series explanatory notes, SE 53-12. Northern Territory Geological Survey, Darwin.
(1:250 000 geological map series, ISSN 0814-7485)
Bibliography
ISBN: 978-0-7245-7162-8
Keywords: Northern Territory, Mount Drummond, Murphy Inlier, Lawn Hill Platform, South Nicholson Basin, Georgina
Basin, Dunmarra Basin, geological mapping, sedimentary geology, stratigraphy, structural geology, economic geology,
geochemistry, geophysics, Palaeoproterozoic, Mesoproterozoic, Neoproterozoic, Cambrian, Cretaceous, Cenozoic.
EDITORS: TJ Munson and KJ Johnston
Northern Territory Geological Survey
3rd floor Paspalis Centrepoint Building
Smith Street Mall, Darwin
GPO Box 3000
Darwin NT 0801, Australia
Arid Zone Research Institute
South Stuart Highway, Alice Springs
GPO Box 8760
Alice Springs NT 0871, Australia
For further information contact:
Minerals and Energy Information Centre
Phone +61 8 8999 6443
Website: http://www.minerals.nt.gov.au/ntgs
Email: [email protected]
1
2
Centre for Ore Deposit Research, University of Tasmania, GPO Box 252-79, Hobart TAS 7001. Currently at: Toro Energy Ltd,
3 Boskenna Ave Norwood SA 5067 (formerly Northern Territory Geological Survey).
31 Courtice Close, Fadden ACT 2904.
© Northern Territory Government, April 2008
Disclaimer
While all care has been taken to ensure that information contained in Mount Drummond 1:250 000 geological map series
explanatory notes is true and correct at the time of publication, changes in circumstances after the time of publication may
impact on the accuracy of its information. The Northern Territory of Australia gives no warranty or assurance, and makes no
representation as to the accuracy of any information or advice contained in Mount Drummond 1:250 000 geological map
series explanatory notes, or that it is suitable for your intended use. You should not rely upon information in this publication
for the purpose of making any serious business or investment decisions without obtaining independent and/or professional
advice in relation to your particular situation. The Northern Territory of Australia disclaims any liability or responsibility or
duty of care towards any person for loss or damage caused by any use of, or reliance on the information contained in this
publication.
ii
CONTENTS
Border Waterhole Formation (_Cmo) ........................ 64
Currant Bush Limestone (_Cmc) ............................... 64
Barkly Group ................................................................ 65
Wonarah Formation (_Cmw) ..................................... 65
Ranken Limestone (_Cmk) ........................................ 66
Camooweal Dolostone (_Cmd) .................................. 66
Mesozoic: Dunmarra Basin .............................................. 68
Undivided Cretaceous (Kl) ....................................... 68
Cenozoic........................................................................... 68
Cleanskin beds (Tl)................................................... 68
Palaeogene–Neogene (Cz, Czl, Czm, Czs, Czb, Czz) ....... 69
Quaternary (Qa)........................................................ 70
Geophysics....................................................................... 70
Structure.......................................................................... 71
Economic geology ........................................................... 73
Iron ............................................................................... 73
Base metals ................................................................... 73
Manganese.................................................................... 74
Phosphate...................................................................... 75
Diamonds...................................................................... 75
Petroleum...................................................................... 76
Other commodities ....................................................... 77
Groundwater ................................................................. 77
Geochemistry .................................................................. 77
Geological history ........................................................... 77
Acknowledgements ......................................................... 78
References ....................................................................... 78
Appendix 1 – New and revised stratigraphic names ... 86
Appendix 2 – Whole-rock geochemistry ..................... 102
Appendix 3 – Stream sediment geochemistry ............ 102
Abstract ............................................................................. v
Introduction ...................................................................... 1
Location, access and land use ......................................... 1
Physiography .................................................................. 1
Climate and vegetation ................................................... 2
Previous geoscientific investigations.............................. 3
Methodology................................................................... 3
Related publications and datasets ................................... 3
Terminology ................................................................... 4
Mapping conventions...................................................... 5
Regional geological setting ............................................... 5
Stratigraphy ...................................................................... 8
Palaeoproterozoic (Orosirian): Murphy Inlier .................... 8
Murphy Metamorphics (L
Plm) ..................................... 8
Connelly Volcanics (P
Llc)............................................ 8
Palaeoproterozoic (Statherian)–Mesoproterozoic
(Calymmian): Lawn Hill Platform.................................... 10
Carrara Range Group.................................................... 11
Don Creek Sandstone (P
Lcd)...................................... 12
Mitchiebo Volcanics (P
Lcm) ...................................... 13
Gator Sandstone (P
Lcg).............................................. 13
Top Rocky Rhyolite (P
Lct)......................................... 14
Benmara Group............................................................. 17
Breakfast Sandstone (P
Lbr) ........................................ 17
Buddycurrawa Volcanics (P
Lbb)................................ 17
Unassigned to group ..................................................... 19
Surprise Creek Formation (L
Pr).................................. 19
McNamara Group ......................................................... 21
Drummond Formation (L
Pmd) ................................... 21
Brumby Formation (L
Pmb)......................................... 24
Shady Bore Quartzite (L
Pms) ..................................... 26
Bullrush Conglomerate (L
Pmu) .................................. 26
Plain Creek Formation (L
Pma) ................................... 27
Lawn Hill Formation (L
Pmh) ..................................... 29
Synthesis of McNamara Group................................. 30
Fickling Group.............................................................. 30
Doomadgee Formation (L
Pfd) .................................... 31
Age and correlations of Surprise Creek
Formation and McNamara and Fickling groups ........... 32
Mesoproterozoic (Calymmian): South Nicholson
Basin................................................................................. 34
Caulfield beds ........................................................... 34
South Nicholson Group ................................................ 36
Wild Cow Subgroup ..................................................... 37
Playford Sandstone (P
Lsa).......................................... 37
Bowgan Sandstone (L
Psb) .......................................... 42
Crow Formation (P
Lso) .............................................. 43
Accident Subgroup ....................................................... 50
Constance Sandstone (L
Psc) ....................................... 50
Mittiebah Sandstone (P
Lsi)......................................... 54
Mullera Formation (P
Lsm) ......................................... 57
Neoproterozoic (Ediacaran) to Cambrian:
Georgina Basin ................................................................. 60
Kiana Group ................................................................. 60
Bukalara Sandstone (P
Lu) .......................................... 60
Kalkarindji Volcanic Group.......................................... 61
Helen Springs Volcanics (_Clp)................................. 62
Narpa Group ................................................................. 63
FIGURES
1.
2.
3.
4.
5.
6.
Location of MOUNT DRUMMOND ........................... 1
Geomorphic provinces .................................................. 2
Regional geological setting........................................... 6
Regional tectonic framework ........................................ 7
Stratigraphic columns ................................................... 9
Murphy Metamorphics: metasiltstone and
metagreywacke ........................................................... 11
7. Murphy Metamorphics: banded iron formation .......... 11
8. Summary of stratigraphic nomenclature for Lawn
Hill Platform ............................................................... 12
9. Don Creek Sandstone: quartzose sandstone................ 13
10. Mitchiebo Volcanics: peperite breccia........................ 14
11. Top Rocky Rhyolite: lithophysae ............................... 16
12. Top Rocky Rhyolite: stacked quartz folia................... 16
13. Top Rocky Rhyolite: autobreccia ............................... 16
14. Top Rocky Rhyolite: boulder conglomerate ............... 17
15. Buddycurrawa Volcanics: debris-flow facies ............. 19
16. Buddycurrawa Volcanics: chertified carbonate .......... 19
17. Buddycurrawa Volcanics: chert in ferruginous
sandstone and siltstone................................................ 20
18. Surprise Creek Formation: coarse pebble to cobble
conglomerate............................................................... 20
19. Surprise Creek Formation: sublithic sandstone........... 21
20. Drummond Formation: stromatolitic chert ................. 23
21. Drummond Formation: shale outcrop ......................... 24
iii
22. Brumby Formation: type section in Carrara Range..... 25
23. Plain Creek Formation: alternating mudstone
and sandstone beds ..................................................... 28
24. Plain Creek Formation: tool marks and flute casts ..... 28
25. Thickness summary for McNamara Group................. 31
26. Doomadgee Formation: load casts .............................. 32
27. Gamma ray log summary from Carrara Range
measured sections with interpreted correlations ......... 33
28. Caulfield beds: strongly banded outcrop..................... 34
29. Caulfield beds: pebbly sandstone................................ 35
30. Caulfield beds: tor-like outcrop habit ......................... 35
31. Wangalinji Member of Playford Sandstone:
pseudomorphs, probably after gypsum ...................... 41
32: Top Lily Sandstone Member of Playford Sandstone:
very large-scale cross-beds ......................................... 41
33. Top Lily Sandstone Member of Playford Sandstone:
convolute bedding....................................................... 41
34. Contact between Top Lily Sandstone and No Mans
Sandstone members of Playford Sandstone ............... 42
35. Unconformity between Crow Formation and
Constance Sandstone .................................................. 44
36. Tobacco Member of Crow Formation: deepshelf facies .................................................................. 44
37. Crow Formation: thinly bedded siltstone and
sandstone..................................................................... 44
38. Crow Formation: polymict pebble conglomerate........ 46
39. Crow Formation: granule to pebble conglomerate...... 46
40. Crow Formation: sandstone turbidite facies................ 46
41. Tobacco Member of Crow Formation: shallowwater sandstone facies................................................. 47
42. Crow Formation: parting (current)
lineations in sandstone ................................................ 47
43. Tobacco Member of Crow Formation: quartzose
sandstone with amalgamated HCS.............................. 47
44. Tobacco Member of Crow Formation: lithic
micaceous sandstone with HCS .................................. 48
45. Crow Formation: saprolite .......................................... 48
46. Mittiebah Sandstone: large-scale planar cross-bed ..... 55
47. Mittiebah Sandstone: outcrop habit of subunit 2 ....... 56
48. Mittiebah Sandstone: large-scale sigmoidal
cross-bed .................................................................... 57
49. Mullera Formation: banded hematite/goethite in
‘upper ironstone bed’ .................................................. 58
50. Mullera Formation: shaly facies ................................. 59
51. Mullera Formation: gutter casts .................................. 59
52. Middle Creek Member of Mullera Formation:
silicified quartzose sandstone...................................... 60
53. Lower Bukalara Sandstone: conglomerate and
lithic sandstone ........................................................... 62
54. Massif of Helen Springs Volcanics capped by
Wonarah Formation .................................................... 63
55. Contact between Helen Springs Volcanics and
Wonarah Formation .................................................... 63
56. Infilled vertical fissure at top of Helen Springs
Volcanics .................................................................... 63
57. Border Waterhole Formation: creek bank exposure ... 64
58. Currant Bush Limestone: bioclast floatstone .............. 65
59. Wonarah Formation: brecciated chert ........................ 66
60. Camooweal Dolostone: siliceous nodules in
dolosparstone .............................................................. 67
61. Mesa of Cretaceous sandstone and claystone ............. 69
62. Blacksoil (clay-rich soil) plains ................................. 69
63. First vertical derivative of aeromagnetic data ............. 70
64. Chevron folds and boxfolds in Crow Formation......... 72
65. Distribution of microdiamonds and kimberlitic/
lamproitic pipes in north-central Australia ................. 76
TABLES
1. Geomorphic provinces in Gulf of Carpentaria region... 3
2. Summary of previous geoscientific investigations........ 4
3. Stratigraphy of Murphy Inlier, Carrara Range Group
and Benmara Group .................................................... 10
4. Stratigraphy of Surprise Creek Formation,
McNamara Group and Fickling Group ....................... 22
5. Stratigraphy of South Nicholson Group and
Caulfield beds ....................................................... 38, 39
6. Stratigraphy of Georgina Basin................................... 61
iv
ABSTRACT
MOUNT DRUMMOND 1 is situated adjacent to the Queensland border, on the northern margin of the Barkly Tableland in
the Northern Territory. The sheet area is composed of resistant sandstone ranges, including the Carrara, Canyon and
Mittiebah ranges, surrounded by topographically depressed, recessive shaly units and Cenozoic alluvium and colluvium.
Geologically, MOUNT DRUMMOND is located in the central part of the Palaeoproterozoic to Mesoproterozoic North
Australian Craton. More specifically, it lies at the southern edge of the Murphy Inlier and includes the western part of the
Lawn Hill Platform, a part of the Mount Isa Inlier, and the overlying South Nicholson Basin succession. It is presumed to be
contiguous in the subsurface with the McArthur Basin to the northwest. The oldest exposed strata are the Murphy
Metamorphics, a mainly turbiditic succession that was metamorphosed and deformed during the Barramundi Orogeny at
ca 1870 Ma. The Murphy Metamorphics are overlain by the felsic Connelly Volcanics of ca 1850 Ma age. Resting
unconformably on the igneous and metamorphic basement is the ca 1790–1720 Ma Carrara Range Group, which has a
combined thickness of 2500 m. It comprises a basal fluvial quartzose sandstone and flood basalt succession, overlain
unconformably by subaerial rhyolitic volcanic and proximal alluvial epiclastic rocks.
An unconformity divides the Carrara Range Group from a thin siliciclastic veneer of Surprise Creek Formation. Another
unconformity marks the base of the overlying ca 1670–1590 Ma McNamara Group, a mixed succession of siliciclastic and
carbonate rocks deposited in a variety of shallow-marine settings. The lower two formations include shallow-marine
sandstone, red beds, peritidal stromatolitic and evaporitic dolostone and chert. The upper formations comprise mainly
deeper-marine finer-grained rocks – storm-dominated shelf to basinal mudstone, siltstone and minor dolostone. Shallowmarine to fan delta sandstone and conglomerate at the base of the upper interval preserve evidence of major faulting and
uplift during development of the Lawn Hill Platform. Carbonate sediments of the Fickling Group, exposed in the
northeastern corner of MOUNT DRUMMOND, are probably contiguous with the McNamara Group to the south in the
Carrara Range. Siliciclastic rocks and intermediate volcanics of the Benmara Group unconformably overlie basement in the
northwestern corner of the mapsheet, but their age is uncertain. They are tentatively interpreted to be the thin (400 m)
volcanic expression of the McNamara Group at the northern basin margin.
The unconformably overlying ca 1500–1400 Ma South Nicholson Group occupies a large proportion of the overall
outcrop area in MOUNT DRUMMOND and ranges up to 6500 m thick. It comprises two subgroups (Wild Cow and
overlying Accident subgroups), each containing a couplet of: (i) fine-grained shelf tempestites and shales; and (ii) coarsegrained fluvial and shallow-marine siliciclastic rocks. This group exhibits the characteristic features of a medial to proximal
foreland basin, including coarsening- and shallowing-upward sequences, and localised, coarse fan-delta deposits.
A thin cover of coarse-grained fluvial to shallow-marine siliciclastic rocks of the late Neoproterozoic Bukalara Sandstone
occurs in northwestern MOUNT DRUMMOND, representing the basal deposits of the Georgina Basin. Along the margins of
the ranges in southern and western MOUNT DRUMMOND, the basal deposits of the basin are the younger (Early
Cambrian) Helen Springs Volcanics, which correlate with a cratonic-scale flood basalt event in northern Australia. The
overlying, Middle Cambrian, shallow-marine carbonate-dominated succession underlies most of the blacksoil (clay-rich soil)
plains in southern and western MOUNT DRUMMOND.
Small outliers of Cretaceous shallow-marine and terrestrial sedimentary rocks, part of the Mesozoic Dunmarra Basin, are locally
preserved. A thin veneer of Cenozoic sand, alluvium, blacksoil, laterite and other soil covers large parts of MOUNT DRUMMOND.
All Proterozoic and Palaeozoic units in this region are deformed to some extent. The most significant tectonic feature in
MOUNT DRUMMOND is the southwesterly extension of the Murphy Inlier (or ‘Tectonic Ridge’) in the northwestern
corner of the mapsheet, which is controlled to some extent by the arcuate, northeast-trending Benmara Fault. The eastern
half of the mapsheet is characterised by a series of east-northeast-trending strike-slip and reverse fault systems, including the
Mitchiebo, Little Range, Wild Cow and Rocky Creek faults. Broad-scale open folding is evident in map patterns, mainly in
the South Nicholson Group, and the present edge of the Georgina Basin appears to have been structurally reactivated.
Lateral thickness and facies variations in a number of formations indicate that early movement on some of the faults was
synsedimentary, resulting in the shedding of debris into adjacent downthrown areas. Many of the faults in MOUNT
DRUMMOND were apparently reactivated at various times later during the Proterozoic and Phanerozoic. In some cases,
coarse fan-delta sediments are interdigitated with fine-grained marine shelf sediments, providing an exploration play for
sediment-hosted base metals. Diamondiferous magmatic pipes were emplaced within the Murphy Inlier immediately to the
north at Coanjula in CALVERT HILLS. A tract of microdiamond and indicator mineral anomalism, accompanied by unusual
intermediate volcanics of the Benmara Group, stretches southward along the Benmara Fault, providing potential for
diamonds in MOUNT DRUMMOND. The South Nicholson Group contains several ironstone units which correlate with the
large Constance Range iron deposits in adjacent Queensland. The iron mineralisation process involved early synsedimentary
iron being remobilised and locally concentrated by basinal fluid movement along faults and by Cenozoic lateritisation. Also
present in the South Nicholson Group are organic-rich source rocks with low to high maturity, and potential hydrocarbon
reservoir formations. Significant phosphorite resources have been delineated near the base of the Middle Cambrian Georgina
Basin in adjacent mapsheets, along a major north-trending palaeotopographic corridor, the Alexandria–Wonarah Basement
High, which extends into southern MOUNT DRUMMOND.
1
Names of 1:250 000 and 1:100 000-scale mapsheet areas are given in large and small capitals respectively, eg MOUNT DRUMMOND,
CLEANSKIN.
v
is restricted to pastoral properties at Mittiebah and Connells
Lagoon and the Aboriginal outstation Wangalinji; the
population is less than 100. The mapsheet incorporates parts
of the adjoining Brunette Downs, Alexandria, Gallipoli and
Benmara properties, as beef cattle raising is the main industry
in the region. The Waanyi/Garawa (Nicholson) Aboriginal
Land Trust covers the remaining 5200 km 2 northeastern
portion of the mapsheet, incorporating Cleanskin, northern
Carrara and Mitchiebo, and eastern Benmara. Airstrips
suitable for light aircraft at Mittiebah and Wangalinji are
serviced by a weekly mail run from Mount Isa.
Introduction
Location, access and land use
These explanatory notes and accompanying Second
Edition 1:250 000-scale geological map describe the
geology, geophysics and mineral resources of MOUNT
DRUMMOND, an area bounded by latitudes 18°00'S and
19°00'S, and longitudes 136°30'E and 138°00'E in the
Northern Territory (Figure 1). The area is bounded to the
east by the Queensland border and covers 17 100 km 2.
Access to MOUNT DRUMMOND is via the Barkly Stock
Route, a major gravel road linking the sealed Tablelands
and Barkly Highways that service the Gulf Region and Top
End of Australia, respectively (Figure 1). Well maintained
gravel access roads to Aboriginal outstations and pastoral
properties, and station tracks and fencelines provide dry
seas on four-wheel-drive access to most of Carrara,
Mitchiebo and Mittiebah, and to limited parts of northern
MOUNT DRUMMOND. The remaining scrubby and rocky
terrain is accessible only via cross-country four-wheeldrive vehicle or helicopter. Tennant Creek, 400 km to the
southwest, and Mount Isa, 300 km to the southeast, are the
main service and supply centres.
MOUNT DRUMMOND is very sparsely inhabited and
poorly developed. At the time of writing, human habitation
Physiography
MOUNT DRUMMOND encompasses parts of the Gulf Fall
and Barkly Tablelands physiographic divisions, defined by
Stewart (1954) and Yates (1963). The Gulf Fall includes
dissected hilly country surrounding the Gulf of Carpentaria,
where the principal drainage is toward the coast. The Barkly
Tablelands incorporates the low-relief area inland of the
Gulf Fall, where drainage is mostly to the south.
Aldrick and Wilson (1990) defined six geomorphic
provinces in the Gulf Fall and Coastal Plains of the western
Gulf of Carpentaria region, four of which are recognised in
MOUNT DRUMMOND (Figure 2, Table 1). The areas of
highest relief (including the Carrara, Bluff, Little, Mittiebah
136°30'
135°00'
17°00'
WALHALLOW
138°00'
CALVERT HILLS
139°30'
17°00'
WESTMORELAND
Klana
Wollogorang
Roadhouse
Greenbank
Calvert
Hills
Walhallow
oad
Benmara
Doomadgee
18°00'
MOUNT DRUMMOND
LAWN HILL
dd
Bu
urr
yc
AN
k
lla
DS
ee
Cr
re
Co
Fish
Brunette
Downs
Corella
Lake
Creek
Hole
ON
a Creek
EL
BL
aw
TA
Tarrabool
Lake
LS
HO
IC
Wangalinji N
H
UT
SO
QUEENSLAND
BRUNETTE DOWNS
RIVER
18°00'
ert R
Calv
NORTHERN TERRITORY
Anthony
Lagoon
Lawn Hill
BA
RK
LY
Lake
Sylvester
Mittiebah
Lake
De Burgh
K
OC
ST
ALROY
HIGHW A Y
19°00'
PL
AY
FO
RD
RANKEN
19°00'
CAMOOWEAL
Alexandria
ER
V
RI
ROU
TE
Alroy
Downs
ER
EN RIV
RANK
ER
RB
HE
T
BA
LY
RI
RK
Cre
Gunpowder
R
ne
Lor
VE
ek
HI
Barkly
GH
W
Homestead
A
Y
Camooweal
20°00'
135°00'
136°30'
02
Major road
20°00'
139°30'
138°00'
55
07
Minor road
5
100 km
Hydrology
Camooweal
Town, settlement
A07-224.ai
Figure 1. Location of MOUNT DRUMMOND.
and Canyon ranges) are in central-eastern, northeastern and
northwestern MOUNT DRUMMOND, where Proterozoic
sedimentary rocks are being actively incised by major
watercourses and a dendritic drainage network (the Gulf
Fall, Provinces G2, G3 and G5). Elevated plains at ca 150 m
above sea level may be relicts of a once widespread
lateritic surface (Stewart 1954, Province G1). The eastflowing Nicholson River, the South Nicholson River, and
Buddycurrawa, Carrara, and Musselbrook creeks drain the
Gulf Fall, whereas the south-flowing Playford River and
southwest-flowing Fish Hole and Peaker Piker creeks drain
the Barkly Tableland.
temperature that ranges from 38°C in January to 27°C in
July (Bureau of Meteorology 1988).
Most watercourses are strictly seasonal, with scattered
waterholes remaining during the dry season. The Nicholson
River, which has a large catchment and is fed partly by
springs, flows year round.
Vegetation in MOUNT DRUMMOND reflects the
seasonal monsoonal climate, but pronounced geological
control is also evident. Much of the lowland area is
covered by open eucalypt woodland, with stands of native
pine (Callistris spp) and Acacia (including lancewood)
near the ranges. These areas generally have sandy, well
drained soils, supporting sparse annual grasses and
spinifex (Triodia spp). Major watercourses are lined by
tall eucalypts and locally, by paperbarks (Melaleuca spp).
The Barkly Tableland is characterised by blacksoil (clayrich soil) plains, with Mitchell and Flinders grasses, and
rare stands of low shrubs or trees. The perennial species
are generally fire resistant and much of the annual growth,
particularly near communities and roads, is burnt using
traditional Aboriginal fire lighting practices during the
dry season. Vegetation in the Gulf Fall and Barkly regions
has been described by Perry and Christian (1954) and
Aldrick and Wilson (1990).
Climate and vegetation
MOUNT DRUMMOND has a humid monsoonal climate,
with a distinct wet season from about November to April,
during which time most of the annual rainfall occurs and
unsealed roads are generally impassable, and a dry season
from about May to November. Skies are clear during
the dry months and rain is rarely recorded. There are no
meteorological stations in the sheet area. Based on adjacent
recording stations, mean annual rainfall is approximately
450 mm, accompanied by a mean daily maximum
135°00'
Rope
r
136°00'
137°00'
River
GULF
OF
CARPENTARIA
er
Riv
15°00'
Hodgson
Co
x
River
Sir Edward Pellew Group
G5
G6
G6
G3
G3
r
G4
r
n R
iv
Rive
River
son
bin
AY
G4
Calve
rt
Ro
TAB
LELANDS
17°00'
G3
HIGHW
G1
rya
AY
HW
HIG
r
RIA
Riv
e
CARPENTA
G5
che
G2
We
a
Mc
Art
hu
r
Borroloola
Foels
16°00'
er
ve
Ri
r
e
Nicholson Riv
G5
G1
G2
G4
G1
For description of geomorphic provinces
refer to Table 1
on
ols
ch
Ni
South
G3
River
18°00'
G2
G3
G5
19°00'
G6
MOUNT DRUMMOND
Survey boundary
0
50
100 km
A07-225.ai
Figure 2.
Geomorphic
provinces
recognised in Gulf of Carpentaria region
and MOUNT DRUMMOND (modified
after Aldrick and Wilson 1990).
Previous geoscientific investigations
Methodology
Geoscientific investigations before the 1960s were
reported by Smith and Roberts (1963). It was their
mapping of MOUNT DRUMMOND in 1959 that resulted
in publication of the First Edition geological map and
explanatory notes. They were part of a team from the
Bureau of Mineral Resources [BMR, now Geoscience
Australia (GA)], which developed the first systematic
regional appraisal of the McArthur Basin and established
the current lithostratigraphic framework. Further BMR
and Geological Survey of Queensland mapping took place
in and to the east/northeast of MOUNT DRUMMOND
during 1972–1977, and led to the publication of First
Edition 1:100 000-scale geological maps and explanatory
notes for Seigal and H edleys Creek (Sweet et al 1981),
Carrara R ange R egion (Sweet 1984, Sweet et al 1984),
and Lawn H ill R egion (Sweet and Hutton 1982), and
a map only of the Constance R ange R egion (Slater and
Mond 1980). Revised 1:250 000-scale maps were also
produced for WESTMORELAND (Grimes and Sweet
1979), and LAWN HILL (Hutton and Grimes 1983).
Mapping for the present Second Edition 1:250 000 map
and explanatory notes took place at the latter stages of a
systematic program to examine major mineral provinces
and upgrade geological maps of the McArthur Basin
by the Northern Territory Geological Survey (NTGS).
CALVERT HILLS (Ahmad and Wygralak 1989),
immediately to the north of MOUNT DRUMMOND,
was mapped as a part of this program. First Edition maps
and explanatory notes are available for other adjacent
Northern Terrritory mapsheets, including WALHALLOW
(Plumb and Rhodes 1964), BRUNETTE DOWNS (Randal
1966a) and ALROY (Randal 1966b). Second Edition map
and explanatory notes are available for RANKEN (Kruse
and Radke 2008). Mineral exploration and geoscientific
investigations in MOUNT DRUMMOND since 1950 are
chronicled and briefly summarised in Table 2.
Geological mapping for the Second Edition of MOUNT
DRUMMOND was undertaken by DJ Rawlings and IP Sweet
(NTGS) in 2001–2002. PD Kruse also undertook a study of the
Georgina Basin portion in 2003. The geology for the part of
MOUNT DRUMMOND that falls within the Nicholson Land
Trust was interpreted from 1:82 630-scale black-and-white
RC9 aerial photographs, flown in 1968. The remainder was
interpreted from 1:50 000-scale colour aerial photographs, the
‘Mittiebah/Mount Drummond/Alexandria’ and ‘Walhallow
Leases’ surveys, flown in 1991 and 1994, respectively. Field
observations were plotted directly onto aerial photographs
and were also collected as GPS waypoints. A suite of
representative hand specimens, hard rock geochemical
samples and opportunistic stream sediment geochemical
samples was collected during the mapping. Airborne
magnetic and radiometric images, together with Landsat data,
were used to interpret the geology of remote areas and areas
under thick Cenozoic cover. Geological data were plotted onto
1:50 000-scale and 1:82 630-scale planimetric bases, which
were rectified from the existing Mount Drummond 1:250 000
topographic map using a network of GPS waypoints and
Landsat imagery. The drainage and road network on the
accompanying map is therefore considered to be accurate at
the published scale. Geological data on the compilation sheets
were then captured digitally in MicroStation and generalised
for 1:250 000-scale map production.
These explanatory notes were prepared by a compilation
of data from field notebooks and subsequent laboratory-based
studies, literature reviews and interpretation of remotely
sensed data (aerial photographs, Landsat, aeromagnetic and
radiometric images).
Related publications and datasets
Detailed information associated with mapping in MOUNT
DRUMMOND is presented in Rawlings and Sweet (2004).
Geomorphic province
Main characteristics
Rate of natural erosion
Rate of sediment removal
G1*
Intact areas of mature laterite on old,
stable erosional surfaces and areas of
old, mature claypans
Slow to very slow (very old stable
drainage network; low to very low
relief, and permeable)
Slow to very slow (little sediment
produced due to very low relief; streams
have low competence)
G2*
Escarpments, low hills, foot-slopes and
gentle plains where laterite, clay or
sandstone cap rock has been incised,
exposing softer underlying materials
Rapid (soft rock with high relief)
Rapid (high relief and low competence
streams)
G3*
High-level rocky plateaux and ridges of
resistant sandstone and igneous rock
Slow (erosion-resistant rocks)
Rapid (high relief and high stream
competence; however, little sediment
available for transport)
G4
Areas where a series of linear sandstone
ridges across the direction of drainage
impose strong structural control and
cause local accumulation of sediment
Slow to moderate (local base levels and
sediment accumulation lead to broad,
shallow valleys; only upper parts of
relief are subject to strong erosion, but
these are mostly resistant rocks)
Slow to moderate (local base levels slow
stream incision and inhibit sediment
removal; sediment accumulates)
G5*
Gentle erosional slopes on coastward
side of sandstone ridges that influence
G4
Slow to moderate (low relief)
Moderate (low relief and low stream
competence)
G6
Almost flat coastal terrace
Very slow (very low relief with a very
young, immature, weakly developed
drainage pattern, and permeable soils)
Very slow (very low relief and low
stream competence, disintegrated stream
patterns)
Table 1. Factors defining and characterising geomorphic provinces recognised in Gulf of Carpentaria region (after Aldrick and Wilson
1990). Provinces marked by * are present in MOUNT DRUMMOND.
Year
Comments
References
1950–1960
Exploration and evaluation of iron deposits in South Nicholson Group in
CLEANSKIN and Constance Range in Queensland
Carter and Zimmerman (1960), Harms (1965)
1959–1963
MOUNT DRUMMOND mapped as part of Bureau of Mineral Resources (BMR)
1958–1963 McArthur Basin mapping project; publication of First Edition
MOUNT DRUMMOND 1:250 000 geological map and explanatory notes
Smith and Roberts (1963)
1965–1970
Data collected from 11 km regional grid of gravity stations in McArthur Basin
and environs
Whitworth (1970)
1966–1967
Base metals exploration in Carrara Range by Australian Geophysical
Dechow (1967)
1967–1976
Phosphate exploration south of Carrara Range by ICI and Australian Geophysical
McMahon (1969), Perrino (1970), Hackett (1977)
1977–1982
Geological mapping by BMR in Lawn Hill Platform, including publication of
1:100 000 scale geological map Carrara Range Region
Sweet (1982, 1983, 1984, 1985), Sweet et al
(1984)
1980
Base metals and uranium exploration in Carrara Range by Afmeco
Orridge (1981)
1983–present
Diamond exploration throughout MOUNT DRUMMOND and at adjacent
Coanjula prospect by Ashton Mining, Australian Diamond Exploration (ADX),
Redfire Resources, Aberfoyle Exploration, Stockdale Prospecting, CRA
Exploration and BHP Minerals
Ashton Mining (1984, 1989), Mitchell (1988),
Ong (1995), Rogers (1996b), Kammermann
(1997), Reddicliffe (1998), Pang (1998) and
others
1990
Stream sediment sampling for gold in Canyon Range
Hitchman (1991)
1990–1992
Assessment of petroleum potential of South Nicholson Group in MOUNT
DRUMMOND and drilling of stratigraphic hole DD92SN1
Lanigan (1993)
1991–1994
Aerial photo survey flown by NT Government
This report
1990–2000
Base metals and diamonds exploration in Carrara Range area by CRA
Exploration and Rio Tinto, including drilling of numerous RAB holes
Stegman (1992), Moody and Stegman (1993),
MacKay (1996), Walker (2000), Walker and
Johnson (2001) and others
1995–1997
Measurement of geological sections in Carrara Range by NABRE project and
publication of various articles relating to Lawn Hill Platform
Bradshaw et al (1996, 2000), Juodvalkis and
Barnett (1997), Page and Sweet (1998), Domagala
et al (2000), Krassay et al (2000), Page et al
(2000), Southgate et al (2000)
2001
Barkly airborne magnetic and radiometric survey by Tesla Airborne Geoscience
for NTGS
Tesla (2001), this report
2001–2003
Geological mapping of MOUNT DRUMMOND by NTGS
Rawlings and Sweet (2004), this report
Table 2. Summary of previous geoscientific investigations and principal mineral and petroleum exploration in MOUNT DRUMMOND
since 1950. Full listing of open file company reports available from NTGS on request.
use of Folk’s (1974) terminology for classification (eg
sublitharenite). The term ‘blacksoil’ refers to soil types
with abundant grey–black expanding clays (vertosols). The
abbreviation ‘HCS’ is used throughout for ‘hummocky
cross-stratification’.
Proterozoic carbonate rock terminology is based
mainly on grainsize. Dololutite is composed of mudsized dolomite grains, dolarenite of sand-size dolomite
grains and dolorudite of dolomite grains larger than
2 mm. The modifiers ‘sandy’ and ‘muddy’ refer to the
presence of small (5–25%) quantities of sand- and mudsized siliciclastic components (mainly quartz), eg sandy
dolarenite. For Phanerozoic carbonate rocks, in which
textures are better preserved, the classification of Wright
(1992) has been employed. Dolostone is a general term
for a rock composed mainly of the mineral dolomite
and is not necessarily of intraclastic origin. Because
many carbonate rock outcrops are totally leached and/or
silicified, it is often not possible to determine the former
composition (ie whether dolostone or limestone). In these
cases, the non-specific term ‘carbonate’ is often used in
descriptions.
Definitions and classification of volcanic rocks follow
the QAPF scheme set down by the International Union
of Geological Sciences (Le Maitre et al 1989). The
compositional/textural terms, basalt, microdolerite and
dolerite, are used in a non-genetic sense and do not imply
an extrusive or intrusive origin. The terms lava, flow,
Digital, generalised, geological mapping data, comprising
linework and field data points, are available on request from
NTGS at any scale in MicroStation (dgn) and MapInfo
formats, or as hard copy. Multi-element geochemical
analyses of representative rock units and NTGS-generated
stream sediment data are available from the NTGS
geochemical database. Hand specimens are available for
viewing at the NTGS core facility in Darwin and a listing
of coordinates and related data is available from the NTGS
rock sample database; this is tabulated in Rawlings and
Sweet (2004).
Airborne magnetic, radiometric and DTM data for the
‘Barkly survey’ (400 m line spacing, north–south orientation
and 80 m terrain clearance) were acquired by Tesla Airborne
Geoscience on behalf of the Northern Territory Government
in 2001 (Tesla 2001). These datasets can be obtained
from NTGS in digital format, or can be viewed online at
the NTGS website using Image Web Server technology
(http://www.dme.nt.gov.au/ecw/ProdNT_wide.htm).
Terminology
For consistency, the terminology used for description of
rock types in MOUNT DRUMMOND follows that of
MOUNT YOUNG (Haines et al 1993). Field classification
of siliciclastic sedimentary rocks is based essentially on
grainsize and probable composition (eg medium-grained
lithic sandstone). Later petrological studies allow the
dyke and sill are used to infer origins. The descriptions
and classification of volcanic and volcanogenic deposits
follows the schemes of McPhie et al (1993) and Cas and
Wright (1987). The Proterozoic geological timescale
proposed by the International Union of Geological Sciences
(Plumb 1991) has been adopted for the chronostratigraphy
of this sheet area.
northwest trend from Cloncurry to Doomadgee near the
Queensland–Northern Territory border, and in a series
of discontinuous outcrops westwards to northwestern
MOUNT DRUMMOND. It is bounded to the northwest
by older Palaeoproterozoic rocks of the Murphy Inlier.
The most comprehensive studies of the Inlier are provided
by Blake (1987), Stewart and Blake (1992) and Southgate
(2000).
Several tectonic elements, which variously controlled
sedimentation and deformation, are identified within the
Mount Isa Inlier (Figure 4, Plumb and Derrick 1975, Plumb
et al 1980, 1990). Of these, only the Lawn Hill Platform
– the less deformed equivalents of rocks around Mount
Isa – extends into MOUNT DRUMMOND. The Murphy
Tectonic Ridge controlled deposition within the Lawn Hill
Platform at various times (Plumb et al 1990, Bradshaw et al
2000).
The sedimentary succession of the Mount Isa Inlier
was deposited largely in shallow-water, marginal marine,
fluvial, and lacustrine intracratonic settings (Blake 1987).
Integrated geochemical, geochronological, geophysical and
sequence stratigraphic studies show that it can be divided
into four depositional packages (Scott et al 1998, Bradshaw
et al 2000, Krassay et al 2000a, b, Southgate et al 2000); all
are represented in MOUNT DRUMMOND. These packages
are designated ‘superbasins’, using sequence-stratigraphic
terminology, and replace terminology introduced by
Blake (1987), in which rocks in the Inlier were assigned to
basement and ‘cover sequences’ 1 to 3.
The Leichhardt Superbasin (ca 1800–1750 Ma; Jackson
et al 2000a), the oldest succession, unconformably overlies
basement terranes in the Murphy and Mount Isa inliers
(Figure 3). It comprises a regionally extensive platform
cover of shallow-marine to fluvial sandstone and lesser
mudstone, conglomerate, dolostone, and bimodal volcanic
and high-level intrusive rocks, up to ca 15 km thick (Derrick
1982, Blake 1987). Major stratigraphic units are the
Bottletree Formation, Haslingden Group (including Myally
Subgroup), and Quilalar Formation in the Leichhardt River
Fault Trough, and Kamarga Volcanics, lower Peters Creek
Volcanics, and lower Carrara Range Group in the Lawn Hill
Platform.
The Leichhardt Superbasin was terminated by uplift
and erosion at about 1750–1740 Ma (Jackson et al 2000a),
and was succeeded by a new phase of volcanic and
siliciclastic sedimentation – the Calvert Superbasin. Major
lithostratigraphic units assigned to this superbasin phase
are the Bigie Formation and Fiery Creek Volcanics and
their correlatives, the overlying Surprise Creek Formation
(Jackson et al 2000), and the lowermost McNamara
Group (Torpedo Creek Quartzite and lower Gunpowder
Creek Formation). Although developed in both the Mount
Isa Inlier and McArthur Basin, the Calvert Superbasin
succession is relatively thin – the volcanics, although
extensive, are rarely more than a few hundred metres
thick, whereas the Surprise Creek Formation ranges from
zero to over 2000 m thick.
The Isa Superbasin (ca 1670–1595 Ma; Page et al 2000)
is a stromatolitic and evaporitic dolostone-sandstonemudstone succession, deposited in environments ranging
from shallow-water, marginal marine, peritidal shelf and/
Mapping conventions
The map datum is GDA94 and the Map Grid of Australia
(MGA) zone is 53K. Grid references are quoted as UTMs
and are generally accurate to ± 50 m (eg Mittiebah at
719950mE 7919500mN).
Polygons on the accompanying map that contain more
than one unit (eg ‘L
P sat, P
Lso’) indicate where several small
polygons have been combined for clarity at map scale, or
where boundaries have been difficult to assign to rock units
in areas of flat-lying strata, or where sparse scattered outcrops
cannot be differentiated sensibly from surrounding areas of
alluvium (eg ‘L
Pso, Czs’). In all cases, the dominant unit is
listed first.
In some map areas, the rock unit underlying extensive
tracts of low-relief regolith can be indicated. It is often
possible to identify the underlying rock unit with
confidence, based on a combination of untransported rock
fragments in skeletal soils, the composition of residual soils,
geomorphology, or the geophysical signature. In these cases,
unique symbology is used to indicate regolith covering the
rock unit (eg ‘Czl/_Cmp’).
Regional geological setting
The geological setting of MOUNT DRUMMOND is
depicted in Figure 3. Five principal tectonostratigraphic
components of the North Australian Craton are represented
in the mapsheet area: the Murphy Inlier, Lawn Hill Platform,
and South Nicholson, Georgina and Dunmarra basins.
Basement in the mapsheet is represented by small
pockets of the Palaeoproterozoic Murphy Inlier, which
forms a large east-trending outcrop belt, immediately to
the north in CALVERT HILLS (Ahmad and Wygralak
1989). Turbidites of the Murphy Metamorphics were
multiply deformed and metamorphosed to greenschist
facies during the Barramundi Orogeny at about
1880–1870 Ma (Page and Williams 1988, Rawlings 2002).
There are currently no age constraints for their deposition.
A comagmatic felsic volcanic and intrusive suite (Cliffdale
Volcanics and Nicholson Granite) was then emplaced at
about 1860–1845 Ma (Page et al 2000).
MOUNT DRUMMOND lies at the western limit of
exposure of the Palaeoproterozoic to Mesoproterozoic
Mount Isa Inlier (Figure 4). This is a thick ‘platform cover’
succession of unmetamorphosed to polydeformed and
metamorphosed sedimentary and lesser volcanic rocks,
deposited on the North Australian Craton (Plumb 1979).
The Murphy Inlier separates the Mount Isa Inlier from the
southeastern part of the coeval McArthur Basin (Rawlings
1999), immediately to the north in CALVERT HILLS.
Exposures of the Mount Isa Inlier cover an area
of some 50 000 km 2 (Blake 1987), in a roughly north-
136°30'
138°00'
M10
M10
K
WESTMORELAND
d6
M6b
Westmoreland Prospect
M6
K
M10
18°00'
BRUNETTE DOWNS
Y5
MOUNT DRUMMOND
C1b
r
ma
a
Be
n
Y4
LAWN HILL
BAUHINIA
DOME
K
K
L7
MALONEY CREEK
INLIER
L7
C1b
Carrara Range
Region
ALROY
RANKEN
18°00'
K
L9
K
Fa ult
hiebo
Mitc
19°00'
L7
L8
L7
L9
Cz
g5
L6b
L8
M10
Fa
ult
L7
SW extension of
Murphy Range
f6
g5 L6
Y4
L9
C2
Eva Au-U
M6
g5
Coanjula
Y5
L6
Alexandria
L7
Little Range
Fault
Constance Range
Highland
C1b
Plains
f6
L6b K
Y4
C2
Cz
L9
136°30'
C2
g5
Century
NORTHERN TERRITORY
M6
M6
L6b
19°00'
QUEENSLAND
CALVERT HILLS
WALHALLOW
CAMOOWEAL
138°00'
A07-226.ai
Cz
Sand, clay, calcrete and lacustrine limestone
f6
Top Rocky Rhyolite
K
Cretaceous
L6b
Mitchiebo Volcanics (and equivalents)
C2
Middle Cambrian Georgina Basin
L6
Carrara Range Group (and equivalents)
C1b
Helen Springs Volcanics (and equivalents)
Y5
Cliffdale Volcanics (and equivalents)
M10
Neoproterozoic Georgina Basin (Bukalara Sst)
g5
Nicholson and Yeldham granites
L9
South Nicholson Group
Y4
Murphy Metamorphics
L8
upper Fickling Group (Doomadgee Fm)
L7
McNamara, Benmara and Fickling Groups (and equivalents)
M6b
Tawallah Group mafic volcanic rocks
M6
Tawallah Group siliciclastic rocks
Mineral occurrence with name and commodity
Diamonds
Phosphate
Zinc-lead
Iron ore
Uranium
Figure 3. Regional geological setting of MOUNT DRUMMOND.
or continental sabkha, to deep basinal settings (Domogala
et al 2000, Southgate et al 2000, Krassay et al 2000a, b).
In the Mount Isa Inlier, it includes the Mount Isa Group,
and all except the lowermost McNamara Group and
Fickling Group. The inclusion of the lowermost Mount
Isa and McNamara groups in the underlying Calvert
Superbasin resulted from recognition of a significant
hiatus in sedimentation between about 1690 and 1670 Ma
(Southgate et al 2000).
The Roper Superbasin (ca 1500–1400 Ma) is the
youngest succession in the McArthur–Mount Isa region,
comprising a widely distributed cyclic succession of
fine- and coarse-grained siliciclastic rocks, deposited in
predominantly shallow-marine, nearshore to shelf, and
minor basinal environments (Powell et al 1987, Jackson
et al 1987, 1988, 1999, Abbott and Sweet 2000, Abbott
et al 2001). It includes the ca 6.5 km-thick South Nicholson
Group, best developed in MOUNT DRUMMOND, and the
2–5 km-thick Roper Group to the northwest of MOUNT
DRUMMOND, overlying the McArthur Basin succession.
The rocks are typically gently dipping, and are concealed
southwest of the McArthur region in the Beetaloo Subbasin (Plumb and Wellman 1987), and south and west of
MOUNT DRUMMOND. The Roper Superbasin overlies
all older basin packages with regional unconformity, with
an apparent hiatus of nearly 100 my. Its age is constrained
133°00'
137°00'
ARAFURA SEA
GOVE
Arafura Basin
Coast
Pine
Creek
Inlier
Bu
lm
Fa
t
NORTHERN
Arnhem
Shelf
Arnhem Inlier
Range
ul
an
Caledon
Shelf
McARTHUR
Fault
14°00'
BASIN
Walker Fault Zone
Urapunga
KATHERINE
GULF OF
CARPENTARIA
Fault
Hells Gate
Hinge Line
Batten Fault Zone
SOUTHERN
Bauhinia
Shelf
h
Tawalla
DALY BASIN
lt
Fau
h
ya
un
t
ap
ul
all
Fa
M
McARTHUR BORROLOOLA
BASIN
a
Emu F
Beetaloo
Sub-basin
(undercover)
McArthur River Mine
Wearyan
Shelf
ult
Ca
lve
rt
REDBANK
Fa
ult
Peters Creek
Volcanics
MURPHY INLIER
WISO
BASIN
SOUTH
NICHOLSON
BASIN
MOUNT
MOUNT DRUMMOND
Tennant
Region
QUEENSLAND
GEORGINA BASIN
Ewen Block
NORTHERN TERRITORY
LAWN HILL
PLATFORM
TENNANT CREEK
18°00'
CARPENTARIA
BASIN
Century Mine
ISA
Mary Kathleen
Fold Belt
Mount Isa Mine
Malbon
Block
MOUNT ISA
Leichhardt
River
Fault Zone
Arunta Region
0
200 km
INLIER
KalkadoonLeichhardt Block
22°00'
A07-227.ai
Basement units
post-McArthur Basin-Mount Isa Inlier units
Figure 4. Regional tectonic framework for Mount Isa Inlier, Lawn Hill Platform and McArthur Basin. Box shows location of MOUNT
DRUMMOND.
between ca 1324 Ma (Derim Derim Dolerite; Jon ClaouéLong, GA, pers comm 1997) and ca 1590 Ma (Nathan
Group, Jackson et al 2000b). Deposition also postdates
the 1590–1500 Ma Isan Orogeny in the Mount Isa Inlier
(O’Dea et al 1997), and a depositional age of 1492 ± 4 Ma
for the Mainoru Formation (Jackson et al 1999) indicates
that deposition in the superbasin probably began at around
1500 Ma. A Rb-Sr age of 1429 ± 31 Ma for the McMinn
Formation, near the top of the Roper Group (Kralik 1982),
may date diagenesis rather than deposition, but provides a
tentative minimum age for deposition.
Several models have been proposed to explain the
nature of tectonic processes during deposition of the Isa
Superbasin and the McArthur and South Nicholson basins,
and the resulting stratigraphic and structural imprint.
Derrick (1982), Plumb (1987), Plumb and Wellman (1987),
Blake (1987), Etheridge and Wall (1994), O’Dea et al (1997)
and Betts et al (1998) interpreted basin evolution in terms
of a series of extensional phases, separated by hiatuses
involving deformation and uplift. Scott et al (1998, 2000)
and Rawlings (2002) interpreted the cover sequences of
north-central Australia in terms of diverse mantle-dynamic,
thermal, flexural and isostatic processes, inboard of, and
geodynamically linked to an evolving convergent margin
in central Australia.
Neoproterozoic to Palaeozoic successions in northern
and central Australia include the Georgina Basin, a part
of which outcrops along the southern and western parts
of MOUNT DRUMMOND, where it onlaps Proterozoic
basement of the Lawn Hill Platform and South Nicholson
Basin. Only a thin remnant of late Neoproterozoic fluvial
to shallow-marine Bukalara Sandstone is recognised there.
The remainder of the succession is Cambrian in age.
Thin remnants of marine and terrestrial Cretaceous
deposits are recognised throughout northern Australia
(Skwarko 1966, Frakes et al 1987). In MOUNT
DRUMMOND, these comprise the Mesozoic Dunmarra
Basin. Laterite/ferricrete, soil, colluvium and alluvium now
form a thin cover over much of the Gulf of Carpentaria and
Barkly Tablelands regions, and constitute about half the
area of MOUNT DRUMMOND.
Murphy Metamorphics (L
Plm)
The Murphy Metamorphics (Ahmad and Wygralak 1989)
outcrop in two main areas: in the headwaters of Benmara
and Murphy Creeks in northeastern Boxer; and as small
inliers along the southern margin of the Carrara Range
in Carrara. In both cases, distribution appears to be
controlled by major fault systems, the Benmara and Little
Range faults, respectively.
In most areas, the Murphy Metamorphics are composed
of ferruginised outcrop and float of red/brown to purple or
yellow, finely-laminated micaceous metasiltstone (phyllite),
metagreywacke (Figure 6) and quartz-mica schist. Minor
rock types include metaquartzite and calc-silicate rock.
Locally present is a ca 5 m-thick horizon of banded iron
formation (eg at 704350mE 7992200mN, Figure 7), with
intricate banding of iron-rich and silica-rich domains. In
some cases, outcrop of the Murphy Metamorphics is poor,
comprising white saprolitic siltstone, usually containing
abundant quartz veins. This resembles the ‘whiterock’ style
of weathering of the Crow Formation along Murphy Creek.
The grade of metamorphism is lower greenschist facies.
Metagreywacke has at least one good cleavage, parallel
to bedding. A second, steeply dipping cleavage is locally
developed. Epithermal-style quartz veins, with or without
hematite or pyrite, are generally abundant as tension gashes,
but locally, they are scarce and are developed only along
bedding planes. Folding on a centimetre to decimetre scale
is common, the most common style being open to closed
symmetric folds with upright or inclined axes and angular
hinges (chevron style, Figure 7). Locally developed are
asymmetric boxfolds and microfaults, particularly in the
banded iron formation.
The lithology of the Murphy Metamorphics is consistent
with deposition as turbidites, and pelagic and minor
chemical sediments on a deep submarine fan or shelf. The
geometry of the former enclosing water body is unknown,
but is thought to have been extensive (Rawlings 2002). The
age of sedimentation is unknown, but must predate the
onset of deformation and high-temperature metamorphism
associated with the 1880–1870 Ma Barramundi Orogeny
(Page and Williams 1988). Similar ‘flysch’ sedimentation in
the Pine Creek Inlier only marginally predates this orogeny.
Stratigraphy
The lithostratigraphy of MOUNT DRUMMOND is
described in terms of five principal tectonostratigraphic
units – the Murphy Inlier, Lawn Hill Platform, and South
Nicholson, Georgina and Dunmarra basins – each of which
is described separately below and summarised in Figure 5.
Palaeoproterozoic (Orosirian): Murphy Inlier
The Murphy Inlier is a narrow, elongate, east–westoriented outcrop belt, which separates the McArthur
Basin in the north from the Isa Superbasin in the south
(Figures 3, 4). It is likely that this basement belt acted
as a depositional barrier or ‘tectonic ridge’ between the
two basins during much of their history (Plumb et al
1990). In CALVERT HILLS, the Murphy Inlier consists
of the Murphy Metamorphics, Nicholson Granite and
comagmatic Cliffdale Volcanics (Ahmad and Wygralak
1989). Immediately southward in MOUNT DRUMMOND,
it incorporates a number of small outcrops of Murphy
Metamorphics and a restricted belt of altered felsic igneous
rocks, the Connelly Volcanics (Figure 5, Table 3). The
latter probably correlate with the ca 1850 Ma Cliffdale
Volcanics to the north. These are overlain unconformably
by various younger cover successions, mainly the Benmara
and South Nicholson groups.
Connelly Volcanics (P
Llc)
The Connelly Volcanics (new name, see Appendix 1)
is only exposed in a small area of northeastern Boxer
(710000mE 8007000mN), near the boundary with
CALVERT HILLS. It is a recessive unit of red/brown
‘brick’-coloured, altered/weathered porphyritic rhyolite
or rhyodacite, which generally has a mottled and highly
weathered appearance, here termed ‘redrock’. Outcrop
is characterised by locally abundant epithermal-style
quartz veins and clay-rich slickenside surfaces, defining
a crude foliation. In thin section, the Connelly Volcanics
are composed of equant and euhedral K‑feldspar and
subhedral to anhedral embayed quartz phenocrysts of
ca 3 mm diameter in a recrystallised, equigranular,
ferruginous quartzofeldspathic groundmass. There are
no recognisable primary ferromagnesian minerals and
CROW
FORMATION
BOWGAN
SANDSTONE
MITTIEBAH
SANDSTONE
Pso t
L
P
L so
P
L sb
T OBACCO MBR
CROW
FORMATION
_Clp
510 Ma
BUKULARA
SANDSTONE
Pu
L
MULLERA
FORMATION
Psm
L
CAULFIELD BEDS
NO MANS SST MBR
WANGALINJI MBR
1590 Ma
Pbb
L
Pbr
L
?
Pc
L
PLAYFORD
SANDSTONE
(L
Psa)
MULLERA
FORMATION
MULLERA
FORMATION
CONSTANCE
SANDSTONE
PANDANUS
SILTST MBR
Psc p
L
?
Pso s
L
Pso
L
CROW
FORMATION
Psa n
L
NO MANS SST MBR
Psa t
L
TOP LILY SST MBR
Psa w
L
WANGALINJI MBR
Pmh w
L
WIDDALLION SST MBR
CONSTANCE
SANDSTONE
CROW
FORMATION
PLAYFORD
SANDSTONE
Psm 2
L
Pmu
L
CONSTANCE
SANDSTONE
Psc
L
WIDDALLION SST MBR
Pmh
L
LAWN HILL
FORMATION
PLAIN CREEK
FORMATION
Pma
L
PLAIN CREEK
FORMATION
Pms
L
SHADY BORE
QUARTZITE
Pmb
L
BRUMBY
FORMATION
Pmd
L
DRUMMOND
FORMATION
BULLRUSH
CONGLOMERATE
Pr
L
1725 Ma
DOMINANT DEPOFACIES
CONNELLY
VOLCANICS
MURPHY
METAMORPHICS
P
L lc
Plm
L
TOP ROCKY
RHYOLITE
Pcg
L
GATOR SANDSTONE
Pcd
L
MITCHIEBO
VOLCANICS
DON CK
SANDSTONE
Plm
L
MURPHY
METAMORPHICS
Mafic volcanic rocks
MURPHY INLIER
WALLIS SILTST MBR
BURANGOO SST MBR
PANDANUS SILTST MBR
HEDLEYS SST MBR
L sc s
P
Psc w
L
Psc b
L
Psc p
L
Psc h
L
Pfd
L
DOOMADGEE
FORMATION
FICKLING
GROUP
1590 Ma
McNAMARA GROUP
1640 Ma
SURPRISE CREEK
FORMATION
Pct
L
Pcm
L
Felsic volcanic rocks
MULLERA
FORMATION
SCHULTZ SST MBR
1450 Ma
LAWN HILL
FORMATION
DRUMMOND
FORMATION
?
Psm m
L
Psm 1
L
WIDDALLION SST MBR
BENMARA GROUP
1640 Ma
1850 Ma
MIDDLE CREEK
SANDSTONE MBR
MULLERA
FORMATION
Psc
L
CONSTANCE
SANDSTONE
Psi
L
TOP LILY SST MBR
BUDDYCURRAWA
VOLCANICS
BREAKFAST
SANDSTONE
_Cmo
NEOPROTEROZOIC
TO CAMBRIAN
BORDER W.HOLE
FORMATION
?
MITTIEBAH
SANDSTONE
1450 Ma
CURRANT BUSH
LIMESTONE
_Cmd
_Cmc
MESOPROTEROZOIC
_Cmd
_Cmk
_Cmw
MULLERA
FORMATION?
TOBACCO MBR
CAMOOWEAL
DOLOSTONE
ACCIDENT SUBGROUP
HELEN SPRINGS
VOLCANICS
NORTHEAST
(Nicholson River)
SOUTHEAST
(Carrara Range)
CONSTANCE
SANDSTONE
510 Ma
EAST-CENTRAL
(Maloney Creek Inlier)
CENTRAL
(Mitchiebo Waterhole)
WILD COW
SUBGROUP
CAMOOWEAL
DOLOSTONE
RANKEN LIST
WONARAH
FORMATION
NORTH-CENTRAL
(Bauhinia Dome)
1725 Ma
CARRARA RANGE
GROUP
PALAEOPROTEROZOIC
SOUTHWEST
(Mittiebah Range)
SOUTH NICHOLSON GROUP
NORTHWEST
(Benmara)
1850 Ma
Shelf dolostone and shale
Shelf mudstone and fine sandstone
Marine debris flow
Shallow marine or fluviatile sandstone
Disconformity or erosional surface
Other unconformity
Figure 5. Stratigraphic columns for MOUNT DRUMMOND.
A07-230.ai
Unit,
(map symbol), thickness
Lithology
Depositional environment
Stratigraphic relationships
Buddycurrawa
Volcanics
(P
Lbb) up to 300 m
Ferruginous coarse sandstone, massive
and brecciated trachyte, poorly sorted
immature lithic sandstone and pebble
conglomerate, mature sandstone,
ferruginous siltstone and fine sandstone;
minor stromatolitic chert
Braided fluvial, shallow
lacustrine and/or marine (fine
sediments); lava flows; marginal
ephemeral alluvial and debris
flow (coarse sediments)
Conformable on Breakfast Sandstone;
probably unconformably overlain by
Bowgan Sandstone and Crow Formation
Breakfast Sandstone
(P
Lbr) up to 80 m
White to pink, medium- ± coarse-grained
silicified sublithic sandstone; thin basal
pebble or cobble conglomerate; rare
chertified stromatolitic carbonate
Braided fluvial and/or shallow
marine
Unconformable on Murphy Metamorphics;
conformably overlain by Buddycurrawa
Volcanics
Top Rocky Rhyolite
(P
Lct) up to 400 m
Lower: pink, porphyritic (K-feldsparquartz), massive to flow banded,
spherulitic to microgranophyric
rhyolite; local autobreccia, peperite
and hyaloclastite. Upper: poorly sorted
matrix-supported pebble to boulder
conglomerate
Moderate-aspect-ratio lava
flow(s); marginal ephemeral
alluvial and debris flows
Unconformable on Gator Sandstone;
unconformably overlain by Surprise
Creek Formation and locally, by Bullrush
Conglomerate
Gator Sandstone
(P
Lcg) up to 700 m
Pink to purple, fine- to medium-grained,
variably ferruginous, sublithic to lithic
sandstone with local beds of very coarse
and pebbly sandstone; minor basalt and
microdolerite
Braided fluvial with sporadic
intertidal marine inundation and
mafic lava flows
Conformable on Mitchiebo Volcanics;
unconformably overlain by Top Rocky
Rhyolite
Mitchiebo Volcanics
(P
Lcm) 500–1000 m
Weathered and/or altered, massive to
vesicular or microvesicular basalt and
microdolerite; lesser sandstone, mudstone
and peperite
Subaerial lava flows and
invasive flows
Conformable between Don Creek Sandstone
and Gator Sandstone
Don Creek Sandstone
(P
Lcd) 400–500 m
White to pale maroon, silicified to friable,
medium ± coarse-grained, locally pebbly
lithic to quartzose sandstone
Braided fluvial
Unconformable on Murphy Metamorphics;
conformably overlain by Mitchiebo
Volcanics
Connelly Volcanics
(P
Llc)
Red/brown, altered/weathered porphyritic
rhyolite or rhyodacite (‘redrock’) with
locally abundant quartz veins
Probably extrusive volcanic
Probably unconformable on Murphy
Metamorphics. Unconformably overlain by
Benmara and South Nicholson groups
Murphy Metamorphics
(P
Llm)
Purple micaceous metasiltstone (phyllite),
metagreywacke and quartz-mica schist
with locally abundant quartz veins; minor
metaquartzite, banded iron formation and
calc-silicate rock
Submarine fan or shelf
Base not observed. Unconformably overlain
by Benmara and South Nicholson groups
Benmara Group
Carrara Range Group
Murphy Inlier
Table 3. Stratigraphy of Murphy Inlier, Carrara Range Group and Benmara Group in MOUNT DRUMMOND.
the rock is significantly altered to ferruginous material,
suggesting that they may have been obliterated. Euhedral
zircons are abundant. At 711900mE 8010800mN, the
Connelly Volcanics are intensely altered to a white clayrich rock and contain abundant quartz veins; this area is
interpreted as a small epithermal alteration zone.
Field relationships cannot discriminate an intrusive
versus extrusive origin for the Connelly Volcanics and
there are no preserved microscopic textures indicative of
a pyroclastic or lava mode of emplacement. The Volcanics
were formerly included within the Murphy Metamorphics
(Smith and Roberts 1963). However, owing to their
distinctive lithology and the lack of a definitive cleavage
and folding, the Connelly Volcanics are thought to be
younger than the metamorphic rocks and are therefore
excised from them. The boundary between these two units
is very poorly exposed, the best locality being at 707400mE
8009250mN, where there is a juxtaposition of ‘redrock’
(Connelly Volcanics) and grey psammitic schist (Murphy
Metamorphics). In the contact zone, the ‘redrock’ becomes
progressively more foliated westward over a few tens of
metres and grades into schist. The Connelly Volcanics most
likely correlate with the Cliffdale Volcanics in CALVERT
HILLS (Ahmad and Wygralak 1989), which are in the age
range 1860–1845 Ma (Page et al 2000).
Palaeoproterozoic (Statherian) – Mesoproterozoic
(Calymmian): Lawn Hill Platform
The Lawn Hill Platform (LHP), the western part of the
Mount Isa Inlier, comprises the ‘less deformed equivalents’
(Plumb and Derrick 1975) of rocks in the Leichhardt River
Fault Trough. It is a composite tectonostratigraphic unit,
and includes elements of the Leichhardt, Calvert and Isa
superbasins (Jackson et al 2000, Southgate et al 2000).
It lies on rocks affected by the Barramundi Orogeny
– mainly Murphy Metamorphics – and is overlain by
the South Nicholson Basin, an element of the Roper
Superbasin (Jackson et al 1999). Within the LHP, rocks
of the Carrara Range Group, within which there is a
pronounced unconformity (Sweet 1985), are assigned to the
Leichhardt (Don Creek Sandstone, Mitchiebo Volcanics,
10
which underlies the Haslingden Group in the Leichhardt
River Fault Trough. The Eastern Creek Volcanics, near
the base of the Haslingden Group, are correlated with the
Mitchiebo Volcanics in MOUNT DRUMMOND (Jackson
et al 2000). The Top Rocky Rhyolite, the only dated unit in
MOUNT DRUMMOND, is 1725 ± 3 Ma (Page et al 2000),
providing an age range for the Carrara Range Group, and a
maximum age for the overlying Surprise Creek Formation
and McNamara Group. The McNamara Group ranges in
age from about 1690 Ma to 1595 Ma (Page et al 2000 – see
discussion on sequence stratigraphy and correlations after
McNamara Group descriptions herein).
Gator Sandstone) and Calvert (Top Rocky Rhyolite)
superbasins. The overlying Surprise Creek Formation is
also assigned to the Calvert Superbasin. The McNamara
Group in the Lawn Hill region (Sweet and Hutton 1982),
and the Fickling Group farther north (Sweet et al 1981),
components of the Isa Superbasin, extend westward into
MOUNT DRUMMOND. The Fickling Group is present
in a single anticlinal structure in northeastern MOUNT
DRUMMOND. Rocks in the Bauhinia Dome in central
northern MOUNT DRUMMOND, previously mapped by
Smith and Roberts (1963) as Fickling beds (Group), are
now assigned to newly recognised elements of the younger
South Nicholson Group in the South Nicholson Basin (Roper
Superbasin). The various elements of the LHP in MOUNT
DRUMMOND are summarised in Figure 5. Changes in
stratigraphic nomenclature (Figure 8) are discussed in the
text dealing with each formation or group.
The age of the LHP cover in MOUNT DRUMMOND
ranges from around 1790 Ma to 1595 Ma, based on isotopic
age determinations. The maximum age limit is imposed by
the 1790 Ma Bottletree Formation (Blake and Stewart 1992),
Carrara Range Group
The Carrara Range Group (Sweet 1982) constitutes the
basal portion of the western Lawn Hill Platform and
outcrop is confined to the Carrara Range in eastern
MOUNT DRUMMOND (Sweet 1984, Figure 3). It lies
unconformably on Orosirian basement units of the Murphy
Inlier and is, in turn, unconformably overlain by the
Figure 6.
Steeply-dipping
foliated
metasiltstone
(phyllite)
and
metagreywacke outcrop that typifies
the Murphy Metamorphics. Boxer,
704250mE 7992200mN, Whiterock
Creek.
Figure 7. Banded iron formation (BIF) of
Murphy Metamorphics, showing intricate
interlamination of iron-rich and silica-rich
bands. Boxer, 704550mE 7992150mN,
Whiterock Creek.
11
Don Creek Sandstone (P
Lcd)
Statherian to Calymmian Surprise Creek Formation and
McNamara Group (Figure 5). It is internally constrained
by a SHRIMP U‑Pb zircon date of 1725 ± 3 Ma for the
Top Rocky Rhyolite at the top of the group (Page et al
2000). The lithostratigraphic components of the Carrara
Range Group are summarised in Table 3 and Figure 5.
Lithological comparisons were used by Sweet (1984) to
suggest that the Carrara Range Group is a correlative of
the Peters Creek Volcanics in the eastern Murphy Inlier,
and this has been confirmed by isotopic geochronology
by Page et al (2000). Geochronology has also confirmed
correlations with the Tawallah Group in the southern
McArthur Basin (Page and Sweet 1998, Page et al 2000,
Rawlings 2002) and the Eastern Creek Volcanics through
to Fiery Creek Volcanics on the eastern Lawn Hill
Platform and Leichhardt River Fault Trough (Jackson et al
2000). Its temporal relationship with the Benmara Group
in northwestern MOUNT DRUMMOND is difficult to
establish, but we prefer the scenario that the Benmara
Group is younger (Figure 5).
The Carrara Range Group is dominated by braided
fluvial and perhaps minor shallow-marine sandstone, with
lesser mudstone and bimodal (basalt-rhyolite) volcanic and
high-level intrusive rocks up to 2500 m thick. Resistant,
steeply dipping sandstone ranges with recessive valleys
occur in a narrow east–west belt stretching over 50 km
from No Mans Creek to Don Creek near the Queensland–
Northern Territory border. The group is largely concealed
by younger units, and is therefore thought to have a
significantly wider extent in the subsurface. It may be
contiguous with coeval packages in the Tennant Creek and
Mount Isa inliers.
Smith and Roberts (1963)
The Don Creek Sandstone (Sweet 1982) is the basal unit of
the Carrara Range Group and is exposed as strike ridges
and a broad anticline, north of the Little Range Fault, in
the headwaters of Fish Hole and Boomerang Creeks, near
781000mE 7930000mN (Carrara, Sweet 1982, 1984,
Sweet et al 1984). It lies unconformably on the Murphy
Metamorphics, although the contact is not exposed, and is
in turn, conformably overlain by the Mitchiebo Volcanics.
At the type section, outcrop is composed of 400–500 m
of white to pale maroon, silicified to friable, medium–
coarse-grained, lithic to quartzose sandstone. It also
includes rare to common intervals of coarse to very coarse
sandstone with scattered, rounded, quartz, ‘quartzite’
and metasedimentary pebbles or cobbles up to 10 cm in
diameter. Conglomerate is rare. Bedding is generally very
thick, with individual beds containing up to ten stacked
decimetre-scale trough cross-bed sets. A typical bed
appears to coarsen upward from pebble-free sandstone
to pebble/cobble-rich sandstone (Figure 9). Mudstone
intraclasts are a local phenomenon in discrete beds. The
overall upward stratigraphic trend of the formation is
toward finer grainsize and more lithic composition, with
a gradual decrease in clast size, average grainsize and the
number of coarser beds. However, cyclicity on a 10–50 m
scale is also evident. The Don Creek Sandstone is locally
deformed with diffuse bedding, hydraulic breccia, quartzfilled tension gashes and cataclasite bands.
The depositional setting for this formation is envisaged
to be braided fluvial, not unlike that of its probable
correlatives, the Westmoreland Conglomerate and Yiyintyi
Sweet (1984)
This report
Widdallion Sst Mbr
Widdallion Sst Mbr
Lawn Hill Formation
Plain Creek Formation
L
Pma5
McNamara Group
Bluff Range beds
McNamara Group
Lawn Hill Formation
Plain Creek Formation
Shady Bore Quartzite
Bullrush
Cgl
Brumby Formation
Drummond Formation
Musselbrook Formation
Surprise Creek Formation
unnamed
volcanic
unit
L
Pcm5
Mitchiebo Volcanics
Don Creek Sandstone
Figure 8. Summary of past and present stratigraphic nomenclature for Lawn Hill Platform.
12
Top Rocky Rhyolite
Carrara Range
Group
Carrara
Range
Formation
Carrara Range
Group
Top Rocky Rhyolite
Gator Sandstone
Mitchiebo Volcanics
Don Creek Sandstone
A07-231.ai
Sandstone in the southern McArthur Basin (Ahmad and
Wygralak 1989, Haines et al 1993).
sandstone, mudstone and peperite. Sandstone interbeds,
1–5 m thick, are white to maroon, medium grained and
sublithic to lithic, with small trough cross-beds. Mudstone
is purple to red/brown, micaceous and possibly dolomitic,
as it is typically associated with caliche in the soil profile.
Peperite comprises blocky to lobate vesicular basalt clasts
in a silicified red mud ± sand matrix (Figure 10), not unlike
that described by Rawlings (1993). In many cases, peperite
forms a cap to coherent basalt units. The main valley in
which the Mitchiebo Volcanics occur (the headwaters of
Boomerang Creek, centred on 780000mE 7932000mN) is
composed largely of gravel float with scattered inliers of
in situ basalt, sandstone or peperite.
The Mitchiebo Volcanics are lithologically and
geochemically indistinguishable from the widespread
‘Seigal flood basalt succession’ recognised in the McArthur
Basin (Seigal and Nungbalgarri volcanics, Rawlings 2002);
and to the Eastern Creek Volcanics and Buddawadda Basalt
(Sweet et al 1981) to the northeast and southeast in the
Mount Isa Inlier. Correlation between these formations is
considered highly likely (Rawlings 1994). The basalt was
probably emplaced as a series of lava flows and shallow
invasive flows in a subaerial to shallow-water lacustrine
setting. Rawlings (2002) has documented an emplacement
model, based on the Gold Creek Volcanics in the southern
McArthur Basin.
Mitchiebo Volcanics (P
Lcm)
The Mitchiebo Volcanics (Sweet 1982) are exposed mainly
north of the Little Range Fault in the headwaters of Fish
Hole and Boomerang Creeks, near 780000mE 7932000mN
(Carrara; Sweet 1984, Sweet et al 1984). Small outcrops
are present to the northwest in the headwaters of Rocky
Creek (near 768000mE 7935000mN) and Wild Cow Creek
(immediately north of the Wild Cow Fault near 758000mE
7939000mN). The Mitchiebo Volcanics mapped here include
only the lower volcanic part of the formation (L
Pcm b ), defined
and mapped by Sweet (1984). The upper sandstone part of
the formation (L
Pcms , Sweet 1984) is now excluded and is
defined as a new unit, the Gator Sandstone. As such, the
type section for the Mitchiebo Volcanics, originally defined
by Sweet (1984), is modified slightly here – from (base)
783800mE 7930250mN to (top) 785100mE 7931150mN.
In most cases, the Mitchiebo Volcanics lie conformably
between the Don Creek and Gator sandstones. However, in
the Wild Cow Creek area, the overlying Gator Sandstone
and Top Rocky Rhyolite have been removed by erosion and
the Mitchiebo Volcanics are unconformably overlain by the
Surprise Creek Formation.
The Mitchiebo Volcanics are composed largely of
brown, grey, pink or red weathered and/or altered, massive
to vesicular or microvesicular basalt and microdolerite; they
total 500–1000 m in thickness. Fresh black pyritic basalt
and microdolerite, and minor examples of porphyritic
basalt with K‑feldspar phenocrysts up to 1.5 cm in diameter
(?xenocrysts), are similar to that in the middle of the Seigal
Volcanics type section in the McArthur Basin (Jackson
et al 2000). Basalt contains a ubiquitous centimetre- to
decimetre-spaced joint set and there is local brecciation and
veining, with quartz, carbonate, hematite or K‑feldspar infill.
The main form of alteration appears to be of orthoclasechlorite type, as is common in the southern McArthur Basin
(Pietsch et al 1991, Cooke et al 1998). Mafic rock tends to
form 5–30 m-thick ‘flow’ units within thinner intervals of
Gator Sandstone (P
Lcg)
The Gator Sandstone (new name, see Appendix 1) is
exposed mainly as narrow strike ridges north of the Little
Range Fault in the headwaters of Fish Hole and Boomerang
creeks (centred on 777000mE 7932000mN, Carrara). It
also occurs to the northwest in the headwaters of Rocky
Creek around 770000mE 7934000mN. It incorporates
what was formerly mapped by Sweet et al (1984) as the
‘upper sandstone member’ of the Mitchiebo Volcanics
(L
Pcms ). This is clearly a distinct and mappable unit and has
been given formation status herein. The Gator Sandstone
lies conformably on the Mitchiebo Volcanics and is
unconformably overlain by the Top Rocky Rhyolite (Sweet
Figure 9.
Thick-bedded
quartzose
sandstone of Don Creek Sandstone,
containing stacked, decimetre-scale,
trough cross-bed sets and scattered
quartz pebbles. Carrara, 783700mE
7929550mN, Boomerang Creek.
13
1983). Locally, the Gator Sandstone and overlying Top
Rocky Rhyolite have been removed by erosion preceding
the Surprise Creek Formation (eg at Wild Cow Creek).
In the vicinity of 786000mE 7931000mN (the type
section), the Gator Sandstone is ca 150–200 m thick,
comprising lower and upper sandstone subunits separated
by a thin recessive volcanic interval. Neither of these
subunits is sizeable enough or of adequate lateral extent to
be distinguished on the MOUNT DRUMMOND mapface,
but both are shown on Carrara R ange region (Sweet et al
1984). The lower sandstone subunit is about 25 m thick,
comprising pink to purple, fine- to medium-grained,
sublithic sandstone with local beds of coarse, very coarse
and granule sandstone. It is medium to very thickly bedded,
with planar bedding and low-angle planar cross-beds
20–80 cm thick. The overlying recessive (volcanic)
subunit is about 20 m thick and contains minor loose
float of vesicular basalt and brown, laminated, lithic
sandy mudstone (?volcaniclastic sandstone). The upper
sandstone subunit is about 100–150 m thick and is
composed of pink to pale purple, medium- to very coarsegrained (mostly medium-grained) sublithic sandstone,
with scattered quartz granules and pebbles up to 2 cm in
diameter and minor local beds or laminae of mudstone
intraclasts and brown oxidised ?basalt clasts 0.1–1 cm in
diameter. Sandstone is thickly to very thickly bedded,
with decimetre-scale (5–50 cm amplitude) low-angle
trough cross-beds, planar bedding, parallel lamination and
lesser, large-scale planar cross-beds. Along the remainder
of the outcrop belt, the middle basaltic subunit appears
to be absent and the Gator Sandstone is a homogeneous
sandstone interval 100–700 m thick, with a gradual
increase in thickness from east to west.
Around 770000mE 7934000mN (Rocky Creek
headwaters, the reference area), a thicker and marginally
different sequence is evident. There, the Gator Sandstone
incorporates a lower, white, resistant sandstone subunit
and an upper, dark, moderately recessive, ferruginous
sandstone subunit. The lower subunit is ca 200–400 m
thick, and comprises thickly bedded, white to pink, fineto medium-grained quartzose sandstone with trough
cross-beds. The upper subunit is ca 100–150 m thick and
is dominated by red/brown to pink, friable, fine-grained,
ferruginous lithic sandstone. It is thin to medium bedded
with trough cross-beds, symmetric ripples and mudclasts.
The middle ca 20 m of the subunit is distinctly muddier and
more ferruginous than sandstone above and below, with
chocolate brown sandstone interbedded with micaceous
siltstone and mudstone. Mudstone intraclasts, desiccation
cracks and cross-lamination with 10 cm wavelength are
prolific. This facies closely resembles the ‘redbeds’ of the
Wununmantyala Sandstone in the southern McArthur Basin
(Jackson et al 1987, Pietsch et al 1991). The upper few tens
of metres of sandstone are pink and notably more silicified
than that below.
The Gator Sandstone is locally deformed with diffuse
bedding, quartz-filled tension gashes and cataclasite bands.
The depositional setting for this formation is envisaged
to be braided fluvial, with sporadic supratidal marine
inundation and mafic volcanism. Based on stratigraphic
position and lithology, the Gator Sandstone is correlated
with the Sly Creek Sandstone in the southern McArthur
Basin, which also contains a local basalt interval (Haines
et al 1993).
Top Rocky Rhyolite (P
Lct)
The Top Rocky Rhyolite (Sweet 1982) is exposed mainly
as narrow strike ridges, within a broad anticline bordering
the Little Range Fault in the headwaters of Fish Hole and
Boomerang creeks (centred on 777000mE 7933000mN,
Carrara; Sweet 1984, Sweet et al 1984). A small inlier has
also been mapped along Moloney Creek in the Maloney
Creek Inlier (778200mE 7955800mN).
The Top Rocky Rhyolite unconformably overlies the
Gator Sandstone; however, the base of the rhyolite cuts
down hundreds of metres through the underlying sandstone
along strike, so that it locally sits on Mitchiebo Volcanics
(Sweet 1983). Although there is obvious discordance at
aerial photograph and map scale, there is no evidence of
outcrop-scale discordance, nor of a basal conglomerate
or obvious erosional surface. There appears to be partial
Figure 10. Peperite breccia in Mitchiebo
Volcanics, comprising blocky to lobate
vesicular basalt clasts in pale silicified red
mud ± sand matrix. Carrara, 783600mE
7931100mN, Boomerang Creek.
14
structural control of this contact also, with rhyolite draping
some faults that truncate the underlying Gator Sandstone.
The sandstone also appears to be more deformed than
the Top Rocky Rhyolite. These relations are similar to
those of the Tanumbirini Rhyolite–Warramana Sandstone
contact in the southern McArthur Basin (Rawlings 2002).
The Top Rocky Rhyolite is unconformably overlain by
the Surprise Creek Formation along its length. In one
area, the unconformity has removed a thickness of 150 m
of rhyolite over a distance of 1 km. In the Maloney Creek
Inlier, the Top Rocky Rhyolite is unconformably overlain
by the Bullrush Conglomerate (middle McNamara Group),
indicating a highly irregular palaeotopography in that area
during McNamara Group time.
The Top Rocky Rhyolite is up to 400 m thick and, in
many areas, comprises a lower coherent rhyolite unit,
overlain by a conglomerate unit. These constituent units
are too thin to be differentiated on the mapface of MOUNT
DRUMMOND, but are mapped in Carrara R ange region
(Sweet et al 1984).
texture, set in a massive pink silicified mudstone matrix.
Clasts range considerably in size (up to 30 cm in diameter)
and shape (from concavo-convex to blocky and irregular),
and there is no evidence of stratification or reworking. This
breccia closely resembles peperite of the Fagan Volcanics in
the northern McArthur Basin (Rawlings et al 1997).
Conglomerate unit
The conglomerate unit (L
P ctc of Sweet 1984, Sweet et al 1984)
is up to 200 m thick and is discontinuous along strike. It is
composed of poorly sorted pebble to boulder conglomerate
(Figure 14) and is largely matrix-supported, with subangular
to subrounded, locally imbricated clasts set in a pink lithic
gravel-sand-mud matrix. At stratigraphically lower levels,
clasts are on average pebble sized, and together with the
matrix, are composed entirely of rhyolite-derived material
(ie no exotic clasts). The unit gradually coarsens upwards
to comprise mainly cobbles, with scattered boulder-sized
clasts up to 0.5 m in diameter. Clasts become progressively
more polymict, and large silicified sandstone clasts are
present, comprising up to 10% of the rock volume. In
general, the conglomerate is crudely horizontally stratified
and ungraded, but there are local horizons of trough crossbedded or planar bedded, white to red, medium- to coarsegrained lithic sandstone infilling palaeochannels and as
sheets. This facies is identical to that of the lower Pungalina
Member of the southern McArthur Basin (Rawlings 2002).
A flood cycle debris flow mechanism probably dominated
during deposition.
Coherent rhyolite unit
Coherent rhyolite (L
Pctr of Sweet 1984, Sweet et al 1984)
occurs as a continuous unit up to 350 m thick, composed
of bouldery to blocky outcrop of hard, silicified or crumbly,
weathered pink, purple or orange porphyritic rhyolite. It
contains euhedral to subhedral K‑feldspar (ca 25%) and
quartz (<5%) phenocrysts up to 1 cm diameter, set in a
cryptocrystalline quartzofeldspathic groundmass. Many
samples are altered/weathered to some extent to clay or
low-temperature orthoclase-hematite. A SHRIMP U‑Pb
zircon date of 1725 ± 3 Ma has been obtained for coherent
rhyolite (Page et al 2000).
The texture of the basal 20–50 m of the unit varies
considerably and non-systematically along strike, including:
(i) massive; (ii) intensely flow-banded and/or lithophysaespherulite bearing; (iii) massive with scattered lithophysae
or spherulites (up to 2 cm diameter); (iv) massive with
decimetre-spaced quartz folia; and (v) autobrecciated.
Lithophysae are up to 10 cm in diameter and sometimes
contain an open star-shaped cavity or are infilled with quartz
crystals (Figure 11). They tend to form chains parallel to
flow banding, which is locally contorted and complexly
folded. Quartz folia are centimetre- to decimetre-spaced,
5–15 cm-long, subparallel, discontinuous foliated stringers
of amorphous quartz (Figure 12), perhaps formed by
the collapse of vesicles (Rawlings 2002). Autobreccia is
composed of randomly oriented, centimetre- to decimetresized (up to 1 m) rhyolite clasts, with variable internal
texture, set in a massive to crudely banded rhyolite matrix
(Figure 13).
Above the basal section, the bulk of the unit is composed
of massive microgranophyric rhyolite, with or without
quartz folia; only minor flow banding is present and no
lithophysae have been identified. Rare mafic mineral clots
and red mudstone clasts have been identified locally. Where
preserved, the upper 5–10 m of the coherent rhyolite unit
is distinctly different, with the development of vesicular
zones (vesicles 2–3 mm in diameter with quartz infill),
autobreccia and hydroclastic breccia (peperite). The latter
comprises angular pink rhyolite clasts with varied internal
Overall setting
The coherent rhyolite is interpreted to have originally
formed a horizontal sheet, about 300 m thick, with an aerial
extent of at least 20 km (Sweet 1983). Although the local
presence of peperite would suggest minimal removal of
material at the top of the sheet, the top is visibly irregular
and eroded along strike. The dominance of debris flow
facies and the local and ubiquitous rhyolitic provenance
of the overlying conglomerate indicate that the coherent
rhyolite formed a high-relief body that dominated the
landscape. Loose material was quickly stripped off and
redeposited, before it was possible to entrain ‘basement’
sandstone into the depositional system. This implies a close
temporal and spatial link between rhyolite emplacement,
relief development, erosion, conglomerate deposition and
burial. A similar relationship is evident in most rhyolitic
units and their immediately overlying epiclastic deposits
in the Tawallah and Donydji groups of the McArthur
Basin (eg Hobblechain Rhyolite and Pungalina Member,
Rawlings 2002). The emplacement model proposed here is
much the same, involving the rapid eruption of a single or
composite lava dome, with physical properties appropriate
for long-term rheomorphic flow and development of a
widespread lava sheet. There is no evidence to support
an ignimbrite origin, although this cannot be ruled out
(eg Sweet 1983). Epiclastic conglomerate formed at the
margins of the flow, during and soon after emplacement,
under the influence of sporadic and large-scale flood
events. Local structure played an important role in the
localisation of the magmatic conduit (yet to be identified)
and the development of topography prior to extrusion, to
15
Figure 11. Lithophysae within massive
Top Rocky Rhyolite. These spherical
devitrification features are up to 10 cm in
diameter and form during rapid cooling
of glassy felsic magmas. Carrara,
772100mE 7925900mN, Fish Hole
Creek.
Figure 12.
Stacked
quartz
folia
within massive Top Rocky Rhyolite.
These centimetre- to decimetre-scale,
discontinuous foliated stringers of
amorphous quartz are interpreted to
have formed by the collapse of vesicles
or the central gas cavity of lithophysae.
Carrara, 792050mE 7932800mN, Don
Creek.
Figure 13. Autobreccia of Top Rocky
Rhyolite, composed of randomly
oriented, centimetre- to decimetre-scale
rhyolite clasts with variable internal
textures, set in massive to crudely banded
rhyolite matrix. Carrara, 771650mE
7933750mN, Carrara Range.
16
which also contain abundant felsic volcanics and shallow
intrusive rocks. However, an alternative age closer to
1660–1580 Ma could be implied by their compositional
similarity to magmatic rocks in the Coanjula area (see
Buddycurrawa Volcanics), leading to a possible correlation
with the McNamara Group.
generate the unconformity at the base of the Top Rocky
Rhyolite. An isotopic age of 1725 ± 3 Ma for the Top Rocky
Rhyolite is identical to the ages of intrusive phases of the
Peters Creek Volcanics south of the Murphy Inlier, and
to the Hobblechain Rhyolite and Packsaddle Microgranite
of the southeastern McArthur Basin (Page et al 2000),
and indicates a regional event. Jackson et al (2000), in
discussing this, discounted the likelihood of rifting as a
driving mechanism.
Breakfast Sandstone (P
Lbr)
The Breakfast Sandstone (new name, see Appendix 1)
comprises a resistant, banded strike ridge of white to
maroon or pink, medium- to coarse-grained, silicified
sublithic sandstone, up to 80 m thick in northeastern
Boxer. The base is rarely exposed, but at some localities
(eg 707200mE 8000900mN), the lower few metres contain
abundant quartz pebbles and lesser cobbles, where it rests
on Murphy Metamorphics with extensive quartz veining.
The unit tends to fine upwards, with small-scale (decimetrewavelength) trough cross-beds, planar bedding, symmetric
ripples, desiccation cracks and current lineation becoming
increasingly common. Otherwise, it is medium to thickly
bedded, with mudclasts, scattered quartz granules and small
pebbles, and white angular silicified mudstone (‘chert’) clasts
up to 5 cm diameter. The unit also contains rare laminae or
thin beds of chertified mudstone and chertified carbonate
with relict domical stromatolites. The depositional setting is
interpreted to have been moderate- to high-energy braided
fluvial and/or shallow marine. The Breakfast Sandstone
was largely mapped as part of (ie not differentiated from)
the ‘Benmara beds’, and partly mismapped as Constance
Sandstone by Smith and Roberts (1963).
Benmara Group
The Benmara Group (Table 3, Figure 5, and redefinition
in Appendix 1) incorporates most of the outcrops formerly
mapped as Benmara beds by Smith and Roberts (1963). It
includes a basal sandstone (Breakfast Sandstone), overlain
by a recessive interval containing a trachyte sheet and
various clastic rocks (Buddycurrawa Volcanics). In some
areas, it is difficult to distinguish these two units, in which
case outcrop is assigned to undifferentiated Benmara
Group. Outcrop is restricted to a northeast-trending belt
in northeastern Boxer, where it unconformably overlies
the Murphy Metamorphics and Connelly Volcanics. The
contact with the overlying South Nicholson Group is
poorly exposed and the relationship cannot be resolved
with any certainty. Pinching out of the Benmara Group
to the north near 705000mE 8007000mN is consistent
with both an unconformity and a low-angle structural
boundary (detachment) dividing the Benmara and South
Nicholson groups. Geochronological studies have failed
thus far to establish the absolute age of the Buddycurrawa
Volcanics. If the Benmara Group is of similar age to (and
is therefore contiguous with) the South Nicholson Group,
then a conformable boundary can be invoked. However,
an older age is implied by the presence of volcanics in the
Benmara Group, which are notably absent from the South
Nicholson Group and correlatives in northern Australia,
supporting an unconformable contact (our preference; see
Bowgan Sandstone). The obvious interpretation is that the
Buddycurrawa Volcanics are the same age as the Carrara
Range Group and Peters Creek Volcanics (ca 1725 Ma),
Buddycurrawa Volcanics (P
Lbb)
The Buddycurrawa Volcanics (new name, see Appendix 1)
form recessive to mildly resistant outcrops in northeastern
Boxer. The formation comprises a basal ferruginous
sandstone unit, overlain by a mixed interval of coherent
trachyte, debris flow sandstone and conglomerate, mature
sandstone, ferruginous siltstone/fine sandstone and minor
but distinctive stromatolitic chert. The thickness of this
Figure 14. Boulder conglomerate of Top
Rocky Rhyolite, composed of poorly
sorted, subangular to subrounded rhyolite
clasts in pink lithic sandstone matrix.
Cleanskin, 778200mE 7955800mN,
Moloney Creek.
17
and Mitchiebo volcanics, or the Top Rocky Rhyolite. Instead,
the trachyte has affinities with alkaline volcanics and shallow
intrusive rocks from Coanjula, about 20 km to the north,
which are probably no older than ca 1665 Ma (Ong 1991, Lee
et al 1994). Correlation with the older igneous units implies
an age that immediately precedes the McNamara Group.
Correlation with the younger units implies contemporaneity
with the upper McNamara Group.
The Buddycurrawa Volcanics have a moderately strong
magnetic response, presumably due to the component
trachytic sheet(s). This implies the presence of primary
magnetite phenocrysts, as seen in the Fagan Volcanics in
the northern McArthur Basin (Rawlings et al 1997). The
Buddycurrawa Volcanics also exhibit a strong radiometric
response, most notably in the potassium channel.
formation is difficult to determine, but a maximum of
300 m is inferred from outcrop width and dips. The basal
ferruginous sandstone itself is 10–20 m thick. Clastic facies
resemble those of the upper Wollogorang Formation in the
southern McArthur Basin (Jackson et al 1987), although no
correlation is suggested here. The Buddycurrawa Volcanics
rest conformably on the Breakfast Sandstone and are overlain
by the Bowgan Sandstone and, locally, Crow Formation of
the South Nicholson Group. As discussed above, the upper
contact is not well exposed and relationships and age are
speculative.
Ferruginous sandstone
This facies forms a discrete basal unit, which has been
described in the field as ‘ironstone’. It is a red/brown or
chocolate brown, coarse-grained and pebble-bearing,
poorly sorted lithic sandstone, with elevated Fe content
(9% Fe2O3; n=1). A close spatial and temporal association
with overlying debris flow sandstone is evident. A shallow
supratidal or fluvial depositional setting is suggested.
Debris-flow sandstone
This facies comprises brown, massive to crudely bedded,
poorly sorted, coarse-grained pebbly lithic sandstone
and pebble/cobble conglomerate, with a distinct volcanic
provenance (Figure 15). It is characterised by planar bedding
(horizontal stratification) or small trough cross-beds, but
locally there are thin siltstone interbeds with desiccation
cracks. The debris-flow facies exhibits a close spatial and
temporal association with the coherent trachyte, from which
it was probably derived. The depositional model proposed
thus involves rapid deposition of fluvial-modified talus and
debris aprons at the margins of trachyte lava bodies, during
and immediately following their emplacement (cf Pungalina
Member, Rawlings 2004).
Trachyte
Trachyte is massive to amygdaloidal, porphyritic and red/
brown to pink in colour, with K‑feldspar and minor quartz
phenocrysts set in a microcrystalline quartzofeldspathic
groundmass. Outcrop is universally altered or weathered
to an assemblage of clay-sericite-quartz-hematite. Locally
common are quartz-agate-lined vesicles and rare vugs up
to 20 cm in diameter. The unit also contains occasional
‘baked’ red/brown mudstone veins/dykes and zones of
heterogeneous mudstone-rhyolite breccia (peperite; cf
Rawlings 1993). Due to poor outcrop and the possibility of
structural complexity, it is difficult to determine whether
the Buddycurrawa Volcanics comprises more than one
igneous sheet. At 703400mE 7991900mN, a single trachyte
sheet ca 30–40 m thick is exposed, the top of which has
about 10 m of local erosional relief. The outcrop pattern
is very similar to that of the Top Rocky Rhyolite. The
emplacement model proposed here involves lava flows with
peripheral zones of peperite, where these intermingled with
wet unconsolidated sediments.
Attempts have been made to date the trachyte using
SHRIMP U–Pb geochronology. However, the rock
samples have proven to contain only minor zircon and are
weathered (Rawlings and Sweet 2004). Geochemically,
the Buddycurrawa Volcanics are very unusual, because
they are characterised by ‘intermediate’ concentrations of
SiO2 (ave 57.6wt%, n=4), high Al2O3 (ave 17.3%), high K 2O
(ave 13.5%), high Nb (55 ppm), high Y (50 ppm) and high
Zr (330 ppm). Samples classify geochemically as trachyte
and phonolite, but the latter appears to be at odds with the
presence of modal quartz. One sample, in particular, has
anomalously high Zr (1500 ppm), accompanied by high Nb
(210 ppm), U (16 ppm) and rare earths (eg Ce = 750 ppm,
La = 270 ppm). These high Zr concentrations, in concert
with heavy rare earths, appear to be at odds with the
sparsity of zircon in the samples. Perhaps the zircon is
very fine grained and difficult to separate. Importantly,
the geochemical characteristics of the trachyte are
completely unlike those of any igneous unit of the regional
1700–1860 Ma timeframe, such as the Cliffdale, Peters Creek
Mature sandstone and mudstone
These include fine- to coarse-grained, yellow to red/brown,
lithic to sublithic ferruginous sandstone, with planar
bedding, trough cross-beds, mudclasts, desiccation cracks
and thin mudstone laminae. They were probably deposited
in a moderate-energy fluvial setting, in the absence of active
volcanism.
Ferruginous siltstone/fine sandstone
This facies includes flaggy to slabby outcrop of red/brown
to purple or yellow micaceous siltstone and fine sandstone
with parallel lamination. A shallow lacustrine setting is
suggested, based on a close association with terrestrial
facies, such as debris flow sandstone.
Stromatolitic chert or dolostone
Within the Buddycurrawa Volcanics are several discrete
units of white, partly brecciated chert, with well preserved
stratiform and domical bioherms, 1–2 m in diameter, bearing
internal digitate microbial lamination (Figure 16). These
resemble the ‘beehive stromatolites’ of the Wollogorang
Formation in the southern McArthur Basin (Jackson et al
1987). Other horizons contain conical stromatolites or
massive textureless chert. Chert is interbedded with yellow
to red/brown, dirty, lithic medium–coarse sandstone with
trough cross-beds. In places (eg 702550mE 7993100mN),
fresh dolostone rather than chert is present. At 712300mE
8010100mN, chert is interbedded at various scales with
ferruginous sandstone and siltstone, forming parallel
laminae, through to decimetre-scale beds, many of which
18
have been fractured, desiccated and/or boudinaged into
articulated clasts or nodules (Figure 17). Chert is parallel
to wavy laminated and apparently contains occasional,
small, relict domical or button stromatolites. A shallow,
intertidal, marine depositional setting is suggested for the
various chert facies.
distinct angular unconformity by younger components
of the former Musselbrook Formation, eg, in the western
Carrara Range, at 754920mE 7939110mN; and (ii) the base
of the overlying Drummond Formation at the same locality
is marked by a 2 m conglomeratic layer. In other outcrops,
the overlying Drummond Formation is concordant with the
Surprise Creek Formation. The base of the Surprise Creek
Formation is a regional angular unconformity, as it overlies
progressively older formations of the Carrara Range Group
from east to west (Sweet 1984).
The Surprise Creek Formation (Figure 5, Table 4)
includes basal lenses and beds of pebble to boulder
conglomerate, intertonguing with and overlain by sublithic
to quartz sandstone. The formation ranges from 300 m thick
in the east, where there is no conglomerate, to 350–450 m
in the central and western Carrara Range. The thicker
conglomerate beds, mapped out by Sweet et al (1984) as
mb1a, range from 0 to 200 m in thickness, but are generally
too thin to distinguish on the accompanying 1:250 000
mapsheet. The conglomerate consists of sub-rounded to
well rounded pebbles and cobbles, and scattered boulders to
Unassigned to group
Surprise Creek Formation (L
Pr)
The Surprise Creek Formation is widespread in the
Mount Isa region, where it is overlain by the Mount Isa
and McNamara groups, either conformably or with minor
disconformity. It was defined by Derrick et al (1980) and
has been assigned to the Calvert Superbasin, of which it is
the uppermost unit (Jackson et al 2000). Sweet (1984) did
not recognise the Surprise Creek Formation in the Carrara
Range Region, but mapped it as units L
Pmb1a and L
Pmb1b of the
now obsolete Musselbrook Formation. It is now recognised
as a separate unit for two reasons: (i) it is overlain with
Figure 15. Debris-flow facies of
Buddycurrawa Volcanics, comprising
brown, massive to crudely bedded,
poorly-sorted, coarse-grained, pebbly
lithic sandstone with a distinct volcanic
provenance.
Boxer,
703250mE
7991350mN, Whiterock Creek.
Figure 16. Chertified carbonate of
Buddycurrawa Volcanics with well
preserved digitate stromatolites. Boxer,
702600mE 7992150mN, Whiterock
Creek.
19
30 cm, of quartz, pink quartzite and quartz sandstone, set
in a matrix of coarse-grained to granule lithic sandstone.
A few rhyolite clasts were noted in interbedded pebbly
sandstone and conglomerate, immediately above a well
exposed unconformable contact with the underlying
Top Rocky Rhyolite at 771340mE 7926420mN. Eight
kilometres north, at 772010mE 7934290mN, is the thickest
(150–200 m) conglomeratic section, comprising interbedded
pebble to boulder conglomerate (Figure 18), pebbly
sandstone and medium- to very coarse-grained sublithic to
quartzose sandstone. The contact with the underlying Top
Rocky Rhyolite is a well exposed angular unconformity.
The conglomerate is poorly sorted and largely matrixsupported, with locally imbricated and rounded clasts of
quartz, quartzite and minor rhyolite set in a pink mediumto coarse-grained sublithic sandstone matrix. Bedding is
very thick and the main bedforms are amalgamated trough
cross-beds, planar cross-beds and planar bedding. There
is an overall trend toward a decreasing grainsize and clast
content up-section, although with significant vertical and
lateral variability. Rhyolite clasts are present near the base,
whereas the proportion of quartz clasts increases upwards.
Above the ca 150 m level, pebble-free sandstone dominates,
but there are sporadic beds of conglomerate or trains of
cobbles and pebbles, indicating a somewhat arbitrary
boundary with the remainder of the formation.
The remainder of the Surprise Creek Formation consists
of white to pink, thickly to very thickly bedded, sublithic
to quartz sandstone. Grainsize is mainly medium to coarse,
with some very coarse to granule sandstone containing
pebbly intervals and rare scattered cobbles. The easternmost
outcrops, north of Boomerang Creek, are fine to medium
grained. Bedforms include amalgamated small trough
cross-beds, planar cross-beds, planar bedding, parallel
lamination with current lineation, and HCS with 5–20 cm
wavelength (Figure 19).
The basal conglomeratic rocks are proximal deposits,
laid down in either a braided fluvial or locally alluvial
fan setting. The sandstone component of the formation is
probably a braided fluvial deposit, as it appears to grade up
from, or intertongue with the conglomerates, and forms a
continuous sheet.
Figure 17. Articulated clasts/nodules
of chert in ferruginous sandstone and
siltstone of Buddycurrawa Volcanics.
Coanjula
(CALVERT
HILLS),
712300mE 8010100mN, northern Canyon
Range.
Figure 18. Very thick bed of coarse
pebble to cobble conglomerate in the
Surprise Creek Formation. Carrara,
772150mE 7934600mN, headwaters of
Rocky Creek.
20
stratigraphic studies in the Mount Isa region. As part of
this study, a reconnaissance of the Carrara Range led
to somewhat improved correlation with the type area of
the McNamara Group and recognition of the Shady Bore
Quartzite at the base of the Plain Creek Formation. Our
mapping has led to a further refinement of links between
the two regions, and a modification of the nomenclature:
‘Musselbrook Formation’ is abandoned and split into
the Surprise Creek Formation (which is excluded from
the McNamara Group), the Drummond Formation, and
Pmb3), the Brumby
an upper unit (formerly L
Pmb2 and L
Formation (Figure 8).
McNamara Group
The McNamara Group includes sandstone, conglomerate,
siltstone, shale and various carbonate rocks, commonly
silicified to chert in outcrop (Table 4). Its topographic
expression ranges from steep ridges associated with the
sandstones, to more subdued ridges, undulating terrain and
plains over some of the finer-grained and dolomitic units. It
lies disconformably, or locally with angular unconformity,
on the Surprise Creek Formation, except in the Maloney
Creek Inlier, where it is unconformable on Top Rocky
Rhyolite. The group was mapped by Smith and Roberts
(1963) as the Bluff Range beds (Figure 8). Following a
re‑examination of these rocks in 1977, Sweet (1984) included
them in the McNamara Group, the main outcrops of which
lie to the east in LAWN HILL, from where the stratigraphy
was defined (Sweet and Hutton 1982, Hutton et al 1981).
Three formations were recognised: the Musselbrook
Formation, consisting of several sandstone units overlain
by mixed siliciclastic and carbonate rocks (much of which
is altered to chert); the Plain Creek Formation, a mainly
siltstone and shale unit with minor sandstone; and the
Lawn Hill Formation, also predominantly siltstone and
shale, but with minor carbonate rocks and a distinctive
sandstone member (Widdallion Sandstone Member) at the
top. Only the Lawn Hill Formation can be traced from its
type area in LAWN HILL, the two lower units being newly
named because a one-for-one equivalence with the other
eight formations in LAWN HILL could not be established.
Sweet (1984: figure 4) attempted broad correlations of the
units in the two regions. Further work in central MOUNT
DRUMMOND, in the Maloney Creek Inlier north of the
Carrara Range, led Sweet (1985) to also include the Maloney
Formation in the McNamara Group, rocks previously
mapped by Smith and Roberts (1963) as part of the overlying
South Nicholson Basin succession. Present mapping shows
that the succession is thinner than in the Carrara Range, and
a fourth formation, the Bullrush Conglomerate, has been
identified.
Southgate et al (2000) erected a new chronostratigraphic
framework for the Isa Superbasin following sequence
Drummond Formation (L
Pmd)
The Drummond Formation (new name, see Appendix 1) is
dominated by sandstone, but includes minor chert, siltstone,
claystone and dolomitic rocks. It forms several resistant
ridges, and lower ridges and undulating terrain, in the
Carrara Range and Maloney Creek Inlier. The formation is
divided into units L
Pmd1 to L
Pmd4 [formerly L
Pmb1c to L
Pmb1f ,
respectively, of the now abandoned Musselbrook Formation
of Sweet (1984)] in the Carrara Range. These units are too
thin to be shown on the accompanying 1:250 000 mapsheet,
but are identified herein for descriptive purposes. Sweet
(1985) recognised only a lower sandstone ‘member’ and
an upper conglomerate ‘member’ in the Musselbrook
Formation in the Maloney Creek Inlier. The lower unit is
assigned to the Drummond Formation and the upper unit
to the newly named Bullrush Conglomerate.
The thickness of the Drummond Formation is
350–400 m in outcrops north of Boomerang Waterhole;
perhaps only 300 m in the central Carrara Range;
550–600 m west of the type section, in the headwaters
of Wild Cow Creek; and at least 400 m in the Maloney
Creek Inlier. Part of the type section of the now-obsolete
Musselbrook Formation is retained as the type section
for the Drummond Formation (see Appendix 1), where
it is about 460 m thick. A composite section measured by
McConachie and Krassay (1997), 6 km east of the type
section, is 420 m thick.
Figure 19. Intermediate-scale hummocky
cross-stratification (HCS) in finegrained sublithic sandstone of Surprise
Creek Formation. Carrara, 792300mE
7933400mN, Carrara Range.
21
Unit, (map symbol),
thickness
Lithology
Depositional
environment
Stratigraphic
relationships
Marine shelf, ranging from
basinal, through storm-dominated
shoreface to shallow peritidal
environments.
Base not seen, but conformable on
Mount Les Siltstone to the north in
SEIGAL. Overlain disconformably
and with low-angle unconformity by
South Nicholson Group.
Fickling Group
Doomadgee Formation
(P
Lfd) 200–250 m
P
Lfd 3: Coarsening-up cycles from grey and
green carbonaceous? shale, through flaggy
red brown to maroon, dolomitic, micaceous,
fi ne-grained sandstone and siltstone, to
white to grey sublithic fi ne-grained sublithic
sandstone and medium to coarse sandstone
with scattered granules and pebbles; minor
lithic sandstone.
Thin and medium beds of dololutite,
dolarenite and sandy dolarenite; minor
dolomitic sandstone and intraclast breccia.
P
Lfd 2: Poorly exposed carbonaceous shale and
siltstone.
Deeper-water marine shelf.
Widdallion Sandstone
Member
(P
Lmhw) 50–370 m
Greyish red to brown, purple-weathering,
highly lithic and micaceous fi ne to coarse
sandstone; minor glauconite; siltstone and
claystone.
Inner shelf – high energy
shoreface environment.
Conformable on lower Lawn Hill
Formation; overlain disconformably,
or locally with angular unconformity,
by South Nicholson Group.
Lawn Hill Formation
(excluding L
P mhw)
(P
Lmh) 125–2600 m
Interlaminated and thinly interbedded
red, grey and brown siltstone and fi negrained sandstone; green to grey shale and
siltstone, dolomitic siltstone, laminated and
intraclastic dolostone.
Storm-dominated shelf.
Conformable on Plain Creek
Formation; overlain conformably
by Widdalion Sandstone Member;
overlain disconformably or locally
with angular unconformity by South
Nicholson Group.
Plain Creek Formation
(P
Lma) 400–1000 m
Micaceous siltstone and shale, fine- to coarsegrained lithic and sublithic sandstone; minor
pebble conglomerate, graded sandstone beds,
and pebble- to boulder-bearing mudstone–
turbidite and mass flow sediments.
Shallow to deep marine basin,
including fan deltas.
Both lower and upper contacts
concordant and conformable.
Bullrush Conglomerate Polymict granule, pebble and cobble
(P
Lmu) 50–500 m
conglomerate, cross-bedded sandstone;
clasts of quartzite, quartz sandstone,
quartz, chert, brown porphyritic rhyolite
and claystone set in lithic sand-granule
matrix; stromatolitic chert and chert-clast
conglomerate, fi ne-grained lithic sandstone
and siltstone.
Alluvial fan to fan delta.
Unconformable on Top Rocky
Rhyolite and Drummond Formation;
overlain conformably by Plain Creek
Formation.
Shady Bore Quartzite
(P
Lms) up to 50 m
White, very fi ne- to medium-grained lithic
and sublithic sandstone; prominently waverippled bedding surfaces.
Shallow marine.
Conformable on Brumby Formation;
overlain conformably by Plain Creek
Formation.
Brumby Formation
(P
Lmb) 350–800 m
Interbedded fi ne- to medium-grained, rarer
coarse to granule sandstone; laminated,
brecciated and stromatolitic chert; chert-clast
breccia and conglomerate with sandstone
matrix; siltstone and shale dominate upper
part.
Intertidal to supratidal, including
sabhka environments; deeper
shelf in upper part.
Both lower and upper contacts
concordant and conformable.
Drummond Formation
(P
Lmd) 350–600 m
Pmd1: Thin polymict conglomerate overlain
by thin- to medium-bedded, fi ne-grained
lithic sandstone, laminated siltstone, red
beds of brown lithic dolomitic sandstone
and chertified dolostone; cauliflower chert;
dark grey medium-bedded pyritic coarse
sandstone. Pmd 2 and Pmd4: White to brown,
medium- to thick-bedded, fi ne to medium
sublithic to quartzose sandstone; scattered
coarse and granule laminae; minor grey
chert. Pmd 3: Laminated kaolinised and
chertified claystone (altered carbonate
rocks?), fi ne ferruginous sandstone, siltstone,
and stromatolitic chert; fi ne, sublithic
siltstone and sandstone.
Shallow marine, from shoreface
to intertidal; peritidal mud- and
carbonate-flats, and fluvial.
Unconformable on Surprise Creek
Formation; overlain conformably
by Brumby Formation, and
unconformably by Bullrush
Conglomerate in Maloney Creek
Inlier.
Local pebble to boulder conglomerate at
base; clasts of quartz, quartzite and rhyolite
in matrix of pink, medium- to coarse-grained
sublithic sandstone; remainder is white to
pink, thick- to very thick-bedded, medium- to
coarse-grained, sublithic to quartz sandstone.
Mainly braided fluvial, with local
alluvial fan deposits at base.
Unconformable on Top Rocky
Rhyolite, and locally on older
formations of Carrara Range
Group; unconformably overlain by
Drummond Sandstone (McNamara
Group).
McNamara Group
Unassigned to group
Surprise Creek
Formation
(P
Lr) 300 to 450 m
Table 4. Stratigraphy of Surprise Creek Formation, McNamara Group and Fickling Group in MOUNT DRUMMOND.
22
P
Lmd1 (previously P
Lmb1c )
This unit, although sandstone dominated, is a mainly
recessive interval at the base of the Drummond Formation.
It contains a variety of sandstone types in the lower part
and finer grained, more thinly bedded rocks in the upper
part; it is around 100 m thick throughout the region.
Outcrops in the headwaters of Wild Cow Creek, at
754830mE 7939110mN, reveal a 2 m-thick conglomeratic
layer at its base, at a stratigraphic level where truncation
of the underlying Surprise Creek Formation occurs. The
conglomerate contains subangular to subrounded pebbles
and cobbles, and rare boulders to 30 cm of quartzite or
sandstone, set in a brown sandstone matrix. The upper
contact is rarely exposed, but in eastern outcrops, appears
to be gradational into L
Pmd 2.
The best outcrop of L
Pmd1 is north of Boomerang
Creek around 786700mE 7932040mN, where there is up
to 80 m of flaggy facies, a slabby, mottled, yellow, lithic
fine sandstone with planar bedding. The top 10–20 m, a
redbed facies, consists of brown lithic, possibly dolomitic
sandstone, with interbeds of white, rubbly, chertified
stromatolitic dolostone (Figure 20), sandy dolarenite,
peloid grainstone and dolorudite. Irregular clast-like chert
nodules are cauliflower shaped, apparently after evaporites.
At Wild Cow Creek, the basal conglomerate is overlain by
brown, thinly bedded fine sandstone and medium-bedded,
dark grey, sulfidic coarse sandstone. Much of the remainder
of the unit is not exposed, except the uppermost 2–3 m;
this consists of laminated coarse siltstone to very fine
sandstone, the laminae of which are wavy, probably small
HCS. This appears to belong to the flaggy facies; redbeds
were not observed.
ridge that is commonly strongly banded and has several
subsidiary benches, reflecting the arrangement of the
sandstones as a series of cycles. Its thickness is estimated
at nearly 200 m in the Wild Cow Creek outcrops, but only
50–70 m to the east.
In the east, the redbed facies of L
Pmd1 grades up into the
basal beds of L
Pmd 2; the basal 10–20 m contains thin chert
beds and laminae, and is more lithic and ferruginous than
the overlying rocks. Elswhere, this is not observed and near
Wild Cow Creek, where outcrop is poor, the lowest rocks
observed are laminated light grey chert and sandy chert
with small circular stromatolitic forms. Resistant mediumbedded sandstone is observed only near the top of the unit.
P
Lmd3 (previously P
Lmb1e )
Sweet (1984) described L
Pmd3 as consisting mainly of siltstone
and shale, and assigned to it a 170 m-thick interval in eastern
Carrara Range outcrops. Our estimate of the thickness of
this section is 100–150 m. The rocks include white to purple,
laminated, kaolinised and chertified ?claystone, probably
altered carbonate rocks, fine ferruginous sandstone, siltstone,
and massive stromatolitic chert. In relatively good exposures
4 km northwest of Boomerang Waterhole, 30 m of redbed
facies is overlain by 50 m of flaggy facies, which in turn, is
overlain by another 40–60 m of redbeds. These are very similar
to the facies in L
Pmd1; the redbeds include knobbly, chertified
and ferruginised dolostone and mottled brown dolomitic
sandstone with discontinuous, irregular, contorted chert beds.
The chert is parallel laminated, or with some domical and
‘button’ stromatolites. The flaggy facies is grey to white, fine
sublithic sandstone and siltstone, with parallel and sinuous
lamination and HCS. In outcrops to the west, the recessive
interval mapped as L
Pmd3 is thinner (around 80 m) and outcrop
is sparse. At 772660mE 7935560mN, exposures of the upper
part are mainly flaggy facies – centimetre-thick beds of grey to
white, parallel-laminated siltstone and sandstone, with crosslamination, lenticular bedding, HCS, flutes, tool marks, gutter
casts and rare load casts (Figure 21). A section measured by
McConachie and Krassay (1997), 8 km to the northwest, reveals
100 m of L
Pmd3 , with a similar poorly exposed lower half and
better outcropping, flaggy fine sandstone in the upper half.
P
Lmd2 (previously P
Lmb1d )
P
Lmd2 includes white, pink, brown or mottled maroon,
friable to silicified, medium to thickly bedded, fine to
medium sublithic to quartzose sandstone, and grey chert.
Mudclasts are very common and the unit displays parallel
lamination, planar bedding, and small trough cross-beds,
which commonly display a herringbone pattern with
one current direction dominant. L
Pmd2 forms a resistant
Figure 20. Stromatolitic chert, closely
associated with redbeds in lower
Drummond
Formation.
Carrara,
792300mE 7933400mN, Carrara Range.
23
P
Lmd4 (previously P
Lmb1f )
This is a white, medium- to thickly bedded, fine- to
medium-grained sublithic to quartzose sandstone, with
scattered coarse laminae and granules. Sedimentary
structures include planar bedding, trough cross-bedding,
current lineations, wave ripple marks and mudclasts.
L
Pmd4 is similar to L
Pmd 2, although generally more lightly
coloured, and ranges from 40 to 100 m thick. It appears
to grade upwards from L
Pmd3. McConachie and Krassay
(1997) reported hematite clots at several stratigraphic levels
and interpreted them as pseudomorphs after gypsum.
south of Bullrush Spring, there are good exposures of dark
purple to red, laminated and structureless mudstone, with
scattered coarse sand grains, and metre-scale interbeds
of mauve, medium and thickly bedded, medium to coarse
lithic sandstone; this is commonly poorly sorted and has
linguoid current ripples and scattered mudclasts. Some
outcrops weather in a fashion suggesting the presence of
dolomitic rocks, although none was identified in outcrop.
These reddish mudstone, siltstone and sandstone interbeds
Pmd3 to
probably equate to the redbeds in units L
Pmd1 and L
the south in the Carrara Range, although no subdivision
into units is possible. The base of the Drummond Formation
is not exposed and the top may be eroded, so the estimated
thickness of 400 m by Sweet (1985) for the Maloney Inlier
is a minimum.
Based on the range of rock types preserved, depositional
environments for the Drummond Formation are inferred to
have been: shallow marine, from shoreface to intertidal,
and dominated by siliciclastic facies; peritidal mud- and
carbonate flats (sabkhas); and fluvial. The association of
recessive redbeds, carbonate rocks and chert with resistant,
better-sorted cross-bedded sandstone suggests that the
formation was built up of a succession of prograding cycles
across a shallow-marine shelf, culminating in largely
supratidal environments.
Maloney Creek Inlier
Sweet (1985) recognised two informal ‘members’ (Pmbs
and L
Pmbc ) in the now abandoned Musselbrook Formation in
the Maloney Creek Inlier. The lower unit, L
Pmd (previously
L
Pmbs ), is assigned to the Drummond Formation, although
it is possible that the upper part extends into the Brumby
Formation. The four-fold subdivision of the formation
in the Carrara Range is not applicable in the Inlier. The
conglomerate interval (previously L
Pmbc ) is assigned to a
new unit, the Bullrush Conglomerate (discussed below).
The base of the Drummond Formation is not exposed in
the Inlier; the oldest beds lie in the core of an anticline near
Moloney Creek and are faulted at other localities. The upper
contact is sharp and overlain by conglomerate of the Bullrush
Conglomerate; it is interpreted as an unconformity.
The Drummond Formation in the Maloney Creek Inlier
is characterised by pink, medium to thickly bedded, fine to
medium sandstone (Sweet 1985). Decimetre-scale coarser
beds include granules and pebbles of chert, sandstone and
quartz up to 2 cm across. Sweet (1985) noted the presence
of oolitic dolostone pebbles near the base of the exposed
section. Sedimentary structures include planar bedding,
medium-scale trough cross-bedding, wave and current
ripples, and mudclasts. Recessive intervals up to 10 m thick
consist of thinly to medium bedded, red-brown to maroon,
medium-grained sandstone and white to purple siltstone
with carbonate nodules (‘caliche’). Outcrop is poor in the
western part of the Maloney Creek Inlier, between George
and Little Cleanskin creeks, due a pervasive, resistant
weathering crust of ?Cenozoic age (Sweet 1985). However,
Brumby Formation (L
Pmb)
The Brumby Formation (new name, see Appendix 1)
consists of siltstone, shale, sandstone and granule
conglomerate, laminated and stromatolitic chert,
dolostone, and chert-clast conglomerate and breccia. The
carbonate and fine siliciclastic rocks are generally highly
weathered or altered, and Sweet (1984) considered this to
be mainly due to the effects of Cenozoic deep weathering,
silicification and lateritisation, and to a lesser extent, to
their inferred dolomitic nature. The formation outcrops as
subdued strike ridges, flanking the more resistant ridges
of the underlying Drummond Formation throughout the
Carrara Range. The uppermost parts are very poorly
exposed in undulating low rises. The Brumby Formation
comprises the unnamed former ‘members’ L
Pmb2 and L
Pmb3
Figure 21. Shale outcrop in upper
Drummond Formation (L
Pmd 3 ). Carrara,
772650mE 7935550mN, 10 km north of
Fish-Hole Waterhole.
24
of the now abandoned Musselbrook Formation of Sweet
(1984). Although the two-fold subdivision remains valid,
it is not shown on the accompanying 1:250 000 mapsheet.
The formation overlies the Drummond Formation
conformably, the contact being placed at the stratigraphic
level at which chert and fine siliciclastics dominate
over sandstone. The Shady Bore Quartzite overlies the
formation throughout the Carrara Range. Although the
contact is not exposed, the quartzite is interpreted as the
uppermost part of a shallowing-up cycle, and is therefore
believed to lie conformably on the Brumby Formation.
The Brumby Formation is absent from the Maloney Creek
Inlier, where Bullrush Conglomerate unconformably
overlies Drummond Formation.
The Brumby Formation is 725 m thick in the now
obsolete type section of the Musselbrook Formation
nominated by Sweet (1982). It thins to 350 m in a new type
section, 6.5 km to the east (Figure 22), and thickens to
nearly 800 m, 5.5 km to the west of the old type section.
Sweet (1984) inferred a thickening eastwards from the
former Musselbrook type section, but this cannot be
substantiated and may be due to fault repetition of the
succession.
Sandstone, conglomerate, and chert are common in the
lower half of the type section of the Brumby Formation
(L
Pmb2), exceeding the proportion of siltstone and shale,
whereas the latter dominate in the upper half (L
Pmb3). The
rare outcrops of the fine siliciclastic rocks are invariably
leached or limonitic, and sedimentological information is
lacking. Coarser siliciclastic rocks include both sandstone
and conglomerate. Sandstones are more thinly bedded and
finer grained than those in the Drummond Formation, and
are therefore less resistant to weathering. They include
grey to pink, well sorted quartz arenites, and some that
are purple and more hematitic. Most sandstones are fine
grained, ranging into medium and less common coarsegrained varieties with scattered granule and pebble lags,
and are thinly to medium bedded and planar or trough
cross-bedded. Many bedding surfaces are rippled;
sinuous-crested asymmetric forms are most common.
McConachie and Krassay (1997) reported that many of
the sandstones have a matrix, or thin laminae, of chert
intimately associated with sand grains, but much of this
could be secondary, replacing mudstone or carbonate
laminae. Hematite clots, interpreted by them as probable
gypsum pseudomorphs, are present. Thicker units of chert
are closely associated with sandstone in the lower 200 m
of the Brumby Formation. At least ten bands of laminated
and stromatolitic chert were recognised by McConachie
and Krassay (1997, Figure 22), ranging in thickness from
1 to 12 m. They include pink laminated chert, chert breccia
with circular (stromatolitic) laminae, hematitic and cherty
sandstone with vague stromatolite-like structures, and
clearly stromatolitic rocks, in which the forms range from
small columns, 1–5 cm diameter and several centimetres
high, to broad domes up to 25 cm across. Much of the
chert has a high quartz sand content, or ranges into cherty
sandstone, indicating a mixed siliciclastic–carbonate
lithology prior to silicification. Many chert layers are
highly brecciated and primary structures have been
largely obliterated, due to silicification and weathering.
Key to symbols
trough cross-beds
asymmetric ripples
300
pseudomorphs after gypsum
domical stromatolites
columnar stromatolites
hematitic cement
chert-clast conglomerate/breccia
sandstone
pebble-cobble conglomerate/breccia
silicified carbonate rocks
200
100
0
silt, mud
vf mvc p
A07-233.ai
Figure 22. Type section of Brumby Formation in Carrara Range,
11 km northwest of Mount Drummond; base of section is at
766720mE 7938870mN [generalised from unpublished NABRE
measured section, archival material summarised in McConachie and
Krassay (1997)]. Proportion of carbonate rocks is underestimated
because of silicification; outcrop is poor to absent in upper part of
section.
25
Sedimentary chert breccia and conglomerate are also
common, occurring as intervals up to a few metres thick
throughout the lower half of the formation. Beds range from
1 to 5 m thick, and comprise angular to subrounded, white
to pink chert clasts, 1–10 cm in diameter, set in cherty or
fine to medium sandy matrix; they are generally associated
with sandstone beds. Rarely, breccias are associated with
stromatolitic chert layers.
The upper part of the Brumby Formation is unexposed
in the type section (Figure 22) and is poorly exposed
elsewhere. Sweet (1984) reported that the rocks are
predominantly siltstone, much of which is possibly
dolomitic. Rare outcropping beds include a stromatolitic
chert with columnar stromatolites up to 10 cm diameter.
Near the top of the formation is a flaggy to blocky, thin to
medium bedded, medium to coarse sandstone with granulerich bands, overlain by a conglomerate in which the clasts
are tabular angular chert and claystone clasts, 10–20 cm
across.
The mixed siliciclastic/carbonate/chert association
that characterises the lower Brumby Formation appears
to represent a carbonate ramp environment, similar to
that of the Paradise Creek and Esperanza formations, but
given the higher proportion of siliciclastic material, in a
more proximal position relative to sediment source. Much
of the chert, particularly that associated with quartz sand
in conglomerate and breccia layers, resulted from early
lithification and silicification, and was reworked into the
coarse clastic layers. This suggests that there were repeated
episodes of exposure and silicification, followed by
erosion and renewed inundation, placing the depositional
environment in very shallow water, probably intertidal
and supratidal. The upper Brumby Formation, which is
dominated by fine-grained rocks, is likely to represent
deeper water (shelf) environments, but no analysis of these
is possible.
The Shady Bore Quartzite consists of white, thinly to
thickly bedded, fine- and medium-grained lithic and sublithic
sandstone, displaying some cross-bedding and prominent
wave ripple marks on bedding surfaces. In exposures in the
headwaters of No Mans Creek, at 754376mE 7940724mN,
the formation consists of at least five to six major cycles of
upward-thickening beds. Mudstone partings are present in
the lower parts of the cycles, indicating a subtle upwardcoarsening trend as well. Above the uppermost thick
sandstone bed is an abrupt thinning of beds and a trend to
very fine-grained lithic sandstone, over some 5 m, marking
a rapid transition into lower-energy facies of the overlying
Plain Creek Formation. A ridge of similar fine-grained
lithic sandstone, bearing extensive ripple-covered bedding
surfaces, between Bull and Wild Cow Creeks at 758038mE
7934706mN, is reinterpreted as Shady Bore Quartzite
rather than middle Musselbrook Formation, as mapped by
Sweet et al (1984). Thus, the succession above it to the west
comprises the Plain Creek and Lawn Hill formations.
The Shady Bore Quartzite in MOUNT DRUMMOND
represents a series of upward-shallowing cycles in a wavedominated, marine shoreline environment.
Bullrush Conglomerate (L
Pmu)
The Bullrush Conglomerate (new name, see Appendix 1)
replaces the former unnamed conglomerate ‘member’
L
Pmbc, the upper part of the now obsolete Musselbrook
Formation, as described by Sweet (1985) in the Maloney
Creek Inlier. It overlies the Drummond Formation in most
outcrops, but also overlies a small inlier of Top Rocky
Rhyolite in Moloney Creek, around 778127mE 7955860mN.
The contacts with both are interpreted as unconformable.
The conglomerate is overlain by the Plain Creek Formation,
probably conformably.
Sweet (1985) estimated the thickness of the Bullrush
Conglomerate to be 500 m in the type section, north of
the confluence of Moloney Creek and the South Nicholson
River. It thins rapidly westward to 50 m or less, 1.5 km
southwest of Bullrush Spring, where it appears to truncate
underlying redbeds of the Drummond Formation. Sweet
(1985) described the unit as consisting of polymict granule,
pebble and cobble conglomerate in units up to 20 m thick,
alternating with cross-bedded sandstone. Conglomerates
are massive or crudely planar bedded, trough cross-bedded
or graded. They are largely clast supported, comprising
clasts of quartzite or quartz sandstone, quartz, chert,
brown porphyritic rhyolite, and claystone (probably
altered/weathered dolomitic rocks), set in a matrix of lithic
sand to granules. Subangular to well rounded clasts of pink
quartzose to brown ferruginous sandstone account for up
to 50% of all clasts in most outcrops. However, some beds
are richer in angular to subangular chert and claystone
clasts.
Our investigations show that the range of rock types
is broader than that presented by Sweet (1985); carbonate
interbeds are present in the lower part of the section,
and sandstone and siltstone are present throughout. The
carbonates are massive, white and chalky (altered) chert
with relict stratiform, domical, conical and digitate
stromatolites, and parallel lamination. These are overlain
Shady Bore Quartzite (L
Pms)
The Shady Bore Quartzite outcrops extensively in the
Lawn Hill Platform in LAWN HILL and CAMOOWEAL
(Hutton et al 1981, Sweet and Hutton 1982, Hutton and
Wilson 1985), 100 km east of MOUNT DRUMMOND.
Mapped by Sweet et al (1984) as an unnamed basal
sandstone ‘member’ (L
Pmas) of the Plain Creek Formation
in Carrara R ange R egion, it was nevertheless considered
by Sweet (1984: 14) as being equivalent to the Shady Bore
Quartzite, a view supported by McConachie and Krassay
(1997). The name therefore now replaces the former L
Pmas in
MOUNT DRUMMOND. The formation forms a distinctive
upstanding ridge, flanked on either side by recessive rocks.
Contacts are not observed, but in a measured section at
767706mE 7939459mN (McConachie and Krassay 1997),
stromatolitic chert is present 3 m below the lowest sandstone
bed, and the contact is likely to be conformable. The upper
contact is conformable, and is marked by an abrupt upward
fining of the sandstone. A thickness of around 50 m was
estimated by Sweet (1984: 13) for the Shady Bore Quartzite
in the Plain Creek Formation type section (767727mE
7944567mN). In the section measured by McConachie and
Krassay (1997), 5 km to the south, it is 40 m thick.
26
by matrix- to clast-supported chert-clast conglomerate,
comprising white to blue-grey and pink chert clasts, and
lesser rounded sandstone clasts, in a pale brown chert–
quartz sand matrix that lacks obvious stratification. Clasts
average 2–5 cm, but are up to 35 cm in diameter, and are
angular and ungraded. This unit may be a palaeoregolith
on the carbonate unit. The sandstone is white, silicified,
medium- to very thickly bedded, fine- to very coarsegrained, and sublithic; it is trough cross-bedded and
contains scattered pebbles and cobbles. Finer siliciclastics,
similar to the flaggy facies in the Drummond Formation to
the south, form 10–50 m-scale interbeds. They include redbrown to fawn, fine-grained lithic sandstone and siltstone.
Sedimentary structures include small trough cross-beds,
planar lamination, current lineation, mudclasts, symmetric
ripples (sinuous and interference types with wavelengths to
10 cm), and probable HCS.
The apparent superposition of several contrasting facies
types is puzzling, as is the considerable variation in clast
composition between conglomerates in the succession.
Assuming that there are not unrecognised strike-parallel
faults within the succession, it is likely that major eastnortheast-trending mapped faults have been reactivated
along older basement fractures. These may represent sites
of strike-slip faulting at local sub-basin margins, and
could account for the variable composition of clasts in the
conglomerates. The Brumby Formation, which overlies
the Drummond Formation to the south in the Carrara
Range, is absent from the Maloney Creek Inlier, implying
that substantial erosion took place before the Bullrush
Conglomerate was laid down. Clast types in the conglomerate
suggest that a lower McNamara Group terrane, mainly of
Drummond and Brumby formations, with minor outcrop of
the underlying Carrara Range Group, was rapidly eroded.
Sweet (1985) interpreted the overlying rocks (now Plain
Creek Formation) as fan delta deposits, and this model also
fits the Bullrush Conglomerate; the coarse clastic beds are
most likely alluvial fans, and the intercalated finer beds,
with a range of sedimentary structures including wave
ripples and HCS, indicate that they are probably marine.
Alluvial fans were building out into a standing body of
water, leading to an alternation of marine and non-marine
environments. The Bullrush Conglomerate was deposited
in dominantly subaerial environments, whereas the Plain
Creek Formation was predominantly subaqueous.
the recessive interval below it are now included in the Plain
Creek Formation.
The Plain Creek Formation is dominantly siltstone
and shale, but contains several sandstone units, resulting
in a series of parallel ridges and valleys in outcrop. This
distinguishes it from the overlying, predominantly recessive
Lawn Hill Formation. The lower contact, with the Shady
Bore Quartzite, is conformable and gradational; in the
headwaters of No Mans Creek, at 754370mE 7940730mN,
it grades upward over 5 m, from thickly bedded white
sandstone of the Shady Bore Quartzite to thin beds of very
fine-grained lithic sandstone, and then into siltstone or shale.
The upper boundary is not exposed, but is placed at the top
of the uppermost topographically resistant unit and is also
presumed to be conformable. In the Bluff Range around
784030mE 7946170mN, the Plain Creek Formation is overlain
with angular unconformity by the Constance Sandstone. The
formation ranges in thickness from less than 400 m north
of Bullrush Spring in the Maloney Creek Inlier and about
500 m near No Mans Creek, to nearly 1000 m in the Bluff
Range, although it is possible that there is fault repetition
in this section. Sweet (1984) estimated the type section as
550 m thick (excluding the Shady Bore Quartzite).
Sweet (1984) described the Plain Creek Formation
as mainly micaceous siltstone and shale, with interbeds
of flaggy to blocky, fine- to medium-grained, wellsorted quartz-rich sandstone with micaceous partings.
Observations from the present survey reveal that most of the
sandstone units are of a distinctive type; they are arranged
in cycles, a few metres thick, of upward-thickening and
-coarsening beds, which are stacked to form the resistant
units observed during mapping (Figure 23). The bases
of the cycles are shale or laminated siltstone, grading up
through laminated and thinly bedded, very fine-grained
lithic sandstone to thin to medium beds of very fine or
fine-grained sandstone. Rarely, medium to coarse-grained
sandstone, some with mudstone intraclasts, is present in
the upper parts of cycles. The thicker and coarser beds
range from 20 to 40 cm thick, and some are individual
hummocky cross-stratified units. Most of the finer rocks
are parallel laminated, although minor lenticular or rippled
forms are present. In the thick Bluff Range section, the
lowest resistant ridge is of this type, whereas the next ridge
is of medium-bedded, coarse- to very coarse-grained lithic
sandstone. Bedding is undulating, with shallow troughs,
gently inclined laminae and planar bedding, suggesting
swaley cross-stratification. Within 15 m stratigraphically
above this level is a 1 m thick, internally structureless
grey chert bed. Higher in the same section the sandstones
are mainly fine-grained, and locally, are convolute
laminated.
In the Maloney Creek Inlier, unit P
Lmh t and the finegrained rocks below it, mapped by Sweet (1985) as
Lawn Hill Formation, are now recognised as Plain Creek
Formation; P
Lmht is not delineated on the map. Sweet
(1985) described four lithofacies in the formation in the
Inlier. Facies 1 (fine-grained clastics) includes shale,
siltstone and very fine-grained sandstone as described
above. Desiccation cracks (not synaeresis cracks) were
observed in one outcrop of this facies. Facies 2 (crossbedded sandstone and conglomerate) is a 1 m bed of
Plain Creek Formation (L
Pma)
The Plain Creek Formation was defined by Sweet (1982) on
the basis of mapping in the Carrara Range region (Sweet
1984), where it is a mainly recessive unit punctuated by
several upstanding sandstone ridges. A sandstone unit
previously included as a basal unit of the formation is now
excluded, and is instead recognised as Shady Bore Quartzite
(L
Pms). The remainder of the Plain Creek Formation is
therefore redefined (see Appendix 1), and although the
type section is retained, a reference section is nominated
at the location of the section measured by McConachie
and Krassay (1997), 5 km south of the type section. Sweet
(1985) mapped a turbidite unit, L
Pmh t within the Lawn Hill
Formation in the Maloney Creek Inlier, but this unit and
27
well sorted pebble conglomerate grading up into pebbly
cross-bedded sandstone. Clasts include quartzite, chert
and claystone (altered carbonate?). Facies 3 and 4 are,
respectively, graded coarse to fine clastic rocks and pebbly
mudstone; both are present in Pmh t. The coarse beds are
2 cm to 0.5 m thick, with sharp bases bearing tool marks
and flute casts (Figure 24). Facies 4, which also occurs as
interbeds below P
Lmh t, contains clasts up to 0.3 m, set in a
structureless sandy mudstone matrix.
Thin films and veins of manganese and iron oxides
are common throughout the Plain Creek Formation in
the region, particularly in the No Mans Creek section.
Unusual, irregularly and wavy-bedded, granular porous
rocks are interbedded with the lowest sandstone unit
in this locality; these may be intraclast conglomerates,
perhaps containing carbonate, but their origin is
unknown. The upper resistant ridges in this section
are either structureless silicified siltstone/claystone, or
very fine-grained sandstone; no coarse sandstones were
observed.
The combination of mainly fine-grained siliciclastic
rocks, and cycles of upward-thickening and -coarsening
beds, with associated hummocky and swaley cross-
stratification and minor intraclast conglomerates and
ripples, points to a storm-dominated shelf environment,
with the coarsest rocks indicating shoreface facies. The
convoluted beds indicate that there was some gravitational
instability and slumping, due perhaps to a combination of
high depositional slopes and the water content of newly
deposited sediments. The thin succession in the Maloney
Creek Inlier contains both very shallow-water sands with
evidence of desiccation, and graded and massive rocks
(facies 3 and 4), which are turbidites and mass flow
(slump) deposits, respectively, suggestive of deeper water
and relatively steep or unstable depositional slopes. These
facies are consistent with rapid changes in water depth,
due perhaps to the existence of small fault-generated
sub-basins, into which subaerial fans were building. The
coarse rocks are not fan deposits, but rather gravity flow
deposits generated beyond the toe of fans, which may have
built out into standing water rather than being subaerial;
ie they fit the description of a fan delta, as proposed by
Sweet (1985). Turbidites may also be present outside of
the Maloney Creek Inlier, although the poor outcrop and
alteration of the rocks precludes definite identification
of these.
Figure 23. Alternating mudstone and
sandstone beds in Plain Creek Formation.
Recessive beds are laminated to thinly
interbedded shale, siltstone and very fine
sandstone; white to grey, well indurated
beds are very fine to fine sandstone with
HCS. Cleanskin, 814800mE 7956420mN,
headwaters of Right Creek, 2 km west of
NT/Queensland border.
Figure 24. Tool marks and flute casts
on base of sandstone bed in Plain Creek
Formation, Maloney Creek Inlier.
Cleanskin,
778120mE 7960770mN,
15 km northeast of Murun Murula.
28
Lawn Hill Formation (L
Pmh)
Hill Formation is much thinner in the Maloney Creek Inlier
north of Bullrush Spring; depending on the assumed dip,
it is between 300 m and 450 m, including the Widdallion
Sandstone Member. The lower recessive part of the
formation is only 125–200 m thick, indicating a substantial
northward thinning overall.
Subdivision of the Lawn Hill Formation into units L
Pmh1 to
L
Pmh6, as introduced by Sweet and Hutton (1982) in the Lawn
Hill region 100 km to the east, is not possible in MOUNT
DRUMMOND. Only a lower fine-grained component and
an upper coarse one, the Widdallion Sandstone Member
(L
Pmh5), are recognised. It is also unclear whether the lower
fine-grained rocks are equivalent to units L
Pmh1 to L
Pmh6, as
the base of the formation cannot be traced from the Lawn
Hill area. The lower unit consists, in outcrop, of grey,
green and red, variably leached, laminated shale, siltstone
and very fine-grained sandstone. Sweet (1984) observed
concretions at 802930mE 7946660mN and regarded these
as an indicator of likely equivalence to L
Pmh1 at Lawn Hill,
as this unit contains similar concretions (Sweet and Hutton
1982: 22). However, the outcrops are isolated, and on the
basis of regional structure, it is possible that these rocks
could be as old as upper Brumby Formation.
Data on the lithology of the Lawn Hill Formation
have come from base metals exploration by Rio Tinto in
2000–2001 (Walker 2000, Walker and Johnson 2001).
Cuttings are available from an extensive grid of RAB holes
drilled over areas named Brumby and Monsoon, in the
lower reaches of Brumby and Western Creeks, respectively.
The cuttings are overwhelmingly of siltstone and range
in colour from oxidised red, yellow and brown, through
to grey. They are commonly interlaminated with finegrained sandstone on a sub-centimetre scale. Dolostone is
present in several of the holes in an area 2–3 km south and
southwest of the confluence of Brumby and Western creeks,
and dolomitic siltstone occurs 13 km to the southwest. All
of these occurrences appear to be from stratigraphically
low levels in the formation. In contrast, the only dolostone
occurrences in outcrop have been recorded from near the
top of the formation in eastern MOUNT DRUMMOND,
in the Border Waterhole section. There, Sweet (1984) and
McConachie and Krassay (1997) recognised laminated and
intraclastic dolostone and dolomitic siltstone in the upper
100 m of the approximately 800 m-thick exposed section.
Shale dominates the lithology in most of that section.
The fine-grained rocks of the Lawn Hill Formation are
characteristic of a marine shelf environment, mainly below
wave-base, although the interbedded sandstone indicates
some slightly higher-energy conditions above wave base,
consistent with storm influence.
Previously mapped as Bluff Range beds by Smith and
Roberts (1963), the Lawn Hill Formation was recognised
in the Carrara Range Region by Sweet (1984) on the
basis of a broad similarity with the formation in its type
area in LAWN HILL to the east (Sweet and Hutton 1982).
A particularly distinctive feature is the presence of a
sandstone unit (Widdallion Sandstone Member) at its top.
In MOUNT DRUMMOND, most areas underlain by the
Lawn Hill Formation are recessive. They are mantled by a
thin veneer of Cenozoic sand and gravel, and outcrops are
largely confined to creek beds and gullies. The exception
is southwest of Border Waterhole, where the formation is
exposed in low hills and benches. The Widdallion Sandstone
Member is more resistant and forms a low strike ridge in
most outcrops.
The lower boundary of the Lawn Hill Formation is
conformable and is placed at the top of the uppermost
resistant sandstone of the Plain Creek Formation. The upper
contact is invariably unconformable; the Playford Sandstone
lies disconformably, or with angular unconformity on the
Widdallion Sandstone Member in most outcrops. However,
in eastern outcrops, the Constance Sandstone lies with
a gentle angular unconformity on the lower Lawn Hill
Formation, and indeed truncates the underlying Plain
Creek Formation in an east-northeast-trending belt from
784030mE 7946170mN. Both the Lawn Hill and Plain
Creek formations are truncated by Cambrian rocks south
of Border Waterhole, at the eastern margin of MOUNT
DRUMMOND.
Sweet (1984) estimated a thickness of 1000–1500 m
for the Lawn Hill Formation in an east-northeast-striking
belt paralleling the course of Western Creek. Given that
the Widdallion Sandstone Member is now recognised to be
more restricted than previously believed (see below) and that
dips may be lower than assumed by Sweet, a maximum of
1000 m for this section is now estimated. The outcropping
section southwest of Border Waterhole, which lacks any
Widdallion Sandstone Member, includes 780 m of Lawn Hill
Formation (McConachie and Krassay 1997). A very thick
section of subcrop and a local depocentre is inferred to exist
to the west of Wild Cow Creek, on the basis of measured
dips and outcrops of the surrounding units (Wild Cow
Sub-basin). To the east of this sub-basin, rocks previously
mapped (Sweet et al 1984) as Musselbrook Formation, and
reinterpreted as Plain Creek Formation, dip west at 20–50°.
Sandstone, 2.5 km northwest of Wild Cow Creek, dips at 40°
northwest and is now recognised as Widdallion Sandstone
Member rather than lower Musselbrook Formation. These
outcropping rocks are separated by a 4 km-wide nonoutcropping zone, potentially underlain by the Lawn Hill
Formation. Depending on the assumed dip, this yields an
inferred thickness of between 1400 and 2600 m for the finegrained lower part, or between 1700 and 3000 m including
the Widdallion Sandstone Member, which is substantially
more than elsewhere in the region. The limits of the Wild Cow
Sub-basin are not known, as Proterozoic rocks are overlain
by Cambrian rocks to the southwest, but the possibility
exists that the thicker section extends west-southwest into
the covered area south of Mitchiebo Waterhole. The Lawn
Widdallion Sandstone Member (L
Pmh w )
The Widdallion Sandstone Member, the second-youngest
mappable member of the Lawn Hill Formation in LAWN
HILL (Sweet and Hutton 1982), was defined from that area
by Hutton et al (1981). It was subsequently recognised in the
Carrara Range Region by Sweet (1984, 1985), on the basis of
stratigraphic position and lithological similarity to the type
area. The member forms low banded strike ridges in most
outcrops. Present mapping has shown that the upper parts
of the unit, as mapped by Sweet (1984), are best assigned
29
to the overlying Playford Sandstone, and the Widdallion
Sandstone Member is thus thinner than previously stated.
The youngest component of the Lawn Hill Formation in the
type area, L
Pmh6 (Sweet and Hutton 1982), is absent from
MOUNT DRUMMOND.
The lower contact of the Widdallion Sandstone
Member is not exposed, as the recessive part of the Lawn
Hill Formation below it is invariably soil-covered, but it
is presumed to be conformable. An angular unconformity
with the overlying Wangalinji Sandstone Member
of the Playford Sandstone is evident 7 km southwest
of Mitchiebo Waterhole, at 717100mE 7932300mN.
Elsewhere, the contact is concordant, but an abrupt
change from lithic sandstone to white granule- to pebblerich sandstone (Wangalinji Sandstone Member) has led to
our interpretation of a disconformable relationship. The
Widdallion Sandstone Member is about 50 m thick in the
Western Creek–Mitchiebo Waterhole outcrops, although
this is a minimum estimate, given the unexposed lower
contact and the likelihood of erosion of the top. It is
between 175 and 250 m thick in the Maloney Creek Inlier,
and even thicker (around 370 m) in the Wild Cow Subbasin, 3 km northwest of Wild Cow Creek, at 749230mE
7936900mN.
The characteristic lithology of the Widdallion Sandstone
Member is grey-red to brown, purple-weathering, highly
lithic and micaceous, fine-, medium- and less commonly
coarse-grained sandstone. Beds are medium to very
thick (up to several metres) and are commonly arranged
in cycles from 5 to 20 m thick; cycles typically become
coarser, better sorted, slightly less lithic and lighter
coloured upwards. Scattered granules and small pebbles
of quartz and sandstone occur in the upper parts. Western
outcrops are all of sandstone, whereas laminated siltstone
and claystone occur to the east. Lower parts of cycles
display large low-angle cross-beds, and an outcrop north of
Bullrush Springs at 766820mE 7961830mN is hummocky
cross-stratified, in places, transitional into angle-of-repose
foresets. Upper parts of cycles are trough cross-bedded on
a medium to large scale, and in the westernmost outcrop,
7 km southwest of Mitchiebo Waterhole, the sandstone
appears to be glauconitic. Wave and interference ripple
marks and primary current lineation are common on bed
tops and in foreset laminae, respectively. In northern
outcrops, 1.5 km northwest of Bullrush Spring, a 10 mthick band of sandstone is cross-bedded on a very large
scale.
The character of the sedimentary cycles in the
Widdallion Sandstone Member, and the presence of HCS,
large cross-beds, and wave ripples indicate repeated
progradational episodes in a high-energy shoreface
environment. The highly lithic nature of the sandstone
suggests that sedimentation was rapid and was derived
from an actively uplifting source terrain.
• A very thin section in the Maloney Creek Inlier (columns
4, 5). There, the whole section is condensed, but in
addition, much of the lower part of the section has been
eroded or not deposited and the facies reflect a much
more active depositional setting and instability in that
area.
• The relatively thin lower units (Drummond and Brumby
formations) in the central Carrara Range; these may
thicken slightly into the Wild Cow Sub-basin.
• Units above the Shady Bore Quartzite that thicken
slightly towards the east and markedly into the Wild
Cow Sub-basin, and thin markedly to the north into the
Maloney Creek Inlier.
Overall the range of facies is somewhat broader than
those in the equivalent units to the east in LAWN HILL.
For instance:
• Coarse sandstone and chert breccia in the Brumby
Formation suggest greater subaerial exposure,
silicification and possibly a more proximal position
relative to the sediment source, than in the Paradise
Creek–Esperanza formations.
• Conglomeratic rocks of the Bullrush Conglomerate
in the Maloney Creek Inlier are unlike facies seen
elsewhere and indicate active uplift and local erosion
of older units of the McNamara Group and underlying
Carrara Range Group.
• The Plain Creek Formation is not as thick and contains
a lower proportion of turbiditic sandstone, compared
with the Riversleigh and Termite Range formations,
although more proximal facies (pebbly mudstone–
slump deposits) indicate steeper depositional slopes
locally.
• The Lawn Hill Formation lacks carbonaceous shales in
the observed outcrops, although the imputed thickening
of both this and the Plain Creek Formation into the Wild
Cow Sub-basin offers the possibility that such facies
may exist locally.
Fickling Group
The Fickling Group, in northeastern MOUNT
DRUMMOND, is an extension of a wide belt of outcrop
which extends from Hedleys Creek, in Queensland, westsouthwest into Seigal. In mapping Seigal, to the north of
Cleanskin, Sweet et al (1981) raised the status of the Fickling
beds of Carter (1959) to Fickling Group, and recognised
four formations: from base to top, Fish River Formation,
Walford Dolomite, Mount Les Siltstone and Doomadgee
Formation. The Doomadgee Formation was divided into
three informal ‘members’ and of these, the upper two,
units L
Pfd 2 and L
Pfd3, extend south into Cleanskin, where
they include shale and siltstone, dolostone, and a range
of sandstones from fine-grained lithic through to coarsegrained and granule-rich quartz-dominated varieties.
Bradshaw et al (2000) demonstrated that the Doomadgee
Formation to the west of the Gorge Creek area in Hedleys
Creek, and therefore in Seigal, differs from that to the
east. Since both the Mount Les Siltstone and Doomadgee
Formation are defined from the western area, it appears
Synthesis of McNamara Group
Estimates of thickness made by Sweet (1984, 1985),
supplemented by new data, including that of McConachie
and Krassay (1997), are summarised in Figure 25. Although
the data are incomplete, notable features include:
30
by Sweet et al (1981: 18). The original thickness of the unit
is not known, as the uppermost strata were eroded before
being overlain disconformably or with gentle angular
unconformity by the South Nicholson Group. The contact
is locally concordant in Cleanskin, but the angular nature
of the unconformity is quite clear in Seigal, where the basal
member of the Constance Sandstone truncates progressively
lower units of the Fickling Group northward towards the
Murphy Inlier.
that useage of the name Doomadgee Formation in MOUNT
DRUMMOND remains appropriate, although a further
reappraisal of the stratigraphy in Hedleys Creek is likely to
lead to further changes in the stratigraphic nomenclature.
Doomadgee Formation (L
Pfd)
The presence of informal unit L
Pfd3 in a northeast-trending
anticline in northeastern Cleanskin is based on its continuity
of outcrop from Seigal (Sweet et al 1981). Outcrop consists
of low rubbly rises and terraced low hills, except for a ridgeforming resistant sandstone bed in the lower part. This
bed, near the anticlinal axis, is cut by a northeast-trending
fault on the southeastern limb, resulting in two horseshoeshaped ridges open to the southeast. It is interpreted as
the basal sandstone of L
Pfd3, and recessive beds in the core
of the anticline are therefore mapped as L
Pfd 2. Only a few
tens of metres of L
Pfd 2 are present, whereas L
Pfd3 is at least
200 m thick, perhaps up to 250 m at the northern margin of
Cleanskin, but less than the 400 m ‘south of Seigal’ stated
Unit P
L fd3
In L
Pfd3, four distinct lithofacies, interbedded on a
10–100 m scale, and totalling over 200 m, are recognised.
The dominant flaggy facies, consists of flaggy, red-brown
to maroon, dolomitic, micaceous, fine-grained sandstone
MALONEY CREEK INLIER
4
5
w
h
a
Unit P
L fd2
P
L fd2 is not exposed, but is assumed to consist of a few tens
of metres of carbonaceous shale and siltstone, based on
descriptions by Sweet et al (1981: 18).
h
u
a
d
u
d
w
3
w
w
h
a
a
h
d
r
7
a
h
h
b
6
a
s
CARRARA RANGE REGION
b
d
2000
r
Little
a
e
R a ng
F au
lt
1500
metres
1
2
s
1000
500
b
0
South Nicholson Basin
Lawn Hill Platform and basement
Formation incomplete fault or unconformity contact
Formation boundary present
1
Wild Cow
2
Carrara west
3
Carrara central
4
Bullrush Spring
5
10
w
Widdallion Sandstone Member
h
Lawn Hill Formation
a
Plain Creek Formation
Moloney Creek
s
Shady Bore Quartzite
6
Bluff Range
u
Bullrush Conglomerate
7
Border Waterhole
b
Brumby Formation
d
Drummond Formation
r
Surprise Creek Formation
A07-232.ai
Cambrian and younger
5
kilometres
Figure 25. Thickness summary for McNamara Group. Fence diagram showing seven sections of parts of the group. Carrara central section
is based on measured sections by McConachie and Krassay (1997); other sections are calculated from outcrop widths, aerial photographs
and measured dips.
31
individual formations (Southgate 2000). These studies,
and a sequence stratigraphic reconnaissance in MOUNT
DRUMMOND by McConachie and Krassay (1997), permit
meaningful estimates to be made for the age and correlations
of the formations in MOUNT DRUMMOND. Figure 27
summarises the correlations we prefer and minor differences
with the scheme of McConachie and Krassay (1997). In
addition to the overall similarities in lithofacies, which led
to the broad correlations made by Sweet (1984), sequence
stratigraphic studies rely on the recognition of significant
surfaces within the stratigraphic succession. These include
subtle unconformities (sequence boundaries), which are
in part recognised on the basis of detailed lithological
and gamma logs of measured sections (Southgate et al
2000). Several surfaces, labelled A to H, were recognised
during initial studies in the Lawn Hill region (Southgate
et al 1997). Although they have largely been replaced by
supersequence boundaries, they are shown on Figure 27,
as they were the basis for correlation of the Carrara Range
rocks by McConachie and Krassay (1997).
The age of the Top Rocky Rhyolite, 1725 ± 3 Ma
(Page et al 2000), provides a maximum limit to the age of
the overlying Surprise Creek Formation and McNamara
Group in MOUNT DRUMMOND. Southgate et al (2000)
and Page et al (2000) showed that there are two elements
to the Surprise Creek Formation in the Leichhardt River
Fault Trough: one is a little more than 1700 Ma in age and is
assigned to the Big Supersequence; the younger component
is a little less than 1700 Ma (based on an age of 1694 ± 3 Ma
for tuffs from the overlying Gunpowder Creek Formation)
and is assigned to the Prize Supersequence. Detailed
evidence is lacking, but the Surprise Creek Formation in
MOUNT DRUMMOND is considered likely to belong to
the Prize Supersequence. McConachie and Krassay (1997)
designated informal unit L
Pmd 2 of the Drummond Formation
as an equivalent of the Torpedo Creek Quartzite in the
lower McNamara Group section, but we interpret all of the
Drummond Formation as equivalents of the Gunpowder
Creek Formation and lower Paradise Creek Formation, ie
the Gun Supersequence (Figure 27). The lengthy hiatus
between the Prize and Gun supersequences, documented by
and siltstone with abundant cross-lamination, parallel
lamination, small wave ripples, HCS, parting lineation, tool
marks, and flute, gutter and load casts (Figure 26). Rare
beds of medium-bedded, fine- to medium-grained sandstone
with small trough cross-beds are present. The dolostone
facies includes dololutite, dolarenite and sandy (siliciclastic)
dolarenite with small trough cross-beds, cross-lamination
and parallel lamination, and some dolomitic sandstone,
dolorudite and flat-pebble intraclast breccia. Coarser beds
contain chert and quartz clasts in a recrystallised dolomitic
matrix. The sandstone facies is present in units up to 10 m
thick, and consists of white to grey sandstone of variable
grainsize. It includes fine-grained sublithic sandstone with
parting lineations and planar bedding, medium and coarse
sandstone with scattered granules and small pebbles of
chert and quartz, and lithic sandstone with trough crossbeds, ripples and synaeresis cracks. A resistant sandstone
unit observed in a small anticlinal dome near the base of the
exposed section at 805270mE 8001870mN is delineated on
the map as L
Pfd3s, and is inferred to be the basal sandstone of
L
Pfd3. The poorly exposed shale facies consists of red-brown
to green and grey (?carbonaceous) fissile shale.
The various facies appear to be arranged in upwardcoarsening cycles from shale, through flaggy, to sandstone
facies. These are punctuated by the dolostone facies,
which represents areas of low siliciclastic input within the
shallower-water sandstone facies. The flaggy facies bears
many of the hallmarks of a storm-dominated shoreface
environment, and we conclude that the whole unit represents
repeated episodes of progradation across a storm-dominated
shelf, culminating with shallow-water, probably intertidal
sands and carbonate sediments.
Age and correlations of Surprise Creek Formation and
McNamara and Fickling groups
Regional sequence stratigraphic studies, covering most of
the major outcrops in the Lawn Hill Platform and Leichhardt
River Fault Trough, with associated isotopic geochronology
based on dating of tuffaceous layers, have allowed a very
detailed understanding of the age and correlations of
Figure 26. Load casts in flaggy facies
(laminated to thinly interbedded siltstone
and fine sandstone) in uppermost
Doomadgee
Formation.
Cleanskin,
803900mE 8002600mN, 14 km west of
NT/Queensland border.
32
Southgate et al (2000), is equated to the unconformity at the
base of the Drummond Formation. It can also be inferred
that the Drummond Formation is around 1660 Ma in age,
based on a series of dates around 1658–1654 Ma for the
lower Paradise Creek Formation (Page et al 2000).
Carbonate–chert–conglomerate facies that constitute
the lower Brumby Formation are Paradise Creek–
Esperanza Formation equivalents. The upper, finergrained part of the Brumby Formation correlates with the
Lady Loretta Formation, ie the Loretta Supersequence.
The Gun–Loretta and Loretta–River supersequence
boundaries can only be inferred because of a paucity of
outcrop in the upper Brumby Formation. No such problem
exists at the equivalent time in the Maloney Creek Inlier,
where the beginning of the River Supersequence is marked
by the Bullrush Conglomerate lying unconformably
on the Drummond Formation, and marked local uplift
resulted in erosion of all of the Loretta and part of the Gun
supersequences.
A correlation between the Plain Creek Formation and the
Riversleigh Siltstone and Termite Range Formation (Sweet
1984) was maintained by McConachie and Krassay (1997),
who pointed out that the upper Plain Creek Formation
may include lower Lawn Hill Formation equivalents. For
instance, it is a plausible interpretation that the uppermost
Plain Creek Formation sandstone unit is equivalent to the
Bulmung Sandstone Member rather than to the Termite
Range Formation. Page et al (2000) obtained dates of
1611 ± 4 Ma and 1616 ± 5 Ma for a lower unit in the Lawn
Hill Formation (Lawn Supersequence) and 1595 ± 6 Ma for
the mudstone beneath the Widdallion Sandstone Member,
in the Wide Supersequence. On this basis, it is clear that
the McNamara Group in MOUNT DRUMMOND spans
the same time range as in the type area of the group to the
LAWN HILL
Super- Thickness
sequence
(m)
MOUNT DRUMMOND
McConachie and Krassay (1997)
2400
South Nicholson Group
This report
Symbol
Formation
Constance Sandstone
L
Psc
Constance Sandstone
None known
L
Psa
Playford Sandstone
Widdallion
Sandstone Member
‘Murraburra Sandstone’
L
Pmhw
Wide
Group
South
Nicholson
Group
2000
H
Lawn
Hill
Formation
Lawn
Lawn
Hill
Formation
L
Pmh
Lawn
Hill
Formation
Term
1200
800
Termite Range
Formation
E
Riversleigh
Siltstone
Shady Bore Quartzite
Lady Loretta
Formation
Esperanza Formation
D
Gun
B
Gunpowder Creek
Formation
A'
Torpedo Creek Quartzite
A*
Prize
Shady Bore Quartzite
L
Pms
L
Pmu
Shady Bore
Bullrush
Quartzite
Conglomerate
Brumby Formation (upper)
Lady Loretta Formation
Esperanza Formation
L
Pmb
Paradise Creek
Formation
Gunpowder Creek
Formation
Surprise Creek
Formation
Plain
Creek
Formation
Riversleigh
Siltstone
Paradise Creek Formation
C
400
Termite Range
Formation
L
Pma
F?
River
Loretta
G?
McNamara Group
1600
Surprise Creek
Formation
Brumby Formation (lower)
L
Pmd4
L
Pmd3
L
Pmd2
Drummond Formation
L
Pmd1
L
Pr
Surprise Creek
Formation
Not
grouped
A07-234.ai
Figure 27. Gamma ray log summary from Carrara Range measured sections by McConachie and Krassay (1997), with interpreted correlations
with the type area for the McNamara Group in LAWN HILL, Queensland [from McConachie and Krassay (1997) and this report]. Columns
on the right show MOUNT DRUMMOND stratigraphy used in this report.
33
The rocks are flat lying to gently dipping (Figure 28) and
are not metamorphosed or significantly deformed. The base
of the Caulfield beds and underlying units are not exposed.
The beds are unconformably overlain by the Constance
Sandstone of the South Nicholson Group (Figure 5), with
only minor discordance at the contact.
The Caulfield beds are informally divided into two
parts with a cumulative thickness of at least 600 m; they
are not distinguished on the mapface. The lower part is at
least 500 m thick and comprises coarse lithic sandstone
and conglomerate, with minor intercalated carbonate
and siltstone. The upper part is approximately 100 m
thick and consists of interlayered 10–30 m-thick units of
fine- to medium-grained sublithic sandstone, chert and
siltstone.
east, except that there is no evidence of the existence of the
youngest, Doom Supersequence.
Intrusive rhyodacites in the Peters Creek Volcanics
at 1729 ± 4 Ma are indistinguishable in age from the Top
Rocky Rhyolite, and provide a maximum age for the
Fickling Group (Page et al 2000). Sweet et al (1981: 22)
made very general lithostratigraphic correlations between
the Fickling Group and the McNamara Group, and these
correlations have been much refined using U–Pb isotope
geochronology (Page and Sweet 1998, Page et al 2000) and
sequence and seismic stratigraphy (Bradshaw et al 2000).
Unit L
Pdf 2 of the Doomadgee Formation containing tuffs of
1613 ± 5 Ma (Page and Sweet 1998), is equated to the middle
Lawn Hill Formation (units L
Pmh3, lower L
Pmh4; Page et al
2000), ie the Lawn Supersequence (Bradshaw et al 2000),
whereas the upper Doomadgee Formation is equated to
the upper unit L
Pmh4 of the Lawn Hill Formation, dated at
1595 ± 6 Ma by Page and Sweet (1998), and is assigned to
the Wide Supersequence.
Lower Caulfield beds
Three sedimentary facies are recognised in the lower
Caulfield beds. The dominant coarse facies consists of
yellow to red-brown or pink, lithic, micaceous, coarse- to
very coarse-grained, poorly sorted, lithic-pebble-bearing
sandstone (Figure 29) and pebble to boulder conglomerate.
Subrounded clasts up to 40 cm diameter include mudstone,
silicified sandstone (fine- to medium-grained quartzite),
quartz, micaceous metapelite and felsic ?volcanic rock;
these are consistent with a sedimentary and low-grade
metamorphic-felsic igneous provenance. Conglomerate and
coarse sandstone, in beds 0.5–8 m thick, outcrop as a series
of benches. The beds generally lack internal stratification,
but in the upper part of the easternmost outcrops, they
display lighter-coloured, better-sorted upper surfaces.
Crude bedding is locally present. Neither chert nor carbonate
appear as clasts in this facies. The massive character of
the coarse facies results in tor-like outcrops (Figure 30)
of distinctive brown colour, often with a honeycombed
weathering surface.
Fine facies occurs as minor thin intervals of fine- to
medium-grained, highly micaceous lithic sandstone and
siltstone, with small- to medium-scale trough cross-beds,
planar bedding, parting lineation and interference ripples.
This facies is sometimes amalgamated with the massive
beds and sometimes forms discrete beds. Olive shale is also
recognised locally in the lower Caulfield beds.
Mesoproterozoic (Calymmian): South Nicholson Basin
The term South Nicholson Basin was introduced by Smith
and Roberts (1963), following their mapping of MOUNT
DRUMMOND and the combining of the Constance
Sandstone and Mullera Formation into the South Nicholson
Group. Until the present mapping, this group was regarded
as the only constituent of the South Nicholson Basin.
However, the Caulfied beds are herein also assigned to the
basin, as they are tentatively correlated with older parts of
the South Nicholson Group.
Caulfield beds
The Caulfield beds (new name, see Appendix 1) are
restricted to north-central MOUNT DRUMMOND and
incorporate outcrops in the Bauhinia Dome that were
previously mapped as Fickling beds by Smith and Roberts
(1963). This recessive unit forms the low-relief core of the
Bauhinia Dome, which is centred on 755000mE 8000000mN
(northeastern Benmara) and drained by Norris and Little
Pandanus creeks. The structural setting is an anticlinal
dome with a principal east- to east-northeast-trending axis.
Figure 28. Aerial view of strongly
banded outcrop in Caulfield beds, eastern
Bauhinia Dome. Banding results from
alternating very thick beds of pebble
conglomerate and pebbly sandstone, and
poorly exposed finer siliciclastic rocks.
Benmara, 751600mE 8001200mN, 37 km
north-northwest of Wangalinji.
34
Carbonate facies occurs as small discontinuous patches
of fresh, locally brecciated dolostone; it accounts for less
than 5% of the lower Caulfield beds. Rock types include
interbedded sandy and pebbly dolarenite, dolorudite
(including flat-pebble breccia), dololutite and dolomitic-lithic
sandstone. Microbial lamination is locally present. This
facies appears to be genetically related to the interbedded
sandstone; however, contacts are not well exposed and it is
possible that individual carbonate outcrops actually represent
allochthonous blocks or large clasts within the sandstone.
30 cm thick of red-brown to green or yellow micaceous
siltstone, fine- to very fine-grained lithic sandstone, and
shale. Bedding is planar or lenticular with common parallel
lamination.
Interpretation and correlation
The contrasting mix of facies that characterises the
Caulfield beds is unusual and is indicative of sedimentation
coeval with tectonism. The principal sources of siliciclastic
detritus were the Murphy Metamorphics, Nicholson Granite
and Cliffdale Volcanics, and possibly remnants of the
Westmoreland Conglomerate. We interpret sedimentation to
have been coincident with foreland development and uplift
of the Murphy Inlier, 20 km to the north (Murphy Tectonic
Ridge, Plumb et al 1990). During periods of tectonism,
sand and gravel originating in uplands coincident with the
tectonic ridge were rapidly transported and deposited by
gravity flows to form massive sandstone and conglomerate
beds. The total lack of stratification or grading in most
beds indicates that the flows were debris flows rather than
turbidites. Better sorted, less lithic tops to some beds show
that they were subaqueous, and were subjected to winnowing
Upper Caulfield beds
Three lithofacies are recognised in the upper Caulfield
beds. Sandstone facies is a yellow, fine- to medium-grained,
quartzose to sublithic, silicified micaceous sandstone, with
small trough cross-beds, planar bedding and a parting
lineation. It is not unlike the overlying Constance Sandstone
in appearance, but is devoid of mudclasts and quartz pebbles/
granules. Chert facies occurs as white featureless chert,
lacking stratification and any discernible features. It could
be altered claystone, but is most likely chertified dolostone.
Fine facies consists of shaly outcrop or tabular beds up to
Figure 29. Pebbly, highly lithic, very
coarse-grained sandstone in Caulfield
beds. Clasts are of sandstone/quartzite and
quartz. Benmara, 761070mE 8002560mN,
eastern Bauhinia Dome, 35 km north of
Wangalinji.
Figure 30. Tor-like outcrop habit of
Caulfield beds from same locality as
Figure 29.
35
the Fickling and McNamara groups appears less likely, but
cannot be ruled out, as somewhat similar facies are present
in the middle McNamara Group (Bullrush Conglomerate)
and in the overlying Plain Creek Formation in the Maloney
Creek Inlier. A problem in correlating the Caulfield beds
with either the Fickling Group or the Crow Formation is
that, during that time, it is likely that the nearest parts of
the Murphy Tectonic Ridge were blanketed by sediments.
The Walford Dolomite is present 10–20 km directly north
of the Caulfield beds, but basement metamorphic and
igneous rocks are present to the northeast. To the northwest,
basement is obscured by the South Nicholson Group, but
could have been exposed at the time of deposition of the
Caulfield beds, regardless of their age. Thus, we tentatively
correlate the Caulfield beds with the Crow Formation.
by wave or current action after deposition. During times
of tectonic quiescence, sedimentation took place under the
influence of waves and currents in a shallow-marine shelf
environment, forming carbonate and depositing fine-grained
siliciclastic sediments, and reworking minor amounts of
the debris flow facies. These processes are best interpreted
in terms of a fan delta. The advent of finer-grained and
better-sorted sandstones and beds of dolostone higher in
the section indicates that traction current and chemical
deposition became more important upwards, with a waning
of tectonism. The lack of turbidites and conglomerate in the
upper Caulfield beds indicates a cessation of tectonism.
The age and absolute stratigraphic position of the
Caulfield beds are difficult to constrain, thus necessitating
the status of ‘beds’. They are obviously older than the
Constance Sandstone, but are presumed to be considerably
younger than the Nicholson Granite and Cliffdale Volcanics
in the Murphy Inlier, dated by Page et al (2000) at about
1850 Ma. Sweet (1985) followed Smith and Roberts (1963)
in assigning them to the Fickling beds (Group), and regarded
the facies as similar to those in the Maloney Creek Inlier,
interpreting them as alluvial fan deposits shed from faults
bounding the Murphy Tectonic Ridge. We interpret the
environment as subaqueous, rather than subaerial, but agree
that the likely source is the ridge to the north. An alternative
source to the south (ie between the Bauhinia Dome and
the Maloney Creek Inlier) is also possible, in an area now
concealed beneath a thick cover of South Nicholson Group,
but insufficient data are available to assess this. Facies in
the Caulfield beds are quite proximal, implying that fault
scarps were close. The east-northeast-trending Fish River
Fault lies 9 km north of the nearest Caulfield beds outcrops,
but is poorly expressed in the Walford Dolomite (Fickling
Group) in that area (Ahmad and Wygralak 1989). A more
prominent unnamed east-southeast-trending fault cuts
the Constance Sandstone within 4 km of the northeastern
extremity of outcrops. The latest movement on these faults
is clearly post-South Nicholson Group, but many faults in the
region have been reactivated and the most recent movement
is not necessarily the major activity on them. The Fish River
Fault, for instance, has been shown to be active during
deposition of the Mount Les Siltstone. Rohrlach et al (1998:
65–66) stated that this movement led to the development
of submarine talus breccias, described as ‘a series of
allochthonous, interdigitating clast-supported dolomite
breccia [which] extend several hundred metres basinwards
where they grade into matrix-supported dolomite debrisflow sedimentary breccias beyond the base of the Fish River
Fault palaeoscarp’. Thus, a mechanism exists that could
explain the coarse facies in the Caulfield beds, perhaps of
Fickling Group age. However, the problem of the source
terrain remains, as it is difficult to demonstrate that there
was exposed basement to the north at the time.
An alternative correlation with the Crow Formation
(South Nicholson Group) is considered more likely. The
Caulfield beds contain coarse-grained mass flow facies
similar to the Crow Formation in the Benmara–Canyon
Range area. In addition, the contact with the overlying
Constance Sandstone (a probable correlative of the
Mittiebah Sandstone, Figure 5) is essentially concordant
and may represent only a minor hiatus. Correlation with
South Nicholson Group
The South Nicholson Group overlies rocks of the western
Lawn Hill Platform in western Queensland and eastern
Northern Territory. It occupies the largest areal extent of
any group in MOUNT DRUMMOND, accounting for some
80% of all outcropping strata. It lies unconformably on the
McNamara Group in the Carrara Range region (Figure 3), and
unconformably on the Murphy Metamorphics and probably
unconformably on the Benmara Group in Boxer. It is, in turn,
unconformably overlain by the Bukalara Sandstone, Helen
Springs Volcanics, Wonarah Formation and an assortment of
Cretaceous and Cenozoic rocks and sediments.
Satisfactory radiometric dating is currently unavailable
for any part of the South Nicholson Group, and its age is
therefore internally unconstrained. A shale total-rock Rb-Sr
date of 1510 ± 120 Ma from presumed Mullera Formation
from Brunette Downs-1 is unreliable, as the possibility of
inclusion of detrital material, principally micas, cannot be
discounted (Plumb and Derrick 1975). Additionally, it is
possible that the rocks dated were from the Crow Formation,
not the Mullera Formation, based on the revised stratigraphy
presented below. Page et al (2000) analysed zircons from
a basal feldspathic sandstone in the Constance Sandstone,
20 km south of the Century Deposit in LAWN HILL, and
concluded that the age of 1591 ± 10 Ma represents reworked
tuffaceous material from the underlying Lawn Hill
Formation, thus providing a maximum age for the Constance
Sandstone. A similar maximum age of 1595 ± 6 Ma comes
directly from the Lawn Hill Formation in the same area
(Page and Sweet 1998). No minimum age constraints are
imposed by overlying units, apart from late Neoproterozoic
to Cambrian units of the Georgina Basin. The interpreted
age range for the group, of 1500–1400 Ma, is based on its
correlation with the Roper Group of the southern McArthur
Basin (Dunn et al 1966), with which it makes up the Roper
Superbasin (Jackson et al 1999, Abbott and Sweet 2000,
Abbott et al 2001). Ages of 1492 ± 4 Ma and 1493 ± 4 Ma for
tuffaceous material from the lower Roper Group (Jackson
et al 1999) provide the most reliable estimate for the age of
the lower part of that group, and hence, for the lower South
Nicholson Group.
The lithostratigraphic components of the South
Nicholson Group are summarised in Table 5 and Figure 5.
The group is divided into two subgroups, the Wild Cow and
36
• The ‘Mitchiebo belt’, an east-northeast-trending outcrop
belt between Mitchiebo Waterhole and Western Creek,
except for outcrops south of Western and No Mans
creeks, which were shown by Sweet (1984) to belong to
the McNamara Group.
• Several structural domes between the Mitchiebo and
Benmara faults, including those in the headwaters of
Waterfall and Breakfast Creeks and the Playford River,
but not the northernmost anticline at the confluence of
Murphys and Benmara Creeks.
Accident subgroups, based on the presence of an intervening
disconformity. Outcrops mapped in the Maloney Creek
Inlier as ‘Maloney Formation’ and included in the South
Nicholson Group by Smith and Roberts (1963) were excluded
by Sweet (1985) and assigned to various formations in the
underlying McNamara Group.
The South Nicholson Group is dominated by braided
fluvial and shallow-marine sandstone, siltstone, shale and
minor conglomerate and ironstone, and is up to 6500 m
thick. Structurally, it is gently folded with an intricate domeand-basin map pattern. Sandstones outcrop as resistant
ranges (mostly ‘domes’ and east-trending strike ridges) with
moderate dips, rarely exceeding 30°. Finer-grained units
tend to be recessive, occupying low-relief sand-covered
plains bounding the ranges, and hence, are poorly exposed
and their internal stratigraphy poorly constrained.
In the type area for the Wild Cow Subgroup, around
Mitchiebo Waterhole, the Playford Sandstone outcrops
strongly as a series of alternating strike ridges and narrow
valleys, reflecting the presence of finer-grained rocks
interbedded with the sandstone. Elsewhere, outcrops are
predominantly low sandstone ridges and plateaux. The
formation has been divided into three named members:
the basal Wangalinji Member consists of a basal sandstone
overlain by siltstone and sandstone, the Top Lily Sandstone
Member is predominantly fine-grained lithic sandstone
with minor siltstone, ironstone and stromatolitic carbonate
rocks; and the No Mans Sandstone Member is a prominent,
coarse-grained to granule-bearing, cross-bedded sandstone
unit, recognisable only in the Mitchiebo belt. Because all
outcrops of the Playford Sandstone have been subdivided
into these members, detailed lithological descriptions are
given under the appropriate headings below. The Playford
Sandstone is 390 m thick in the type section, 4 km southeast
of Mitchiebo Waterhole, but at least 1400 m in the Playford
Anticline and more than 1300 m in the Ten Mile Anticline.
Wild Cow Subgroup
The Wild Cow Subgroup (new name, see Appendix 1) is
restricted to the western half of MOUNT DRUMMOND.
It incorporates three formations, the Bowgan and Playford
sandstones and an overlying recessive siltstone- and
sandstone-dominated unit, the Crow Formation (Table 5,
Figure 5). The correlation of the two sandstone formations
is uncertain, but both represent the base of the South
Nicholson Group in their respective areas (see below) and are
overlain by the Crow Formation. The Wild Cow Subgroup
unconformably overlies the Murphy Metamorphics and
McNamara Group. The contact with the Benmara Group
is poorly exposed and the relationship cannot be resolved
with any certainty (see Bowgan Sandstone), but a partly
reactivated unconformity is favoured. The Wild Cow
Subgroup is in turn overlain disconformably, and locally
with angular unconformity, by the Accident Subgroup.
Rocks now assigned to the Wild Cow Subgroup were
originally mapped by Smith and Roberts (1963) as younger
components of the South Nicholson Group (Constance
Sandstone, Mullera Formation, Mittiebah Sandstone; now
Accident Subgroup). Recognition of an unconformity
within the group north of No Mans Creek has enabled us
to demonstrate that the rocks beneath the unconformity
surface (Wild Cow Subgroup) occupy much of western
MOUNT DRUMMOND, whereas the younger formations
dominate outcrops in eastern MOUNT DRUMMOND and
LAWN HILL. The Mittiebah Sandstone, which overlies the
Wild Cow Subgroup concordantly, is a probable equivalent
of the Constance Sandstone.
Wangalinji Member (P
Lsa w )
The Wangalinji Member of the Playford Formation (new
name, see Appendix 1) comprises a lower, coarse-grained
to granule and pebbly sandstone, overlain by interbedded
siltstone and fine-grained sandstone. It was formerly
mapped as part of the Constance Sandstone in outcrops
stretching west-southwest from the headwaters of Moloney
Creek in central southern MOUNT DRUMMOND: the
‘Mitchiebo belt’. Several other outcrops occur in a 50 km
belt immediately north of the Mitchiebo Fault, from the exact
centre of the sheet area west to the headwaters of Waterfall
Creek. The member forms a low ridge corresponding to the
basal sandstone and an adjacent valley or undulating terrain
corresponding to the upper, finer-grained part. An angular
unconformable relationship with the underlying Widdallion
Sandstone Member of the Lawn Hill Formation is evident
at 717310mE 7932910mN, 6.5 km southwest of Mitchiebo
Waterhole. In other exposures to the east, the units are
concordant, and the contact is a disconformity. The contact
is marked by an abrupt change from purple-brown lithic
sandstone of the Widdallion Sandstone Member, to white,
blocky, very coarse-grained to granule-bearing quartz-rich
sandstone of the basal Wangalinji Member.
In the type section, 4 km southeast of Mitchiebo
Waterhole at 724360mE 7934820mN, the basal sandstone
is 25 m thick and consists of a lower 4 m of white, thickly
bedded, coarse-grained cross-bedded sandstone, fining
upward over 5 m to medium-grained sandstone with current
ripples and primary current lineation; this is overlain by
Playford Sandstone (P
Lsa)
The Playford Sandstone (new name, see Appendix 1) forms
the base of the South Nicholson Group, from Moloney
Creek in southeastern MOUNT DRUMMOND, westwards
to the western limit of Proterozoic outcrop around Waterfall
Creek in Mittiebah, and north to an isolated exposure in
the headwaters of Benmara Creek in Boxer. North of the
Benmara Fault, the basal unit of the South Nicholson Group
is the Bowgan Sandstone. The formation now includes
much of the Constance Sandstone mapped by Smith and
Roberts (1963) in:
37
Unit, (map symbol),
thickness
Lithology
Depositional
environment
Stratigraphic
relationships
Mullera Formation
(P
Lsm) >1100 m (includes
(P
Lsmm)
Green or red/brown to maroon, micaceous,
locally ferruginous siltstone, shale and finegrained, lithic to quartzose sandstone; minor
ironstone, organic-rich shale and mediumgrained quartzose sandstone.
Shallow-marine shelf, partly
above storm wave-base
(‘tempestite facies’) and partly
below (‘organic ’ and ‘shalerich facies’).
Conformable on Constance
Sandstone; top not exposed,
but unconformably overlain by
Georgina Basin.
Middle Creek Sandstone
Member
(P
Lsmm) up to 70 m
White, silicified, fine ± medium-grained,
sublithic glauconitic sandstone with distinctive
decimetre-scale amalgamated trough cross-beds
defined by hematite dustings on foresets.
Shallow marine intertidal and
shoreface, above fair-weather
wave-base.
Conformable within Mullera
Formation.
South Nicholson Group
Accident subgroup
Constance Sandstone (L
Psc) 75–1100 m; subdivided into five members
Schultz Sandstone Member
(P
Lscs) 120–600+ m
White to brown, friable, medium-, coarse- and
very coarse-grained to granule sandstone; thick
intercalated unit of platy, thinly laminated, very
fine-grained sandstone.
Shallow marine: upper
shoreface to intertidal; may
include braided fluvial.
Disconformable on Wallis
Siltstone Member; overlain
conformably by Mullera
Formation.
Wallis Siltstone Member
(P
Lscw) 0–200 m
Green-brown-weathering, very fine- to finegrained laminated sandstone with micaceous
partings; minor siltstone and shale; interbed
of white, well sorted, coarse- to very coarsegrained quartz sandstone with large mudstone
intraclasts.
Deeper marine: lower shoreface
and storm-dominated shelf.
Conformable on Burangoo
Sandstone Member; overlain
disconformably, and
locally with subtle angular
unconformity by Schultz
Sandstone Member.
Burangoo Sandstone
Member
(P
Lscb) 35–150 m
White to pale yellow, silicified to friable, fine- to
coarse-grained, quartzose to sublithic sandstone
with minor scattered granules and rare small
pebbles of quartz.
Shallow marine: upper
shoreface to intertidal; may
include braided fluvial.
Conformable between
Pandanus and Wallis Siltstone
members.
Pandanus Siltstone Member
(P
Lscp) 20–50 m
Flaggy, brown, micaceous, lithic fine-grained
sandstone; minor siltstone and shale.
Deeper marine: lower shoreface
and storm-dominated shelf.
Conformable within Constance
Sandstone, between Hedleys
and Burangoo Sandstone
members.
Hedleys Sandstone Member
(P
Lsch) 10–15 m
White, silicified to friable, thick to very thick
bedded, fine- to medium-grained sublithic and
quartzose sandstone with mudclasts, and minor
granules and small pebbles of quartz.
Shallow marine: upper
shoreface to intertidal; may
include braided fluvial.
Unconformable on Fickling
Group in northeastern
MOUNT DRUMMOND and
on Caulfield beds in central
part of mapsheet; overlain
conformably by Pandanus
Siltstone Member.
Mittiebah Sandstone
(P
Lsi) 450–2200 m
Fine- to coarse-grained, quartzose to lithic
sandstone; minor interbeds of pebble or cobble
conglomerate and siltstone.
Alternating shallow storminfluenced marine and braided
fluvial.
Conformable to disconformable
on Crow Formation; top
not exposed but probably
conformably overlain by
Mullera Formation.
Interbedded lithic micaceous siltstone and
fine-grained sandstone, red/brown to grey
shale, chalky white claystone, fine- to mediumgrained, quartzose to sublithic sandstone; minor
local red/brown, poorly sorted, feldspathic,
micaceous, ferruginous and lithic, medium- to
very coarse-grained sandstone, pebbly sandstone
and matrix-supported conglomerate.
Shallow- to deep-marine
shelf (tempestite and parallellaminated facies), with
development of fan delta in
northwest adjacent to tectonic
uplift (localised interdigitated
turbidite and debris flow
facies).
In northwest: conformable on
Bowgan Sandstone; locally
unconformable on Benmara
Group; conformably overlain by
Tobacco Member or Mittiebah
Sandstone.
White silicified, fine- to very coarse-grained
± pebbly, quartzose to lithic, often glauconitic
sandstone and localised pebble-cobble
conglomerate; minor interbedded white flaggy
shale and siltstone.
Shallow intertidal to storminfluenced marine shelf.
Conformable at top of Crow
Formation in west; overlain
disconformably or with angular
unconformity by Mittiebah
Sandstone.
Wild Cow Subgroup
Crow Formation
(P
Lso) up to 2500 m
Tobacco Member
(P
Lsot) 300–600 m
In south and east: conformable
on Playford Sandstone; overlain
disconformably or with angular
unconformity by Constance
Sandstone (or Mittiebah
Sandstone in south).
Table 5. Stratigraphy of South Nicholson Group and Caulfield beds in MOUNT DRUMMOND (continued next page).
38
Unit, (map symbol),
thickness
Bowgan Sandstone
(P
Lsb) up to 100 m
Lithology
Maroon, variably ferruginous, lithic to sublithic,
fine- to coarse-grained ± pebbly sandstone;
possible rare chertified digitate stromatolites;
local basal chert clast conglomerate or breccia.
Depositional
environment
Stratigraphic
relationships
Braided fluvial to shallow
marine intertidal.
Probably unconformable on
Murphy Metamorphics and
Benmara Group; conformably
overlain by Crow Formation;
locally absent.
Playford Sandstone (P
Lsa) composite 390–1400+ m; subdivided into three members
No Mans Sandstone Member
(P
Lsan) 130–200 m
Medium to coarse-grained sandstone with
granule to pebble lags; sublithic to quartz-rich;
strongly trough cross-bedded.
Fluvial or intertidal marine.
Sharp, erosive but conformable
base on Top Lily Sandstone
Member; conformably overlain
by Crow Formation.
Top Lily Sandstone Member
(P
Lsat) 140–1100 m
White, pink, and darker pink-red, thickly to
very thickly bedded, very fine- to fine-grained,
well sorted lithic sandstone; minor, more
thinly bedded, ferruginous very fine-grained
sandstone and siltstone, and hematitic siltstone
to ironstone.
Marine shelf to shoreline, and
possibly tidal channel; minor
supratidal, including aeolian.
Conformable on Wangalinji
Member; overlain conformably
by No Mans Sandstone
Member, or by Crow
Formation.
Wangalinji Member
(P
Lsaw) 115–750 m
Basal, white, thickly bedded, medium- to coarsegrained, silicified to friable, locally pebbly,
sublithic to quartzose sandstone; overlain by
laminated shale, thinly bedded siltstone, very
fine-grained lithic sandstone, and interbeds of
coarser white sandstone similar to basal beds.
Basinal, through stormdominated shelf, to shoreface or
marginal marine.
Overlies Widdallion Sandstone
Member, disconformably
in most outcrops; angular
unconformity southwest of
Mitchiebo Waterhole; overlain
conformably by Top Lily
Sandstone Member.
Coarse-grained, poorly sorted lithic sandstone
and matrix-supported conglomerate; minor
intercalated carbonate, chert and siltstone.
Debris flows and sandy
turbidites in shallow to deep
marine shelf setting (fan-delta);
syntectonic deposition.
Base not exposed;
unconformably overlain by
Constance Sandstone.
Unassigned to group
Caulfield beds
(P
Lc) >600 m
Table 5. Stratigraphy of South Nicholson Group and Caulfield beds in MOUNT DRUMMOND (continued from previous page).
20 m of fine- to medium-grained sandstone with similar
structures. The uppermost beds become thinly bedded
over 2 m and apparently grade upwards into mudstone
of the upper Wangalinji Member. The basal sandstone is
10–20 m thick in most exposures and is locally
conglomeratic, containing lags and scattered granules and
pebbles, mainly of quartz. In an outcrop 2 km southwest of
the type section, it is a thickly bedded, white quartz arenite
with scattered clay (lithic?) grains and mudstone intraclasts.
The sandstone is strongly planar cross-bedded on a medium
scale, and medium-grained with granule to pebbly layers.
Elsewhere, ripple cross-lamination and small-scale trough
(possibly herringbone) cross-bedding is evident.
The remainder of the member is not exposed in the
type section, but based on measured dips in adjacent units,
it is about 90 m thick, yielding a total of 115 m. It is well
exposed and at least 750 m thick in the Playford Anticline.
The dominant rock types are laminated shale with thinly
bedded siltstone and very fine-grained lithic sandstone
interbeds. Highly ferruginous and manganiferous, rather
gossanous weathering crusts suggest that some of the
mudstones are pyritic. At least two white, quartz-rich,
more thickly bedded, coarser-grained sandstone layers,
a few metres thick and similar to the basal sandstone,
are present. The younger of these contains moulds of
probable bladed gypsum crystals (Figure 31). Towards
the top of the Member, soils and weathered rock are
red in colour, and calcrete in the soil and a loose block
of stromatolitic chert indicates that carbonates are
present in the section. Similar rocks are present in the
core of the Ten Mile Anticline, where the uppermost
200–300 m of the member is exposed, but the total thickness
is not known. An interval of purple-red mudstone with
discontinuous disrupted laminae, ubiquitous mudflakes,
and desiccation cracks indicates a period of shallow-water
deposition with periodic emergence. Within the member on
the eastern limb of the anticline are well exposed upwardcoarsening and -thickening beds several metres thick.
Wavily interlaminated shale-siltstone on a sub-centimetre
scale are overlain by several sharp-based interbeds of sublithic, medium- to coarse-grained sandstone packed with
shale intraclasts. The thinnest is 0.3 m thick; the top one
is greater than 1 m thick. The surface of the uppermost
sandstone is strongly wave rippled, with scattered granules
and small pebbles of quartz. A similar sandstone near the
core of the anticline contains weathered out grains which
may have been glauconite.
The basal coarser sandstone is a trangressive deposit,
which is succeeded by finer sand, indicating a rapid
deepening of the environment. The association of shale
(some of it pyritic), siltstone and fine-grained sandstone
with intervals of coarser sandstone beds in the upper
Wangalinji Member is consistent with a series of upwardshallowing cycles from relatively deep basinal, through
storm-shelf facies, to shoreface or marginal marine
sand environments. Occasional emergence is indicated
by desiccation cracks and gypsum pseudomorphs. The
appearance of carbonate rocks towards the top indicates
an overall shallowing of the basin. The marked increase in
thickness north of the Mitchiebo Fault suggests that there
may have been syndepositional movement during Playford
Sandstone time.
39
Top Lily Sandstone Member (P
Lsat )
The Top Lily Sandstone Member (new name, see
Appendix 1) is the dominant component of the Playford
Sandstone. It outcrops as a series of ridges and plateaux,
particularly in the Playford and Ten Mile anticlines,
although in both areas, outcrop is surprisingly poor, as the
plateau surfaces are deeply weathered and the sandstone
has been altered to ferruginous and silicified sandstone
rubble. The member also forms the southern part of the
ridge forming the ‘Mitchiebo belt’ in southeastern MOUNT
DRUMMOND. Excellent outcrops are preserved in this
belt, both southwest of Mitchiebo Waterhole and in the
type section, 4 km southeast of the waterhole. The member
is 143 m thick in the type section, where lower and upper
intervals of fine-grained lithic sandstone, each 50–60 m
thick, are separated by a slightly recessive 20 m interval
of finer-grained, more thinly bedded, dark red ferruginous
sandstone. It thickens north of the Mitchiebo Fault to 750 m
in the Playford Anticline and to 1100 m in the western limb
of the Ten Mile Anticline. The middle recessive zone is
present at all localities, but its composition is poorly known
because of a lack of good exposures. At least 300 m of the
member is preserved in the northernmost outcrops, in an
anticline in the headwaters of Benmara Creek, although the
exposure is not complete. The lower contact is not exposed
in the type section, but the member is concordant with the
Wangalinji Member and is presumed to be conformable
on it, as it is clearly gradational in the Ten Mile Anticline.
The upper contact with the No Mans Sandstone Member in
the type section is sharp and erosive. Although it may be
locally disconformable, on a regional scale, it is concordant
and essentially conformable. Away from the type section,
the No Mans Sandstone Member becomes finer grained,
thinner and lenses out, and the Top Lily Sandstone Member
is overlain with an abrupt transition by the Crow Formation,
with which it is inferred to be conformable.
The dominant facies in the Top Lily Sandstone Member
is a distinctive, white to pink or darker pink-red, thickly to
very thickly bedded, fine-grained, well sorted micaceous
and lithic sandstone. Grainsize occasionally extends to
medium-grained, and rarely, to coarse-grained, granulebearing and pebbly. White clay grains, either weathered
lithic fragments or feldspar, constitute up to 30% of the
volume of the rock. Cross-beds range from a metre up to
several metres thick (Figure 32), include both gentlycurved troughs and tabular forms, and display thin foreset
bedding that is commonly deformed (Figure 33). Massive
beds with erosive bases and crude upward grading are
present; these also display convolute bedding. A second
facies, somewhat finer grained than the dominant one and
interbedded with it, is prominently parallel laminated and
primary current lineated. In some outcrops, curved surfaces
with current lineation and long-wavelength truncations are
evident, suggesting large-scale HCS. Straight-crested and
interference ripples are also present.
Exposure is generally poor, because of intense weathering
of the plateau surface in the Ten Mile Anticline, except near
creek level, which is below the weathered zone. The lower
contact is well exposed at 686250mE 7936660mN, where
red to grey laminated siltstone grades up into very fine- to
fine-grained sandstone with few siltstone interbeds. The
siltstone beds are packed with mudstone intraclasts, and
the sandstone displays desiccation cracks and small ripple
marks. Straight and sinuous-crested ripples on nearby beds
are probably of wave origin. The sandstone immediately
above the contact is cyclic on a dekametre scale, suggesting
a series of upward-shallowing cycles.
Rare good outcrop of the middle recessive interval at
689950mE 7932570mN includes thinly to medium bedded,
fine-grained, slightly porous, highly ferruginous sandstone.
Iron oxides are present as grains as well as interstitially,
indicating either altered glauconite or other sedimentary
iron minerals. In the western limb of Ten Mile Anticline,
rubble of dark purple-red pure hematite is present at several
localities at the base of the recessive zone. It thus appears
to be a sedimentary layer, rather than being fault or veinrelated. A single displaced block of stromatolitic chert
near the middle of the member, at 686900mE 7940950mN,
shows that minor carbonate is present.
The gradational contact with the underlying Wangalinji
Member and the presence of upward-shallowing and
‑coarsening cycles indicate that the Top Lily Member is
a shallow-marine or shoreline deposit. The fine grainsize,
good sorting and large cross-beds are consistent with
non-marine (aeolian) environments, but the presence of
granules and pebbles is more indicative of a subaqueous
environment. A shallow-marine shelf, dominated by tidal
sandwaves, is considered most likely. The occurrence
of massive beds and convolute foreset lamination in the
Mitchiebo Waterhole area may indicate deposition in a tidal
or fluvial channel system, where sedimentation was more
rapid and the deposits more unstable, or even in deeper-water
channels as massflow deposits, although the dominance of
cross-bedded sandstone points to a mainly shallow-water
setting. The highly ferruginous beds and stromatolitic chert
are suggestive of minor peritidal environments with low
siliciclastic input.
No Mans Sandstone Member (P
Lsan )
The No Mans Sandstone Member (new name, see
Appendix 1) is recognised only in the Mitchiebo belt, where
it outcrops strongly in the northern part of a long ridge of
outcrop, previously mapped as Constance Sandstone by
Smith and Roberts (1963) and Sweet (1984). The member
is 130 m thick at the type section and may thicken to as
much as 200 m, further east in the Mitchiebo belt. It is
tentatively recognised in the Playford Anticline, where
some 50 m of sandstone above typical Top Lily Sandstone
Member rocks is subtly coarser-grained and more quartzrich than the rocks below, reflecting a feather edge of the
No Mans Sandstone Member in that area. The lower contact
is regionally conformable, but is sharp in the type section;
typical Top Lily facies are overlain by strongly trough
cross-bedded, very coarse-grained to pebbly, quartz-rich
sandstone with a clearly erosive contact (Figure 34). The
upper contact is conformable and is a rapid transition from
thickly bedded to more thinly bedded sandstone, then into
mudstone of the Crow Formation.
Exposure in the type section approaches 100%, and
consists mainly of coarse-grained sandstone with granule
to pebble lags. Several fine-grained intervals also display
similar coarse lags. The sandstone is trough cross-bedded
40
Figure 31. Blade-like pseudomorphs,
probably after gypsum, in white quartz
sandstone interbed in Wangalinji Member
of Playford Sandstone, Playford Anticline.
Mitchiebo, 710660mE 7943350mN,
21 km north of Mount Morgan.
Figure 32. Very large-scale cross-beds in
Top Lily Sandstone Member. Sandstone
is mainly coarse-grained, with granule
and pebble intervals; toeset beds display
prominent downward-migrating current
ripples. Regional bedding (dipping right
at shallow angle) visible at top. Mitchiebo,
722000mE 7937000mN, 200 m south of
Mitchiebo Waterhole.
Figure 33. Convolute bedding, possibly
prolapsed foresets, in medium to thickly
bedded Top Lily Sandstone Member.
Mitchiebo, 731200mE 7938200mN,
10 km east of Mitchiebo Waterhole.
41
throughout, at a medium to large scale. Although foreset
measurements have not been treated quantitatively, a clear
south-to-north palaeocurrent pattern is evident. Primary
current lineation is present in the finer-grained sandstone,
and mudstone intraclasts were recorded in the uppermost
beds. Most pebbles are less than 1 cm, but range up to
5 cm. White quartz sandstone and vein quartz dominate,
but scattered chert pebbles and flat pebbles of fine-grained
lithic sandstone suggest erosion and local transport of the
underlying Top Lily Sandstone Member. The No Mans
Sandstone Member in the western limb of the Playford
Anticline is mapped as such, because there is a sudden
switch from fine-grained sandstone to medium and coarse
varieties, with a corresponding change to more massive
character.
The ubiquitous trough cross-bedded sandstone facies
of the No Mans Sandstone Member is very similar to
the tidal platform sandstone facies in the Roper Group
(Sweet 1986, Abbott and Sweet 2000). It differs in having
a higher granule and pebble content, and this, combined
with the unidirectional palaeocurrents, suggest that it is
a fluvial sandstone body. In sequence stratigraphic terms,
the upper contact is a conformable, Roper-type sequence
boundary, with a rapid transition into deeper-water facies.
The member can be assigned to the uppermost part of a
highstand systems tract, and the basal contact may be an
intrasequence erosion surface of the type described as
being typical of the Roper Group (Abbott and Sweet 2000).
Alternatively, the sequence boundary may be at the base of
the member, which is a lowstand fluvial deposit.
Murphy Metamorphics and Benmara Group is poorly
exposed and either a low-angle unconformity or a layerparallel fault can be invoked. The latter could imply that
the Benmara and South Nicholson groups were once
stratigraphically contiguous and conformable, but are now
structurally juxtaposed. An unconformity is favoured
herein, based on the consistent stratigraphic position of the
discontinuity and the different facies of the two groups (eg
volcanics occur in the Benmara Group, but not in the South
Nicholson Group; see also Buddycurrawa Volcanics). The
Bowgan Sandstone is conformably overlain by the Crow
Formation, but the contact is not well exposed, due to the
recessive nature of the transition zone.
The Bowgan Sandstone is generally thin (<100 m,
average ca 10 m) and is locally absent, particularly in
the north (eg around 705000mE 8008000mN, near the
MOUNT DRUMMOND–CALVERT HILLS boundary).
It is composed of maroon to pink or red-brown, variably
ferruginous, lithic to sublithic, fine- to coarse-grained
sandstone, with occasional laminae of quartz granules and
small pebbles. In hand specimen, the sandstone has a notably
‘speckled’ appearance, due to the presence of white lithic
fragments in a pink ferruginous background. It is mediumto thickly bedded with planar bedding, parting lineations,
small-scale trough cross-beds and mudstone intraclasts.
Subtle large bedforms may also be present. Chert pebbles
and cobbles have been recognised in the basal sandstone at
some localities (eg 702650mE 7992300mN). At 701850mE
7989650mN, possible chertified digitate stromatolites are
interbedded with white claystone and sandstone in the
upper few tens of metres of the formation.
At 705200mE 8081800mN, a thin interval of polymict
breccia at the base of the formation consists of angular
clasts of sandstone, claystone and ?chert in a coarse-grained
sandstone matrix. In most instances, the upper contact with
the Crow Formation is marked by the development of a
distinctive chert horizon, secondary ironstone or clay-rich
saprolite.
Overall, facies present in the Bowgan Sandstone
resemble the upper siliciclastic portion of the Buddycurrawa
Volcanics, and in many cases, discrimination of the two
is difficult or impossible. This has led to uncertainty as
Bowgan Sandstone (P
Lsb)
The Bowgan Sandstone (new name, see Appendix 1) is
the basal sandstone of the South Nicholson Group in the
Benmara–Canyon Range area, northwest of the Benmara
Fault, in northwestern MOUNT DRUMMOND. Outcrop
stretches along a north-northeasterly belt on the eastern
fringe of the Canyon Range, from the headwaters of
Benmara Creek in the south (695000mE 7982000mN) to
Pandanus Creek in the north (705000mE 8012000mN,
CALVERT HILLS). The boundary with the underlying
Figure 34. Sharp, erosive contact
between pink-brown, fine-grained lithic
sandstone of Top Lily Sandstone Member
(below), and medium- to coarse-grained
and pebbly cross-bedded sandstone of No
Mans Sandstone Member (above). Type
section for both members. Mitchiebo,
724230mE 7935820mN, 3 km eastsoutheast of Mitchiebo Waterhole.
42
to whether they are part of the same succession. In one
area (702500mE 7992600mN), these two units could
not be differentiated and have been mapped collectively.
The Bowgan Sandstone is also similar to the Warramana
Sandstone in the southern McArthur Basin (Pietsch et al
1991), which is interpreted as a braided fluvial to shallowmarine intertidal deposit. A similar setting is envisaged
for the siliciclastic and carbonate rocks of the Bowgan
Sandstone.
The Bowgan Sandstone is interpreted to be a lateral
equivalent of the Playford Sandstone, principally because
they both underlie the Crow Formation and mark the base
of the South Nicholson Group. If this is so, then there
is a substantial change in facies and thickness across
the Benmara Fault. For example, in the headwaters of
Benmara Creek, the Bowgan Sandstone is <10 m thick to
the west of the fault (696100mE 7977900mN), whereas
the Playford Sandstone is >300 m thick to the east of the
fault (698800mE 7974700mN). The latter is typified by
sublithic and quartzose sandstone, whereas the Bowgan
Sandstone is typically more lithic. These changes take place
over a distance of only 5 km, implying either depositional
growth or subsequent juxtaposition of differing parts of
the succession across the Benmara Fault. One explanation
is that the ‘Murphy Tectonic Ridge’ and associated fault
systems (including the Benmara Fault) were active at the
initiation of the South Nicholson Group, and basal sandstone
deposition onlapped (thinned) northward onto the faults and
tectonic ridge. This is consistent with trends evident in the
overlying Crow Formation, which is notably more lithic and
debris-flow dominated on the western side of the Benmara
Fault. Uplifted Murphy Inlier rocks along this fault may
have provided large volumes of coarse labile detritus to the
Bowgan Sandstone and ‘coarse-grained’ Crow Formation.
This detritus was reworked into more distal settings to the
southeast to form the Playford Sandstone and ‘fine-grained’
Crow Formation.
by a variety of other unusual rock types (see below). Locally,
the Bowgan Sandstone is absent and the Crow Formation sits
directly on the Benmara Group and Murphy Metamorphics
(eg around 705000mE 8008000mN, near the MOUNT
DRUMMOND–CALVERT HILLS boundary). South and
east of Benmara Fault, the Crow Formation conformably
overlies the Playford Sandstone. In the Canyon and Mittiebah
ranges, the Crow Formation is conformably or disconformably
overlain by the Mittiebah Sandstone. Elsewhere, it is
overlain disconformably or with angular unconformity by
the Constance Sandstone (Figure 35). The Mittiebah and
Constance sandstones are tentatively correlated. West and
southwest of Mitchiebo Waterhole and along strike to the east
near No Mans Creek (755000mE 7944000mN), the Crow
Formation pinches out, probably due to erosion. There, in the
absence of the Crow Formation, the Constance Sandstone sits
unconformably on the Playford Sandstone.
The Crow Formation is composed of up to 2500 m
(maximum thickness, see below) of interbedded siltstone,
sandstone, shale and lesser conglomerate. These rock types
can be divided into several facies that appear to be restricted
to specific areas, although the lack of good outcrop does
not enable a complete assessment of facies distribution,
or a subdivision of the formation into mappable members
(apart from the Tobacco Member). Each facies is described
separately below, and their distribution and thickness
variations collectively summarised.
Deep-shelf facies
This facies comprises fissile to flaggy outcrop of white clayey
siltstone and fine-grained lithic micaceous sandstone, redbrown to grey shale and leached, chalky white or maroon,
mottled porcellanous claystone (Figure 36). The shale is
interpreted to have a carbonaceous and/or pyritic component,
based on the presence of mottled ferruginous and saprolitic
weathering products, but this has not been demonstrated
in outcrop or by drilling. Local features in outcrop include
massive bedding (claystone), parallel lamination and rare
current lineations (siltstone). There is generally no evidence
of traction current deposition, indicating a probable belowstorm-wave-base marine-shelf depositional setting. Some
claystone may have a tuffaceous component.
Crow Formation (P
Lso)
The Crow Formation (new name, see Appendix 1) is a largely
recessive unit that outcrops poorly throughout the western
two-thirds of MOUNT DRUMMOND. It encompasses about
half of the outcrops that were formerly mapped by Smith and
Roberts (1963) as the Mullera Formation, a unit now recognised
only in eastern MOUNT DRUMMOND; the remainder is now
recognised as Constance Sandstone. The Crow Formation
also incorporates a narrow strip of moderately resistant
outcrop at the northern edge of the Mittiebah Range that was
previously mapped as Mittiebah Sandstone. This Mittiebah
Range outcrop, plus a similar narrow strip of Crow Formation
along the Canyon Range, are identified here as a separate
upper member of the Crow Formation (Tobacco Member).
The Crow Formation also includes a small anticlinal area
of outcrop in the Canyon Range (710000mE 7995000mN,
Whiterock Creek), which was incorrectly mapped as Benmara
beds by Smith and Roberts (1963).
The Crow Formation lies conformably on the Bowgan
Sandstone in the Canyon Range area, on the northwestern
side of the Benmara Fault. The base of the formation is
poorly exposed and is locally altered to saprolite or covered
Storm shelf facies
The storm shelf facies is composed of flaggy white, fawn,
red-brown or purple micaceous siltstone and fine- to
medium-grained quartzose to sublithic (± micaceous)
sandstone (Figure 37). Sedimentary structures include
planar, wavy and lenticular bedding, cross- and parallel
lamination, HCS, small-scale trough cross-bedding,
symmetric ripples, mudclasts, flute moulds, tool marks,
current lineation, runzel marks, load casts and convolute
bedding. Siltstone is locally ferruginous and there are
minor beds of vuggy, mottled or spotted, medium- to
coarse-grained glauconitic sandstone. Drillhole DD92SN1
(Lanigan 1993), in central MOUNT DRUMMOND,
intersected a monotonous succession of interlaminated and
interbedded mudstone, siltstone and sandstone, with planar
to wavy bedding, probably equating to storm shelf facies.
These rock types are arranged into 0.5–3 m-thick upwardcoarsening cycles, comprising: (i) a basal lag of mudclasts
43
Figure 35. Unconformity between Crow
Formation (recessive unit in foreground)
and Constance Sandstone (resistant
ridge in background). Note truncation
of shallowly west-dipping sandstone
bed of Crow Formation at unconformity.
Mitchiebo, 745000mE 7947000mN,
No Mans Creek, looking south.
Figure 36. Parallel-laminated siltstone
and shale forming deep-shelf facies of
Tobacco Member of Crow Formation.
Mittiebah, 692350mE 7918850mN,
central Mittiebah Range.
Figure 37. Lenticular thinly-bedded
siltstone and fine-grained sandstone
of Crow Formation, with low-angle
truncations
probably
associated
with hummocky cross-stratification.
Storm shelf facies. Boxer, 699950mE
7958200mN, Top Lily Waterhole.
44
crudely planar-bedded, parallel laminated or cross-bedded
(with small-scale trough cross-beds). The sandstone turbidite
facies merges with the debris flow facies in its characteristics.
It forms beds 5–100 cm thick that are interbedded within
other facies or form amalgamated packages up to 30 m thick.
These graded beds are sometimes seen to initiate upon a
sharp erosional base and grade upward from coarse-grained,
poorly sorted sandstone into fine-grained sandstone, capped
by laminated siltstone and shale (Figure 40). They were
probably deposited as sand-rich, high-density turbidity
currents, deposited below fair-weather wave-base.
and/or quartz granules; (ii) a lower interval of dark grey
interlaminated mudstone and siltstone, or very fine-grained
sandstone as centimetre-scale upward-fining cycles with
sand-filled shrinkage cracks; (iii) a middle interval of dark
greenish grey mudstone and siltstone with locally massive
or chaotic bedding; and (iv) an upper interval of pale grey,
very fine- to medium-grained sandstone with planar to
massive bedding and sporadic coarse-grained glauconitic
sandstone beds. Storm shelf facies of the Crow Formation
closely resembles that of the Mainoru and Cottee formations
in the McArthur Basin (Pietsch et al 1991, Haines 1997).
Sedimentary structures are typical of ‘tempestite facies’
(Ager 1974), involving storm-influenced deposition below
fair-weather wave-base in a marine shelf setting.
Shallow-water sandstone facies
The shallow-water sandstone facies takes on a variety of
forms within the Crow Formation and is likely to include
a number of different, but overlapping variants. Most
commonly, this facies is composed of thick units of white to
red-brown or maroon, silicified, fine- to very coarse-grained
quartzose to lithic sandstone, with locally abundant rounded
pebble (plus rare cobble) trails and localised, poorly sorted
pebble–cobble conglomerate. Clasts are generally less
than 3 cm, but range up to 20 cm in diameter, and include
rounded silicified sandstone, quartzite, quartz, chert and
mudstone. Sandstone is locally ferruginous, micaceous and
glauconitic, particularly in coarser beds, with hematitedefined laminations and mottled oxidation spots (Figure 41),
not unlike the Middle Creek Sandstone Member of the
Mullera Formation. Bedding is medium to very thick, with
planar and trough cross-beds of various dimensions, planar
bedding, current lineation (Figure 42), mudclasts, synaeresis
cracks and rare symmetric ripples of 10–20 cm wavelength
and 3–5 cm amplitude. Large and small bedforms with both
concave- and convex-up laminae have also been recognised
locally, and are interpreted as HCS, not unlike that seen in the
Crawford Formation of the McArthur Basin (Jackson et al
1987, Figures 43, 44). Bedforms, composition and grainsize
are consistent with high-energy traction-current deposition,
perhaps in a shallow intertidal or storm-influenced marine
environment, but including braided fluvial settings in some
instances. Thus, it is likely that this facies encompasses a
variety of nearshore and coastal depositional environments.
Debris flow facies
This facies is composed of red-brown, orange, pink,
white or yellow, poorly sorted, feldspathic, micaceous,
ferruginous and lithic, medium- to very coarse-grained
sandstone, pebbly sandstone and lesser matrix-supported
conglomerate (Figure 38). These constitute beds up to
several metres thick, but generally 10–100 cm thick, which
occur within stacked cycles and as sporadic entities within
‘background’ shelf facies. Beds are massive or crudely
parallel laminated and generally assume the outcrop
appearance of weathered porphyritic granite (‘whiterock’)
or basalt/dolerite (‘redrock’). Sporadic, diffuse low-angle
cross-beds have been recognised, and may be large-scale
hummocky or swaley cross-stratification, or even antidunes.
Beds are generally ungraded, but crude normal grading
is locally evident within individual beds (eg 709950mE
7992450mN). In this respect, they merge with sandstone
turbidite facies (see below).
Clasts comprise up to 40% by volume of some of the
beds and are up to 5 cm in diameter. They include angular
to subrounded vein quartz, K‑feldspar fragments and whole
crystals, rounded lithic fragments (of metamorphic, granitic
and sedimentary provenances), chert (some with microbial
lamination) and coarse muscovite flakes. These are set in
a clay-rich ferruginous lithic sandstone matrix of variable
grainsize. Platy clasts are generally oriented parallel to
bedding.
Conglomerate is generally more thickly bedded than
sandstone with a more obvious sedimentary texture
(Figure 39). It is quite variable in composition. At some
localities, the conglomerate comprises well rounded
cobbles of quartz and quartzite in a coarse ferruginous
sandy matrix, and in other places, it is dominated by clasts
formed of single, subrounded, pink K‑feldspar crystals, and
lacks clasts of quartz and quartzite.
The debris flow facies is interpreted to have been
deposited by sand- and gravel-rich debris flows (mass
flows), perhaps by coarse turbidity flows into a marine
environment below fair-weather wave-base.
Saprolite ‘ facies’
Recessive intervals in the Crow Formation are locally
covered by or altered to a veneer of surficial material,
including knobbly massive ferruginous chert, silcrete and
calcareous clayey saprolite. The latter has the appearance
of a quartz-phyric volcanic rock (‘redrock’ and ‘whiterock’;
eg 710000mE 7995000mN, Whiterock Creek). This is
interpreted to be the result of surficial weathering of
carbonaceous and/or pyritic shale, or the breakdown of the
labile component in siltstones and sandstones. Saprolitic
deposits are notably common at the very base of the
Crow Formation in the Canyon Range area (eg 704950mE
7999900mN and Figure 45) and are a useful mapping aid
for the lower part of the formation.
Sandstone turbidite facies
This facies is composed of white to grey, silicified, fine- to
coarse-grained, sublithic to lithic sandstone with locally
abundant rounded pebble (plus rare cobble) trails. Clasts
include rounded silicified sandstone, quartz, chert and
mudstone. Sandstone is thinly to thickly bedded, massive to
Lateral facies and thickness characteristics
Canyon Range
The Canyon Range area incorporates outcrop north and west
of Benmara Fault. The Crow Formation outcrops well in this
45
Figure 38. Massive, poorly sorted,
polymict pebble conglomerate of Crow
Formation. Clasts are of subrounded
quartz and K-feldspar. Debris flow facies.
Boxer, 703950mE 8000200mN, Murphys
Creek.
Figure 39. Massive to streakily planarbedded granule to pebble conglomerate
in Crow Formation. Clasts are mainly of
K-feldspar and quartz. Boxer, 703700mE
8008220mN, Canyon Range.
Figure 40. Decimetre-scale beds of grey
massive, poorly sorted lithic micaceous
sandstone interdigitated with thin intervals
of white laminated claystone and siltstone
of Crow Formation. Sandstone turbidite
facies. Boxer, 710000mE 7992500mN,
Whiterock Creek.
46
Figure 41. Scattered oxidation spots,
possibly after glauconite or evaporites,
in medium-grained lithic sandstone,
Tobacco Member of Crow Formation.
Shallow-water
sandstone
facies.
Mittiebah, 699300mE 7915650mN,
eastern Mittiebah Range.
Figure 42. White, fine-grained sublithic
sandstone with stacked horizons of
parting (current) lineations, middle
Crow Formation. Mitchiebo, 724000mE
7952100mN, Flemington Racecourse.
Figure 43.
Silicified
fine-grained
quartzose sandstone with amalgamated
hummocky cross-stratification, Tobacco
Member of Crow Formation. Mittiebah,
697800mE 7916750mN, eastern Mittiebah
Range.
47
area, due to recent erosional incision of the Canyon Range
and relatively steep dips. Based on measured outcrop width
and dips, the thickness of the formation (including Tobacco
Member) is estimated to range from ca 1500 m in the north
near the boundary with CALVERT HILLS, to ca 2200 m
approximately 30 km to the south, near the inflection of the
Benmara Fault. However, structural repetition appears likely
along the Canyon Range, so these nominal thicknesses may
not reflect true thickness variations (see Structure).
In the Canyon Range, the Crow Formation is
characterised by the presence of interdigitated deep-shelf,
storm shelf, sandstone turbidite, debris flow and shallowwater sandstone facies. The scale of interdigitation varies,
but is generally in the order of 1–20 m. Overall, the formation
in this area is moderately more resistant and is notably coarser
and more locally sourced than areas to the south and east of
Benmara Fault. This is the only area where debris flow and
sandstone turbidite facies are prolific, although these facies
may be concealed in other areas, where exposure is poorer.
The Crow Formation appears to gradually coarsen
upwards in the Canyon Range. Evidence of traction current
deposits and the interpreted energy level of the depositional
environment also appear to increase upwards. In contrast,
the grainsize of turbidite beds appears to decrease upwards.
The basal ca 500 m of the formation is very recessive and
poorly exposed, and is locally represented by saprolite along
creeks. The lowermost 20–50 m is sometimes an interval of
massive ferruginous cherty outcrop, perhaps after sulfidic or
carbonaceous shale. Where genuine outcrop is recognised,
this part of the formation is dominated by the the deepshelf and storm shelf facies. Sandstone turbidite and debris
flow facies appear to be concentrated into the middle
1000–1500 m, where they are interbedded with the finer shelf
facies. The shallow-water sandstone facies is only present
in the banded, resistant upper 300–500 m of the formation
(Tobacco Member), where it is interlayered with the storm
shelf facies.
Crow Creek
The Crow Creek area encompasses a large flat area of poor
outcrop, stretching north from Eight Mile Creek to the
headwaters of Benmara Creek, and centred on Crow Creek
(693000mE 7960000mN). The Crow Formation thickens
westward from Flemington Racecourse Claypan to an
Figure 44. Friable, fine-grained, lithic
micaceous sandstone with hummocky
cross-stratification, Tobacco Member of
Crow Formation. Mittiebah, 699600mE
7915950mN, eastern Mittiebah Range.
Figure 45. Saprolite: white, highly
leached ?carbonaceous shale in lower
Crow Formation. Boxer, 704480mE
8008236mN, Canyon Range.
48
shelf facies make up the bulk of the formation, the thickness
for which is impossible to estimate. Shallow-water sandstone
facies and minor interbedded storm shelf facies constitute
the 400–600 m-thick banded resistant Tobacco Member
(see below).
estimated 1500–2500 m. This is a gross estimate, because
outcrop is poor and measurable dips are rare. From the small
amount of outcrop investigated, the formation appears to be
dominantly of deep-shelf and storm shelf facies, with sparse
outcrop of sandstone turbidite facies. In the probable middle
of the Crow Formation are occasional anomalous decimetrescale beds of coarse red-brown ferruginous lithic sandstone
with small trough cross-beds (eg 698300mE 7949850mN)
and vuggy fenestral chert that may be of tuffaceous origin
(eg 698000mE 7950950mN). These beds may be lateral
equivalents of the major intervals of sandstone turbidite and
debris flow facies in the Canyon Range area and/or L
Psos
to the west. The succession appears to coarsen upwards
overall, although this is poorly constrained.
Tobacco Member (P
Lso t )
The Tobacco Member (new name, see Appendix 1) is
mapped at the top of the Crow Formation in the Canyon and
Mittiebah Ranges. Locally, including in the Crow Formation
type section, this Member cannot be differentiated from the
Crow Formation. Outcrop consists of banded white to pale
red-brown, resistant strike ridges that are clearly visible on
aerial photographs. Banding is due to sedimentary cyclicity
and the interlayering of diverse facies with alternating
oxidation state, much like the Rosie Creek Sandstone in the
southern McArthur Basin (Haines et al 1993). Due to the
presence of fine recessive intervals and the prominence of
feldspathic labile components, it is designated as a member
of the Crow Formation rather than the overlying Mittiebah
Sandstone. The Tobacco Member also has a high background
gamma ray signature relative to the underlying and overlying
packages on radiometric images, making it generally easy
to distinguish. Total thickness is in the order of 300–600 m,
with the thicker intervals restricted to the Mittiebah Range.
The Tobacco Member is a composite of stacked sandstone
units; the thickest are about 80 m, but most are in the range
5–30 m. The dominant facies is resistant (ridge-forming),
shallow-water sandstone facies with lesser recessive storm
and deep-shelf facies (as described above, Figure 36). In
the Mittiebah Range, the shallow-water sandstone facies
consists of interbedded: (i) medium to very thickly bedded,
diffusely bedded, quartzose to lithic, locally ferruginous
and micaceous (± glauconitic), fine- to medium-grained
sandstone with amalgamated low-angle trough and HCS
(Figures 43, 44), as seen in the lower Aquarium Formation,
southern McArthur Basin (Rawlings 2002); (ii) mediumto coarse-grained glauconitic sandstone, containing small
red/brown mudstone flakes, pits after evaporites and trough
cross-beds (Figure 41); and (iii) minor decimetre-scale beds
of very coarse to granule-bearing, pebbly lithic sandstone,
with parallel lamination. Interlayering of facies up into the
overlying Mittiebah Sandstone indicates a conformable
gradational contact.
A shallow intertidal to storm-influenced marine shelf
depositional setting is likely for this unit. The cycles
represent repeated progradation of shallow-water sands
over the deeper shelf facies.
Flemington Racecourse Claypan
This area includes the west-southwest-trending belt of outcrop
north of the Mitchiebo Fault and Mitchiebo Waterhole, centred
on 720000mE 7952000mN. It is an area of poor exposure,
with a broad sand and laterite cap. The only part of the Crow
Formation that is well exposed is a narrow ridge of shallowwater sandstone facies belonging to P
Lsos, in about the middle
of the formation (see mapface). Information for the recessive
parts of the succession is limited. Drillhole DD92SN1
(Lanigan 1993) intersected the lower third of the formation
below P
Lsos within a large recessive belt, and penetrated
458.6 m of the South Nicholson Group, of which 430 m is
herein interpreted as the lower Crow Formation. The drillhole
intersected a monotonous interval of storm shelf facies,
indicating that this facies dominates at least in the lower part
of the formation. Sparse outcrops of sandstone turbidite facies
are also recognised. Thicknesses in this area are estimated
to be: 800–1200 m for the complete Crow Formation;
500–700 m for the lower P
Lso; ca 100 m for P
Lsos; and
200–400 m for upper P
Lso. The top of the formation is
not exposed and a degree of uncertainty exists for these
thicknesses.
Mitchiebo Waterhole
This area includes the narrow valley of Crow Formation
that stretches east-northeast from Mitchiebo Waterhole to
No Mans Creek, centred on 735000mE 7942000mN. The
succession is thin (up to 800 m), but this is probably due to
erosion at the Constance Sandstone unconformity. The true
thickness may also be structurally modified by splays of
the Mitchiebo Fault (Rawlings and Sweet 2004). The Crow
Formation is generally not well exposed here, but appears
to be dominated by storm shelf facies with lesser deep-shelf
facies. It also contains a few well exposed sandstone and
conglomerate units [eg Figure 35, one of which (L
Psos ) is
thick enough to be represented on the mapface (at 748000mE
7947000mN)]. The contact with the overlying Constance
Sandstone is often strongly ferruginised in this area (see
Economic Geology).
Unnamed subunit (L
Psos )
This subunit is recognised in two areas, where it serves as a
useful but relatively restricted marker: (i) east-northeast of
Mitchiebo Waterhole, around 748000mE 7947000mN; and
(ii) 15 km north of Mitchiebo Waterhole, around 720000mE
7952000mN. It occurs as a low discontinuous strike ridge
within valleys of otherwise recessive Crow Formation. It is
up to 150 m thick, with a poorly exposed, probably erosional
base and conformable top.
East-northeast of Mitchiebo Waterhole, L
Psos comprises
yellow to pale orange, mottled, shallow-water sandstone
facies (as described above), locally dominated by pebble
Mittiebah Range
This area includes the west- to southwest-trending belt of
outcrop immediately north of Mittiebah Range. It includes
a recessive lower part (undivided Crow Formation) and
moderately resistant upper part (Tobacco Member). From
the small amount of outcrop investigated, deep- and storm
49
Metamorphics?) or by K‑feldspar-rich granite (Nicholson
Granite Complex). Beyond the Canyon Range, Murphy
Inlier uplift was manifested as a gradual shallowing of the
depositional environment, either due to increasing sediment
supply or reduced accommodation space. The upper part of
the Crow Formation (Tobacco Member) shows evidence for
a greater tractional influence, with current-laid sandstone
facies dominant, suggesting further shallowing over time.
This is consistent with a conformable relationship with
the overlying Mittiebah Sandstone, which presumably
represents high-energy fluvial or shallow-marine deposition,
possibly also sourced from the Murphy Tectonic Ridge.
There is a gradual overall coarsening and shallowing
of facies upward through the Crow Formation, consistent
with foreland basins in general (DeCelles and Giles 1996).
Abbott and Sweet (2000) have proposed a foreland model
for the Roper Superbasin, but have not stipulated the
location or general direction of the foreland(s). The Murphy
Tectonic Ridge has generally not been thought to have been
active at the time of deposition of the South Nicholson or
Roper groups (Plumb et al 1990). However, an alternative
interpretation is that the ridge was part of a regional set of
small foreland flexures that affected local development of
the basin in different areas and at different times.
conglomerate (eg 746000mE 7947300mN). Lithological
character and grainsize vary significantly both vertically
and laterally, and a complex intertidal/shallow-marine/
fluvial setting (braid or fan delta) is envisaged.
North of Mitchiebo Waterhole, L
Psos is composed of
three distinct facies, which are interbedded on a dekametre
scale: (i) a shallow-water sandstone facies that is mottled,
lithic and micaceous, with trough and swaley cross-beds
(ca 10–50 cm wavelength) and discrete convoluted beds;
(ii) a shallow-water sandstone facies that is more quartzose
with a prominent parting lineation (Figure 42); and (iii) a
storm shelf facies that is notably micaceous, ferruginous
and silty. It is likely that these three facies belong to a single
storm shelf setting, with a higher than normal, but variable
sediment supply.
L
Psos has overall upward-coarsening and -thickening
beds. Notably, the upper few decimetres to metres of this
unit contain numerous cobbles (up to 40%); centimetreto decimetre-scale, yellow, silicified/chertified mudstone
interbeds; and large (2–10 cm diameter), angular to
rounded, ellipsoidal pebbles and cobbles. Locally capping
the immature beds is a thin (<2 m) blanket of white, blocky,
fine-grained sublithic sandstone, with prominent current
lineations. This is overlain by poorly exposed shale and
siltstone (deep-shelf facies) of undivided Crow Formation.
Accident Subgroup
Interpretation
The facies, provenance, palaeogeographic setting and
depositional architecture of the Crow Formation clearly have
a spatial relationship with the Murphy Inlier. The restriction
of immature debris flow and sandstone turbidite facies to
the Canyon Range area indicates that this area was proximal
to the principal sediment source. A close relationship with
the Murphy Inlier becomes more pronounced if the debris
flow-rich Caulfield beds are correlated with the Crow
Formation. Elsewhere, more distal sedimentation prevailed
and deposition was not greatly influenced by these rapid
and proximal processes. Based on this, we have developed
a general model for deposition of the Crow Formation.
The model involves turbidites and debris flows entering a
marine shelf setting adjacent to an active tectonic province
(Murphy Tectonic Ridge, Plumb et al 1990). Coarse detritus
was supplied rapidly from a beach and fluvial setting at the
edge of the ridge (ie fan or braid delta). The adjacent shelf
environment alternated between below and above storm
wave-base (background parallel lamination and tempestite
overprint, respectively).
The stratigraphic succession within the Crow Formation
can also be explained in terms of this model. Persistent
and widespread deep-shelf facies in the lower part of
the formation indicates that the setting was probably
below the influence of tractional currents for the most
part and no single sediment source is apparent. Midway
through the formation, tectonism and uplift of the nearby
palaeotopographic high initiated the deposition of debris
flow and sandstone turbidite facies in the Canyon Range
area. This was manifested as localised and repeated
interruptions to background shelf sedimentation by influxes
of coarse clastic material. The spatially restricted clast
assemblage and provenance suggests that this tectonic high
was locally dominated by quartzite and quartz (Murphy
The Accident Subgroup (new name, see Appendix 1,
Table 5) is introduced to describe that part of the South
Nicholson Group that overlies the newly recognised
Wild Cow Subgroup in central and western MOUNT
DRUMMOND. As the Wild Cow Subgroup is absent from
eastern MOUNT DRUMMOND, the Accident Subgroup
comprises the whole of the South Nicholson Group in that
area. The contact between the two subgroups is conformable
in the west, but disconformable and even an angular
unconformity in the central parts of the sheet area. In the
east, where the Wild Cow Subgroup is absent, the Accident
Subgroup overlies the McNamara and Fickling groups with
a disconformity or angular unconformity. In the Bauhinia
Dome, it unconformably overlies the Caulfield beds. The
Accident Subgroup is unconformably overlain by various
units of late Neoproterozoic and Phanerozoic age, including
the Georgina Basin succession. The subgroup incorporates
four formations: the Constance and Mittiebah sandstones
at the base, an overlying mainly recessive shaly unit, the
Mullera Formation (Figure 5), and the Tidna Sandstone,
which is present only in LAWN HILL in Queensland
(Carter and Zimmerman 1960, Hutton and Grimes 1983).
Correlation between the two basal sandstone formations
is uncertain, but both represent the base of the Accident
Subgroup in their respective areas (see below).
Constance Sandstone (L
Psc)
The Constance Sandstone, defined by Carter et al (1961),
has been mapped across a broad area within MOUNT
DRUMMOND and the adjacent mapsheets CALVERT
HILLS (Roberts et al 1963, Ahmad and Wygralak 1989),
WESTMORELAND (Grimes and Sweet 1979, Sweet et al
1981), and LAWN HILL (Carter and Öpik 1961, Hutton and
50
and southwest, including the belt of rocks from Border
Waterhole through the Bluff Range to Moloney Creek, the
formation consists of a single sandstone unit. It has not
been assigned to a named member, although preliminary
studies in LAWN HILL suggest that it may incorporate the
Burangoo Sandstone and/or Schultz Sandstone members.
On this basis, these sandstone members and the intervening
Wallis Siltstone Member are recognised from outcrops west
of Moloney Creek to outcrops 4 km northeast of Mitchiebo
Waterhole.
Grimes 1983). As a result of the present mapping program, the
Constance Sandstone in western MOUNT DRUMMOND, as
mapped by Smith and Roberts (1963) and Sweet (1984), has
been split; the lower part is now recognised as the Wild Cow
Subgroup (see above). The key to this revised subdivision is
the recognition of an angular unconformity at 750000mE
7946600mN, where Sweet (1984) mapped a conglomerate
lens and a tongue of Constance Sandstone (now mapped as
Burangoo Sandstone Member) extending to the west within
fine-grained rocks then mapped as Mullera Formation.
However, these fine-grained rocks are now mapped as Crow
Formation and the lens of conglomerate at the top of this
older unit is clearly overlain with angular unconformity by
the tongue of Burangoo Sandstone Member. The revised
Constance Sandstone can be traced to the southwest to the
Mitchiebo Waterhole area, where it also appears to lie with
angular unconformity on the Crow Formation and Playford
Sandstone; faults cutting the Playford Sandstone extend into
the Crow Formation but do not appear to be present in the
Constance Sandstone, and the Crow Formation thins, or is
absent locally, presumably due to pre-Constance Sandstone
erosion. In southeastern MOUNT DRUMMOND, the
Constance Sandstone oversteps the Wild Cow Subgroup, to
lie with angular unconformity directly on various formations
within the McNamara Group. A similar relationship is seen
between the Constance Sandstone and the Fickling Group in
the northeast of the mapsheet, although the angular nature
of the unconformity is very subtle and best seen further to
the north, in Seigal.
The dominant rock type in the sandstone members
of the Constance Sandstone is a thickly bedded, crossbedded, medium- to coarse-grained, granule-rich and
occasionally pebbly, quartz or sublithic sandstone.
Interbedded red and grey to grey-green, very finegrained sandstone and siltstone dominate in the siltstone
members, which also contain coarser-grained sandstone
interbeds and minor shale. Details of the lithology are
discussed below. Considerable lateral thickness variation
of members is evident within the formation, and this is
discussed following the descriptions of the individual
members. Overall, the formation ranges from 100 m to
1100 m thick in MOUNT DRUMMOND.
Two siltstone members are recognised within the
Constance Sandstone: the Pandanus and Wallis Siltstone
Members, which were first recognised in CALVERT
HILLS by Roberts et al (1963). A third siltstone member
(Bowthorn Siltstone Member), defined by Sweet (1981)
in Hedleys Creek and Bowthorn, is now abandoned, and
the siltstone lenses absorbed into the Schultz Sandstone
Member (new name, see Appendix 1). The intervening
sandstone members were not named, but were identified by
Sweet et al (1981) as, from oldest to youngest, L
Psc1, L
Psc2,
L
Psc3 and L
Psc4. These have been assigned names herein: L
Psc1
is the Hedleys Sandstone Member (L
Psch ), L
Psc2 becomes the
Burangoo Sandstone Member (L
Pscu ), and L
Psc3 and L
Psc4,
and at least two thin siltstone lenses, become the Schultz
Sandstone Member (L
Pscs ). All members, both sandstone
and siltstone, are present in MOUNT DRUMMOND,
although not all members are present in all outcrops. The
most complete and thickest sections are in the northeast,
where all members are recognised. In outcrops to the south
Hedleys Sandstone Member (L
Psch )
The Hedleys Sandstone Member (new name, see
Appendix 1), previously identified as L
Psc1 by Sweet et al
(1981) in Hedleys Creek and Seigal, and by Slater and
Mond (1980) in the Constance R ange region, is that part
of the Constance Sandstone below the Pandanus Siltstone
Member. It is now recognised in northeastern and central
MOUNT DRUMMOND, and around the Bauhinia Dome in
the north. In the northeast, it is 10–15 m thick and consists
of white, thickly to very thickly bedded, fine- to mediumgrained sublithic and quartzose sandstone, which contains
mudclasts and minor granules and small pebbles of quartz.
The basal few decimetres of the member is medium- to
coarse-grained, and contains flat siltstone pebbles. In
this area, the unit lies unconformably on the Doomadgee
Formation (Fickling Group). Fifty kilometres to the west,
in the Bauhinia Dome, the lithology and thickness are
similar and the unit can be seen to lie with slight angular
unconformity on the Caulfield beds, truncating 100 m of
underlying strata along strike in the western part of the
dome. Quartz pebbles to 1 cm in size are present in the
basal beds.
Pandanus Siltstone Member (P
Lscp )
Defined by Roberts et al (1963) in CALVERT HILLS, the
Pandanus Siltstone Member was traced southwards into
MOUNT DRUMMOND by Smith and Roberts (1963),
and later recognised to the east in WESTMORELAND
(Grimes and Sweet 1979, Sweet et al 1981) and LAWN
HILL (Constance R ange region; Slater and Mond 1980).
In northeastern MOUNT DRUMMOND, it comprises 50 m
of flaggy, brown, micaceous, lithic fine-grained sandstone
with parting lineations, HCS, small trough cross-beds,
parallel lamination, slumping and convolute bedding, and
lesser siltstone and shale. It is present around at least the
southern perimeter of the Bauhinia Dome in northern
MOUNT DRUMMOND, but is there mapped with the
Hedleys Sandstone Member, as it is only 20 m thick and too
thin to distinguish at 1:250 000 scale.
Burangoo Sandstone Member (P
Lscu )
The Burangoo Sandstone Member (new name, see
Appendix 1) is that part of the Constance Sandstone
between the Pandanus and Wallis Siltstone Members and was
informally designated L
Psc2 by Sweet et al (1981). It outcrops
in northeastern and northern MOUNT DRUMMOND, and
is tentatively recognised in the Mitchiebo belt in central
MOUNT DRUMMOND. It is the thickest member in
the Constance Sandstone, and in areas of low dip, forms
extensive rocky plateaux, commonly with pseudokarstic
51
by the overlying Schultz Sandstone Member, due to faulting
prior to deposition of that member, rather than stratigraphic
thinning of the Wallis Siltstone Member. In a complete section
2 km west of Border Creek, at 814640mE 7995040mN, the
unit is at least 200 m thick, its greatest recorded thickness.
Although poorly exposed, recessive rocks in the lower part
include green-brown-weathering, very fine- to fine-grained
laminated sandstone, with highly micaceous partings and
faint sole marks. About 130 m above the base, a resistant
sandstone unit consists of at least two thick beds of white,
well sorted, coarse- to very coarse-grained quartz sandstone.
These beds are lenticular, thinning from 2–3 m to less than
0.5 m over 200 m of strike-length. Bed surfaces are littered
with moulds of large shale ripup clasts (up to 10 cm). Only
red-brown siltstone rubble is exposed in the upper 70 m of
the formation. The member is present north and east of the
Bauhinia Dome, where it appears to consist of similar thinly
bedded sandstone and siltstone as in the northeast, but there
it is less than 100 m thick.
Rocks in the Mitchiebo belt that were previously mapped
as Mullera Formation by Sweet (1984) are now interpreted as
Wallis Siltstone Member, since they are similar in lithology
to that member elsewhere and overlie the basal sandstone
unit in that area. This member is up to 100 m thick and can
be traced west-southwestward to 725000mE 7939000mN.
Although it is present in the arcuate outcrops to the north
and southwest of Mitchiebo Waterhole, it is not delineated
on the mapface due to its thickness being as little as 5 m
in outcrops 6 km to the southwest of the waterhole. The
member consists of flaggy to fissile, red-brown to maroon,
micaceous, lithic, fine-grained sandstone and siltstone,
interbedded on a centimetre to decimetre scale. Locally, the
lower part of the unit is highly ferruginous over a thickness
of greater than 7 m, apparently due to secondary enrichment
and discordant pisolite development. This concentration of
iron may have occurred during Cretaceous or Cenozoic
deep weathering, rather than being a primary iron-rich
horizon. Above this zone, the rocks are less ferruginous
and paler coloured (locally grey and tuffaceous looking),
with parallel and wavy lamination, cross-lamination,
HCS, synaeresis cracks, mudclasts, and prominent (but not
common) current lineations and low- to high-relief gutter
casts. A similar facies at 723931mE 7954022mN, 13 km
southeast of the Flemington Racecourse Claypan, contains
large gutter casts; these are up to 20 cm across and 10 cm
deep, with smooth bases bearing tool marks. Flute moulds
and multidirectional drag and tool marks are also present.
The member has been mapped as a lens in this area, but
may be more extensive.
weathering surfaces. It overlies the Pandanus Siltstone
Member with a sharp, but presumably conformable contact,
and is overlain equally abruptly by the Wallis Siltstone
Member in outcrops near Border Creek, around 814700mE
7995000mN. At the northern sheet boundary, it is overlain by
the Wallis Siltstone Member, but this cuts out within 0.5 km
to the south, where the Burangoo Sandstone Member is
overlain disconformably by the Schultz Sandstone Member.
The member is 130–150 m thick in the northeast, depending
on the dip estimate used in making the calculations, but is
only 35 m in the tentatively recognised outcrops in central
MOUNT DRUMMOND.
In the northeast, the member consists of fine- to coarsegrained, lithic, sublithic and quartzose sandstone. The
uppermost beds at 813800mE 7994990mN are coarse
grained and contain quartz granules and pebbles up to 1 cm
diameter, whereas the upper beds 10 km to the northwest
at 805230mE 7999460mN are medium grained and lack
pebbles. Beds are very thick and are generally trough crossbedded in sets up to 1 m thick; there are also some planar
cross-beds.
The member is tentatively recognised in the Mitchiebo
belt in central MOUNT DRUMMOND, where a supposed
tongue of Constance Sandstone in the Mullera Formation
was mapped by Sweet (1984). This 35 m-thick ‘tongue’ can
be traced westwards from the basal Constance Sandstone
overlying the Crow Formation in the Western Creek area,
around 769500mE 7949000mN, and is clearly the basal
Constance Sandstone to the west. It is almost horizontal
(<2°) and the unconformity with the Crow Formation is
planar to broadly sinuous. The unit forms a resistant ridge,
displaying pseudokarstic weathering in part, of white to
pale yellow, fine- and medium-grained, silicified, quartzose
to sublithic sandstone, with minor scattered granules and
rare small pebbles of quartz. It is medium to very thickly
bedded with planar bedding, decimetre-scale trough crossbedding, scattered symmetric ripples and mudclasts.
The base is locally medium- to coarse-grained. Toward
the top, the unit grades up into thin- to medium-bedded,
flaggy to slabby, fine-grained sandstone, with abundant
mudclasts, and small trough cross-beds, planar bedding,
current lineations, symmetric ripples and synaeresis cracks
(both randomly and parallel-oriented types). This facies is
similar to that in the Constance Sandstone at Flemington
Racecourse (722703mE 7953214mN) and may be a good
regional marker.
Wallis Siltstone Member (P
Lscw )
The Wallis Siltstone Member was defined by Roberts et al
(1963) in CALVERT HILLS, where it comprises about 90 m
of micaceous and glauconitic siltstone and fine-grained
sandstone (Sweet et al 1981). Both lower and upper contacts
are sharp. The lower contact is conformable, but the contact
with the overlying Schultz Sandstone Member is clearly
erosional, at least locally, and is deemed to be disconformable
or to have a very subtle angular discordance. The member
thins southwards and pinches out 0.5 km into MOUNT
DRUMMOND, at 801130mE 8007160mN, only to reappear
abruptly 10 km to the southeast, south of the Border Creek
Fault Zone. This is interpreted as a structural effect and it is
probably the result of minor uplift, erosion and truncation
Schultz Sandstone Member (P
Lscs )
The Schultz Sandstone Member (new name, see
Appendix 1) is that part of the Constance Sandstone above
the Wallis Siltstone Member. As noted above, its contact
with the underlying Wallis Siltstone Member is erosional
at the northern sheet margin: a local disconformity or
subtle angular unconformity. It is overlain by the Mullera
Formation, apparently conformably, in northern MOUNT
DRUMMOND and in CALVERT HILLS. The Bowthorn
Siltstone Member, mapped in WESTMORELAND by
Sweet et al (1981) and in Constance R ange region by
52
thick at that locality and is directly overlain by the Mullera
Formation.
In the Mitchiebo belt, the rocks range from fine to
coarse grained, although medium-grained sublithic and
lithic sandstone dominate. In the headwaters of George
Creek, the member contains elongate, parallel, inclined,
planar or tubular features superficially similar to the
trace fossil Skolithos; these are probably water-escape
structures. Bedding is commonly very thick and bedforms
include generally large-scale (2–3 m amplitude), lowangle trough and planar cross-beds (some sigmoidal),
planar bedding and HCS. The rocks north of Mitchiebo
Waterhole include a succession of medium to very thickly
bedded, amalgamated hummocky units, individual beds
becoming thicker and of higher amplitude upward, over
tens of metres. These beds include HCS, swaley crossstratification, and angle-of-repose cross-beds, indicating
that either grainsize or current strength were at a threshold
level for a switch from HCS to cross-bedding. In places,
the HCS beds bear a striking resemblance to the Crawford
Formation in the Roper Group. Southwest of Mitchiebo
Waterhole, the member is about 230 m thick and is
virtually all medium to coarse-grained, thickly bedded,
brown clayey/lithic sandstone. It displays little clear
internal stratification, but there are hints of large crossbeds, possibly some HCS, and one prolapsed foreset. There
is a clear depositional cyclicity on a <20 m scale, based on
resistant and recessive zones of sandstone. The uppermost
beds are whiter weathering, and are thickly bedded, coarse
to very coarse grained and strongly cross-bedded, locally
with well sorted granule-rich layers.
Slater and Mond (1980), is herein abandoned, the beds
assigned to that member being subsumed into the Schultz
Sandstone Member. Although the upper contact is sharp, it
is presumed to be conformable (see Discussion). A notable
feature of the member is the outcrop style of the basal beds;
they form spectacular, bare rocky platforms cut by deeply
eroded joints, a form of pseudokarstic weathering, and giant
displaced blocks commonly litter scarp slopes underlain by
the Wallis Siltstone Member.
The Schultz Sandstone Member is up to 300 m thick in
its type section in LAWN HILL and is substantially thicker,
at least 450 m and possibly up to 600 m, in a well exposed
section northeast from 814940mE 7995040mN, near Border
Creek in MOUNT DRUMMOND. The basal beds at this
section reveal the nature of the massive outcrops referred to
above. They are white to brown, medium, coarse- and very
coarse-grained to granule sandstone. Internal lamination
results from medium-grained through to granule sandstone,
with planar bedding and cross-bedding on a 2–5 cm (ripple)
to 0.2–0.3 m (cross-bed) scale, giving a distinctive streakily
bedded appearance. The sandstone lacks bedding partings;
ie there are no mudstone laminae separating sandstone
intervals, suggesting no pauses in sedimentation. It is this
feature that has resulted in the weathering out of very large
blocks. At the top of the interval, bedding planes appear
and are commonly surfaced with faint interference ripples.
Most of the member consists of light brown-weathering,
very friable, medium to coarse sandstone, cross-bedded on
a medium scale (to 0.5 m), amalgamated into very thickly
bedded units. Faint wave ripples and mudstone intraclasts,
some densely packed on bedding planes, were observed.
The now-obsolete Bowthorn Siltstone Member, named
and mapped from mapsheets to the east and north (Sweet
1981, Sweet et al 1981), forms a recessive interval in the
Schultz Sandstone Member around 815786mE 7995800mN,
in the Border Creek section. It is 220 m thick and consists
of poorly outcropping, platy, thinly laminated very finegrained sandstone. Low in the interval is an interbed of
medium to coarse sandstone with a marked lamination, due
to the weathering out of grains of iron oxides. These may
have originally been glauconite or another iron mineral
and the bed is of identical facies to ferruginous beds in the
Middle Creek Sandstone Member of the Mullera Formation.
The upper part of the interval does not outcrop, indicating
a continuation of fine-grained rocks. The rocks above the
former Bowthorn Siltstone Member (L
Psc4 of Sweet et al
1981), now also included in the Schultz Sandstone Member,
outcrop in the Border Creek section around 817000mE
8096000mN. Only the lowermost 50 m is exposed and this
is of the same facies type as the sandstone below it: very
thick bedded white, sublithic or quartzose sandstone. It is
cross-bedded on a large (>1 m) scale, and displays a range
of grain-sizes, both between and within foresets, from
coarse or very coarse in basal/toeset laminae, through to
fine-grained in individual laminae.
The upper part of the member, exposed in the bed of
the Nicholson River at 782680mE 8005430mN, is a well
indurated pink to brown, coarse- to very coarse-grained
to granule sandstone, trough and planar cross-bedded
throughout, and with patches of rippled sandstone on
undulating bedding planes. The member is 120–130 m
Undivided Constance Sandstone
The sandstone members within the Constance Sandstone
are recognisable only by virtue of the presence of
intervening siltstone members. Since the siltstones
are lenticular, or are truncated by overlying sandstone
members, the Constance Sandstone is mapped as a single
unit, P
Lsc, where siltstones are absent. This is the situation in
the Bluff Range; eastwards into LAWN HILL; north, west
and east of the Maloney Creek Inlier; and in the northwest
of the sheet area. In these areas, the Constance Sandstone
lies with a pronounced angular unconformity on various
formations of the McNamara Group and disconformably
on the Wild Cow Subgroup. In the northwest, it is faulted
against the Connelly Volcanics and Murphy Metamorphics.
Its thickness in the Bluff Range is difficult to estimate,
as it is flat lying to gently dipping and is strongly jointed
and faulted. An uninterrupted succession occurs in only
one section, to the east of the Maloney Creek Inlier from
784500mE 7961000mN, where a thickness range of 70–
150 m can be estimated. There, the unit includes white,
silicified fine-grained quartzose sandstone and trough
cross-bedded, pebbly coarse-grained sandstone which is
more lithic. The pebbles range up to 2 cm (mostly 0.2–
0.5 cm) and are of quartz. An angular unconformity with
the McNamara Group is evident in the Bluff Range at
787960mE 7954650mN, where the moderately dipping
Widdallion Sandstone Member is overlain by horizontal
Constance Sandstone. At this locality, the unit consists
of white, thickly bedded, strongly trough cross-bedded,
53
fining upward over tens of metres to medium-grained white
sandstone. Mudclasts are common and desiccation cracks
were observed near the top.
coarse-grained to granule sandstone with pebble layers;
the sandstone is quartz-rich with a minor clay/lithic
component. Pebbles up to 4 cm diameter, of fine-grained
lithic sandstone, are present in basal, very thickly bedded,
cross-bedded, medium-grained to granule sandstone
at 776404mE 7950550mN. Sweet (1984) reported local
conglomeratic bands, up to 8 m thick, containing ‘angular
to well rounded pebbles of quartz, quartzite, and chert
set in a poorly sorted, fine to coarse, silicified quartz
sandstone’ and ‘boulder conglomerate containing well
rounded quartz clasts up to 45 cm’. Such lenses are present,
but those shown on the Carrara R ange region map (Sweet
et al 1984) are benches of sandstone, not conglomerate. In
the easternmost outcrops, around 802862mE 7946445mN,
the sandstone is white to pale yellow, blocky and medium
to thickly bedded, fine- to medium-grained, silicified, and
quartzose to sublithic, with planar bedding and decimetrescale trough cross-bedding. It contains minor scattered
granules and rare small pebbles of quartz. Desiccation
cracks, current lineation and mudclasts are present. The
upper part contains interbeds of flaggy ferruginous siltstone
and sandstone, suggesting a conformable gradation into
the Mullera Formation.
The Constance Sandstone is now recognised in central
MOUNT DRUMMOND, south and southeast of Flemington
Racecourse Claypan, in areas previously mapped as
Mullera Formation. There, it is the youngest outcropping
part of a generally north-dipping succession, the thickness
of which cannot be determined. Although the bulk of the
rocks may be the Burangoo Sandstone Member, this is
not distinguished on the map because of poor outcrop and
uncertain stratigraphic relations. The best outcrop is south
of the claypan at 715261mE 7963214mN, where an isolated
10 m-thick interval is exposed. It comprises metre-scale
interbeds of: (i) thickly bedded, medium- to coarse-grained
(some granule-bearing) sublithic sandstone with planar
bedding; (ii) flaggy to fissile, red-brown or white, chalky
micaceous siltstone and claystone with parallel lamination;
and (iii) decimetre-thick beds of fine-grained micaceous
lithic sandstone with planar lamination, convolute bedding,
load casts, cross-lamination and current lineations.
Interbedded sandstone and finer-grained rocks such as these
have only been observed in the siltstone members, leading
us to speculate that this outcrop may be of Wallis Siltstone
Member.
Northwestern outcrops of the Constance Sandstone
demonstrate the reason for equating it with the Mittiebah
Sandstone. A folded series of sandstones between Murphys
and Benmara creeks, south from 710000mE 7998000mN,
overlies the Crow Formation and the facies are identical
to those in the Mittiebah Sandstone further west. The
oldest beds contain pink lithic sandstone with very largescale (several metres-thick) cross-beds. Near the base, at
708050mE 7993976mN, is an interbed of conglomerate,
in which the clasts are cobbles and pebbles of sandstone,
chert, pebble conglomerate with chert and quartz clasts,
and white coarse-grained orthoquartzite. An outcrop of
Constance Sandstone at the northern sheet boundary is an
east-dipping succession 380 m thick, faulted against older
rocks on its western side. It includes pink, coarse-grained
and granule to pebbly cross-bedded sandstone at the base,
Discussion
The Constance Sandstone varies substantially in thickness,
from less than 100 m in the southeast, where no siltstone
members are present, to at least 1000 m in the northeast,
where the section is incomplete. It is up to 400 m thick in
the Mitchiebo belt, and if the Mittiebah Sandstone is indeed
a correlative (see below), it is up to 2200 m thick in the west.
Of the several facies types recognised, two dominate the
formation in most outcrops:
• Thickly bedded, strongly trough or planar crossbedded, sublithic and quartz-rich sandstone of variable
grainsize, mostly in the medium to very coarse range,
with laminae and scattered granules and pebbles.
Minor structures include wave and interference
ripples, and scattered mudstone intraclasts. This
facies is very similar to the major sandstone facies
in the Roper Group (Sweet 1986, Abbott and Sweet
2000) and is interpreted as indicating shallow-marine
tide-dominated environments. The lack of textural
maturity of many sandstones is also consistent with
fluvial deposits, perhaps a braided fluvial system, and
it is possible that there are some non-marine intervals
represented. More detailed studies would be needed
to resolve the internal stratigraphy of the sandstone
members and to determine whether both marine and
non-marine facies are present.
• Laminated and thinly bedded, micaceous, very fine- to
fine-grained sandstone and siltstone, with minor shale
and interbeds of coarser sandstone. This facies indicates
much lower-energy environments, most likely marine
shelf to lower shoreface. The predominance of very finegrained sandstone and siltstone, and the paucity of shale
indicates that it was deposited above wave base. This is
similar to the storm-dominated shelf facies documented
by Abbott and Sweet (2000) at various levels in the
Roper Group, and to those in the Crow Formation (see
above).
The stacking pattern of coarser, tide-dominated sandstones,
and lower-energy, deeper-water micaceous sandstone and
siltstone (storm-dominated shelf facies) is remarkably
similar to the Roper Group, which has been interpreted
as a series of third-order depositional sequences (Abbott
and Sweet 2000). It may be possible to make detailed
correlations between the Constance Sandstone members
and parts of the Roper Group in the future, provided that
more adequate age controls can be established for the
South Nicholson Group.
Mittiebah Sandstone (P
Lsi)
The Mittiebah Sandstone (Smith and Roberts 1963,
Randal 1966a) is a strongly resistant unit that constitutes
the bulk of the Canyon and Mittiebah ranges in
northwestern and southwestern MOUNT DRUMMOND,
respectively. Small dome-shaped inliers within the
54
136°47'E, extending from 688100mE 7916100mN (lower
boundary stratotype) to 689400mE 7908850mN (top of
formation not exposed).
Georgina Basin are also present in adjoining northern
Ranken, eastern Brunette Downs and southern
CALVERT HILLS. The formation encompasses most of
the outcrop formerly mapped as Mittiebah Sandstone by
Smith and Roberts (1963), with the exception of a narrow
strip at the northern edge of the Mittiebah Range, which
is now assigned to the Tobacco Member of the Crow
Formation.
The Mittiebah Sandstone lies conformably to
disconformably on the Tobacco Member of the Crow
Formation, the contact being gradational over several
tens of metres in most areas. The top of the Mittiebah
Sandstone is persistently covered by Georgina Basin
rocks or Cenozoic sediments, and its relationship with any
overlying Mesoproterozoic rocks cannot be determined;
therefore, it is difficult to determine its relationship
with the Mullera Formation. We suspect that Mullera
Formation equivalents are present, and a conformable
boundary, as seen between the Constance Sandstone
and Mullera Formation in the east, is likely. Outcrops
of recessive beds above the Mittiebah Sandstone around
702000mE 8007000mN, in the western Canyon Range,
are tentatively assigned to the Mullera Formation, but
were not ground checked.
The composite thickness of the Mittiebah Sandstone
is at least 2200 m in the Mittiebah Range, with the top
not exposed. In the Canyon Range, its thickness appears
to be in the range 450–1700 m, in part due to structural
complications. A rapid thinning is most apparent in the
northern Canyon Range, near 703500mE 8007000mN,
which is evident on the mapface. The formation is
composed mostly of fine- to coarse-grained, quartzose
to lithic sandstone, with minor interbeds of conglomerate
and siltstone. Several informal subunits are apparent;
these could not be universally differentiated on aerial
photographs and thus do not appear on the mapface. They
are described below from the Mittiebah Range in ascending
stratigraphic order. The depositional setting probably
alternated between shallow storm-influenced marine and
braided fluvial. A type section is nominated herein for the
central Mittiebah Range near latitude 18°52'S longitude
Mittiebah Range
P
Lsi1 (granule facies)
This 200–260 m-thick facies appears to conformably and
gradationally overlie the Tobacco Member. The base is
commonly marked by a break in slope or a scarp and the
beginning of pseudokarstic weathering. The boundary
coincides with the disappearance of fine recessive
intervals and small bedforms from the succession. Instead,
sandstone in the basal 30–40 m of L
Psi1 is consistently fine
to medium grained, pale yellow-orange or white (locally
red-brown ferruginised), silicified to friable, lithic to
sublithic, and medium to very thickly bedded, with large
(up to 5 m amplitude), moderate- to high-angle planar and
lesser trough cross-beds and small-scale trough cross-beds.
Some beds contain randomly scattered quartz granules
and small pebbles, whereas others have laminae defined
by grainsize, including granule laminae. Compared to the
underlying Tobacco Member, bedforms are much larger
and grainsize gradually increases upwards. Above the
30–40 m level, sandstone becomes medium- to very
coarse-grained, with scattered granules and pebbles up
to 1 cm diameter (average 0.2 cm diameter). Bedforms
are equally as large as in the lower 40 m (Figure 46).
Palaeocurrents are mostly to the east and east-northeast
(060–090°). A measured section through this unit is
presented in Rawlings and Sweet (2004).
P
Lsi2 (fine-grained facies)
Conformably overlying L
Psi1 is a prominent dipslope and
change in airphoto pattern that coincides with a uniformly
fine- to medium-grained, medium- to very thickly bedded,
white to pale pink or yellow, sublithic to quartzose sandstone,
which is bland and textureless on aerial photographs and
monotonous in outcrop (Figure 47). It is only possible
to speculate on bedforms from rare in situ outcrops; it is
deduced that they include large planar cross-beds (with lowto moderate-angle foresets) and small-scale trough cross-
Figure 46. Large-scale planar cross-bed
in lower Mittiebah Sandstone. Mittiebah,
699850mE
7915350mN,
Mittiebah
Range.
55
consists of white-yellow, quartzose to sublithic, coarse- to
very coarse-grained sandstone, with beds or laminae of
quartz granules and small pebbles; pebbles are generally
<1 cm, but are rarely up to 3 cm in diameter. This facies is
similar to L
Psi3, with thick bedding and large-scale trough
bedforms. Based on dips and outcrop width, si4 is at least
800 m thick. The top of the subunit is not exposed.
beds. Individual beds are silicified and diffusely laminated
or massive. There are no ripples, pebbles or granules present,
but mudclasts and liesegang banding are locally abundant.
The lower contact with si1 is not exposed, as it is covered
by scree from the overlying ridge; it may or may not be a
recessive interval. Notably, there are rare laminae of quartz
granules in the basal few metres of si2, suggesting that the
contact with si1 is conformable and gradational. Based on
average dips and outcrop widths, si2 is 500–600 m thick.
Canyon Range
In this area, the Mittiebah Sandstone outcrops as resistant
banded ridges. It is typically composed of pale yellow to
pink, fine- to medium-grained (± coarse-grained) quartzose
to lithic sandstone. The basal 20 m of the unit is generally
of medium to coarse sandstone, with scattered pebbles
and cobbles of chert, quartzite and quartz up to 15 cm in
diameter. Interbedded sandstone and conglomerate are
locally developed. The overlying 100–200 m is medium
to very thickly bedded and commonly pseudokarstically
weathered. It contains planar bedding and large-scale
planar and trough cross-beds, bearing curved tabular,
sigmoidal (Figure 48) or concavo-convex foresets (cf
swaley cross-stratification). Overall, grainsize decreases
gradually upsection and bedforms become larger and
are dominated by planar cross-beds up to 5 m thick.
Westerly directed palaeocurrents are apparent, but there
is considerable variability. This facies closely resembles
L
Psi1 in the Mittiebah Range. Above this, outcrop is very
poor and the only demonstrable bedforms are millimetrescale grainsize lamination, planar bedding, rare shortwavelength symmetric ripples and parting lineations. As in
the Mittiebah Range, large planar cross-beds are possibly
prolific in this part of the formation, but are difficult to
distinguish. There is also at least one thin (<50 m) interval
of recessive red/brown siltstone within the middle Mittiebah
Sandstone near 691700mE 7985800mN.
In the Canyon Range, the base of the Mittiebah
Sandstone is not appreciably discordant with the underlying
Crow Formation and there is no obvious unconformity
surface. On the contrary, conglomeratic beds in the upper
Crow Formation and lower Mittiebah Sandstone are
similar, suggesting a continuation of sedimentation without
a significant break.
si3 (pebbly facies)
Apparently conformably overlying si2 is a subunit of
yellow, very coarse-grained (locally pebbly or quartz
granule-bearing), silicified or friable, quartzose to lithic
sandstone, with minor interbeds of fine- to mediumgrained sandstone. Pebbles average 0.2 cm and are up to
4 cm in diameter. The sandstone is very thickly bedded,
with large planar and trough cross-beds and local, smallscale trough cross-beds. In general, pebbly and non-pebbly
sandstone are interdigitated on a 5–20 cm scale, and are
not necessarily divided by erosional surfaces. Instead, they
appear to represent grainsize variations within individual
cross-bed foresets. In contrast, individual cross-bed sets
are divided by high-angle or smooth low-relief erosional
surfaces. Overall, there is an apparent fining upward of
this subunit, with decreasing pebble content and average
grainsize. si3 is commonly pseudokarstically weathered,
spectacularly so in the centre of the Mittiebah Range around
688600mE 7912300mN. This subunit is approximately
500–600 m thick.
si4 (mixed facies)
Gradationally overlying si3 is an interlayered (at 10–50 m
scale) ‘fine facies’ and ‘coarse facies’. The fine facies is pinkorange with white specks and consists of medium- to finegrained, lithic to sublithic sandstone with local scattered
quartz granules. It is medium to very thickly bedded,
with diffuse planar bedding or low-angle planar crossbeds, symmetric ripples (sinuous and interference types)
and crude current lineations. The fine facies is similar in
character to the planar-bedded Warramana Sandstone in
the McArthur Basin (Rawlings 2002). The coarse facies
Figure 47. Loose outcrop habit of
subunit 2 of Mittiebah Sandstone, with
probable disguised large-scale planar
cross-beds.
Mittiebah,
699900mE
7915350mN, Mittiebah Range.
56
Correlation
On the following grounds, the Mittiebah and Constance
sandstones are herein tentatively correlated:
The Mullera Formation lies conformably on the
Constance Sandstone in eastern MOUNT DRUMMOND
and Benmara. Its relationship with the Mittiebah Sandstone
is uncertain, as there is no demonstrable South Nicholson
Group overlying the Mittiebah Sandstone to the west of the
Canyon Range in Boxer or south of the Mittiebah Range in
Mittiebah. The top of this sandstone is generally covered
by Georgina Basin rocks or Cenozoic sediments. Outcrop
of recessive beds around 702000mE 8007000mN (western
Canyon Range) is tentatively assigned to the Mullera
Formation, but was not ground checked. Based on a number
of lines of evidence, it is probable that the Mullera Formation
conformably overlies the Mittiebah Sandstone in this area
(see Mittiebah Sandstone). The Mullera Formation is
overlain conformably by the Tidna Sandstone in LAWN
HILL (Carter and Zimmerman 1960), but this sandstone is
absent from MOUNT DRUMMOND, where fine-grained
Mullera Formation is the youngest component of the South
Nicholson Group.
Thickness estimates for the Mullera Formation in
MOUNT DRUMMOND by Smith and Roberts (1963)
were all based on sections which are now mapped as
Crow Formation or Constance Sandstone. Because the
formation is gently dipping in most outcrops, our thickness
estimates are approximate: 200–300 m below the Middle
Creek Sandstone Member, up to 50 m for the sandstone
member, and 100 m or more above the member, for a total
of 350–450 m. Should it be demonstrated that the Mullera
Formation is present above the Mittiebah Sandstone, there
would be potential for thicker sections to be preserved in
the subsurface, west and south of MOUNT DRUMMOND.
Carter and Zimmerman (1960) recorded a figure of up to
1800 m for the original type area in Queensland, where
both facies and thickness are quite variable. The formation
is composed mostly of shale, siltstone and minor fine to
medium sandstone. One sandstone unit, the Middle Creek
Sandstone Member, is substantial enough to map as a
separate entity. Fine-grained rocks below the sandstone
member are identified on the mapface as L
Psm1, and those
above as L
Psm 2. These two informal intervals are of identical
facies, and are identifiable only by virtue of the presence of
the Middle Creek Sandstone Member. The lower Mullera
• Both formations overlie the Crow Formation with a similar
facies transition. This contact appears to be relatively
conformable in the case of the Mittiebah Sandstone and
disconformable, or an angular unconformity, in the case
of the Constance Sandstone.
• Facies and lithology of the two formations are similar.
Although the Constance Sandstone has several mappable
siltstone intervals in central and northeastern MOUNT
DRUMMOND (eg Pandanus Siltstone Member), these
are lenticular and discontinuous. Recessive interval(s)
are largely absent in the Mittiebah Sandstone to the
west, except in the Canyon Range. Recessive intervals
in the lower Constance Sandstone also potentially
correlate with intercalated sandstone and siltstone of
the Tobacco Member of the Crow Formation, with the
mainly resistant upper Constance Sandstone being
equivalent to the Mittiebah Sandstone.
There are some problems with this interpretation, such
as the significant thickness difference between the two
sandstone formations, and the requirement for substantial
erosion or non-deposition of the Wild Cow Subgroup in
eastern MOUNT DRUMMOND.
Mullera Formation (P
Lsm)
The Mullera Formation, defined by Carter (1959) and initially
mapped in western LAWN HILL, Queensland (Carter and
Zimmerman 1960), is a strongly recessive unit that outcrops in
northern and eastern MOUNT DRUMMOND and southern
CALVERT HILLS. The distribution on the Second Edition
MOUNT DRUMMOND map is substantially revised from
that shown by Smith and Roberts (1963) on the First Edition:
the formation now only encompasses outcrop formerly
mapped as Mullera Formation in Cleanskin, Carrara and
northern Benmara. The remainder, in Boxer, Mittiebah,
Mitchiebo and southern Benmara, is now assigned to the
Crow Formation and Constance Sandstone.
Figure 48. Large-scale sigmoidal crossbed in lower Mittiebah Sandstone.
Amplitude of cross-bed is about 5 m.
Boxer, 702000mE 8000600mN, Murphys
Creek headwaters.
57
7941300mN (RN31196) appears to have penetrated only
green and red shale.
The remainder of the Mullera Formation comprises
flaggy to fissile, green or red-brown to maroon and grey,
micaceous, locally ferruginous siltstone, shale and finegrained lithic to quartzose sandstone, interbedded on
a centimetre to metre scale (Figure 50). Bedding is
characteristically thin, with parallel, lenticular and wavy
lamination, cross-lamination, HCS, symmetric ripples,
gutter casts (Figure 51), synaeresis cracks, runzel marks,
mudclasts and current lineations (‘tempestite facies’; Ager
1974). Locally, shale is altered to a surficial saprolite, as
described for the basal Crow Formation. The formation
also contains several thin sandstone intervals (1–5 m
thick), comprising white to grey, fine- to medium-grained,
medium- to thickly bedded quartzose sandstone, with
small trough cross-beds, ripples and mudstone intraclasts.
A mappable interval with a high proportion of sandstone
beds is mapped as the Middle Creek Sandstone Member.
Some intervals in the Mullera Formation (eg 783400mE
7989200mN) are composed only of red and green shale,
with little sand or silt component and no evidence of
traction current deposition.
Organic-rich shale, tentatively assigned to Mullera
Formation, has been intersected in a pastoral waterbore
near 703000mE 7922000mN (‘Hydrocarbon Bore’, drilled
in 2000, see Economic Geology). The cuttings are rich
in hydrocarbons [Total Organic Carbon (TOC) ca 10%]
and exhibit low thermal maturity (submature with
T Max 372°C), which contrasts with shale from the lower
Crow Formation (TOC <1.5% and T Max ca 460°C; Lanigan
1993). This suggests that there is a fundamental difference
between Mullera and Crow Formation source rocks
[high versus low TOC, respectively], which essentially
precludes their correlation. There is also a discrepancy
in their thermal maturity and implied burial depth, as
determined by T Max. The Crow Formation is highly mature
and was buried to a relatively deep level compared to the
low-maturity Mullera Formation. Therefore, it appears
most likely that Crow Formation underlies a thick basin
package (Mittiebah–Constance Sandstones), whereas the
Mullera Formation overlies it.
Formation also contains several ironstone intervals that
were the focus of exploration in Queensland (Carter and
Zimmerman 1960): the Constance Range deposits (Harms
1965). The main ferruginous beds were grouped together
as the Train Range Ironstone Member in Bowthorn and
Musselbrook (Carter and Zimmerman 1960, Harms 1965,
Slater and Mond 1980). Such ferruginous rocks appear
to have thinned into MOUNT DRUMMOND, although
locally, they are up to 10 m thick.
The conformable lower contact with the Constance
Sandstone is exposed at about 712600mE 8007800mN,
adjacent to the Benmara–Wangalinji road in northwestern
Benmara. In this area, the contact is a sharp interface,
distinguished by bulbous load casts, between sandstone
below and mudstone above. A thin (15 cm) basal layer
of mudstone-clast conglomerate is overlain by >15 m
of claystone. The basal part of the claystone is white,
but the colour merges up through mottled purple, then
red-brown and deep maroon, into highly ferruginous
rock. This dark hematitic rock constitutes the ‘lower
ironstone bed’ in this area. It is separated from a second
4–5 m-thick ‘upper ironstone bed’ by a 10–20 m covered
interval. Liesegang banding is spectacular in places in
the upper bed (Figure 49). Above this level, the only
rocks exposed are white, red-brown to purple-grey, finely
laminated, thinly to medium-bedded, flaggy, fine-grained
sandstone and siltstone. Mudstone is notably ferruginous
immediately below the Middle Creek Sandstone Member at
a number of localities in eastern MOUNT DRUMMOND
and contains some horizons of ironstone concretions. The
iron-rich rocks may correlate with some of the ironstone
deposits to the east in Queensland (Harms 1965).
The lowermost Mullera Formation is also well
exposed north of Mitchiebo Waterhole, near 722800mE
7941000mN, where it rests conformably on the Constance
Sandstone. It comprises a >100 m-thick interval of
upward-fining and -thinning beds, consisting of red-brown
shale, flaggy, parallel- and wavy-laminated micaceous
siltstone, and chocolate brown, flaggy to slabby, fineto medium-grained, micaceous lithic sandstone with
ripples and cross-lamination. Above the stratigraphic
level of these outcrops, a waterbore at 722600mE
Figure 49. Banded hematite/goethite
in ‘upper ironstone bed’ of Mullera
Formation. Banding appears to be of
liesegang ring-like structures formed
by mobility of iron oxides. Benmara,
712850mE 8007815mN, 7 km northwest
of Connelly Waterhole.
58
Middle Creek Sandstone Member (P
Lsmm )
The Middle Creek Sandstone Member, defined by Carter and
Zimmerman (1960) in LAWN HILL to the east, is exposed
only in eastern MOUNT DRUMMOND, principally in
Cleanskin. It was defined as the Mistake Creek Sandstone
Member by Smith and Roberts (1963), but was subsequently
revised to Middle Creek Sandstone Member by Sweet
(1984). It is well exposed in a large syncline, centred on
806000mE 7944000mN in the headwaters of Musselbrook
Creek. There, it is ca 150 m above the base of the Mullera
Formation and comprises two distinct sandstone intervals.
The lower sandstone unit is 20–30 m thick, whereas the
upper is ca 5 m thick. These are shown as separate units
in Carrara R ange region (Sweet et al 1984), but are not
distinguished on the Second Edition MOUNT DRUMMOND
mapface. The position of this member above the base of the
Mullera Formation also appears to vary, suggesting that it
is diachronous, or that there are local depocentres in the
lower Mullera Formation leading to thicker mudstone
sections. To the north, the thickness of the sandstone
member ranges up to 70 m, whereas elsewhere, it locally
pinches out. Two kilometres east of Big Bend Waterhole,
at 798320mE 7975140mN, a 30 m-thick section consists of
at least four cycles of sandstone and interbedded mudstone.
The lowest two beds, totalling 8–10 m, are thickly bedded,
medium-grained, and trough cross-bedded; ferruginous
laminae highlight the foreset laminae in striking fashion.
The uppermost sandstone is also thickly bedded, but whiter,
cleaner and fine grained.
Outcrop of the Middle Creek Sandstone Member is
of blocky or bouldery, medium to thickly bedded, white
silicified, fine- to medium-grained, sublithic and ferruginous
sandstone. It is characterised by mudclasts, synaeresis
cracks and distinctive decimetre-scale trough cross-beds, in
which the laminae are defined by hematitic grains (‘festoon’
cross-beds, Figure 52). The hematite is interpreted as an
alteration product of glauconite grains. Cross-beds are
locally of herringbone type, with alternation of foreset dip
directions. Symmetric ripples (including interference type),
planar laminations and parting lineations are also locally
present, particularly at the top of thick sandstone bodies.
More thickly bedded bench-forming sandstone is typically
Figure 50. Outcrop habit of typical shaly
facies of Mullera Formation. Cleanskin,
788950mE 7959400mN, Spring Creek.
Figure 51. Grey shale of lower Mullera
Formation, with lenticular interbeds
of fine-grained lithic sandstone, some
of which have gutter-casted bases.
Cleanskin, 798330mE 7974640mN, 2 km
east of Big Bend Waterhole.
59
By comparison, NTGS00/1 (southern RANKEN), sited
on the Alexandria-Wonarah Basement High, penetrated
only 223 m of Cambrian rocks, including 32 m of Lower
Cambrian volcanic rocks (see Helen Springs Volcanics).
MOUNT DRUMMOND includes portions of the
northern end of the Alexandria-Wonarah Basement High
and northern margin of the Undilla Sub-basin (Figure 5,
Table 6). Southgate and Shergold (1991), in a sequence
stratigraphic analysis of the Middle Cambrian succession in
the Georgina Basin, recognised an early Middle Cambrian
(Ordian–early Templetonian) sequence 1 (including a
surmounting, tectonically enhanced subsequence 1a) and
a succeeding sequence 2 (late Templetonian–Floran to
early Mindyallan), spanning the remainder of the Middle
Cambrian. Gravestock and Shergold (2001) modified this
scheme by transferring subsequence 1a to basal sequence 2.
They subsequently reassigned the Bronco Stromatolith
Bed and correlative lower Beetle Creek Formation of the
northeastern Georgina Basin, as well as the ‘probably
contemporaneous Burton beds’ of the central Georgina Basin
(Gravestock and Shergold 2001: 124), to basal sequence 2.
interbedded on a metre scale with recessive, thinly bedded,
flaggy fine-grained sandstone, claystone and siltstone,
showing wavy and parallel lamination.
Interpretation
The depositional setting of the Mullera Formation is
interpreted as a marine shelf, partly above storm wavebase (‘tempestite facies’) and partly below (‘organicand shale-rich facies’). Periodic shallowing above fairweather wave-base is manifested as more thickly bedded,
shoreface to intertidal sandstone, most notably the Middle
Creek Sandstone Member, which is interpreted as a
series of prograding sandstone bodies, related to repeated
shallowing events. The thickness and iron content of the
sandstone member varies markedly laterally, and it is
possible that the highly ferruginous lower beds in some
outcrops are equivalent to the Train Range Ironstone
Member to the east.
Neoproterozoic (Ediacaran)
to
Cambrian: Georgina Basin
The Georgina Basin is one of the most extensive geological
regions in the Northern Territory. Its accumulated
sedimentary and minor volcanic rocks mantle a region
bounded by the South Nicholson and McArthur basins
to the north, Tennant Region to the west, Arunta Region
to the south, and Mount Isa Inlier to the east in western
Queensland. The succession is most complete in the
south, adjacent to the Arunta Region, where rocks of
Neoproterozoic to Devonian age are preserved in basinal
depocentres. The more platformal succession north of
latitude 21°S (including MOUNT DRUMMOND) is much
thinner, and restricted in age to the Ediacaran to Middle
Cambrian. This platformal region is transected by the
meridionally oriented Alexandria-Wonarah Basement
High, separating the Undilla Sub-basin on the east from
the Barkly Sub-basin on the west. Drillhole NTGS01/1
(southern RANKEN) intersected 440 m of Undilla Subbasin rocks before penetrating the South Nicholson
Group, and drillhole NTGS02/1 (BRUNETTE DOWNS)
encountered a 343 m-thick Barkly Sub-basin succession
above South Nicholson Group equivalents (Kruse 2003).
Kiana Group
This new group name comprises the Bukalara Sandstone
and in HODGSON DOWNS–MOUNT YOUNG, the
conformably overlying Cox Formation (see Appendix 1).
It groups all putative Neoproterozoic formations on the
northern margin of the Georgina Basin.
Bukalara Sandstone (P
Lu)
The Bukalara Sandstone (Smith and Roberts 1963) is a
coarse siliciclastic succession that locally represents the
basal unit of the northern Georgina Basin. In northwestern
MOUNT DRUMMOND, it rests unconformably on various
Proterozoic units, most notably the South Nicholson Group.
No overlying unit is present in MOUNT DRUMMOND, but
the unfossiliferous Cox Formation conformably overlies it
in MOUNT YOUNG (Haines et al 1993). Sandstone dykes
of the Bukalara Sandstone were reported to project into
the overlying Nutwood Downs Volcanics of the Georgina
Figure 52.
Fine-grained
silicified
quartzose sandstone of Middle Creek
Sandstone Member of Mullera Formation,
showing hematite-defined cross-bed
laminations. Cleanskin, 791800mE
7988550mN, No Return Creek.
60
Basin in HODGSON DOWNS (Dunn 1963). A concordant,
but probably disconformable relationship with the younger,
Middle Cambrian Top Springs Limestone is known from
BAUHINIA DOWNS (Pietsch et al 1991).
The Bukalara Sandstone is estimated to be up to
50 m thick in MOUNT DRUMMOND, but is over 200 m
thick in southwestern ROBINSON RIVER to the north
(Rawlings 2004) and 300 m in BAUHINIA DOWNS
to the northwest (Smith 1964). The age of this unit
remains uncertain. Pietsch et al (1991), following Muir
(1980), suggested a tentative Early Cambrian age, based
largely on the presence of vertical and inclined tubelike
structures, interpreted as the trace fossil Skolithos.
In addition, its relationship with the Nutwood Downs
Volcanics (see above) suggests conformity and, hence,
an Early Cambrian age and this is consistent with a late
Early Cambrian 513 ± 12 Ma age for a probable feeder
dyke for the coeval Antrim Plateau Volcanics (Hanley
and Wingate 2000). However, the presence of Skolithos
has not been confirmed in MOUNT DRUMMOND and
this ichnofossil is relatively long ranging and unsuitable
for accurate correlation. Other observations (see Helen
Springs Volcanics) suggest that the HODGSON DOWNS
sandstone dykes may derive from a lag or regolith
mantling the Nutwood Downs Volcanics, rather than from
the Bukalara Sandstone or from the volcanics themselves.
Rawlings et al (1997) recognised a disconformity at this
level in the correlative Arafura Basin, and reinterpreted
the ‘trace fossils’ as non-biogenic dewatering structures.
Unit,
(map symbol), thickness
On this basis, they assigned the Bukalara Sandstone and
correlatives to the late Neoproterozoic.
In MOUNT DRUMMOND, the Bukalara Sandstone
consists of isolated mesas and incised plateaux with a
characteristic strongly jointed photopattern. Outcrop
comprises mainly pseudokarstically weathered, pink or
yellow, friable, medium- to coarse-grained lithic sandstone
and lesser fine-grained sandstone (Figure 53). Pebbly
(quartz) sandstone and pebble to cobble conglomerate
are also common near the base. There is an abundance of
chert fragments up to 3 cm diameter; however, clasts of
metamorphic rocks, sandstone and vein quartz are also
common. Sandstone is thickly to very thickly bedded,
with planar and lenticular bedding, diffuse large-scale
planar and trough cross-beds, and occasional symmetric
ripple pavements and desiccation cracks in finer-grained
lithofacies. Reconnaissance analysis suggests north- to
northwest-directed palaeocurrents. Outcrop appears very
gently warped on a 100–500 m scale, but is essentially flatlying overall. The Bukalara Sandstone is interpreted to have
been deposited in a high-energy braided fluvial to shallowmarine environment (Rawlings 2004).
Kalkarindji Volcanic Group
This new group, named after the Kalkarinji Continental
Flood Basalt Province of Glass (2002), encompasses all
Lower Cambrian continental volcanic rocks in northern
Australia (see Appendix 1).
Lithology
Depositional
environment
Stratigraphic relationships
Barkly Group
Camooweal Dolostone
(–Cmd) 167+ m in RANKEN
Pale microbial dololaminite with nodular chert,
dolosparstone; minor peloid and ooid dolostone,
conglomerate, dolomitic limestone, marl; lower
high-energy interval of quartzic, intraclast and
ooid dolograinstone and quartz sandstone.
Peritidal to restricted
and open shallow
subtidal marine.
Conformably overlies Currant Bush
Limestone; unconformably overlain
by Cretaceous rocks in sheet area.
Ranken Limestone
(–Cmk) notionally 80 m
Pervasively chertified fossiliferous bioclast and
bioclast-ooid rudstone.
High-energy shallow
subtidal marine.
Discontinuous within lower highenergy interval of Camooweal
Dolostone.
Wonarah Formation
(–Cmw) 36+ m; 146 m in
RANKEN
Pervasively chertified fossiliferous limestone,
shale and siltstone; minor phosphorite; basal
sandstone.
Shallow marine.
Disconformable on Helen Springs
Volcanics; conformably overlain by
Camooweal Dolostone.
Currant Bush Limestone
(–Cmc) 50–75 m
Partially dolomitised foetid argillaceous,
quartzic and bioclast limestone; interbeds of
ooid grainstone, sandstone, shale, siltstone and
marl.
Shallow marine.
Apparently conformable on Border
Waterhole Formation; conformably
overlain by Camooweal Dolostone.
Border Waterhole Formation
(–Cmo) 30–180 m
Siliceous shale, siltstone, chertified limestone,
bedded to nodular chert; basal quartz-lithic
sandstone, granule to pebble conglomerate.
Shallow marine.
Overlies McNamara Group with
angular unconformity; apparently
conformably overlain by Currant
Bush Limestone.
Variably altered, locally amygdaloidal basalt
and microdolerite; thin basal pebbly sandstone
and conglomerate.
Subaerial lava flows
and invasive flows.
Unconformable on South Nicholson
Group; relationship with Bukalara
Sandstone unknown; disconformably
overlain by Wonarah Formation.
Pink or yellow, friable, medium- to coarsegrained lithic (chert) sandstone; minor finegrained sandstone; basal pebbly sandstone and
pebble ± cobble conglomerate.
Braided fluviatile to
shallow intertidal.
Unconformable on South Nicholson
Group; no overlying units of Kiana
Group present in sheet area.
Narpa Group
Kalkarindji Volcanic Group
Helen Springs Volcanics
(–Clp) 156 m
Kiana Group
Bukalara Sandstone
(P
Lu) up to 50 m
Table 6. Stratigraphy of Georgina Basin in MOUNT DRUMMOND.
61
_
Helen Springs Volcanics (Clp)
of variably altered basalt and microdolerite that is locally
amygdaloidal (with clay, chlorite or celadonite infill). Rare
slickenside surfaces indicate minor deformation of the
Cambrian succession. At 710500mE 7916700mN, the base
of the Helen Springs Volcanics is a thin (<15 m) pebbly
sandstone and conglomerate, unconformable on the Mittiebah
Sandstone, comprising cobbles of silicified sandstone in a
ferruginous, medium- to coarse-grained sandstone matrix.
At 722800mE 7941000mN, the base of the volcanics is a 10–
100 cm-thick bed of ‘baked’, massive, pebbly lithic sandstone,
overlain by weathered basalt. Dykes of this baked sandstone
protrude up into the base of the basalt. The uppermost
ca 5 cm of mudstone of the underlying Mullera Formation is
also contorted and silicified (‘baked’).
The upper contact is well exposed at 691250mE
7925700mN in ridges to the south of Peaker Piker Creek
(Figure 54), where maroon-brown amygdaloidal basalt
bearing an intensely weathered reddish cap is succeeded
by shale of the basal Wonarah Formation (Figure 55). Thin
maroon-brown sandstone interbeds are preserved within
the upper Helen Springs Volcanics. Nearby, at 691300mE
7925750mN, a 10 cm-wide vertical fissure in the volcanics
is infilled by quartz sandstone from the overlying Wonarah
Formation (Figure 56).
More typically, in most areas where Helen Springs
Volcanics are mapped, outcrop is confined to sporadic
basalt corestones in the soil profile. Their presence in the
shallow subsurface is indicated by dark red-brown pisolitic
sandy soils, with a float of massive featureless ferruginous
rock (eg areas mapped as mp, Czl and Czl/ mp in western
MOUNT DRUMMOND).
Although the Helen Springs Volcanics exhibit a
characteristic dark red-brown phototone, their distribution
in the subsurface is most easily discerned using airborne
geophysics. The radiometric signature, in particular, is very
pronounced for both the volcanics and the pisolitic soils
developed immediately above them. Similarly, the sparsity
of magnetic units in the underlying stratigraphy makes
it relatively simple to track the base of the Helen Springs
Volcanics to great depths throughout the mapsheet. A linear
magnetic high characterises the boundary of the Georgina
Outcrop of Early Cambrian volcanic rocks in MOUNT
DRUMMOND was assigned to the Peaker Piker Volcanics
by Smith and Roberts (1963). Recently acquired NTGS
airborne magnetic data indicate that there is contiguity of
subcrop beneath the central Georgina Basin between this
region and the Helen Springs Volcanics on the eastern flank
of the Tennant Region. The two volcanic units are therefore
synonymised as Helen Springs Volcanics.
In MOUNT DRUMMOND, the Helen Springs Volcanics
outcrop in the western sheet area with an estimated thickness of
40 m. The distinctive aeromagnetic signature of the volcanics
can be traced through eastern BRUNETTE DOWNS into
southeastern ALROY, where the formation attains a maximum
known thickness of 156 m in cored drillhole AY06DD01 (Kruse
in prep). These expressions coincide with the AlexandriaWonarah Basement High (Perrino in Howard 1972), which
separates the Undilla Sub-basin to the east from the Barkly Subbasin (Brunette Sub-basin of Howard 1990) to the west. Where
contacts have been observed, the Helen Springs Volcanics in this
region unconformably overlie sandstone and mudstone attributed
to the South Nicholson Group. They are in turn overlain by the
Wonarah Formation in MOUNT DRUMMOND and RANKEN.
Based primarily on the reported interbedding of volcanic rocks
with mudstone of the overlying Wonarah Formation (Smith and
Roberts 1963), the former Peaker Piker Volcanics were regarded
as early Middle Cambrian up to 1990 (eg Smith 1972, Freeman
et al 1990). Subsequent sequence stratigraphic studies
(Southgate and Shergold 1991) have relegated the Volcanics to
the Early Cambrian. Thus, together with other Georgina Basin
volcanic units, they are considered to be correlative with the
Antrim Plateau Volcanics, corresponding to a continent-scale
flood basalt event. A probable feeder dyke of this latter unit in
Western Australia has been dated at 513 ± 12 Ma (late Early
Cambrian) by Hanley and Wingate (2000), and the Helen
Springs Volcanics have been directly dated at 508 ± 2 Ma by
Glass and Phillips (2002).
Smith and Roberts (1963) reported basalt, trachyte and
minor dolerite, and a basal sandstone from the former Peaker
Piker Volcanics. The current study indicates the presence
Figure 53. Cobble conglomerate and
planar stratified coarse-grained lithic
sandstone of lower Bukalara Sandstone.
Nicholson River (CALVERT HILLS),
713800mE 8009650mN, Pandanus Creek.
62
Figure 54. View to west showing massif
of Helen Springs Volcanics capped
by Wonarah Formation. Mittiebah,
691250mE 7925700mN, Peaker Piker
Creek.
Basin, where it meets Proterozoic basement, in particular
along the Little Range Fault. This boundary may represent
a feeder system for volcanism, as suggested by Smith and
Roberts (1963), or it may simply be an edge effect generated
by the margin of the volcanic sheet or by upturned volcanics
along a structurally reactivated contact (see Geophysics).
Narpa Group
The Narpa Group (Kruse in Dunster et al 2007)
embraces all Middle to medial Upper Cambrian units
in the eastern and southern Georgina Basin, including
formations in eastern MOUNT DRUMMOND.
Figure 55. Contact of intensely weathered red basalt of Helen
Springs Volcanics (below) and maroon-purple ferruginous
micaceous shale of basal Wonarah Formation (above). Hammer
head marks contact. Mittiebah, 691250mE 7925700mN, Peaker
Piker Creek.
Figure 56. Vertical fissure at top of Helen Springs Volcanics infilled
by quartz sandstone of overlying Wonarah Formation. Mittiebah,
691300mE 7925750mN, Peaker Piker Creek.
63
_
Border Waterhole Formation (Cmo)
conglomerate, with granules to small pebbles of quartz and
chert, taken to be the basal Border Waterhole Formation.
This sandstone passes upward into more typical pale grey
chert and minor, possibly precursor white claystone.
Fossils reported from the formation, but as yet
undocumented, include the trilobites Redlichia, Xystridura,
Lyriaspis, Pagetia and Peronopsis, the molluscs Stenotheca
and Helcionella, hyoliths attributed to Biconulites (Öpik
1960, Carter and Öpik 1961, de Keyser 1969) and sponge
spicules; the trilobites are indicative of an early Middle
Cambrian (Ordian) age. In contrast to the correlations of
earlier authors, such as Smith (1972), de Keyser and Cook
(1972) and Howard (1986), but in accord with de Keyser
(1969), Southgate and Shergold (1991) assigned the Border
Waterhole Formation to their sequence 1 and the remaining
Middle Cambrian formations of MOUNT DRUMMOND
to sequence 2. The Border Waterhole Formation hosts the
Highland Plains phosphate deposit, which straddles the
Northern Territory-Queensland border (see Economic
geology).
The Border Waterhole Formation (Öpik 1960) is the oldest
lithostratigraphic unit of a Middle Cambrian succession
exposed in the Lancewood Creek area of easternmost
MOUNT DRUMMOND. It is unconformable on the Plain
Creek Formation and Lawn Hill Formation of the McNamara
Group, and is overlain by the Currant Bush Limestone. Like
overlying units in the area, the Border Waterhole Formation
extends eastward into LAWN HILL. It comprises 30–180 m
(Shergold and Druce 1980) of siliceous shale, siltstone, grey
and black chertified limestone (including bioclast floatstone
and rudstone), irregularly bedded to nodular chert, chert
breccia, chert conglomerate and a basal pebble conglomerate
(Carter and Öpik 1961, Smith and Roberts 1963, McMahon
1969). Quartzite, and white and kaolinised siltstone, mapped
as Border Waterhole Formation by McMahon (1969), are here
regarded as Cretaceous. The formation is typically obscured
by a regolith of chert breccia and pebbles, so that outcrop
is mainly limited to creek beds (Figure 57). However, the
basal beds are better exposed. At 813750mE 7936800mN
for example, flat-lying Border Waterhole Formation rests
with angular unconformity on shallow-dipping Lawn Hill
Formation. A 6 m-thick stratigraphic gap of sandstone
scree separates purple slate of that unit from gently eastdipping, orange-brown-weathering medium sublitharenite
above. Among the intervening sandstone scree are blocks
of dark brown-purple coarse sublitharenite to granule
_
Currant Bush Limestone (Cmc)
Apparently conformable between the Border Waterhole
Formation and Camooweal Dolostone is the Currant Bush
Limestone (Öpik 1956a, 1960). Shergold et al (1976) inferred
a type area near Currant Bush Creek, 16 km southwest
of Thorntonia homestead (CAMOOWEAL). In MOUNT
DRUMMOND, the contact with the underlying Border
Waterhole Formation is not exposed, and additionally,
is complicated by the fault zone along Lancewood Creek
(McMahon 1969). Eastward in LAWN HILL, the contact is
not affected by faulting. Given the sequence stratigraphic
assignments of Southgate and Shergold (1991), this lower
formation contact may be disconformable.
The Currant Bush Limestone is a unit of bedded grey
and tan, partially dolomitised foetid argillaceous, quartzic
and bioclastic limestone, with interbeds of ooid grainstone,
shale, siltstone and marl. It is 50–75 m thick in MOUNT
DRUMMOND (McMahon 1969), but thickens eastward to
116 m in drillhole Morstone-1 in CAMOOWEAL (Stewart
and Hoyling 1963). Occasional ellipsoidal concretions
are characteristic. This lithological suite represents ramp
carbonates of stratigraphic sequence 2 (Southgate and
Shergold 1991).
In eastern MOUNT DRUMMOND, these limestone beds
are composed of partially dolomitised, grey-tan, centimetrescale, wavy- to nodular-bedded ribbon limestone (mainly
bioclast floatstone), outcropping parallel to Lancewood
Creek as low cuestas up to 1 m high (Figure 58). Minor
friable sandstone and leached and deeply lateritised siltstone
and shale, named the Lancewood Shale by Öpik (1960), were
included in the upper Currant Bush Limestone by Smith
and Roberts (1963), as foreshadowed by Carter and Öpik
(1961). This view is provisionally adopted herein, despite
the reinstatement of the Lancewood Shale by Shergold et al
(1985).
De Keyser (1969) nominated a yellow gritty dolostone
containing angular chert fragments and rounded carbonate
pellets as the uppermost bed of the expanded Currant
Bush Limestone, conformable beneath the Camooweal
Figure 57. Creek bank exposure of Border Waterhole Formation,
comprising silicified dolomudstone and bioclast dolofloatstone.
Carrara, 814600mE 7936150mN, tributary of Lancewood Creek.
64
Figure 58. Partly dolomitised grey/
tan, wavy- to nodular-bedded bioclast
floatstone of Currant Bush Limestone.
Carrara,
815800mE
7935050mN,
Lancewood Creek.
Limestone (Narpa Group) in the central and northern
Georgina Basin.
Dolostone. This formation contact is exposed in a 4 mthick section at the state border (in LAWN HILL, Zone
54, base at 183550mE 7935150mN, top at 183650mE
7935100mN), where it consists of the following beds, from
base to top: ribbon limestone, typical of the Currant Bush
Limestone; then a medium bed of otherwise similar rocks,
but with a ‘sandy’ (quartzic) aspect (cf uppermost Currant
Bush Limestone bed of de Keyser (1969); then medium to
thickly bedded, non-quartzic, light yellow-grey dolostone
with locally preserved wavy-nodular bedding; then thickly
bedded yellow-brown quartzic dolostone forming a
1 m‑high scarp (cf de Keyser 1969); then centimetre-scale
bedded, partially to completely dolomitic grey carbonate
sparstone of undoubted Camooweal Dolostone. The contact
is transitional and therefore conformable.
The formation becomes more extensive eastward in
Queensland, from where a diverse fauna of trilobites,
bradoriides, brachiopods, molluscs, cystoid echinoderms
and sponge spicules has been recorded (Öpik 1960, 1970,
1979, 1982, Carter and Öpik 1961, Jell 1975, Runnegar and
Jell 1976, McKenzie and Jones 1979, Jones and McKenzie
1980, Henderson and MacKinnon 1981), to which hyoliths
are here added. The trilobites are indicative of the Acidusus
atavus to Goniagnostus nathorsti zones (Shergold et al
1985). More recently, the former basal beds of the Currant
Bush Limestone in CAMOOWEAL have been renamed the
Gowers Formation by Southgate (1986), thus restricting the
Currant Bush Limestone there to late Euagnostus opimus
Zone and younger (late Floran to late Undillan). In MOUNT
DRUMMOND, the formation has yielded species of the
agnostine trilobites Euagnostus, Peronopsis, Hypagnostus,
Onymagnostus and Rhodotypiscus (Öpik 1979), the nepeid
Penarosa (Öpik 1970) and the dolichometopids Horonastes,
Fuchouia and Itydeois (Öpik 1982). These denote a briefer
time interval, represented by the Acidusus atavus and
Euagnostus opimus Zones.
_
Wonarah Formation (Cmw)
Unconformably overlying the Helen Springs Volcanics
and South Nicholson Group is the Wonarah Formation
(Wonarah beds of Öpik 1956a, b), which outcrops widely
in western MOUNT DRUMMOND and extends southward
along the Alexandria-Wonarah Basement High, via western
RANKEN and eastern ALROY, into AVON DOWNS and
FREW RIVER. Following Kruse and Radke (2008), the
Wonarah Formation subsumes the former Burton beds of
Smith and Roberts (1963), Alexandria beds of Öpik (1956b)
and Alroy Downs beds of David (1932). The formation
comprises limestone, shale, siltstone (all typically chertified
or ferruginised), minor phosphorite and a basal sandstone.
Randal (1966b) estimated a thickness of 90+ m for the unit
in RANKEN; a 36 m section is exposed at the ‘old well’
near Alexandria homestead (Öpik 1956b, Smith 1972),
and a complete 146 m was intersected in cored drillhole
NTGS01/1 (Kruse 2003). A reported thickness of 535 m
in Alexandria No 1 Bore (Smith 1972) spans the entire
Cambrian succession and may also include other formations.
Smith and Roberts (1963) reported a thickness of 23+ m in
MOUNT DRUMMOND. It is difficult, if not impossible to
distinguish between the Wonarah Formation and a regional
silcrete horizon on aerial photographs.
The lower contact is well exposed at 691250mE
7925700mN in ridges to the south of Peaker Piker
Creek. There, the Wonarah Formation overlies intensely
weathered Helen Springs Volcanics. The unconformity is
a sharp, planar to sinuous surface with decimetre-scale
relief and minor ravinement to 2–5 cm depth. It is not
deeply erosional and there is no apparent development
of a palaeoregolith. The base of the Wonarah Formation
is a 5 m interval of dark maroon-purple, ferruginous and
micaceous shale, with trains of very fine quartz sand.
Interbeds of light yellow-brown sandstone increase
upward through this interval, and sandstone also
penetrates cavities and vertical fissures in the underlying
Barkly Group
The Barkly Group (Kruse and Radke 2008) comprises
all Middle Cambrian units other than the Thorntonia
65
_
Ranken Limestone (Cmk)
volcanic pile (Figure 56). The sandstone is a mediumgrained to granule sublitharenite, with subordinate
chert and siltstone lithic grains. Overlying shale (3 m
thick) is yellow-brown and passes upward into yellowbrown chert, which is more typical of the formation
in the mapsheet. At 676550mE 7962700mN, the base
of the Wonarah Formation is a thin (5–10 cm) band of
brown, ferruginous, medium to coarse lithic sandstone.
Overlying the sandstone is ca 30 cm of flinty, red-brown
mottled silicified claystone, with elongate clayey blebs
(tuffaceous?). This is in turn overlain by a 10 cm interval
of pebbly ferruginous lithic sandstone, thence by chert.
In most areas, outcrop of the Wonarah Formation is
strongly silicified, comprising yellow-brown bouldery
outcrop and low cliffs of white to blue-grey, crudely bedded
and partly brecciated chert, with relict parallel lamination and
rare ovoid concretions (Figure 59). The chert breccia consists
of randomly-oriented angular chert fragments in a siliceous
splintery matrix (silcrete). Clasts are porcelainous and range
up to cobble size. Iron-manganese oxides and liesegang
banding are prominent. In places, coherent chert rock is
interlayered with beds of rotated chert breccia, suggesting
that the brecciation process took place in the subsurface and
not as part of the surface regolith development.
Chertified rocks are moderately fossiliferous. A fauna
of trilobites, bradoriides, brachiopods, hyoliths, molluscs,
echinoderms and sponge spicules indicates an early Middle
Cambrian age (Öpik 1956b, 1968, 1975, Öpik and GilbertTomlinson in Smith and Roberts 1963, Shergold 1969, Jell
1975). The trilobite Xystridura is common. Öpik (1975)
assigned a Templetonian age to the fauna. This was refined
to early Templetonian by Shergold and Druce (1980), but
was subsequently reassigned as late Templetonian/Floran
by Southgate and Shergold (1991; sequence 2). Trilobite
identifications by Laurie (2005) from material collected
in adjacent RANKEN and AVON DOWNS indicate a
latest Ordian to earliest Templetonian age, in terms of the
stage definitions of Laurie (2006). Fossils locally occur
as bioclast coquinas, and ooids are also discernible in the
recrystallised carbonate rocks. Subeconomic phosphorite
has been delineated in the Wonarah Formation in adjacent
RANKEN (see Economic geology).
Following the remapping of adjacent RANKEN by Kruse
and Radke (2008), the Ranken Limestone (Öpik 1956a, b) is
now recognised as a bioclastic lithofacies within the basal
high-energy interval of the Camooweal Dolostone (which
see). The Ranken Limestone is now mapped northward from
its previously known occurrences around Soudan homestead
(northern AVON DOWNS–southern RANKEN), along the
eastern side of the Alexandria-Wonarah Basement High, as
far as the Mittiebah homestead area in southern MOUNT
DRUMMOND.
Subcrop in the Mittiebah homestead area is highlighted
by a distinctive red soil phototone. There, it comprises
pebbles and cobbles of high-energy bioclast and bioclastooid rudstone, typically red-brown and chertified. Bioclasts
include common hyoliths and trilobites, and occasional
molluscs. Two such mollusc taxa were described from
southern RANKEN by Kruse (1998).
The thickness of the formation is not known, but the
Ranken Limestone lithofacies is scattered throughout an
80 m cored interval in drillhole BMR GRG 16 (southern
RANKEN; Milligan 1963). With the recognition (Kruse and
Radke 2008) that the Ranken Limestone overlies the latest
Ordian–Templetonian Wonarah Formation, rather than
underlying it as proposed by Öpik (1956a, b), the Ranken
Limestone is clearly younger than the Ordian (earliest
Middle Cambrian) age deduced by Öpik (1968).
_
Camooweal Dolostone (Cmd)
The Camooweal Dolostone (Camooweal Dolomite of
Öpik 1954, 1956a) conformably overlies the Currant
Bush Limestone, as well as the Wonarah Formation in
southwestern MOUNT DRUMMOND. This is an extensive
unit, occupying large areas of MOUNT DRUMMOND,
LAWN HILL, CAMOOWEAL, RANKEN, AVON
DOWNS, MOUNT ISA and URANDANGI. Öpik
(1954) nominated a type area along the Georgina River
between Lake Mary and Lake Francis, respectively north
and south of Camooweal, with neither the lower, nor the
upper boundary included. The Camooweal Dolostone is
Figure 59. Typical brecciated chert
outcrop of Wonarah Formation. Mittiebah,
696300mE 7925900mN, Peaker Piker
Creek.
66
notionally 240–300 m thick (Shergold et al 1976). The
entire 430 m thickness of carbonate rocks intersected in
drillhole Cattle Creek-1 in AVON DOWNS (see figure 25
of Smith 1972) has been attributed to the formation, but
this interval includes underlying units. Drillhole reports
of identifiable fossils (eg Gatehouse 1968, references
in Öpik et al 1973) may equally be from older strata.
Planar microbial dololaminite is common, implying a
peritidal depositional environment (de Keyser and Cook
1972, Shergold and Druce 1980). Local cross-beds and
intraformational conglomerates denote brief higherenergy episodes.
In MOUNT DRUMMOND, the Camooweal Dolostone
outcrops extensively along the valley of Carrara Creek in
the southeast, and as isolated outcrops and subcrop adjacent
to the Wonarah Formation in the southwest. Intervening
plains conceal the unit beneath grey-black clay-rich soil
(blacksoil).
The basal contact is exposed at the state border in the
Lancewood Creek area (see Currant Bush Limestone).
Prominent beds above the formation boundary in this
area consist of grey, thickly bedded dolosparstone, at least
some after original intraclast or intraclast-ooid grainstone,
bearing bedding-parallel trains of red siliceous nodules
(Figure 60).
Strata slightly higher in the formation are exposed in
the Carrara Creek area. Rippled dolomudstone outcrops in
the bed of the creek, where it is crossed by the Gallipoli–
Border Waterhole track (805600mE 7914700mN). Among
grey dolomudstone beds on the north bank at this locality
is a quartzic intraclast dolograinstone, with rounded to
subrounded, fine sand- to fine pebble-sized intraclasts
bearing micrite envelopes. A minority of the grains are
ooids. Admixed quartz is of coarse silt to medium sand size.
South of the creek, at 806100mE 7914600mN, a similar
but non-quartzic bed of grey intraclast dolograinstone is
distinctive within the more typical pale cream to beige
dolomudstone of the formation. The dolograinstone
comprises rounded to subangular, very fine sand- to
granule-sized intraclasts in an idio- to hypidiomorphic
dolospar mosaic. Many intraclasts show textures
suggestive of reworked precursor intraclast grainstone
and/or calcimicrobial boundstone.
High-energy lithofacies, corresponding to those exposed
in Lancewood and Carrara creeks, have been intersected
in cored drillhole NTGS01/1 (southern RANKEN), where
a 63 m-thick interval of lower Camooweal Dolostone
includes more or less recrystallised, light grey intraclast
dolograinstone and oncoid dolofloatstone. A total of 167 m
of the formation (incomplete) is preserved in this drillhole
(Kruse 2003). This same basal interval is also exposed,
together with bioclastic lithofacies assigned to the Ranken
Limestone (which see), along the eastern flank of the
Alexandria-Wonarah Basement High in western RANKEN
(Kruse and Radke 2008). Oncoid dolorudstone, ooid
dolograinstone, quartzic dolostone and quartz sandstone
also contribute to the basal interval in this tract, which
extends into southwestern MOUNT DRUMMOND as
far as Mittiebah homestead. Individual basal lithofacies,
separately mapped in this area, include grey intraclast
dolograinstone ( _Cmdb ) and brown quartz sandstone
essentially unfossiliferous and bears a close similarity to
parts of the Thorntonia Limestone; consequently, its age
has been disputed. Öpik (1956a) erroneously believed it to
underlie the Middle Cambrian successions exposed around
the margins of the Undilla Sub-basin and assigned it to the
Late Precambrian–Early Cambrian, viewing it as a barrier
separating the Northern Territory and Queensland portions
of the Georgina Basin. Randal and Brown (1962), Smith
and Roberts (1963) and others subsequently corrected the
stratigraphic relations of the unit, recognising it as Middle
Cambrian or younger (see de Keyser 1973). Öpik (in Öpik
et al 1973) has countered that the unit is Ordian (early
Middle Cambrian) or perhaps Early Cambrian to Ordian,
and that ‘the area allotted to the Camooweal Dolomite on
maps includes outliers of younger strata which have no
bearing on the concept of that formation’ (Öpik 1976).
However, the area in question closely coincides with that
originally indicated by him (figures 1 and 2 of Öpik 1956a,
figure 2 of Öpik 1956b).
The formation includes white, cream, buff and light
brown dolostone (including dolosparstone and minor
peloid and ooid dolostone), dolomitic limestone with
nodular chert, minor marl and a basal quartzic dolostone
and quartz sandstone (Carter and Öpik 1961, Brown
1962, Randal and Brown 1962, de Keyser 1969). It is
Figure 60. Camooweal Dolostone, comprising red siliceous nodules
in thickly bedded grey dolosparstone after original intraclast or
intraclast-ooid grainstone. Musselbrook (LAWN HILL, Zone 54),
184075mE 7934777mN, Lancewood Creek.
67
( _Cmds ). The intraclast dolosparstone is locally cross-bedded
and may be recrystallised to dolosparstone, or partially or
completely silicified to red-brown chert. These lower rocks
are associated with subcrop areas of grey, planar to crinkly
microbial dololaminite, which is typical of the bulk of the
formation. As elsewhere, the dololaminite bears red-brown,
early diagenetic, spheroidal and lobate chert nodules, which
locally accumulate to dominate individual subcrop areas.
The Camooweal Dolostone has been observed to
laterally interdigitate with the Age Creek Formation in
CAMOOWEAL and to overlie the Currant Bush Limestone
in LAWN HILL and MOUNT DRUMMOND (Randal
and Brown 1962, Smith and Roberts 1963). This implies
an age ranging from the late Euagnostus opimus Zone to
the Goniagnostus nathorsti or Lejopyge laevigata Zone
(late Floran to late Undillan or early Boomerangian;
Shergold et al 1985, Southgate and Shergold 1991). The
upper age limit conforms well with the observation that the
formation is overlain by the Late Cambrian Arrinthrunga
Formation (Meeta Beds of Randal 1966c) in AVON
DOWNS. The Camooweal Dolostone has also been
postulated to laterally interdigitate with the Currant Bush
Limestone and even with the Border Waterhole Formation
in MOUNT DRUMMOND (Sweet 1984), and with the
Thorntonia Limestone elsewhere. The recognition of a
sequence-bounding disconformity surface at the top of the
Thorntonia Limestone in CAMOOWEAL (Southgate 1986)
casts doubt on this proposed interdigitation, which would
extend the time range of the Camooweal Dolostone down
to the late Ordian. Southgate and Shergold (1991) limited
the formation to the highstand systems tract of their Middle
Cambrian stratigraphic sequence 2 (ie late Templetonian/
Floran or younger).
to Aptian age, and an Albian marine fauna in overlying
beds. Pelecypods identified by Dickins (1960) from western
MOUNT DRUMMOND are within this age span.
On the basis of detailed studies, Cretaceous rocks
along the western and southwestern margins of the Gulf
of Carpentaria in ARNHEM BAY–GOVE (Rawlings et al
1997), BLUE MUD BAY (Haines et al 1999), MOUNT
MARUMBA (Sweet et al 1999), and ROPER REGION
(Abbott et al 2001) that were originally assigned to the
‘Mullaman beds’ by Skwarko (1966), have been subdivided
into the Walker River and Yirrkala formations, of Aptian
to Cenomanian age, by Krassay (1994). These two
Carpentaria Basin formations have not been differentiated
in MOUNT DRUMMOND, but similar units appear to be
present.
The succession in northeastern MOUNT DRUMMOND
typically comprises yellow to red-brown, mottled
porcelainous claystone and clayey lithic medium sandstone
with sporadic burrows. This facies is likely to be mostly of
shallow-marine shelf origin. Rocks are variously friable
to silicified and hard (even flinty). Alternating claystone
and sandstone give rise to metre-scale prominent benches.
There is a local basal conglomerate a few decimetres thick,
containing rounded quartzite clasts in a ferruginous lithic
sandstone matrix. Locally, the succession also includes beds
or trains of pebbly/cobbly sandstone at several levels. Clasts
are of well rounded sandstone and some have the appearance
of dropstones, implying a glacial input. Mesas are capped by
pisolitic ferricrete, which has given rise to the prolific growth
of lancewood (Acacia shirleyi) in thickets on the flanks,
a characteristic feature of lateritised Cretaceous regolith
in the region. The anomalously high mesa at 785300mE
7974500mN is an erosional remnant of a formerly widespread
sheet of Cretaceous rocks over MOUNT DRUMMOND that
has survived Cenozoic incision (Figure 61).
Sandstone and minor siltstone comprise the Cretaceous
section in southeastern MOUNT DRUMMOND, around
Lancewood Creek. The sandstone is brown, variably
ferruginous, medium- to coarse-grained, friable and
quartzose, and supports a discontinuous scatter of
ferruginised, dark maroon-brown ironstone pebbles on
plateau tops.
Rare Cretaceous exposures in western MOUNT
DRUMMOND are composed of white, medium-grained
(± pebbly) quartzose sandstone, with large planar cross-beds
and with basal beds of silicified chert-clast conglomerate.
Smith and Roberts (1963) identified Neocomian marine
fossils, including a belemnite rostrum, in this area. This
facies is likely to be fluvial to shallow marine in origin.
Mesozoic: Dunmarra Basin
Undivided Cretaceous (Kl)
Cretaceous sedimentary rocks of the Dunmarra Basin are
exposed sporadically in mesas and plateaux across much
of the northern part of the Northern Territory. They form
a flat-lying, uplifted, but undeformed siliciclastic coastalplain to shelf succession, resting on mainly Proterozoic
rocks. The Dunmarra Basin succession is a relatively
thin remnant of originally much more laterally extensive
Cretaceous strata, thicker sections of which are preserved in
the mostly offshore Money Shoal, Arafura and Carpentaria
basins. In MOUNT DRUMMOND, Cretaceous rocks of the
Dunmarra Basin are exposed mostly as weathered outcrop
along the flanks of laterite-capped ridges and mesas in the
northeastern part of the mapsheet. The basal unconformity
is variable in elevation, and displays a relief that is little
less than that of the present surface. Small mesas of the
upper Constance Sandstone are surrounded or abutted by
Cretaceous strata sitting at a lower elevation, for instance,
at 817860mE 7983460mN at the border with LAWN HILL.
The Cretaceous section reaches a maximum thickness of
50–70 m in prominent mesas in Cleanskin, but is generally
much thinner (<10 m). Known fossils within the Cretaceous
section are entirely Early Cretaceous in age. Skwarko
(1966) identified a basal non-marine flora of ?Neocomian
Cenozoic
Cenozoic deposits cover more than half of MOUNT
DRUMMOND. These deposits have been, as far as possible,
subdivided into (genetically) unique units that can be
identified on aerial photographs and Landsat imagery.
Cleanskin beds (Tl)
The Cleanskin beds (Smith and Roberts 1963) comprise
loose scattered blocks of white, porous unfossiliferous
68
Palaeogene–Neogene (Cz, Czl, Czm, Czs, Czb, Czz)
limestone and saprolitic limestone along narrow
blacksoil plains, including near Wangalinji, Tin Creek,
Fish Hole Creek and Crow Creek. Pores and ?vugs
in the limestone are commonly infilled by banded
chalcedony. This unit was originally widely mapped
by Smith and Roberts (1963). However, during Second
Edition mapping, many previously mapped ‘outcrops’
were found to be composed solely of clay-rich soil,
with no evidence of limestone. These authors appear
to have extrapolated small areas of known Cleanskin
beds throughout these isolated areas of clay-rich soil.
Certainly, it is very difficult to distinguish outcrop from
clay-rich soil on aerial photographs.
The Cleanskin beds may be synonymous with very
similar Cenozoic limestone occurring in adjacent mapsheets
(Noakes and Traves 1954), including the Brunette Limestone
in BRUNETTE DOWNS, ALROY and RANKEN, and the
Austral Downs Limestone in AVON DOWNS (Kruse and
Radke 2008). The unit may also correlate with Cenozoic
limestone further afield (eg Golliger beds on BAUHINIA
DOWNS, Pietsch et al 1991).
Undifferentiated Cenozoic deposits (Cz) include
predominantly sandy to gravelly skeletal soils. Other
Palaeogene and Neogene deposits, which have not been
differentiated at the map scale, are also included in this unit.
Pisolitic and massive ferricrete and laterite (Cz1),
formed under conditions of intense chemical weathering,
are widespread (Sweet 1984). These deposits have formed
at various times during the Cenozoic and are well developed
over extensive areas where the topography is flat-lying
to undulating. They are probably mainly underlain by
Cretaceous sedimentary rocks and the Helen Springs
Volcanics. Unconsolidated residual sand deposits (Czs)
are extensive along the plateaux and plains bounding the
ranges in MOUNT DRUMMOND, where they overlie
Cretaceous and Proterozoic sandstone units. The most
widespread Cenozoic unit in the mapsheet area is a clayrich soil, ‘blacksoil’ (Czb), which blankets the carbonates of
the Georgina Basin (Figure 62). It is a characteristic greyblack, organic-rich clayey to silty soil with a high carbonate
Figure 61. View of incised landscape
from mesa of Cretaceous sandstone
and claystone. Cleanskin, 785300mE
7974500mN, No Return Creek.
Figure 62. Aerial view of gently
undulating blacksoil (clay-rich soil)
plains near Mittiebah homestead, southcentral MOUNT DRUMMOND.
69
radiometric data were obtained largely during the NTGS
Barkly survey (Tesla 2001). This survey had north–southoriented flight lines, with a line spacing of 400 m and a
mean survey elevation of 80 m above ground. Other highresolution company data have also been incorporated
into the magnetic and radiometric stitches covering
MOUNT DRUMMOND. Full details of NTGS surveys
are accessible at http://www.nt.gov.au/dpifm/Minerals_
Energy/Geoscience/. The data are available in various
digital formats or may be viewed online at the NTGS
website using Image Web Server technology. The gravity
dataset is from the Australia-wide regional gravity survey
conducted by GA at a station spacing of 11 km. These data
are available from NTGS in digital form and as contour
maps of Bouguer and Free Air Anomalies.
Airborne geophysical images define a number of features
in MOUNT DRUMMOND:
component. It is a vertosol (clay soil that cracks when dry)
in the classification of Isbell (1996). It supports a thick
cover of Mitchell grass, the basis for the cattle raising
industry of the Barkly Tableland. Czb is locally associated
with loose scattered blocks of dolostone or saprolite,
belonging to either the Georgina Basin or Cleanskin beds.
Brecciated, light grey, surficial silcrete deposits (Czz) are
common on some carbonate units of the Georgina Basin,
such as the Wonarah Formation. Siliceous and clayey
saprolite is also a common feature over the recessive
lower Crow Formation and lower Mullera Formation
in the Benmara area. However, silcrete is generally not
distinguished from the underlying unit on the mapface of
MOUNT DRUMMOND.
Quaternary (Qa)
Alluvial gravel, sand, silt and clay (Qa) are found in active
drainage channels, floodplains and outwash sheet deposits
around ranges and plateaux. Fine-grained deposits
formed in local depressions, such as ephemeral playas
and swamps, are included in this category. Areas of Qa
flanking major rivers and creeks fan laterally towards the
Barkly Tableland where they intermingle with blacksoil.
• Edge of Georgina Basin. The basal Georgina Basin
is generally highly magnetic, due to the presence of
the Helen Springs Volcanics, which has a pronounced
signature on images (Figure 63). In some areas, there
is a single high-frequency band, consistent with an edge
effect, indicating a steep basinward dip of the volcanics
away from the basement on which it onlaps. An example
is at the southern edge of the Proterozoic outcrop
between Mitchiebo Waterhole (713000mE 7932000mN)
and Wild Cow Creek (753000mE 7933000mN). A less
likely possibility is that the basin margin was the site
Geophysics
MOUNT DRUMMOND is covered by regional gravity,
aeromagnetic and radiometric datasets. The magnetic and
136°30'
18°00'
138°00'
18°00'
BG
HSV
SNG
SNG
?
MG
CRV
MG
HSV
SNG
CRV
MG
MG
CRV
HSV
SNG
HSV
GB
19°00'
136°30'
HSV = Magnetic Georgina Basin with thick basal volcanic rocks (Helen Springs Volcanics)
GB = Non-magnetic Georgina Basin with no basal volcanic rocks
SNG = Non-magnetic South Nicholson Group
MG = Non-magnetic McNamara Group
BG = Magnetic Benmara Group (± Murphy Inlier)
CRV = Magnetic Carrara Range Group
19°00'
138°00'
A07-236.ai
Figure 63. First vertical derivative of aeromagnetic data for MOUNT DRUMMOND, overlaid with annotated solid geology.
70
•
•
•
•
•
•
these areas of volcanic rock, as they are reasonably well
represented in the total count.
of magma extrusion. In other areas, the volcanic rocks
are probably flat-lying and covered by a thin Georgina
Basin veneer, leading to the development of a complex
high-frequency pattern that probably depicts original
volcanic flow architecture. An example is the large,
blacksoil-covered area centred on Fish Hole Creek
(670000mE 7954000mN).
Mafic volcanic rocks of Carrara Range Group. The
highly magnetic Mitchiebo Volcanics are responsible
for the majority of the magnetic pattern in the Carrara
Range. They can be traced east–west across the outcrop
belt at two levels or latitudes, divided by a large
stratigraphy-repeating fault.
East–west structure in Carrara Range. The overall
east-oriented faulting evident on the geological map is
also readily apparent in the airborne magnetic image
(Figure 63). This takes the form of truncated magnetic
markers, such as the Mitchiebo Volcanics, and more
subtle gradients sourced from covered basement.
Volcanic rocks in Benmara Group. A semi-continuous
trail of magnetic highs in the Benmara–Murphys Creek
area between 696000mE 7978000mN and 704000mE
8008000mN is probably due to the presence of a
magnetic igneous unit, the Buddycurrawa Volcanics
(Figure 63). The discontinuous nature and variable
intensity of the anomalies may be due to local faulting
against magnetically transparent basement and the
South Nicholson Group along the Benmara Fault. At
least part of the southern end of this magnetic band may
be due to the presence of banded iron formation in the
Murphy Metamorphics.
Small isolated magnetic highs. High-frequency magnetic
anomalies, some of which may relate to dipolar magnetic
sources, are evident in a number of places. However,
the most notable is a cluster of anomalies near the
Flemington Racecourse Claypan, centred on 721000mE
7959000mN (Figure 63). This cluster appears to
be contained in the shallow subsurface of the South
Nicholson Group and is probably due to the presence of
maghemite in the weathering profile.
Subtle magnetic ‘layering’ in sandstone units. Fine
parallel banding, which is consistent with established
dips and strikes, is present in a number of clastic units
in the South Nicholson Group (Figure 63). The most
notable banding is within the Playford Sandstone
(eg Ten Mile Creek, 689000mE 7940000mN),
Mittiebah Sandstone (eg Mittiebah Range, 688000mE
7913000mN) and Crow Formation (eg Crow Creek,
690000mE 7954000mE). Banding is probably due to
variable and alternating heavy mineral concentrations
in the stratigraphic section, including hematite, rutile,
ilmenite and titanomagnetite. This most likely relates to
simple lithofacies variations (mudstone and sandstone)
and quartzite palaeoplacers. In some cases, it relates to
the presence of weakly magnetic sedimentary ironstone,
of the ‘Constance Range style’.
Radiometric response of Helen Springs Volcanics. In
most areas, these volcanic rocks are covered by a thin
veneer of sand and laterite and their presence is difficult
to substantiate in the field. Radiometric data were used
extensively, in concert with aeromagnetic data, to map
Structure
An easterly- to east-northeasterly structural grain is readily
apparent in the eastern half of MOUNT DRUMMOND,
parallel to the outline and grain of the Murphy Inlier to
the north. This structural fabric is most notable in the
Carrara Range, where there is abundant faulting in this
orientation, juxtaposing the Carrara Range, McNamara
and South Nicholson groups. The Georgina Basin is
also in apparent faulted contact with Proterozoic rocks
at the southern margin of the Carrara Range. The main
faults (Little Range, Mitchiebo, Rocky Creek, Maloney,
Brumby and Wild Cow faults) all show north-side-up
displacement and straight to mildly sinuous plan profiles.
Structural repetition and thickening are recognised locally,
particularly in the Brumby and Drummond formations,
along numerous, small to large strike-parallel faults (many
are unmapped or ‘blind’). Freshwater springs are common
along some of these faults. At least two episodes of uplift
and deformation are evident from the unconformities
at the base of the Top Rocky Rhyolite and McNamara
Group, the latter truncating a fault set in the Carrara Range
Group. There is evidence for stratal growth and fault talus
deposition in the middle–upper McNamara Group to the
north of the Maloney Fault within the Maloney Creek
Inlier. This is an elliptical inlier of coarse-grained facies
of the McNamara Group within the South Nicholson Group
that is bounded to the south by the Maloney Fault and is
internally truncated by splays of the Mitchiebo Fault. There
is also a suspicion of depositional growth north of the
Rocky Creek Fault in the Wild Cow Sub-basin at a similar
time. The current structural geometry is thus interpreted
to reflect compressional inversion of earlier faults. Some
of these early faults were compressional and some were
normal faults, the latter associated with either extension or
transtensional strike-slip deformation, analogous with the
Emu Fault at McArthur River (Hinman 1995). Inversion
appears to have involved partly thrust (north-over-south)
and partly strike-slip geometries. The Little Range Fault, in
particular, is notably linear, indicating a predominance of
strike-slip displacement. In terms of timing, the youngest
fault movement in the Carrara Range at least postdates
the South Nicholson Group. In the case of the Little Range
and Mitchiebo faults, the last movement demonstrably
postdates the Georgina Basin, suggesting a number of
inversion events, stretching between the Mesoproterozoic
and Phanerozoic. The timing of the main inversion event is
difficult to constrain, but may correlate with the post-Roper
deformational event in the McArthur Basin (Rogers 1996a,
Rawlings and Sweet 2004).
The western half of MOUNT DRUMMOND is
dominated by dome-and-basin folding in the South
Nicholson Group, an example being the Mittiebah Range.
Folds of 5–20 km wavelength have subhorizontal to
shallow-plunging axes with inconsistent strike. The axes
of many folds plunge shallowly in opposite directions to
form doubly-plunging synclines and anticlines. The only
major structure that continues across from the eastern half
71
from Benmara homestead toward Fish Hole Creek. This
conclusion differs from Plumb et al’s tectonic framework
interpretation, which shows the ridge continuing to the
west from Benmara homestead and Coanjula in CALVERT
HILLS.
West of the Benmara Fault, mudstone and sandstone of
the Crow Formation (South Nicholson Group) are folded in
spectacular fashion within a north-northeast-trending belt
encompassing the headwaters of Murphys and Benmara
creeks (centred on 700000mE 7990000mN). Kilometrescale, upright symmetric folds with open to tight northnortheast-oriented axes are visible on aerial photographs.
In contrast, folds in outcrop at dekametre scale exhibit axial
planes in various orientations, including vertical, reclined,
inclined and recumbent (ie disharmonic folding). Folds
are open to tight, with angular hinges (chevron type) and
boxfolds developed in places (Figure 64). Dip reversals and
structural repetitions of the Crow Formation are common in
this outcrop belt, occurring locally across subvertical strikeparallel faults that have developed at fold hinges. Folding
and faulting have led to the apparent rapid southward
thickening and northward thinning of the formation, as
seen on the mapface. This thickness variation and the
inconsistent nature of the base of the South Nicholson
Group in the northern zone (705000mE 8007000mN) may
be related to a detachment in the lower Crow Formation. In
support of this is the pinching out of the Benmara Group in
this northern area.
Another large concealed structure is implied in southern
MOUNT DRUMMOND, about 5 km north of Mittiebah
Range. The main valley immediately north of the range
contains outcrop of the Crow Formation, dipping to the south
under the >2000 m-thick Mittiebah Sandstone. In contrast,
organic-rich source rocks recovered ca 2 km north of this
outcrop at ‘Hydrocarbon Bore’ (703000mE 7922200mN),
under thin Georgina Basin cover, are geochemically
inconsistent with the Crow Formation (see Economic
geology). Instead, the data indicate significantly less burial
of this concealed source rock and a possible correlation
with the Mullera Formation. Although there is no surface
or geophysical expression of a fault, the geochemical data
of MOUNT DRUMMOND is the Mitchiebo Fault, which
gradually decreases in throw to the west. The presence of
proximal debris flows in the South Nicholson Group and
Caulfield beds in the far north suggests possible active
tectonism and uplift of the Murphy Tectonic Ridge, from
which immature detritus was shed into adjacent zones
of subsidence to the south. This tectonism may relate to
foreland basin development in the South Nicholson Basin,
coincident with movement along east-trending faults in the
Carrara Range. The presence of a minor unconformity and
the local absence of the Wallis Siltstone Member suggests
the possibility of minor uplift on old, reactivated, fault
systems in northeastern MOUNT DRUMMOND, possibly
on the Nicholson River or Border Creek faults.
The principal structure in the northwestern corner of the
mapsheet is the Benmara Fault, which is arcuate in profile,
juxtaposing the Murphy Metamorphics against the South
Nicholson Group. West-side-up displacement is consistent
along its length and local kinematic indicators suggest
west-over-east thrusting. A strike-slip component is also
apparent in places. Proximal debris flows in the South
Nicholson Group adjacent to this fault suggest it was active
at an earlier time as a synsedimentary growth structure.
Synchronous faulting and sedimentation may also explain
the radical difference in thickness of the basal sandstone
of the South Nicholson Group across the Benmara Fault.
This sandstone is <10 m thick west of the Benmara Fault
(mapped as Bowgan Sandstone; 696100mE 7977900mN)
and >300 m thick east of the fault (mapped as Playford
Sandstone; 698800mE 7974700mN). In the far north
around Pandanus Creek (712000mE 8008000mN), rocks
adjacent to the Benmara Fault have been intensely silicified,
ferruginised, brecciated, folded and quartz ± hematite
veined. Iron enrichment becomes extreme at some points
along the fault, culminating in the development of massive
ironstone (see Economic geology).
The presence of basement immediately to the west
of the north-northeast-trending Benmara Fault, and the
absence of various cover units adjacent to it (eg Carrara
Range and McNamara groups), suggests that the ‘Murphy
Tectonic Ridge’ (Plumb et al 1990) extended southwestward
Figure 64. Irregular 0.5–10 m-scale
chevron folds and boxfolds in flaggy facies
of Crow Formation. Boxer, 693700mE
7985250mN, Benmara Creek.
72
related to the movement of Fe‑rich fluids along large, eaststriking bedding-parallel faults (conduits?) in the South
Nicholson Group. Mudstone of the Crow Formation also
becomes increasingly altered and ferruginous upwards
beneath mesas of laterite along the valley. This close
association is also evidenced by veins of pisolitic laterite
within massive or laminated Crow Formation ironstone.
Rock sampling indicates that economic concentrations
of iron are restricted to laterite that represents a residual
deposit from the weathering of Proterozoic ironstone. In
this instance, economic iron resources would be restricted
to a near-surface layer about 2–5 m thick at the top of the
laterite mesas. No detailed mapping or drilling has been
carried out on these iron occurrences.
could be explained by the presence of a large, probably
east-oriented offset of the Crow Formation in the south and
Mullera Formation in the north.
Economic geology
Although there are no operating mines in MOUNT
DRUMMOND, there are a number of significant mineral
systems and plays, outlined below. Previous exploration is
summarised in Table 2.
Iron
Moderate-grade iron deposits occur within the South
Nicholson Group east of MOUNT DRUMMOND in
Queensland: the Constance Range iron deposits (Carter
and Zimmerman 1960, Harms 1965). Although iron-rich
sediments occur at several stratigraphic levels, the greatest
concentrations are in the Train Range Ironstone Member,
which contains three or four iron-rich beds that reach ore
grade. Fourteen separate deposits are recognised (labelled
from A to N), and published reserves, of 362 Mt at grades
ranging from 42 to 57% Fe (Harms 1965). The mineralisation
consists of oolitic hematite, siderite and chamosite beds,
and is of the ‘Wabana (Newfoundland) type’ (Harms 1965).
Similar-style iron mineralisation is present in the South
Nicholson Group in MOUNT DRUMMOND. The main
iron occurrences identified during First and Second Edition
mapping of MOUNT DRUMMOND have not been properly
assessed by exploration companies, and their economic
and resource status are unknown. Although several new
iron occurrences are indicated on the Second Edition map,
these were discovered by good fortune; numerous other
such occurrences may be expected. At least part of this
mineralisation relates to primary depositional processes,
as recognised by Ferenczi (2001) in the Sherwin Ironstone
Member of the Roper Group in the McArthur Basin and
by Harms (1965) for the Train Range Ironstone Member
occurrences. However, local surficial supergene enrichment
and fault-related fluid movement has also affected some of
the ironstone bodies and led to higher iron concentrations.
Most occurrences occur within siltstone and claystone
of the Mullera and Crow formations, although there are also
occurrences within the Playford and Constance sandstones.
Minor and probably insignificant mineralisation occurs
in the Murphy Metamorphics and Breakfast Sandstone.
Ironstone occurs as stratiform bodies 5–20 m thick and 100s
to 1000s of metres long. Hematite is typically fine grained,
massive, and destructive to bedding. Several examples are
briefly documented below.
Benmara Fault
In the northeastern corner of Boxer (Pandanus Creek,
712000mE 8008000mN), a variety of sedimentary rocks
of the South Nicholson Group have been replaced by
massive ironstone adjacent to the Benmara Fault. Ironstone
is locally discordant and irregular, lacks deformation or
sedimentary fabrics, and replaces cataclasite and sandstone
breccia, indicating that it postdates deposition of the South
Nicholson Group and its subsequent deformation. The iron
content in the Constance Sandstone is up to 71.1% Fe203
(ave 54.2%, n=3), but decreases rapidly away from the fault
zone. Ironstone also occurs as a series of discrete stratiform
horizons in the lower Mullera Formation, up to several
kilometres east of the fault (eg 712800mE 8007800mN and
713300mE 8009850mN). The two main intervals (‘lower
and upper ironstone beds’) range up to 10 m thick, but are
generally about 4–5 m. They are semi-continuous along
strike, but vary in hematite content, up to 84.7% Fe203
(ave 65.2%, n=6). It is speculated here that iron has been
remobilised from sedimentary rocks of the South Nicholson
Group by oxidised basinal fluids and channelled along firstand second-order fault systems, to precipitate in porous
iron-rich beds of the Constance Sandstone and Mullera
Formation.
Murphy Metamorphics
Interstratified within turbidites of the Murphy
Metamorphics in the Canyon Range is a 2–10 m-thick,
laterally continuous interval of banded iron formation
(eg 704350mE 7992200mN, Figure 7). Grades were not
assessed systematically during Second Edition mapping,
but the one sample analysed contains 51.3% Fe203.
Base metals
No established base metal prospects or deposits have yet been
discovered in MOUNT DRUMMOND, but the world-class
Century Zn-Pb-Ag deposit, 60 km to the east in Queensland,
lies within rocks of the upper McNamara Group (Broadbent
et al 1998), a group that is well represented in southeastern
MOUNT DRUMMOND. The host succession (carbonate,
sandstone and shale of the ca 1000 m-thick Lawn Hill
Formation) extends westward into Mount Drummond
(Sweet 1984, Sweet et al 1984, McConachie and Dunster
1998). It is widely distributed at surface and can be
extrapolated into the subsurface under the Georgina Basin,
Mitchiebo Waterhole
The upper part of the Crow Formation is extensively
ferruginised adjacent to the overlying Constance Sandstone
over a strike length of more than 10 km, east-northeast of
Mitchiebo Waterhole. This culminates in the development
of blocky to slabby outcrop of subeconomic ironstone,
including the Fe occurrences marked on the First Edition
MOUNT DRUMMOND. The iron content in the Crow
Formation is up to 42.5% Fe203 (ave 33.3%, n=6). Iron
enrichment appears to be a secondary phenomenon, perhaps
73
flows that emanated from an active (synsedimentary) ‘growth’
fault scarp into shallow- to deep-water environments (fandelta, Sweet 1985). In this respect, they are analogous with
the Barney Creek Formation and Cooley Dolostone at the
McArthur River deposit. There, stratiform base metal sulfide
mineralisation is interpreted to have formed by exhalation
of metalliferous saline basinal fluids into a localised deepwater brine pool along a regional strike-slip fault system
(Large et al 1998). Ore intervals are interlayered with talus
breccia and turbidite beds, indicating synchronous fault-scarp
development, sedimentation and brine exhalation.
south and west of the Little Range Fault. In the northeastern
corner of MOUNT DRUMMOND is a narrow east-trending
belt of Fickling Group, including shale and carbonate of
the Doomadgee Formation, flanking the southern edge
of the Murphy Inlier. The Walford Creek Pb–Zn prospect
(Rohrlach et al 1998), with similar characteristics to the
McArthur River deposit (Williams 1978a, 1978b), occurs
30 km east along strike in Queensland, at the faulted
northern margin of the Lawn Hill Platform. In addition to
the close spatial and temporal relationship with known base
metals deposits of the ‘Carpentaria zinc belt’, MOUNT
DRUMMOND is prospective on other grounds:
Little Range Fault
Probable lower McNamara Group is mapped immediately
south of the Little Range Fault, abutting the Murphy
Metamorphics and Carrara Range Group. The exact position
of the fault is difficult to determine, due to the presence
of a thick onlapping section of Georgina Basin. The large
stratigraphic juxtaposition and linear nature of the fault system
(ie strike-slip) suggests that the southern edge is a potential
target for McArthur River-type base metals deposits.
• It contains the appropriate host rock package in terms
of contained lithology, namely a ‘reduced’ fine-grained,
mixed carbonate-siliciclastic package with variable
permeability (eg Plain Creek, Doomadgee and Lawn
Hill formations; cf Bull 1998).
• The underlying Carrara Range Group has suitable
characteristics to be the ‘engine room’ for a large
regional-scale metallogenic system, with the potential to
form a spectrum of deposits in the overlying or adjacent
successions (eg McArthur River, Kupferschiefer and
MVT styles). This includes a thick ‘oxidised’ sandstone
package with intervals of mafic and felsic volcanic rocks
(cf Cooke et al 1998, 2000, Garven et al 2001).
• It contains faults with similar geometry and features to
the Termite Range and Emu faults, the implied feeders
for Century and McArthur River, respectively. Large
stratigraphic juxtapositions are evident along several
major faults and there is local evidence for stratigraphic
growth and for talus and debris flow deposition adjacent
to fault scarps (‘tectonic facies’; cf Logan et al 1990,
Hinman 1995).
• The prospectivity of the Northern Territory side of the
Lawn Hill Platform has not been rigorously tested by
exploration.
Wild Cow Sub-basin
The Wild Cow Sub-basin is an elliptical area of largely
alluvium-covered upper McNamara Group in the headwaters
of Wild Cow Creek, centred on 754000mE 7936000mN.
Based on dips and outcrop widths, the Lawn Hill Formation
is postulated to thicken to as much as 3000 m there (see
Lawn Hill Formation). The sub-basin is bounded to the
north by the Wild Cow Fault and perhaps to the south by
a westerly extension of the Rocky Creek Fault; however,
the polarity of the sub-basin is unknown. The faulted
juxtaposition with the Carrara Range Group in the north
would be the most logical target zone for McArthur Rivertype base metals deposits, but due to poor outcrop, the exact
position of the fault is difficult to ascertain. The westerly
extent of the sub-basin is unknown; it may extend west to
the area south of Mitchiebo Waterhole, where several faults
may indicate large displacements of the succession.
In Mount Drummond, a ‘McArthur River subbasin model’ (Large et al 1998) can be applied to the upper
McNamara Group, adjacent to major east-oriented fault
systems such as the Little Range and Mitchiebo faults.
A ‘Century hydrocarbon-metalliferous brine model’
(Broadbent et al 1998, Hobbs et al 2000) can be applied to
areas of regional-scale folding (hydrocarbon traps) distal
to these primary faults, adjacent to second-order faults
(metalliferous fluid pathways). The South Nicholson Group
also has some potential. Several specific areas of enhanced
prospectivity are suggested.
Bauhinia Dome and Canyon Range
The Crow Formation and Caulfield beds, adjacent to the
Murphy Inlier in the Canyon Range and Bauhinia Dome,
respectively, contain clear evidence of debris flow and talus
breccia deposition, accompanied by substantial lateral facies
and thickness variation. Large fault structures, such as the
Benmara Fault, with implied synsedimentary movement
and sub-basin development, are present. Recessive shaly
parts of these units are rarely exposed and may contain
blind base metals deposits, perhaps of SEDEX or MVT
style. Currently, there are no significant stream sediment
geochemical grids over the South Nicholson Group, apart
from recent reconnaissance NTGS data, suggesting that
further testing is warranted.
Maloney Creek Inlier
In this partly fault-bounded inlier, ‘tectonic facies’ is
interdigitated with ‘background clastic facies’ adjacent to the
Mitchiebo and Maloney faults. Initial shallow-water fault-scarp
and sub-basin development was accompanied by deposition of
massive polymict breccia, conglomerate and sandstone beds
of the Bullrush Conglomerate. The overlying Plain Creek
Formation comprises an unusual facies association, with
coarse-grained sandstone and conglomerate interbedded with
sub-wave-base carbonaceous shale and siltstone. The facies in
these two formations are interpreted as turbidites and debris
Manganese
Surficial manganese is locally developed in the region and
is particularly common as a weathering crust on the Plain
Creek Formation (eg 755800mE 7937600mN). Although the
economic significance of the manganese occurrences has not
74
DRUMMOND, the sheet area is considered to have excellent
potential, as shown by the extent of previous exploration
(Table 2). It lies within a broad west-northwest-trending
swath of anomalous surficial microdiamond concentrations
in the northern half of the Northern Territory (Smith et al
1990, Figure 65).
An exploration campaign in 1985, based on the
distribution pattern of microdiamonds depicted in Figure 65,
led to the discovery of Coanjula in CALVERT HILLS to
the north (Smith et al 1990, Lee et al 1998). In this area,
there are a number of intrusive alkali basaltic diatremes
(Ong 1995). They consist of magmatic and brecciated
diatreme facies rocks and pyroclastic, air-fall, crater-facies
lapilli tuffs, which are constrained in age by a K-Ar age
of 1665 Ma for a kaersutite megacryst in pipe CJ12 (Ong
1991, Lee et al 1994) and by the unconformably overlying
South Nicholson Group (1490–1430 Ma). However, these
diatremes are barren of diamonds and bear no spatial
coincidence with the diamondiferous deposits. Rather,
abundant non-transported microdiamonds are hosted
exclusively within Palaeoproterozoic metasedimentary
bedrock of the Murphy Metamorphics. Diamond-associated
litharenites in this area have yielded a U-Pb SHRIMP
maximum depositional age of 1867 ± 7 Ma, (Hanley 1996).
Non-diamond-associated litharenites in the same region
have yielded a less well constrained, but overlapping
depositional age of 1870 ± 25 Ma. However, these contain
a higher proportion of older, detrital zircon grains with
concordant age peaks at 2698 ± 20 Ma and 2171 ± 14 Ma
(Hanley 1996). Drilling has established two main deposits,
comprising up to kilometre-scale discontinuous irregular
‘pods’ of elevated microdiamond concentrations. However,
high microdiamond concentrations are correlated with the
occurrence of thin veins of rocks of mica lamprophyric
composition, which yielded a maximum intrusive age
of 1861 ± 10 Ma (Hanley 1996). This coincided with the
discovery of a microdiamond-rich mica lamprophyre dyke in
Canada. The mechanism by which the microdiamonds were
transported from the mantle to the surface and incorporated
into metasediments is unknown.
Lee et al (1994) suggested that the microdiamond
distribution pattern in northern Australia (Figure 65) is
largely due to the dispersal of diamonds from Coanjula by
southwesterly drainage and northwesterly prevailing winds.
This interpretation impacts substantially on the validity of
microdiamond sampling and mapping in the exploration for
macrodiamond deposits in northern Australia.
Clusters of diamondiferous kimberlite pipes also occur
150 km to the northwest at the Merlin field (Lee et al
1998) and in BAUHINIA DOWNS (E.Mu pipes; Atkinson
et al 1990, Smith et al 1990). The Merlin field was openpit mined during 1998–2003 by Ashton Mining Ltd/Rio
Tinto Ltd and produced 507 000 ct of diamonds, including
the largest individual diamond ever found in Australia
(ca 105 ct). North Australian Diamonds Ltd (formerly
Striker Resources NL) acquired the Merlin project from
Rio Tinto in 2004 and, at the time of writing, the field was
undergoing feasibility studies prior to the resumption of
mining. Probable ore reserves, combined with indicated
and inferred resources, are 19.45 Mt @ 18 cpht (ct per
hundred tonnes), representing a total of 3.5 Mct (North
been properly assessed by drilling, it is unlikely to extend
deeply into the host rock (cf Ferenczi 2001).
Phosphate
The Georgina Basin has a long history of phosphorite
exploration (eg de Keyser 1969, Howard 1990, Khan et al
2007), although there are currently no operating mines in its
Northern Territory portion. Apart from Highland Plains (see
below), known deposits of the basin in the NT are located
along the Alexandria-Wonarah Basement High (Howard
1972), which extends southward from southwestern MOUNT
DRUMMOND as far as northeastern FREW RIVER. Two
subeconomic phosphorite deposits have been delineated in
the Wonarah Formation in adjacent RANKEN and ALROY:
Alexandria with 15 Mt @ 10% P2O5, and Alroy with 14 Mt
@ 20% P2O5 (Driessen in Shergold and Southgate 1986;
see also Howard 1972, Cook in Shergold and Southgate
1986, Freeman et al 1990). Further south on the high is the
Wonarah deposit, which is centred in northeastern FREW
RIVER and extends into immediately adjacent sheet areas.
Wonarah is much larger, with an estimated resource of
72 Mt @ 23% P2O5 (AKD Ltd, Australian Stock Exchange
announcement 24 January 2002), based on that portion of
the deposit subjected to closely spaced drilling by Rio TintoAKD in 2000. Phosphatisation is concentrated at the base of
the Wonarah Formation, directly above the Helen Springs
Volcanics. The deposit was briefly described by Howard
(1971, 1972), Howard and Perrino (1976), Howard and Hough
(1979) and Cook in Shergold and Southgate (1986), and has
been reviewed by Freeman et al (1990) and Khan et al (2007).
All three deposits are concealed beneath blacksoil.
In southeastern MOUNT DRUMMOND, the Border
Waterhole Formation hosts the Highland Plains deposit,
which straddles the Northern Territory–Queensland border.
McMahon (1969) delineated two major tabular phosphatic
intervals in the lower part of the formation. The lower of
these intervals (thickness 1.5–17 m) is at the base of the
formation. The upper interval (1.5–11 m thick) is some
7–17 m stratigraphically higher in the succession and grades
16–30% P2O5. Phosphate occurs as pelletal collophane,
dispersed within friable siltstone and fine sandstone.
McMahon (1969) ‘conservatively’ calculated total indicated
and inferred reserves of 81 Mt @ approximately 20% P2O5.
Cook and Shergold (1979) cited a published figure of 84 Mt
@ 13.4% P2O5. Shergold and Druce (1980) reported an
overall thickness of 6–38 m for the phosphorite intervals
and, additionally, noted the presence of non-pelletal
collophane mudstone.
No additional significant concentrations of phosphate
were recognised in MOUNT DRUMMOND during
Second Edition mapping, either from radiometric or from
reconnaissance hand-held scintillometer surveys. However,
there is potential for further phosphorite occurrences
beneath blacksoil mantling the Alexandria-Wonarah
Basement High in the southwestern sheet area.
Diamonds
Although no kimberlitic or lamproitic intrusions or
diamondiferous deposits have been identified in MOUNT
75
Australian Diamonds Ltd, Australian Stock Exchange
Quarterly Report 30 September 2007).
Formation and abandoned the South Nicholson project,
partly due to discouraging petrological data obtained
from DD92SN1. On the basis of new mapping, we suggest
that they inadvertently drilled the Crow Formation rather
than the Mullera Formation. The Mullera Formation
therefore remains untested, unless it is the hydrocarbonrich formation present in ‘Hydrocarbon Bore’ near
Peaker Piker Creek (703000mE 7922200mN). These
rocks are very rich (TOC 10.6%), below the oil window
(T Max 372°C; Rawlings and Sweet 2004), and are
substantially less mature than those in DD92SN1. Other
RockEval pyrolysis data for the ‘Hydrocarbon Bore’
sample include: S1=23.77; S2=65.93; S3=1.9; PI=0.26;
PC=7.47; HI=621; OI=17, where S1 = amount of free
hydrocarbons; S2 = amount of hydrocarbons generated
through thermal cracking of nonvolatile organic matter;
S3 = amount of CO2 (in milligrams CO2 per gram of rock)
produced during pyrolysis of kerogen; PI = production
index; PC = pyrolysable carbon; HI = hydrogen index;
OI = oxygen index.
Petroleum
Petroleum exploration in MOUNT DRUMMOND
has been very limited and includes an evaluation of
stratigraphy and structure by Pacific Oil and Gas in the
early 1980s. Only one drillhole was completed: DD92SN1
(Lanigan 1993) near Flemington Racecourse Claypan
(723500mE 7951200mN), which intersected 430 m of
the lower Crow Formation, thought to have some source
rock potential. Organic intervals comprise ca 15% of the
drill intersection, but TOC is generally less than 1% and
hydrocarbons were found to be beyond the oil window
(T Max 460–470°C). Permeability and porosity are also
very low. This formation is therefore considered to have
low prospectivity for oil or gas.
Based on the knowledge at the time, Pacific Oil
and Gas had assumed this interval to be the Mullera
129°00'
11°00'
TIMOR
138°00'
11°00'
SEA
DARWIN
GULF OF CARPENTARIA
Katherine
15°00'
15°00'
TIMBER
CREEK
ARGYLE
ABNER RANGE
MERLIN
COANJULA
19°00'
19°00'
Tennant
Creek
WESTERN
AUSTRALIA
Mount Isa
NORTHERN TERRITORY
QUEENSLAND
22°00'
22°00'
A07-235.ai
129°00'
138°00'
Contours showing microdiamond frequency
0
200
400 km
MERLIN
high
medium
Macrodiamond-bearing kimberlite/lamproite
low
Microdiamond anomaly
Figure 65. Distribution of microdiamonds and kimberlitic/lamproitic pipes in north-central Australia (modified after Smith et al 1990). Box
outlines MOUNT DRUMMOND.
76
in watercourses are largely derived from groundwater
discharge from Georgina Basin aquifers.
Based on these data, the sections intersected in
‘Hydrocarbon Bore’ and DD92SN1 are unlikely to
correlate, unless they were buried to vastly different extents
by overlying strata. This appears implausible, because
the overlying Mittiebah Sandstone is >2000 m thick
near ‘Hydrocarbon Bore’, implying deeper burial than at
DD92SN1, not shallower.
This interpretation has significant implications for oil and
gas exploration, as genuine Mullera Formation source rock can
now be regarded as untested in MOUNT DRUMMOND.
Geochemistry
Two main geochemical datasets have been generated from
Second Edition mapping in MOUNT DRUMMOND.
Firstly, a total of 73 rock samples were submitted for major
and minor element geochemistry, for the purposes of
identifying petrological characteristics, correlating igneous
units and quantifying the grade of a number of iron and
manganese occurrences. The results and interpretations of
these analyses are discussed in the appropriate sections of
this document and are summarised in Appendix 2 (Excel
spreadsheet). Secondly, a total of 132 stream sediment
samples were submitted for selected analyses to establish
baseline geochemical characteristics in the region. Most of
these were collected outside the area covered by previous
company stream sediment geochemical sampling, hence
broadening the extent of first-pass sampling in the region.
No interpretation of these data is alluded to here. The
results of these surveys are included in Appendix 3 (Excel
spreadsheet).
Other commodities
Quartz veining (partly epithermal) is ubiquitous and clay
alteration zones have been recognised locally within the
Murphy Metamorphics and Connelly Volcanics. The
Murphy Inlier is also characterised by regionally anomalous
Au stream sediment values (Hitchman 1991).
The Carrara Range Group includes a 500–1000 m-thick
flood basalt, not unlike the Eastern Creek Volcanics in the
Mount Isa Inlier. Base metal anomalism is common in stream
sediment samples draining these volcanic rocks along the
Little Range Fault, suggesting that they have potential for
small Redbank-style Cu-Co-Ni deposits (cf Rawlings 2002).
Localised rhyolite domes, cryptodomes and epiclastic
aprons of the Top Rocky Rhyolite have epithermal Au–Ag–U
prospectivity, based on the likelihood of abnormally high
emplacement temperatures and the naturally radiogenic
nature of the rocks. However, rhyolite has anhydrous (‘dry’)
or A-type geochemistry, so hydrothermal systems would
have needed to rely upon the surrounding groundwater
system. Infill stream sediment geochemical data collected
by NTGS indicate broad base metal anomalism in the lower
Wonarah Formation, with Zn values up to 450 ppm and Pb
up to 52 ppm.
Geological history
The geological history of MOUNT DRUMMOND is
summarised below in chronological order. Small temporal
breaks relating to condensed intervals or minor sequence
boundaries are omitted. All age ranges are approximate
only:
• ?2100–1880 Ma: deposition of Murphy Metamorphics
in turbidite basin of unknown extent.
• 1880–1860 Ma: metamorphism of Murphy Metamorphics
to lower greenschist facies.
• 1860–1850 Ma: cooling, rapid uplift and unconformity
development.
• 1850–1840 Ma: emplacement of felsic Connelly
Volcanics and comagmatic Cliffdale Volcanics–
Nicholson Granite to form regional basement (Murphy
Inlier).
• 1840–1790 Ma: uplift and unconformity development.
• 1790–1740 Ma: deposition of fluvial sandstone and flood
basalt of lower Carrara Range Group.
• 1740–1725 Ma: hiatus. Deformation, uplift, erosion
and unconformity development, possibly related to
magmatism.
• 1725 Ma: emplacement of rhyolitic volcanic and
epiclastic rocks of upper Carrara Range Group (Top
Rocky Rhyolite).
• 1725–1700 Ma: hiatus and unconformity development.
• 1700–1690 Ma: deposition of shallow-marine siliciclastic
sediments of Surprise Creek Formation.
• 1690–1670 Ma: period of local deformation and uplift
along faults; regional erosion.
• 1670–1590 Ma: deposition of carbonate and siliciclastic
units of the McNamara and Fickling groups in
environments ranging from fluvial, through shallowmarine peritidal settings, and fan delta to deeper marine.
Local synsedimentary faulting along Little Range,
Groundwater
Groundwater exploration in MOUNT DRUMMOND is
limited to the blacksoil plains of the Barkly Tableland,
where a viable beef cattle industry operates. Operating
bores have been drilled on an approximately 10–15 km
grid and produce large volumes of groundwater suitable for
stock use. All of the outstations and communities also rely
on bore water for consumption and minor crop growing. The
groundwater system in the remaining rocky and scrubby
country is still very much underutilised.
Aquifers occur in cavernous and fractured limestone
of the Georgina Basin, and in fractured Proterozoic and
Georgina Basin siliciclastic rocks (Tickell 2003). The
limestone aquifers are regionally very extensive and can
yield moderately large quantities of groundwater. Aquifer
depths mostly range from 75 to 125 m below the surface,
with depths to the near-horizontal watertable controlled by
elevation. Fractured-rock aquifers, on the other hand, tend
to be localised and yields are mostly low.
Groundwaters are predominantly fresh (Tickell 2003),
with low Total Dissolved Solids (<1500 mg/L), low sulfate
(<250 mg/L) and low fluoride (<0.25 mg/L). The general
direction of flow is easterly towards springs on the edge
of the Georgina Basin in Queensland. Dry season flows
77
•
•
•
•
•
•
•
•
•
•
Mitchiebo and Wild Cow faults, differential uplift
and sub-basin development. Probable deposition of
siliciclastic sediments and intermediate volcanic rocks
of Benmara Group and possibly coeval emplacement of
diamondiferous magmatic bodies in Coanjula–Canyon
Range zone.
1590–1500 Ma: hiatus and unconformity development
(Isan Orogeny).
1500–1400 Ma: deposition of fine- to coarse-grained
siliciclastic sediments of South Nicholson Group
in shallow- to deep-marine shelf, braided fluvial
and localised fan-delta environments. Probable
synsedimentary faulting adjacent to Benmara Fault.
Several episodes of stratiform iron deposition.
1400–?1300 Ma: major deformation event: extensive
faulting and gentle folding, which affected Palaeo- to
Mesoproterozoic rocks throughout much of northern
Australia, resulting in the current regional structural
pattern.
1300?–600? Ma: lengthy period of erosion, with
period(s) of coaxial folding and faulting; remobilisation
of iron in basin.
Ediacaran: deposition of the fluvial to shallow-marine
Bukalara Sandstone (regional initiation of Georgina
Basin).
Early Cambrian: emplacement of Helen Springs
Volcanics during cratonic-scale flood basalt event.
Middle Cambrian: carbonate-dominated part of
the Georgina Basin deposited in open to restricted
shallow-marine settings. Phosphorites deposited along
topographic highs.
Late Cambrian to Jurassic: lengthy hiatus and minor
reactivation of older faults.
Cretaceous: deposition of thin onlapping blanket of
sandstone and mudstone of Dunmarra Basin.
Cenozoic: deposition of colluvium and alluvium and
development of groundwater table, laterite surfaces and
modern soil profile.
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The authors gratefully acknowledge those who have
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85
by Neoproterozoic Bukalara Sandstone in northwestern
MOUNT DRUMMOND, and by Cambrian Georgina Basin
succession in southern MOUNT DRUMMOND and western
LAWN HILL.
Age: Isotopic dating currently unavailable for any part
of South Nicholson Group and age therefore internally
unconstrained. Maximum age of 1595 ± 6 Ma is that of
Lawn Hill Formation at top of underlying McNamara
Group (Page and Sweet 1998). No minimum age constraints
imposed by overlying units, apart from late Neoproterozoic
to Phanerozoic Georgina Basin. Interpreted age range of
Accident Subgroup of 1500-1400 Ma based on correlation
of South Nicholson Group with Roper Group of southern
McArthur Basin, which together comprise Roper Superbasin
(Jackson et al 1999, Abbott et al 2001). Ages of 1492 ± 4 Ma
and 1493 ± 4 Ma for tuffaceous material from Mainoru
Formation in lower Roper Group (Jackson et al 1999)
provide the most reliable estimate for age of that group,
and hence, for South Nicholson Group, including Accident
Subgroup.
Correlatives: Middle to upper Roper (Jackson et al 1999)
and Renner groups (Hussey et al 2001).
Comments: This package of rocks has been accorded
subgroup status because a disconformity has been recognised
within the South Nicholson Group. The lower and upper
parts (both now subgroups) also have distinct facies patterns
and depocentres. Although the Mittiebah Sandstone is
remote from the main outcrop belt, which is in Queensland
and eastern NT, it is included in the subgroup on the basis of
its firm correlation with the Constance Sandstone, the basal
formation of the subgroup.
Appendix 1 – New and revised
stratigraphic names
Accident Subgroup (new name)
Proposer: IP Sweet.
Derivation of name: Accident Creek, passing through
18°05'S, 138°20'E, an east-flowing tributary of Gregory
River in northwestern LAWN HILL, Queensland.
Synonymy: Incorporates all of South Nicholson Group mapped
in Queensland (LAWN HILL and WESTMORELAND),
ie Constance Sandstone, Mullera Formation and Tidna
Sandstone (Carter and Zimmerman 1960, Carter et al 1961),
in southeastern quarter of CALVERT HILLS (Ahmad
and Wygralak 1989), and in eastern third of MOUNT
DRUMMOND (Smith and Roberts 1963). Also includes
all Mittiebah Sandstone, Constance Sandstone and Mullera
Formation mapped in western two-thirds of MOUNT
DRUMMOND. Small areas of Mittiebah Sandstone on
northern RANKEN, eastern BRUNETTE DOWNS and
southwestern CALVERT HILLS also included.
Parent unit: South Nicholson Group.
Constituent units: From base to top: Constance Sandstone
and its members, Mittiebah Sandstone, Mullera Formation
and its members, Tidna Sandstone.
Distribution: Outcrops throughout MOUNT DRUMMOND,
southeastern quarter of CALVERT HILLS, northeastern
BRUNETTE DOWNS, northwestern RANKEN (all in
Northern Territory), and in southwestern WESTMORELAND
and western LAWN HILL (Queensland). Total area of outcrop
and known shallow subcrop approaches 16 000 km2.
Type section: As defined for each constituent formation.
Reference section: Complete section in an area of relatively
high dips, and therefore geographically compact, located south
of Elizabeth Creek (LAWN HILL), from Constance Range
escarpment in east, westwards for 8 km to core of a syncline.
Section extends from base of Constance Sandstone, at
18°14'41"S, 138°23'28"E (224125mE 7980770mN), southwest
for 1.7 km to top of Constance Sandstone, at 18°14'57"S,
138°22'37"E (222623mE 7980270mN), then west for 6.4 km
to youngest beds in Tidna Sandstone in centre of syncline, at
18°14'57"S, 138°18'56"E (216123mE 798017m0N).
Thickness: Minimum 400 m in southeastern MOUNT
DRUMMOND, up to 3350 m in Constance Range region in
western LAWN HILL.
Lithology: Sandstone, siltstone, shale; minor conglomerate
and sedimentary ironstone.
Depositional environment: Mainly shallow marine, ranging
to deeper water, including storm-dominated shelf and
shoreface environments; possibly minor fluvial.
Geomorphic expression: Resistant ridge-forming in
sandstone-dominated basal part, alternating ridge-forming
and recessive upper part (siltstone- and shale-dominated unit
with sandstone and ironstone interbeds).
Relationships: Disconformably overlies Wild Cow
Subgroup in west; unconformably overlies McNamara
and Fickling groups in east; unconformably overlies
Caulfield beds in Bauhinia Dome. Unconformably overlain
Benmara Group (revised definition)
Proposer: DJ Rawlings.
Derivation of name: Benmara Creek, a tributary of Nicholson
River in MOUNT DRUMMOND (18°12'S, 137°E).
Synonymy: Benmara beds of Smith and Roberts (1963).
Constituent units: Breakfast Sandstone, Buddycurrawa
Volcanics.
Distribution: Northwestern MOUNT DRUMMOND.
Thickness: 0–380 m.
Lithology: Mixed succession of sandstone, mudstone,
conglomerate, stromatolitic chert, trachyte and volcaniclastic
sandstone.
Geomorphic expression: Recessive to weakly resistant.
Relationships:
Unconformably
overlies
Murphy
Metamorphics and Connelly Volcanics. Contact with
overlying South Nicholson Group poorly exposed and
relationship cannot be resolved with any certainty. Pinching
out of Benmara Group to north near 705000E 8007000N
is consistent with both an unconformity and a low-angle
structural boundary (detachment) dividing Benmara and
South Nicholson groups, although a partly reactivated
unconformity is favoured.
Age: Constrained only by underlying Murphy Metamorphics
and Connelly Volcanics basement (>1845 Ma; Page et al
2000) and by probable overlying South Nicholson Group
86
(maximum age 1500 Ma by correlation with Roper Group;
Jackson et al 1999, Abbott et al 2001). Geochronological
studies have failed thus far to establish absolute age of
Buddycurrawa Volcanics, because the trachyte contains too
few zircons and is highly weathered. Simplest interpretation
is that Buddycurrawa Volcanics are same age as Carrara
Range Group and Peters Creek Volcanics (1725 Ma), as these
also contain abundant felsic volcanic and shallow intrusive
rocks. However, an age closer to 1660–1580 Ma can be
implied from their compositional similarity to magmatic
rocks in Coanjula area.
Correlatives: Uncertain.
Comments: This package of rocks has been accorded
group status because its stratigraphic position is now better
established and it is unlikely to belong to South Nicholson
Group. In addition, two distinct formations have been
recognised within what was previously known as ‘Benmara
beds’, making group status necessary.
sandstone, with occasional laminae of quartz granules and
small pebbles. In hand specimen, sandstone has notable
‘speckled’ appearance, due to presence of white lithic
fragments in pink ferruginous background. Unit medium
to thickly bedded with planar bedding, a parting lineation,
small-scale trough cross-beds and mudstone intraclasts.
Subtle large bedforms may also be present. Chert pebbles
and cobbles recognised near base at some localities (eg
702650mE 7992300mN). At 705200mE 8081800mN,
a thin interval of polymict breccia is recognised at base
of formation, comprising angular clasts of sandstone,
claystone and ?chert in coarse-grained sandstone matrix.
Depositional environment: Braided fluvial to shallow-marine
intertidal.
Geomorphic expression: Mildly resistant and ridge forming
with white phototones.
Relationships:
Unconformably
overlies
Murphy
Metamorphics and Benmara Group. Base not exposed, but
breccia with polymict clasts recognised at some localities.
Contact either low-angle unconformity or layer-parallel
fault. Latter could imply that Benmara and South Nicholson
groups were once stratigraphically contiguous and
conformable, and subsequently became structurally bound.
Unconformity is favoured herein, based on consistent
stratigraphic position of the discontinuity, and the different
facies of the two groups (eg volcanic in Benmara Group
but not in South Nicholson Group). Conformably overlain
by Crow Formation, but contact not well exposed, due to
recessive nature of rock types in transition zone. In most
instances, contact marked by development of distinctive
chert, secondary ironstone or clay-rich caliche, perhaps
after sulfidic shale. At 701850E 7989650N, possible
chertified digitate stromatolites are interbedded with white
claystone and sandstone at contact.
Age: Maximum age constrained only by underlying Cliffdale
Volcanics basement (>1845 Ma; Page et al 2000). Immediately
underlying Buddycurrawa Volcanics undated, but could
potentially be in range 1725–1580 Ma. Minimum age is that
of overlying late Neoproterozoic to Phanerozoic Georgina
Basin. Based on correlation of South Nicholson Group with
Roper Group, probable age range of 1500-1400 Ma can be
proposed for South Nicholson Group, and hence for Bowgan
Sandstone (Jackson et al 1999, Abbott et al 2001).
Correlatives: Probably Playford Sandstone, which forms
base of South Nicholson Group south and southeast of
Benmara Fault in northwestern MOUNT DRUMMOND.
Comments: Age likely to be near older end of range for
Roper Group (1500–1400 Ma).
Bowgan Sandstone (new name)
Proposer: DJ Rawlings.
Derivation of name: Bowgan Creek, in northwestern corner
of MOUNT DRUMMOND. This creek appears on old
1:250 000-scale topographic and geological maps (Smith
and Roberts 1963), but has been changed to Creswell Creek
on new 1:250 000- and 1:100 000-scale topographic sheets.
Name Bowgan Waterhole still used for a small waterbody
on Creswell Creek in BRUNETTE DOWNS, at 18°6'S,
136°15'E.
Synonymy: Previously mapped within (ie not differentiated
from) Constance Sandstone in First Edition MOUNT
DRUMMOND (Smith and Roberts 1963).
Parent units: South Nicholson Group, Wild Cow Subgroup.
Distribution: Northwestern MOUNT DRUMMOND and
southwestern CALVERT HILLS, in Canyon Range (name
newly approved by Committee for Geographic Names in
Australasia). Outcrop extends along north-northeasterly
belt on eastern fringe of Canyon Range, from headwaters
of Benmara Creek in south (695000mE 7982000mN in
MOUNT DRUMMOND) to Pandanus Creek in north
(705000mE 8012000mN in CALVERT HILLS).
Type locality: Narrow strike ridge at 17°59'S, 137°E
(705200mE 7999800mN) along Murphys Creek in Canyon
Range, MOUNT DRUMMOND. Locality lies along main
outcrop belt and is therefore most representative of formation,
but difficult to access. In this area, Bowgan Sandstone
overlies Buddycurrawa Volcanics of Benmara Group.
Reference section: Narrow isolated strike ridge at 18°5'S,
136°56'E (712400mE 8009850mN) along Pandanus Creek in
northern Canyon Range, MOUNT DRUMMOND. Outcrop
adjacent to Benmara–Wangalinji road and reasonably easy
to access, but may not be representative of whole formation.
At this locality, 50 m of Bowgan Sandstone overlies
Breakfast Sandstone of Benmara Group, with basal lithified
palaeoregolith.
Thickness: Up to 100 m, but generally about 10 m.
Lithology: Maroon to pink or red-brown, variably
ferruginous, lithic to sublithic, fine- to coarse-grained
Breakfast Sandstone (new name)
Proposer: DJ Rawlings.
Derivation of name: Breakfast Creek, around 18°20'S, 137°00'E,
a tributary to Buddycurrawa Creek in MOUNT DRUMMOND.
Synonymy: Previously mapped within (ie not differentiated from)
Benmara beds in First Edition MOUNT DRUMMOND by
Smith and Roberts (1963). Breakfast Sandstone also incorrectly
mapped in part as Constance Sandstone by same authors.
Parent unit: Benmara Group.
87
Distribution:
Northwestern
corner
of
MOUNT
DRUMMOND and southwestern corner of CALVERT
HILLS, in Canyon Range (name newly approved by
Committee for Geographic Names in Australasia).
Type section: Strike ridge along small hill at 18°9'S,
136°55'E in headwaters of Whiterock Creek (name
newly approved by Committee for Geographic Names in
Australasia) in Canyon Range, MOUNT DRUMMOND.
Section extends from 703850mE 7992050mN (lower
boundary) to 703500mE 7991950mN (upper boundary). At
this section, 60 m of Breakfast Sandstone overlies Murphy
Metamorphics.
Reference area: Area 1: Strike ridge along crest of small hill
at 707300mE 8000700mN, in headwaters of Murphys Creek
in Canyon Range, MOUNT DRUMMOND. At this locality,
80 m of Breakfast Sandstone overlies Murphy Metamorphics.
Area 2: Narrow isolated strike ridge at 18°5'S, 136°56'E
(712400mE 8009850mN), along Pandanus Creek in northern
Canyon Range, MOUNT DRUMMOND. Outcrop adjacent
to Benmara–Wangalinji road and reasonably easy to access,
though not fully representative of formation. At this locality,
15 m of Breakfast Sandstone overlies Connelly Volcanics,
but base not exposed. It is apparently overlain by Bowgan
Sandstone of South Nicholson Group (also a reference
area).
Thickness: Up to 80 m.
Lithology: Resistant, banded strike ridge of white to
maroon or pink, medium- ± coarse-grained silicified
sublithic sandstone. Lower few metres contain abundant
quartz pebbles and lesser cobbles. Succession tends to fine
upwards, with small-scale (decimetre-wavelength) trough
cross-beds, planar bedding, symmetric ripples, desiccation
cracks and current lineation becoming increasingly
common. Otherwise, it is medium- to thickly bedded with
mudclasts, scattered quartz granules and small pebbles,
and white angular silicified mudstone (‘chert’) clasts up to
5 cm diameter. Unit also contains rare laminae or thin beds
of chertified mudstone and chertified carbonate with relict
domical stromatolites.
Depositional environment: Moderate- to high-energy braided
fluvial and/or shallow marine.
Geomorphic expression: Mildly to strongly resistant and
ridge forming with white banded phototones.
Relationships:
Unconformably
overlies
Murphy
Metamorphics and Connelly Volcanics. Base rarely exposed,
but at some localities, lower few metres contain abundant
vein quartz pebbles where it rests on extensively quartzveined Murphy Metamorphics. Conformably overlain by
Buddycurrawa Volcanics, boundary marked by transition
from relatively well sorted quartzose sandstone into poorly
sorted ferruginous sandstone and ironstone.
Age: Constrained only by underlying Cliffdale Volcanics
basement (>1845 Ma; Page et al 2000) and overlying South
Nicholson Group (maximum age 1500 Ma by correlation
with Roper Group; Jackson et al 1999, Abbott et al 2001).
Unable to date conformably overlying Buddycurrawa
Volcanics, which could potentially be in range 1725–
1580 Ma.
Correlatives: Uncertain.
Brumby Formation (new name)
Proposer: IP Sweet.
Derivation of name: Brumby Creek, a minor tributary of
South Nicholson Creek which drains north in area around
18°35'S, 137°37'E in MOUNT DRUMMOND.
Synonymy: Mapped as part of Bluff Range beds (now
superseded) by Smith and Roberts (1963) in First Edition
MOUNT DRUMMOND; subsequently mapped as upper
part of also superseded Musselbrook Formation (units L
Pmb2
and L
Pmb3 in Carrara Range region; Sweet 1984).
Parent unit: McNamara Group.
Distribution: Confined to Carrara Range and adjacent plains,
in southeastern MOUNT DRUMMOND.
Type section: Across strike ridges and valleys in central
Carrara Range, from 18°37'33"S, 137°31'36"E (766600mE
7938700mN; base) to 18°37'11"S, 137°31'50"E (767000mE
7939360mN; top).
Thickness: 350 m in type section, thickening to northwest
and west to up to 800 m.
Lithology: Heterogeneous unit includes laminated
and stromatolitic chert and possibly dolostone, chertclast conglomerate and breccia, sandstone and granule
conglomerate, siltstone and shale.
Depositional environment: Mainly shallow marine, ranging
from supratidal to subtidal; some non-marine intervals
(fluvial conglomerates and breccias); deeper-marine, lowenergy environments in upper part of formation.
Geomorphic expression: Low hills and plains adjacent to
main ridges of Carrara Range.
Relationships: Conformable on Drummond Formation,
contact at point where chert and fine siliciclastics become
dominant over sandstone. Upper contact, with Shady
Bore Quartzite, not exposed, but is sharp and probably
conformable. Both upper and lower contacts correspond to
marked topographic changes, which facilitates their mapping
from aerial photographs.
Age: Maximum age constrained by Top Rocky Rhyolite,
dated at 1725 ± 3 Ma (Page et al 2000). Younger limit
established by correlation with McNamara Group in Lawn
Hill region to east: eg, ages of 1658–1653 Ma for Paradise
Creek Formation (Page et al 2000), with which Brumby
Formation in part correlates (see below).
Correlatives: On lithostratigraphic and sequence stratigraphic
grounds, Brumby Formation is correlated with Paradise
Creek, Esperanza, and Lady Loretta formations in Lawn Hill
region, 100 km to east.
Comments: Poor exposure makes detailed analysis of internal
stratigraphy of formation very difficult.
Buddycurrawa Volcanics (new name)
Proposer: DJ Rawlings.
Derivation of name: Buddycurrawa Creek, around 18°10'S,
137°07'E, a tributary to Nicholson River in MOUNT
DRUMMOND.
Synonymy: Previously mapped within (ie not differentiated
from) Benmara beds on First Edition MOUNT DRUMMOND
88
units, although Bullrush Conglomerate is still included in
McNamara Group.
Parent unit: McNamara Group.
Distribution: Restricted to area known (geologically) as
Maloney Creek Inlier (Sweet 1985), in eastern MOUNT
DRUMMOND, in headwaters of South Nicholson River and
one of its tributaries, Moloney Creek.
Type section: From south to north, base at 18°25'53"S,
137°37'55"E (778030mE 7960060mN) in Moloney Creek,
past confluence with South Nicholson River to 18°26'27"S,
137°37'42"E (777630mE 7959010mN). Section accessible
via rough track from Wangalinji Outstation, a small
settlement 20 km west of type section.
Thickness: Maximum of 500 m in type section, to 50 m near
Bullrush Spring, 10 km west of type section.
Lithology: Polymict granule, pebble and cobble conglomerate
in units up to 20 m thick, alternating with cross-bedded
sandstone, minor silicified carbonate rocks and red-brown to
fawn, fine-grained lithic sandstone and siltstone. Carbonate
beds have been altered to chert, with relict stratiform,
domical, conical and digitate stromatolites, and parallel
lamination.
Depositional environment: Alluvial fan and fan delta,
depositing into background sedimentation representing
shallow-marine and peritidal carbonate flat.
Geomorphic expression: Series of ridges in type section,
narrowing to single small ridge to west.
Relationships: Overlies Drummond Formation and Top
Rocky Rhyolite unconformably; contact sharp and marked
by abrupt change to conglomerate. Overlain by Plain Creek
Formation, probably conformably.
Age: Maximum age constrained by Top Rocky Rhyolite,
dated at 1725 ± 3 Ma (Page et al 2000). Younger limit
established by correlation with McNamara Group in Lawn
Hill region to east: eg ages of 1647 ± 8 Ma and 1644 ± 8 Ma
for Riversleigh Siltstone (Page et al 2000), which overlies
Shady Bore Quartzite, the probable Bullrush Conglomerate
correlative (see below).
Correlatives: Probable equivalent of Shady Bore Quartzite
in Carrara Range to south, and in Lawn Hill region 100 km
to east.
Comments: This lithofacies is not present in McNamara Group
at any other locality. It is stratigraphic position of the Bullrush
Conglomerate, in roughly the middle of the McNamara Group
and at the transition from dominantly carbonate environments
below, to deeper-marine siliciclastic-dominated environments
above, which allows its correlation as described above.
by Smith and Roberts (1963). Also partly incorrectly mapped
as Constance Sandstone by same authors.
Parent unit: Benmara Group.
Distribution:
Northwestern
corner
of
MOUNT
DRUMMOND, in Canyon Range (newly approved by
Committee for Geographic Names in Australasia).
Type locality: Along small low-relief hill at 18°8'S, 136°55'E,
in headwaters of Whiterock Creek (newly approved by
Committee for Geographic Names in Australasia) in Canyon
Range, MOUNT DRUMMOND. Section extends from
703500mE 7991950mN (base) to approximately 702600mE
7992200mN (top).
Thickness: Up to estimated maximum 300 m, implied
from outcrop width and dip calculations. Basal ferruginous
sandstone 10–20 m thick.
Lithology: Interval of ferruginous sandstone (basal unit),
overlain by mixed succession of coherent trachyte, debrisflow sandstone and conglomerate, mature sandstone,
ferruginous siltstone/fine sandstone and minor but distinctive
stromatolitic chert horizon(s).
Geomorphic expression: Recessive to mildly resistant with
dark brown phototones.
Relationships: Rests conformably on Breakfast Sandstone;
boundary marked by transition from relatively well sorted
quartzose sandstone into poorly sorted ferruginous sandstone
and ironstone. Overlain by Bowgan Sandstone and, locally,
by Crow Formation of South Nicholson Group. This contact
poorly exposed and relationships speculative. Pinching out
of Benmara Group to north near 705000mE 8007000mN is
consistent with either unconformity or low-angle structural
boundary (detachment) at base of South Nicholson Group; a
slightly reactivated unconformity is favoured herein.
Age: Constrained only by underlying Murphy Metamorphics
and Connelly Volcanics basement (>1845 Ma; Page et al
2000) and probable overlying South Nicholson Group
(maximum age 1500 Ma, by correlation with Roper Group;
Jackson et al 1999, Abbott et al 2001). Attempts to date the
contained trachyte have been unsuccessful due to lack of
zircons and strong weathering. The obvious interpretation is
that Buddycurrawa Volcanics are same age as Carrara Range
Group and Peters Creek Volcanics (1725 Ma), as these also
contain abundant felsic volcanics and shallow intrusives.
However, age closer to 1660–1580 Ma can be implied from
compositional similarities with magmatic rocks in Coanjula
area.
Correlatives: Uncertain, but see discussion on age, above.
Bullrush Conglomerate (new name)
Burangoo Sandstone Member (new name)
Proposer: IP Sweet.
Derivation of name: Bullrush Spring, a small spring in
Little Cleanskin Creek, at 18°41'S, 137°53'E, MOUNT
DRUMMOND.
Synonymy: Previously mapped as Maloney Formation (South
Nicholson Group) in First Edition MOUNT DRUMMOND
by Smith and Roberts (1963), and as lower Musselbrook
Formation (McNamara Group) by Sweet (1985). Both
Maloney and Musselbrook formations are now obsolete
Proposer: IP Sweet.
Derivation of name: Burangoo, or Connellys Waterhole,
in Nicholson River, centred on 17°53'S, 138°15'E, in
WESTMORELAND, Queensland.
Synonymy: Previously undifferentiated from remainder of
Constance Sandstone in First Edition LAWN HILL (Carter
and Öpik 1959), WESTMORELAND (Carter 1959),
CALVERT HILLS (Roberts et al 1963) and MOUNT
89
Wangalinji Outstation in Nicholson Land Trust, MOUNT
DRUMMOND.
Synonymy: Previously mapped as Fickling beds in First
Edition MOUNT DRUMMOND by Smith and Roberts
(1963). This was subsequently revised to Fickling Group
(Sweet 1984).
Distribution: Bauhinia Dome in north-central MOUNT
DRUMMOND, centred on 755000mE 8000000mN, which
is drained by Norris and Little Pandanus creeks.
Type area: Recessive outcrop along Pandanus Creek
in western Bauhinia Dome around 18°6'S, 137°23'E in
MOUNT DRUMMOND. Best outcrops between 749500mE
7994400mN and 749000mE 799280mN.
Thickness: Up to 600 m.
Lithology: Dominated by yellow to red-brown, lithic,
micaceous, coarse- to very coarse-grained, pebble-bearing
sandstone and pebble to boulder conglomerate. These
are poorly sorted with very high lithic component and
dominantly metamorphic-felsic igneous provenance. They
form 0.5–8 m-thick benches/beds, generally lacking internal
stratification. Interbedded with coarse facies is minor fineto medium-grained lithic sandstone and micaceous siltstone
with small- to medium-scale trough cross-beds, planar
bedding, parting lineation and interference ripples. Also
interbedded (or forming allochthonous blocks) are sandy and
pebbly dolarenite, dolorudite, dololutite and dolomitic-lithic
sandstone. Top 100 m of unit comprises chertified dolostone
and yellow, fine- ± medium-grained, quartzose to sublithic,
silicified, micaceous sandstone with small trough crossbeds, planar bedding and parting lineation. Also present
are tabular beds up to 30 cm thick of red-brown to green
or yellow, micaceous siltstone, fine- to very fine-grained
lithic sandstone and shale. Bedding planar or lenticular with
common parallel lamination.
Depositional environment: Probably marine, possibly fandelta debris-flow and submarine talus.
Geomorphic expression: Recessive with dark, moderately
banded phototones.
Relationships: Basal relationship unknown, as underlying
rocks not exposed. Unconformably but concordantly overlain
by Constance Sandstone of South Nicholson Group.
Age: Maximum age constrained by lack of metamorphism
and deformation of Caulfield beds (therefore younger than
nearby >1845 Ma Cliffdale Volcanics basement; Page
et al 2000). Minimum age constrained by correlation of
overlying Constance Sandstone into Mesoproterozoic
Roper Superbasin, which is 1500–1400 Ma (Jackson et al
1999, Abbott et al 2001). Rocks above probable equivalent
of Constance Sandstone in Roper Group yield date of
1493 ± 4 Ma, suggesting that Caulfield beds are about, or
greater than 1500 Ma in age.
Correlatives: Tentatively correlated with Crow Formation
(South Nicholson Group) because it contains similar coarsegrained gravity-flow deposits in Benmara–Canyon Range
area. In addition, contact with overlying Constance Sandstone
(probable correlative of Mittiebah Sandstone, South Nicholson
Group) is essentially concordant, and may represent a relatively
minor hiatus. Correlation with Fickling and McNamara groups
appears less likely, because they only rarely contain similar
DRUMMOND (Smith and Roberts 1963). Distinguished
as L
Psc2 in Second Edition LAWN HILL (Hutton and Grimes
1983), WESTMORELAND (Grimes and Sweet 1979) and
CALVERT HILLS (Ahmad and Wygralak 1989), following
scheme of Sweet et al (1981), who designated undifferentiated
sandstones of Constance Sandstone L
Psc1, L
Psc2, L
Psc3 and L
Psc4
during mapping of Seigal and Hedleys Creek.
Parent units: Constance Sandstone, Accident Subgroup,
South Nicholson Group.
Distribution: Outcrops north of Elizabeth Creek in northern
LAWN HILL, south of Hedleys Creek in southwestern
WESTMORELAND, and in adjacent parts of southeastern
CALVERT HILLS and northeastern and central MOUNT
DRUMMOND.
Type section: Along northern side of Nicholson River,
from 17°53'46"S, 138°15'41"E (209700mE 8021700mN;
base) in westerly to west-southwesterly direction to
17°53'45"S, 138°14'19"E (207300mE 8019000mN; top), in
WESTMORELAND, Queensland. Section accessible from
Bowthorn station and a tourist track to Burangoo Waterhole.
Thickness: Estimated 320 m in type section, based on dip of
5°; 130-300 m in MOUNT DRUMMOND.
Lithology: Fine- to coarse-grained, lithic, sublithic and
quartzose sandstone, with scattered grains and layers of
quartz granules and pebbles up to 1 cm in diameter; strongly
trough cross-bedded in many outcrops; also planar crossbeds, planar bedding and hummocky cross-stratification.
Depositional environment: Mainly shallow marine, intertidal
to upper shoreface; possibly minor braided fluvial.
Geomorphic expression: In areas of low dip forms extensive
rocky plateaux, commonly with pseudokarstic weathering
surfaces; in rarer steeply dipping outcrops forms sharp ridges.
Relationships: Lower boundary, with Pandanus Siltstone
Member, sharp but apparently conformable; upper contact,
with Wallis Siltstone Member, similarly conformable.
In northern MOUNT DRUMMOND, Schultz Sandstone
Member truncates Wallis Siltstone Member to lie
disconformably on Burangoo Sandstone Member.
Age: Interpreted age range for whole South Nicholson Group
of 1500–1400 Ma based on correlation with Roper Group of
southern McArthur Basin (Dunn et al 1966), which together
comprise Roper Superbasin (Jackson et al 1999, Abbott and
Sweet 2000, Abbott et al 2001). Ages of 1492 ± 4 Ma and
1493 ± 4 Ma for tuffaceous material from Mainoru Formation
in lower Roper Group (Jackson et al 1999) provide the most
reliable estimate for age of that group, and hence, for South
Nicholson Group. Age of Burangoo Sandstone Member
judged to lie near middle of this age range.
Correlatives: None known, but likely that sandstone units in
middle Renner Group (Hussey et al 2001) and Roper Group
(Jackson et al 1999) are in part correlative, given overall
correlation between these groups.
Caulfield beds (new name)
Proposer: DJ Rawlings.
Derivation of name: Caulfield Clay Flats, around 18°20'S,
137°25'E, a group of perennial clay lakes 10 km north of
90
Synonymy: Encompasses about half of outcrop formerly
mapped as Mullera Formation by Smith and Roberts (1963)
in western half of First Edition MOUNT DRUMMOND. Also
incorporates narrow strip of moderately resistant outcrop at
southern edge of Mittiebah Range formerly mapped by Smith
and Roberts (1963) as Mittiebah Sandstone. This Mittiebah
Range outcrop, plus similar narrow strip of Crow Formation
along Canyon Range, are reassigned to constituent Tobacco
Member. Crow Formation also includes small anticlinal
outcrop area in Canyon Range (710000mE 7995000mN)
incorrectly mapped as Benmara beds by Smith and Roberts
(1963).
Parent units: Wild Cow Subgroup, South Nicholson Group.
Constituent units: Tobacco Member.
Distribution: Widespread in western half of MOUNT
DRUMMOND, and small part of adjoining southwestern
CALVERT HILLS.
Type section: North-striking valley of moderately resistant
outcrop at 18°5'S, 136°55'E, in headwaters of Murphys
Creek in Canyon Range, MOUNT DRUMMOND. Section
extends from 705200mE 8000000mN (lower boundary) to
702000mE 8000600mN (upper boundary). In this area, Crow
Formation conformably overlies Bowgan Sandstone and
is, in turn, conformably overlain by Mittiebah Sandstone.
Tobacco Member not differentiated at this locality, so the
type section includes correlative section of Tobacco Member,
designated as reference section.
Reference areas: Area 1: Recessive outcrop at 18°39'S,
137°6'E (721500mE 7937800mN) along small creek that
feeds into Mitchiebo Waterhole, MOUNT DRUMMOND.
Outcrop adjacent to Mittiebah–Wangalinji road and
reasonably easy to access, although it only covers small
portion of succession and is not fully representative of
the formation. In this area, Crow Formation conformably
overlies Playford Sandstone and is, in turn, unconformably
overlain by Constance Sandstone. Area 2: Narrow strike
ridge at 18°30'S, 137°7'E (724000mE 7952100mN), 15 km
north of Mitchiebo Waterhole in MOUNT DRUMMOND,
containing unnamed sandstone unit L
Psos.
Thickness: Up to 2500 m. This is a gross estimate, because
exposures are poor and measurable dips rare. There are also
structural complications.
Lithology: Interbedded siltstone, sandstone, shale and lesser
conglomerate, which can be divided into several facies.
Shelf facies present throughout outcrop belt and comprises
shaly to flaggy, white, clayey micaceous siltstone and fineto medium-grained quartzose to sublithic (± micaceous)
sandstone, red-brown to grey shale and leached, chalky white
or maroon, mottled porcelainous claystone. Shale interpreted
to have a carbonaceous and/or pyritic component, based on
presence of mottled ferruginous and saprolitic weathering
products, but this has not been demonstrated in outcrop or by
drilling. Bedding ranges from massive to parallel laminated
to ‘tempestite’ textured, including wavy and lenticular
bedding, hummocky cross-stratification, flute moulds, tool
marks and current lineation. Debris-flow and sandstone
turbidite facies recognised particularly in Canyon Range
area and composed of mottled white to brown, poorly sorted,
feldspathic, micaceous, ferruginous and lithic, medium- to
very coarse-grained sandstone, pebbly sandstone and lesser
lithofacies. However, middle to upper McNamara Group
in Maloney Creek Inlier includes mixed coarse-grained
siliciclastic and carbonate facies (Sweet 1985), and correlation
with this part of McNamara Group cannot be ruled out.
Comments: Age, relationships and absolute stratigraphic
position difficult to constrain, thus necessitating status of
‘beds’.
Connelly Volcanics (new name)
Proposer: DJ Rawlings.
Derivation of name: Connellys Waterhole, on Buddycurrawa
Creek, near 18°07'S, 137°08'E, a tributary to Nicholson
River in MOUNT DRUMMOND and CALVERT HILLS.
Synonymy: Previously mapped within (ie not differentiated
from) Murphy Metamorphics in First Edition MOUNT
DRUMMOND (Smith and Roberts 1963) and CALVERT
HILLS (Roberts et al 1963).
Distribution: Exposed in small area of Canyon Range
(newly approved by Committee for Geographic Names in
Australasia) near 18°S, 136°58'E at boundary of northern
MOUNT DRUMMOND and southern CALVERT HILLS.
Type area: Low discontinuous exposures in vicinity of 18°S,
136°58'E (710000mE 8007000mN).
Thickness: Unknown.
Lithology: Red-brown, ‘brick’-coloured, altered/weathered
porphyritic rhyolite or rhyodacite, which generally has mottled
and highly weathered appearance herein termed ‘redrock’.
Geomorphic expression: Recessive with white or dark redbrown phototones.
Relationships: Field relationships cannot demonstrate an
extrusive origin for Connelly Volcanics and there are no
preserved microscopic textures indicative of pyroclastic or
lava mode of emplacement. Boundary between Murphy
Metamorphics and Connelly Volcanics very poorly exposed,
best locality being 707400mE 8009250mN, where there is
juxtaposition of ‘redrock’ (Connelly Volcanics) and grey
psammitic schist (Murphy Metamorphics). In contact zone,
‘redrock’ becomes progressively more foliated westwards over
a few tens of metres and grades into schist. Connelly Volcanics
unconformably overlain by various units, including Breakfast
Sandstone (Benmara Group), and Bowgan Sandstone and
Crow Formation (South Nicholson Group).
Age: Constrained only by underlying Murphy Metamorphics
[minimum age 1870 Ma (age of Barramundi Orogeny);
Page and Williams 1988] and overlying South Nicholson
Group (maximum age 1500 Ma, by correlation with Roper
Group; Jackson et al 1999, Abbott et al 2001). Most likely
to be 1845–1860 Ma, based on correlation with Cliffdale
Volcanics (dated by Page et al 2000).
Correlatives: Probably Cliffdale Volcanics in CALVERT
HILLS (Ahmad and Wygralak 1989).
Crow Formation (new name)
Proposer: DJ Rawlings.
Derivation of name: Crow Creek, western MOUNT
DRUMMOND, near 18°27'S, 136°50'E.
91
Constituent units: Four informal units recognised in type
Pmd4.
area, from oldest to youngest L
Pmd1 to L
Distribution: Carrara Range, in southeastern MOUNT
DRUMMOND, and to north around Soak Creek and
headwaters of South Nicholson Creek.
Type section: Across series of strike ridges in northwestern
Carrara Range, from south to north: base at 18°37.3'S,
137°28.0'E (760262mE 7939244mN); top at 18°36.8'S,
137°28.0'E (760275mE 7940166mN).
Thickness: 460 m in type section. Thickens to 600 m to west
and thins to 300 m to east in central Carrara Range. Minimum
400 m thick, 20 km north of type section, in Maloney Creek
Inlier. Thickness ranges: L
Pmd1 = 100 m; L
Pmd2 = 50–200 m;
L
Pmd3 = 100–150 m; L
Pmd4 = 40–200 m.
Lithology: Four readily mapped units, from base to top L
Pmd1
to L
Pmd4.
L
Pmd1: Thin polymict conglomerate overlain by thin- to
medium-bedded, fine-grained lithic sandstone, laminated
siltstone, redbeds of brown lithic dolomitic sandstone and
chertified dolostone; cauliflower chert; dark grey mediumbedded pyritic coarse sandstone.
L
Pmd2: White to brown, medium- to thick-bedded, fine to
medium, sublithic to quartzose sandstone; minor grey chert.
L
Pmd3: Laminated kaolinised and chertified claystone (altered
carbonate?), fine ferruginous sandstone, siltstone and
stromatolitic chert; fine, sublithic siltstone and sandstone.
L
Pmd4: White, medium- to thick-bedded, fine to medium,
sublithic to quartzose sandstone, with scattered coarse
laminae and granules.
Depositional environment: Shallow marine and fluvial;
redbeds and carbonate rocks may represent sabkha
environments.
Geomorphic expression: Forms many of higher ridges and
intervening valleys throughout Carrara Range; low hills in
northern outcrops.
Relationships: Sharp lower contact, marked in places
by conglomerate and angular discordance, and therefore
unconformable on Surprise Creek Formation. Gradational
conformable contact with overlying Brumby Formation.
Overlain unconformably by Bullrush Conglomerate in
Maloney Creek Inlier.
Age: Maximum age constrained by Top Rocky Rhyolite, dated
at 1725 ± 3 Ma (Page et al 2000). Younger limit established by
correlation with McNamara Group in LAWN HILL to east, eg
ages of 1658–1653 Ma for Paradise Creek Formation (Page et al
2000). Drummond Formation is likely very close to this age.
Correlatives: Equates to upper Gunpowder Creek and lower
Paradise Creek formations in Lawn Hill region, ie Gun
Supersequence.
Comments: Although the informal units are recognisable in
many exposures, their thinness, faulting and variable quality
of outcrop preclude their formal recognition.
matrix-supported polymict conglomerate. These constitute
decimetre-scale beds that are massive or crudely parallel
or cross-laminated, graded, with typical turbidite features.
Shallow-water sandstone occurs as discrete localised units
within Crow Formation, one of which is mapped informally
(L
Psos); it entails a number of different but overlapping
lithofacies, most commonly white to maroon, fine- to very
coarse-grained, quartzose to lithic sandstone with locally
abundant rounded pebbles and localised, poorly sorted,
pebble-cobble polymict conglomerate. Sandstone locally
ferruginous, micaceous and glauconitic. Bedding medium
to very thick, with planar and trough cross-beds of various
dimensions, planar bedding, current lineations, mudclasts,
synaeresis cracks and hummocky cross-stratification.
Geomorphic expression: Recessive with variably white to
dark phototones.
Relationships: Conformable on Bowgan Sandstone in Canyon
Range area, on northwestern side of Benmara Fault; base
poorly exposed and locally covered by saprolite. Locally,
Bowgan Sandstone is absent and Crow Formation rests
directly on Benmara Group and Murphy Metamorphics (eg
around 705000mE 8008000mN). Conformable on Playford
Sandstone south and east of Benmara Fault. In Canyon and
Mittiebah Ranges, conformably or disconformably overlain
by Mittiebah Sandstone. Elsewhere, disconformably or
unconformably overlain by Constance Sandstone. Crow
Formation pinches out immediately west of Mitchiebo
Waterhole and along strike to east near No Mans Creek
(755000mE 7944000mN), due to erosion, depositional
onlap and/or faulting.
Age: Radiometric dating currently unavailable for any part
of South Nicholson Group and age therefore internally
unconstrained. Maximum age of 1595 ± 6 Ma is that of Lawn
Hill Formation at top of underlying McNamara Group (Page
and Sweet 1998). No minimum age constraints imposed
by overlying units, apart from late Neoproterozoic to
Phanerozoic Georgina Basin. Interpreted age range of Crow
Formation of 1500-1400 Ma based on correlation of South
Nicholson Group with Roper Group of southern McArthur
Basin, which together comprise Roper Superbasin (Jackson
et al 1999, Abbott and Sweet 2000, Abbott et al 2001).
Correlatives: Tentatively equivalent to part of Mainoru
Formation, Roper Group.
Drummond Formation (new name)
Proposer: IP Sweet.
Derivation of name: Mount Drummond, prominent hill at
southern margin of Carrara Range, at 18°42'S, 137°36'E
(MOUNT DRUMMOND).
Synonymy: Mapped as undifferentiated sandstone within
Carrara Range Formation and Bluff Range beds (both
superseded) by Smith and Roberts (1963) in First Edition
MOUNT DRUMMOND; incorrectly mapped as Constance
Sandstone in places in that map; subsequently mapped as
part of now superseded lower Musselbrook Formation (units
L
Pmb1b to L
Pmb1f in First Edition Carrara Range region;
Sweet 1984).
Parent unit: McNamara Group.
Gator Sandstone (new name)
Proposer: DJ Rawlings.
Derivation of name: Gator Waterhole, around 18°29'S,
137°32'E, a permanent waterhole in George Creek, MOUNT
DRUMMOND.
92
Synonymy: Previously mapped within (ie not differentiated
from) Carrara Range Formation in First Edition MOUNT
DRUMMOND (Smith and Roberts 1963). Subsequently
mapped by Sweet (1984) as upper sandstone part of
Mitchiebo Volcanics in Carrara Range region; identified
informally as L
Pcms on mapface.
Parent unit: Carrara Range Group.
Distribution: Carrara Range in southeastern MOUNT
DRUMMOND.
Type locality: Narrow parallel strike ridges at 18°42'S,
137°43'E, along northern edge of Little Range Fault in
headwaters of Boomerang Creek, MOUNT DRUMMOND.
Section extends from 786200mE 7930950mN (base) to
786300mE 7931200mN (top).
Thickness: 100–700 m, with gradual increase from east to
west.
Lithology: Silicified, pink to purple, fine- to very coarsegrained, quartzose to sublithic sandstone, with scattered
quartz granules and pebbles up to 2 cm in diameter and
minor local beds or laminae of mudstone intraclasts
and brown oxidised ?basalt clasts 0.1–1 cm in diameter.
Medium to very thickly bedded with planar bedding and
low-angle planar and trough cross-beds 10–80 cm thick.
Overall, succession tends to coarsen upwards. Locally,
contains thin recessive volcanic interval with loose float of
vesicular basalt and brown laminated lithic sandy mudstone
(?volcaniclastic sandstone). In reference area, marginally
different succession incorporates lower, white, resistant
sandstone subunit and upper, dark, moderately recessive,
ferruginous sandstone subunit. Lower sandstone subunit
comprises thickly bedded, white to pink, fine- to mediumgrained quartzose sandstone with trough cross-beds.
Upper subunit dominated by red-brown to pink, friable,
fine-grained, ferruginous lithic sandstone, with thin to
medium-bedding, trough cross-beds, symmetric ripples and
mudclasts. Middle 20 m of succession distinctly muddier
and more ferruginous than above and below, and contains
chocolate brown sandstone interbedded with micaceous
siltstone and mudstone. Mudstone intraclasts, desiccation
cracks and cross-lamination with a 10 cm wavelength are
prolific. Upper few dekametres of sandstone is pink and
notably more silicified than below.
Depositional environment: Moderate- to high-energy braided
fluvial and/or shallow marine.
Geomorphic expression: Strongly resistant and ridge forming
with white phototones.
Relationships: Conformable on Mitchiebo Volcanics;
unconformably overlain by Top Rocky Rhyolite. Locally
removed by erosion preceding Surprise Creek Formation.
Age: Constrained by underlying Murphy Inlier basement
(>1845 Ma; Page et al 2000) and overlying Top Rocky
Rhyolite (SHRIMP U-Pb zircon date of 1725 ± 3 Ma; Page
et al 2000).
Correlatives: Based on stratigraphic position and
lithology, Gator Sandstone is correlated with Sly Creek
Sandstone in southern McArthur Basin (Rawlings 1999),
which also contains a local basalt interval (Haines et al
1993).
Hedleys Sandstone Member (new name)
Proposer: IP Sweet.
Derivation of name: Hedleys Creek, an east-southeastflowing tributary of Nicholson River; confluence of
these watercourses at 18°52'30"S, 137°24'30"E in
WESTMORELAND, Queensland.
Synonymy: Not differentiated from remainder of Constance
Sandstone in First Edition LAWN HILL (Carter and Öpik
1959), WESTMORELAND (Carter 1959), CALVERT
HILLS (Roberts et al 1963) and MOUNT DRUMMOND
(Smith and Roberts 1963). Distinguished as L
Psc1 in
Second Edition LAWN HILL (Hutton and Grimes
1983), WESTMORELAND (Grimes and Sweet 1979)
and CALVERT HILLS (Ahmad and Wygralak 1989),
following scheme of Sweet et al (1981), who designated the
undifferentiated sandstones of Constance Sandstone L
Psc1,
L
Psc2, L
Psc3 and L
Psc4 in Seigal and Hedleys Creek.
Parent unit: Constance Sandstone, Accident Subgroup,
South Nicholson Group.
Distribution: Outcrops north of Elizabeth Creek in northern
LAWN Hill, south of Hedleys Creek in southwestern
WESTMORELAND, and in adjacent parts of southeastern
CALVERT HILLS and northeastern and central MOUNT
DRUMMOND.
Type locality: South of Wire Creek, in WESTMORELAND,
Queensland. Base at 17°50'04"S, 138°09'01"E (197822mE
8025670mN), top 1.2 km to southeast at 17°50'27"S,
138°09'38"E (198922mE 8024970mN).
Thickness: Around 90 m in type section, thinning westwards.
As thin as 1 m in western Seigal, and 10–50 m to south in
MOUNT DRUMMOND.
Lithology: In type section, unit is cross-bedded, friable,
medium- and coarse-grained quartz-rich sandstone with
scattered granule and pebble bands. Conglomeratic lenses
at base consist of well rounded pebbles and cobbles of
white quartz and quartzite, and subangular to subrounded
clasts of stromatolitic and oolitic chert, all set in matrix of
coarse-grained quartz sandstone (Sweet et al 1981: 19). In
MOUNT DRUMMOND, unit is subtly finer grained, and
lacks conglomerate interbeds.
Depositional environment: Shallow marine, mostly intertidal;
possibly minor fluvial component.
Geomorphic expression: Ranges from low narrow ridge
where unit is thin or steeply dipping, to broad rocky ridges
and plateaux where unit is thicker or gently dipping.
Relationships: Unconformable on Fickling Group in
type area. Disconformable on Doomadgee Formation
throughout Hedleys Creek, but to west, in Seigal, unit
progressively truncates older formations in Fickling Group
westwards (Sweet et al 1981). In MOUNT DRUMMOND,
unit disconformably overlies Caulfield beds in north and
Doomadgee Formation in northeast. Upper boundary,
with Pandanus Siltstone Member, sharp but apparently
conformable and placed at an abrupt upward change from
fine- or medium-grained quartz sandstone to laminated or
thinly interbedded shale, siltstone and fine-grained lithic
sandstone.
93
Age: Interpreted age range for whole South Nicholson
Group of 1500–1400 Ma based on correlation with Roper
Group of southern McArthur Basin (Dunn et al 1966),
which together comprise Roper Superbasin (Jackson et al
1999, Abbott and Sweet 2000, Abbott et al 2001). Ages
of 1492 ± 4 Ma and 1493 ± 4 Ma for tuffaceous material
from Mainoru Formation in lower Roper Group (Jackson
et al 1999) provide the most reliable estimate for age of
that group, and hence, for South Nicholson Group. Age of
Hedleys Sandstone Member judged to lie near middle of this
age range.
Correlatives: None known, but likely that sandstone units in
middle Renner Group (Hussey et al 2001) and Roper Group
(Jackson et al 1999) are in part correlative, given overall
correlation between these groups.
Comments: Hedleys Sandstone Member is that part of
Constance Sandstone lying beneath Pandanus Siltstone
Member, ie the basal sandstone unit within the formation. It
can only be recognised where Pandanus Siltstone Member
is also present, and thus, is mapped only north of Elizabeth
Creek Fault Zone.
maximum 156 m in cored drillhole AY06DD01 in ALROY,
beneath central Georgina Basin (Kruse in prep). Colless
Volcanics: probable minimum of 60 m (Carter 1959).
Type section: Type sections of constituent named units.
Antrim Plateau Volcanics: Spring Creek in DIXON RANGE,
Western Australia (Mory and Beere 1985); Helen Springs
Volcanics: 234.9–243.8 m depth (including basal Muckaty
Sandstone Member) in cored drillhole NTGS96/1 in
HELEN SPRINGS (Hussey et al 2001); Colless Volcanics:
at about 18˚38'55"S, 138˚18'30"E in western LAWN HILL,
Queensland (Carter 1959); Kinevans Sandstone: scarp 1 km
northeast of Kinevans yard, WATERLOO (Sweet et al
1974). None designated for Jarong Conglomerate or Jindare
Formation.
Lithology: Partly vesicular or amygdaloidal tholeiitic
basalt, dolerite and andesite; minor trachyte, microdolerite,
basaltic flow breccia, peperite, pyroclastic deposits, quartz
sandstone, siltstone, conglomerate, sedimentary breccia,
limestone, chert.
Geomorphic expression: Prominent plateaux to minimal.
Relationships: Within group, all volcanic units considered
coeval. Antrim Plateau Volcanics concordantly underlain
by Kinevans Sandstone north of Ord Basin and by Jarong
Conglomerate on southwestern margin of Daly Basin.
Jindare Formation overlies and interdigitates with Antrim
Plateau Volcanics on northern margin of Daly Basin.
Extrusive constituents unconformably overlie variety of
Palaeo- and Mesoproterozoic terranes. Youngest known
underlying units are Neoproterozoic and include Moonlight
Valley Tillite and Bukalara Sandstone. Moonlight Valley
Tillite is correlated with Marinoan glacial event (late
Cryogenian–early Ediacaran) in Adelaide Rift and underlies
Antrim Plateau Volcanics in AUVERGNE (Dunster et al
2000); possibly younger (late Neoproterozoic; Rawlings
et al 1997) Bukalara Sandstone underlies Antrim Plateau
Volcanics in HODGSON DOWNS. In general, group is
unconformably overlain by early Middle Cambrian (Ordian;
sequence 1 of Southgate and Shergold 1991) carbonate units:
Tarrara Formation of Bonaparte Basin, Headleys Limestone
of Ord Basin, Montejinni Limestone of Wiso Basin, Tindall
Limestone of Daly Basin, Top Springs Limestone of northern
Georgina Basin, Gum Ridge Formation of Barkly Sub-basin
(central Georgina Basin) and Thorntonia Limestone of
Undilla Sub-basin (central and eastern Georgina Basin). It
is also unconformably overlain by later Middle Cambrian
(early sequence 2) Wonarah Formation on AlexandriaWonarah Basement High (central Georgina Basin, Kruse
2003).
Depositional environment: Continental extrusive, high-level
intrusive; sedimentary constituents fluviatile to lacustrine or
shallow marine.
Age and evidence: Stratigraphic relationships constrain age
to Ediacaran–Early Cambrian. Among radiometric dates of
varying validity, a probable feeder dyke of Antrim Plateau
Volcanics in Western Australia has been dated by SHRIMP
U-Pb on zircon at 513 ± 12 Ma (late Early Cambrian) by
Hanley and Wingate (2000); Antrim Plateau Volcanics
in LIMBUNYA have been dated by Ar-Ar on plagioclase
separates at 504 ± 2 Ma by Glass and Phillips (2002);
and Helen Springs Volcanics in HELEN SPRINGS have
Kalkarindji Volcanic Group (new name)
Proposer: PD Kruse.
Derivation of name: Kalkarindji township (also known as
Wave Hill), located adjacent to Antrim Plateau Volcanics in
WAVE HILL.
Synonymy: None for group; coincides with geological
region termed Kalkarinji Continental Flood Basalt Province
by Glass (2002). Synonymy for constituent units: Antrim
Plateau Basalts (David 1932), Antrim Plateau Basalt
(McLeod 1965), Antrim Volcanics (Beattie and Brown
1984), Nutwood Downs Volcanics (Dunn 1963), Peaker
Piker Volcanics (Smith and Roberts 1963).
Constituent units: Antrim Plateau Volcanics (Traves 1955)
including Malley Spring Member and Mount Close Chert
Member (both Mory and Beere 1985), Bingy Bingy Basalt
Member and Blackfella Rockhole Member (both Sweet
et al 1974); Jarong Conglomerate (Pontifex and Mendum
1972); Kinevans Sandstone (Sweet et al 1974); Jindare
Formation (Needham and Stuart-Smith 1984); Helen
Springs Volcanics (Noakes and Traves 1954), including
Muckaty Sandstone Member (Kruse in Hussey et al 2001);
Colless Volcanics (Carter 1959); ‘Mount Ramsay dolerite’,
‘Boondawari dolerite/Dolerite’, ‘Milliwindi dolerite’ and
other geochemically similar Early Cambrian volcanic
bodies intruding Halls Creek and King Leopold orogens and
Kimberley Basin of Western Australia (Hanley and Wingate
2000, Glass 2002).
Distribution: Northern Western Australia (intruding Halls
Creek and King Leopold orogens and Kimberley Basin,
and rimming and underlying Ord and Bonaparte basins);
northern Northern Territory (rimming and underlying Ord,
Daly, northern Wiso and northern and central Georgina
basins); northwestern Queensland (rimming and underlying
northeastern Georgina Basin).
Thickness: Antrim Plateau Volcanics: maximum 1100 m
adjacent to Ord Basin in DIXON RANGE, northern Western
Australia (Mory and Beere 1988). Helen Springs Volcanics:
94
been dated by Ar-Ar method on plagioclase separates at
508 ± 2 Ma by Glass and Phillips (2002).
Correlatives: Mount Wright Volcanics and Cymbric Vale
Formation (both Gnalta Group) of Gnalta Shelf, western
New South Wales; Truro Volcanics of Stansbury Basin,
South Australia: all biostratigraphically dated as late Early
Cambrian (Botoman stage of Siberia; Jago et al 1984,
Jenkins and Hasenohr 1989, Gravestock 1995, Kruse and
Shi in Brock et al 2000). Possibly Mooracoochie Volcanics
(Gatehouse 1983), which are unconformable beneath Middle
Cambrian Kalladeina Formation of Warburton Basin, South
Australia. Possibly Table Hill Volcanics (Peers 1969),
together with their probable synonym Kulyong Volcanics
(Jackson and van de Graaff 1981, but see Walter et al 1995:
figure 2), although Major and Teluk (1967) and Stevens and
Apak (1999) have reported Early Ordovician ages for these
formations.
Comments: NTGS airborne magnetic data confirm that, in
addition to their mapped outcrop areas, Early Cambrian
volcanic rocks are extensive in the subsurface beneath
Palaeozoic sedimentary basins of the northern Northern
Territory. An extensive contiguous body flooring the Ord,
Daly, northern Wiso and northern Georgina basins and
abutting the western flank of the Tennant Region includes
rocks referred to Antrim Plateau Volcanics and Nutwood
Downs Volcanics (latter in HODGSON DOWNS), and
these two names are here synonymised as Antrim Plateau
Volcanics. A second contiguous body abutting the eastern
flank of the Tennant Region is extensive beneath the central
Georgina Basin. The names Helen Springs Volcanics and
Peaker Piker Volcanics have been applied to this body; these
are here synonymised as Helen Springs Volcanics. Colless
Volcanics is a further distinct body beneath the eastern
Georgina Basin in Queensland.
interbedded micaceous siltstone and shale; minor shale,
conglomerate and possible carbonate rocks.
Geomorphic expression: Strongly jointed plateaux (Bukalara
Sandstone); low hills and rubbly rises (Cox Formation).
Relationships: Unconformably overlies various units of
McArthur Basin, Murphy Inlier and South Nicholson Basin,
youngest being topmost units of Mesoproterozoic Roper
Group (McArthur Basin) and South Nicholson Group
(South Nicholson Basin). Unconformably overlain by Early
Cambrian Kalkarindji Volcanic Group, or where this is
absent, by Top Springs Limestone of Barkly Group (Kruse
and Radke 2008), or where these are absent, by Cretaceous
sandstone.
Depositional environment: High-energy braided fluviatile,
shallow (including storm-influenced) marine.
Age and evidence: Age stratigraphically constrained to
Ectasian–earliest Cambrian. Carbonaceous macrofossil
Chuaria in coeval Raiwalla Shale of Wessel Group,
Arafura Basin (Haines 1998) favours a Neoproterozoic
age (Rawlings et al 1997). Absence of glacial deposits in
Wessel Group, in conjunction with its undisturbed, flatlying attitude and stratigraphic position immediately below
fossiliferous Middle Cambrian rocks, suggests post-glacial
Neoproterozoic (Ediacaran) age for it and coeval Kiana
Group.
Correlatives: Buckingham Bay Sandstone and Raiwalla
Shale of Wessel Group (Arafura Basin).
Comments: This group unites all putatively Neoproterozoic
rocks along northern margins of Georgina and Dunmarra
basins.
No Mans Sandstone Member (new name)
Proposer: IP Sweet.
Derivation of name: No Mans Creek, which drains western
Carrara Range in southeastern MOUNT DRUMMOND.
Synonymy: Previously included in Constance Sandstone in
First Edition MOUNT DRUMMOND (Smith and Roberts
1963), and in Carrara Range region (Sweet 1984).
Parent units: Playford Sandstone, Wild Cow Subgroup,
South Nicholson Group.
Distribution: Forms west- to west-southwest-trending
outcrop belt in southeastern and central Mount
Drummond, from headwaters of Moloney Creek in east,
to 7 km southwest of Mitchiebo Waterhole in west.
Type section: Three kilometres east-southeast of Mitchiebo
Waterhole, continuing on from Top Lily Sandstone Member
type section. Base at 18°39'25"S, 137°7'33"E (724230mE
7935810mN), top 450 m to north at 18°39'10"S, 137°7'33"E
(724230mE 7936260mN).
Thickness: 130 m in type section, and up to 200 m to east.
Thins to north across Mitchiebo Fault, and only 50 m thick,
17 km to northwest in Playford Anticline; absent in outcrops
of Playford Sandstone further north and west.
Lithology: Very coarse-grained to granule and pebbly,
quartz-rich sandstone, and minor fine-grained sandstone
with coarse to pebbly lags. Strongly trough cross-bedded on
medium to large scale throughout.
Kiana Group (new name)
Proposers: PD Kruse, DJ Rawlings.
Derivation of name: Kiana property in northeastern
WALLHALLOW–northwestern CALVERT HILLS.
Synonymy: Robinson Beds (Noakes 1956).
Constituent units: Bukalara Sandstone, Cox Formation
(Dunn 1963).
Distribution: Along northern margin of Georgina and
Dunmarra basins in MOUNT DRUMMOND, CALVERT
HILLS,
ROBINSON
RIVER,
WALLHALLOW,
BAUHINIA DOWNS, MOUNT YOUNG, TANUMBIRINI
and HODGSON DOWNS.
Thickness: Maximum 300 m in Abner Range (BAUHINIA
DOWNS; Smith 1964).
Type section: Type sections of constituent named units.
Bukalara Sandstone: boundary stratotypes at 15˚50.5'S,
135˚12.9'E (base) and 15˚49.0'S, 135˚8.6'E (top) in
southeastern MOUNT YOUNG (Kruse in Pietsch et al
1992); Cox Formation: type locality surrounding 15˚55'S,
135˚01'E in southeastern MOUNT YOUNG (Haines et al
1993).
Lithology: Thinly to thickly bedded, very fine to very coarse
quartz sandstone, commonly feldspathic, some micaceous;
95
Depositional environment: Braided fluvial and possibly
shallow marine (intertidal).
Geomorphic expression: Forms single low rocky ridge or
narrow plateau up to 0.5 km wide.
Relationships: Lower contact, with Top Lily Sandstone
Member, sharp and probably erosive in type section, placed
at a change from fine-grained, pink lithic sandstone to
coarse-grained and granular to pebbly quartz sandstone.
Upper contact also abrupt; sandstone beds become thinner
upwards and are overlain by mudstone of Crow Formation.
Both contacts conformable.
Age: Maximum age of 1591 ± 10 Ma for Playford
Sandstone as a whole, based on reworked tuffaceous
material from underlying Lawn Hill Formation (Page et al
2000) in LAWN HILL, or 1595 ± 6 Ma, based on tuffs
in Lawn Hill Formation in same area (Page and Sweet
1998). Interpreted age range of 1500–1400 Ma for South
Nicholson Group based on correlation with Roper Group
of southern McArthur Basin (Dunn et al 1966, Plumb and
Derrick 1975). Ages of 1492 ± 4 Ma and 1493 ± 4 Ma
for tuffaceous material from Mainoru Formation in lower
Roper Group (Jackson et al 1999) provide the most reliable
estimate for age of that group, and hence, for Playford
Sandstone and its members.
Correlatives: None known, but likely that sandstones low
in Renner Group (Hussey et al 2001) and Roper Group
(Jackson et al 1999) are in part correlative, given overall
correlation between these groups.
Comments: Playford Sandstone and its members, including
No Mans Sandstone Member, have been recognised
and excluded from Constance Sandstone, as they lie
unconformably beneath Constance Sandstone as defined in
LAWN HILL to east.
Lithology: Cycles of shale or laminated siltstone, grading
up through laminated and thinly bedded, very fine-grained
lithic sandstone to thin to medium beds of very fine or
fine-grained sandstone. Rarely, medium- to coarse-grained
sandstone, some with mudstone intraclasts, present in upper
parts of cycles. Thin to thick graded sandstone and cobbleto boulder-bearing pebbly mudstone interbeds in northern
outcrops.
Depositional environment: Storm-dominated shelf, and
probable fan-delta facies in northern outcrops.
Geomorphic expression: Forms plains and undulating low
hills. Several sandstone interbeds form higher ridges in
some sections.
Relationships: Overlies Shady Bore Quartzite, apparently
conformably; boundary sharply gradational over a few
metres. Upper contact, with Lawn Hill Formation,
invariably concealed, but concordant and presumed to be
conformable.
Age: Palaeoproterozoic, late Statherian. Based on correlations
(see below), age is around 1640–1630 Ma.
Correlatives: Riversleigh Siltstone and Termite Range
Formation in Lawn Hill region, 100 km to east (Sweet
1984). These formations yield ages in range 1647 ± 8 Ma to
1630 ± 5 Ma (Page et al 2000).
Comments: This revised definition is necessary as the
basal sandstone, L
Pmas, mapped by Sweet (1984), has been
excluded from the formation and is now mapped separately
as Shady Bore Quartzite. Revised Plain Creek Formation
consists of those rocks above Shady Bore Quartzite, and
retains/maintains the essential character of the unit: a
predominantly fine-grained, siliciclastic formation.
Plain Creek Formation (revised definition)
Proposer: IP Sweet.
Derivation of name: Playford River, which drains
southwards from Mitchiebo Waterhole area in MOUNT
DRUMMOND.
Synonymy: Previously mapped as Constance Sandstone in
First Edition MOUNT DRUMMOND by Smith and Roberts
(1963). Most of it also mapped as Constance Sandstone by
Sweet (1984) in Carrara Range region, except for basal
part adjacent to Western Creek, which was included in
underlying Widdallion Sandstone Member of Lawn Hill
Formation, McNamara Group.
Parent units: Wild Cow Subgroup, South Nicholson Group.
Constituent units: Subdivided into three members in type
section: from oldest to youngest Wangalinji Member, Top
Lily Sandstone Member, and No Mans Sandstone Member.
The two older members can be traced through most outcrops,
but No Mans Sandstone Member recognised only in type
section and outcrops east of it.
Distribution: South-central and southwestern MOUNT
DRUMMOND, and one isolated outcrop in northwest in
headwaters of Benmara Creek.
Type section: Area 4 km southeast of Mitchiebo Waterhole,
MOUNT DRUMMOND, easily accessible from Mittiebah–
Wangalinji access road. Section runs from south to north:
Playford Sandstone (new name)
Proposer: IP Sweet, after Sweet (1982, 1984).
Derivation of name: Plain Creek, a minor creek which
drains north from Carrara Range in southeastern MOUNT
DRUMMOND.
Synonymy: Previously mapped as part of Bluff Range beds
in First Edition MOUNT DRUMMOND (Smith and Roberts
1963). Delineated and mapped as Plain Creek Formation in
Carrara Range region (Sweet 1984).
Parent unit: McNamara Group.
Distribution: Southeastern MOUNT DRUMMOND, in
Carrara Range, and 10 km to north, between South Nicholson
River and Cleanskin Creek.
Type section: Location unchanged from that nominated
by Sweet (1982), but base begins approximately 50 m
stratigraphically higher, at top of Shady Bore Quartzite. Base
now at 18°34.3'S, 137°32.1'E (767626mE 7944717mN),
whereas top remains at 18°33.9'S, 137° 32.0'E (767426mE
7945467mN).
Thickness: 550 m in type section; 400 m in Maloney Creek
Inlier, 16 km north of type section; 1000 m in Bluff Range,
although there is possibility of fault repetition in that
section.
96
base at 18°39'57"S, 137°7'38"E (724360mE 7934820mN);
top 1.4 km to north, at 18°39'10"S, 137°7'33"E (724230mE
7936260mN).
Thickness: From 390 m in type section, to at least 1450 m in
Playford Anticline, 13 km to northwest.
Lithology: Very coarse-grained to granule quartz-rich
sandstone at base, overlain by interbedded laminated shale
with thinly bedded siltstone and very fine-grained lithic
sandstone; coarse-grained quartz sandstone interbeds.
Thickly to very thickly bedded, large-scale cross-bedded,
very fine- to fine-grained, well sorted lithic sandstone, minor
ferruginous sandstone, ironstone and stromatolitic carbonate
rocks, and strongly trough-cross-bedded, fine- to coarsegrained quartz-rich sandstone with granule to pebble lags.
Depositional environment: Shallow-marine shelf, mainly
tide dominated and nearshore; minor deeper-water, stormdominated facies.
Geomorphic expression: Series of low sandstone ridges with
intervening valleys underlain by finer-grained components
of formation.
Relationships: Rests with angular unconformity on
Widdallion Sandstone Member of Lawn Hill Formation,
6.5 km southwest of Mitchiebo Waterhole (717310mE
7932906mN), and disconformably on same formation over
strike length of some 50 km to east of Mitchiebo Waterhole
outcrops. Contact placed at change from highly lithic,
dark-coloured sandstone below, to light-coloured, coarse
to granule-rich or pebbly, sublithic sandstone (Playford
Sandstone) above. Overlain conformably in virtually all
outcrops by Crow Formation; contact is rapid transition over
a few metres into fine-grained siliciclastic rocks.
Age: Maximum age of 1591 ± 10 Ma, based on reworked
tuffaceous material from underlying Lawn Hill Formation
(Page et al 2000) in LAWN HILL, or 1595 ± 6 Ma, based on
tuffs in Lawn Hill Formation in same area (Page and Sweet
1998). Interpreted age range of 1500–1400 Ma for South
Nicholson Group based on correlation with Roper Group
of southern McArthur Basin (Dunn et al 1966, Plumb and
Derrick 1975). Ages of 1492 ± 4 Ma and 1493 ± 4 Ma for
tuffaceous material from Mainoru Formation in lower Roper
Group (Jackson et al 1999) provide the most reliable estimate
for age of that group, and hence, for Playford Sandstone and
its members.
Correlatives: None known, but likely that sandstones low
in Renner Group (Hussey et al 2001) and Roper Group
(Jackson et al 1999) are in part correlative, given overall
correlation between these groups.
Comments: Basal formation of Wild Cow Subgroup, and of
South Nicholson Group as a whole.
DRUMMOND (Smith and Roberts 1963). Distinguished
Psc4 in Second Edition LAWN HILL (Hutton
as L
Psc3 and L
and Grimes 1983), WESTMORELAND (Grimes and Sweet
(1979) and CALVERT HILLS (Ahmad and Wygralak 1989),
following scheme of Sweet et al (1981), who designated
undifferentiated sandstones of Constance Sandstone L
Psc1,
L
Psc2, L
Psc3 and L
Psc4 in Seigal and Hedleys Creek. Bowthorn
Siltstone Member, identified as L
Psc3 by Sweet et al (1981), is
now obsolete, as it has been absorbed into Schultz Sandstone
Member.
Parent units: Constance Sandstone, Accident Subgroup,
South Nicholson Group.
Distribution: Outcrops north of Elizabeth Creek in northern
LAWN HILL, south of Hedleys Creek in southwestern
WESTMORELAND, and in adjacent parts of southeastern
CALVERT HILLS and northeastern and northern MOUNT
DRUMMOND.
Type section: South of Bowthorn homestead, in northwestern
LAWN HILL, Queensland. Base, accessed from station
track leading south from Accident Creek, at 18°9'7"S,
138°21'E (219620mE 7990970mN), thence 5.9 km to top of
a siltstone interbed at 18°8'39"S, 138°17'43"E (213820mE
7991770mN), then a further 9.9 km to top, at 18°9'55"S,
138°12'16"E (204230mE 7989270mN).
Reference section: Adjacent to, but southwest of Gorge
Creek, from 190600mE 8012800mN (base) to 190700mE
8012050mN (top), in southwestern WESTMORELAND.
Uppermost beds faulted out, but this locality features a
geographically compact section of most of member.
Thickness: 140–300 m in type section, depending on dip
assumed (actual dips in range 1–5°); at least 500 m in
reference section.
Lithology: Basal beds massive, yellow to white, subfriable
medium- to coarse-grained, well sorted quartz sandstone;
some granule layers present. Sandstone becomes medium
grained up-section. Very pure medium-grained quartz
sandstone with siliceous cement continues virtually to top of
formation. Cross-bedded throughout.
Depositional environment: Shallow marine: upper shoreface
to intertidal; may include braided fluvial.
Geomorphic expression: In areas of low dip, forms extensive
rocky plateaux, commonly with pseudokarstic weathering
surfaces; in rarer, more steeply dipping outcrops, forms
banded rocky ridge. Basal beds massive, and form bare
rocky platforms cut by deeply eroded joints.
Relationships: Lower boundary, with Wallis Siltstone
Member, sharp but apparently conformable. Upper contact,
with Mullera Formation, sharp but conformable. In northern
MOUNT DRUMMOND, unit truncates Wallis Siltstone
Member to rest disconformably, or with subtle angular
unconformity, on Burangoo Sandstone Member.
Age: Interpreted age range for whole South Nicholson Group
of 1500–1400 Ma based on correlation with Roper Group of
southern McArthur Basin (Dunn et al 1966), which together
comprise Roper Superbasin (Jackson et al 1999, Abbott and
Sweet 2000, Abbott et al 2001). Ages of 1492 ± 4 Ma and
1493 ± 4 Ma for tuffaceous material from Mainoru Formation
in lower Roper Group (Jackson et al 1999) provide the most
reliable estimate for age of that group, and hence, for South
Schultz Sandstone Member (new name)
Proposer: IP Sweet.
Derivation of name: Schultz Creek in WESTMORELAND,
Queensland.
Synonymy: Previously undifferentiated from remainder of
Constance Sandstone in First Edition LAWN HILL (Carter
and Öpik 1959), WESTMORELAND (Carter 1959),
CALVERT HILLS (Roberts et al 1963) and MOUNT
97
Nicholson Group. Age of Schultz Sandstone Member judged
to lie near middle of this age range.
Correlatives: None known, but likely that sandstones low
in Renner Group (Hussey et al 2001) and Roper Group
(Jackson et al 1999) are in part correlative, given overall
correlation between these groups.
Comments: Schultz Sandstone Member incorporates the
now obsolete Bowthorn Siltstone Member of Sweet (1981).
The obsolete member consisted of at least two thin lenses
within the newly defined (Schultz) member in its type area
and further north, in WESTMORELAND. Because these
‘siltstones’ include a substantial proportion of very finegrained sandstone and several coarser sandstone interbeds,
and because the new Schultz Sandstone Member consists
entirely of sandstone in most of its outcrops, the lithological
term ‘sandstone’ is incorporated into the name.
It extends from base of Constance Sandstone at 18°14'41"S,
138°23'28"E (224125mE 7980770mN), southwest for 1.7 km
to top of Constance Sandstone at 18°14'57"S, 138°22'37"E
(222623mE 7980270mN), thence west for 6.4 km to
youngest beds of Tidna Sandstone in centre of the syncline
at 18°14'57"S, 138°18'56"E (216123mE 7980170mN).
Thickness: Carter and Zimmerman (1960) quoted maximum
figure of 11 000 feet (3350 m) in LAWN HILL, and
this remains best estimate for thickness of the group in
east (Accident Subgroup only). In western MOUNT
DRUMMOND, where underlying Wild Cow Subgroup may
reach 4500 m in thickness and only component of Accident
Subgroup (Mittiebah Sandstone) is about 2000 m, total
is up to 6500 m. If an equivalent of Mullera Formation is
present stratigraphically above Mittiebah Sandstone but in
subsurface, as appears likely, total could be substantially
more. In central and southeastern MOUNT DRUMMOND,
the group is as little as 1000–1500 m thick.
Lithology: Wide range of siliciclastic rock types: very fineto coarse-grained, granule-rich and pebbly sandstones,
ranging from lithic to quartzose; most are sub-lithic. Most
sandstones trough cross-bedded. Very fine sandstones
associated with siltstone and shale intervals. Planar bedding,
current lineation and current and wave ripples common;
desiccation features rare. Highly ferruginous sandstone
and oolitic ironstone, including hematitic, chamositic and
sideritic varieties (Harms 1965), occur in upper part of
group, particularly in Queensland outcrops. Carbonate rocks
rare, known only in upper part of Playford Sandstone.
Depositional environment: Shallow-marine, intertidal or
storm-dominated shelf.
Geomorphic expression: Varies widely, from deeply incised
ridge and valley terrain in LAWN HILL to plains and very
low hills in central and southern MOUNT DRUMMOND.
Where incision sufficient, alternating sandstone and
mudstone units are highlighted; ridges and rocky plateaux
alternate with valleys or plains, reflecting alternating coarseand fine-grained rock units, respectively.
Relationships: Playford Sandstone rests disconformably,
or with angular unconformity on McNamara Group
in southeastern MOUNT DRUMMOND, whereas its
equivalent, Bowgan Sandstone, is unconformable on
Benmara Group in northwestern MOUNT DRUMMOND.
Where Wild Cow Subgroup is absent, Constance Sandstone
forms base of South Nicholson Group. Overlies McNamara
Group disconformably or with angular unconformity in
eastern MOUNT DRUMMOND and western LAWN HILL.
Youngest constituent of group in LAWN HILL (Tidna
Sandstone) is unconformably overlain only by Cretaceous
rocks. In MOUNT DRUMMOND, youngest observed rocks
are Mullera Formation, overlain unconformably by Late
Neoproterozoic or Cambrian rocks of Georgina Basin, or by
Cretaceous sedimentary rocks.
Age: Satisfactory radiometric dating currently unavailable
for any part of South Nicholson Group, and age therefore
internally unconstrained. A shale total-rock Rb–Sr date of
1510 ± 120 Ma for Mullera Formation (R Harding, BMR,
unpublished) is unreliable, as possibility of inclusion of
detrital material, principally micas, cannot be discounted
(Plumb and Derrick 1975). Page et al (2000) analysed zircons
South Nicholson Group (revised definition)
Proposer: IP Sweet, after Smith and Roberts (1963).
Derivation of name: South Nicholson River, which drains
northeastern quarter of MOUNT DRUMMOND, flowing
northwards into Nicholson River in southeastern CALVERT
HILLS.
Synonymy: None.
Constituent units: From base to top: Wild Cow Subgroup
and Accident Subgroup. Wild Cow Subgroup comprises
Playford Sandstone, including Wangalinji Member, Top
Lily Sandstone Member and No Mans Sandstone Member;
Bowgan Sandstone; and Crow Formation, including
Tobacco Member. Accident Subgroup comprises Constance
and Mittiebah sandstones (probable correlatives); Mullera
Formation; and Tidna Sandstone. Constance Sandstone
includes, from base to top, Hedleys Sandstone Member,
Pandanus Siltstone Member, Burangoo Sandstone Member,
Wallis Siltstone Member and Schultz Sandstone Member.
Mullera Formation includes Train Range Ironstone Member
and Middle Creek Sandstone Member.
Distribution: Widespread outcrops in MOUNT DRUMMOND
and adjacent sheet areas: southern CALVERT HILLS (Ahmad
and Wygralak 1989), WESTMORELAND (Grimes and Sweet
1979) and northwestern quarter of LAWN HILL (Hutton and
Grimes 1983, Slater and Mond 1980) in Queensland; minor
outcrops to west and south of MOUNT DRUMMOND, in
WALHALLOW, BRUNETTE DOWNS and RANKEN.
Outcrop and shallow subcrop cover 20 000 km2, and deeper
subcrop under Barkly Tableland covers potentially much
more.
Type section: As defined for each constituent formation.
Reference sections: Wild Cow Subgroup: incorporates type
section of Playford Sandstone, and a reference section of
Crow Formation around 18°39'S, 137°6'E from Mitchiebo
Waterhole at 721222mE 7937170mN (base), for 1.8 km
to northeast, to 722522mE 7938570mN (top), MOUNT
DRUMMOND.
Accident Subgroup: complete section in area of relatively
high dips, and therefore compact, located south of Elizabeth
Creek (LAWN HILL, Queensland), from Constance Range
escarpment in east, westwards for 8 km to core of a syncline.
98
from a basal feldspathic sandstone in Constance Sandstone
20 km south of Century deposit in LAWN HILL, and
concluded that the age, 1591 ± 10 Ma, represents reworked
tuffaceous material from underlying Lawn Hill Formation
and thus, provides maximum age for Constance Sandstone.
Similar maximum age of 1595 ± 6 Ma comes directly from
tuff in Lawn Hill Formation in same area (Page and Sweet
1998). No minimum age constraints imposed by overlying
units, apart from late Neoproterozoic to Cambrian units
of Georgina Basin. Interpreted age range for whole South
Nicholson Group of 1500–1400 Ma based on correlation with
Roper Group of southern McArthur Basin (Dunn et al 1966),
which together comprise Roper Superbasin (Jackson et al
1999, Abbott and Sweet 2000, Abbott et al 2001). Ages of
1492 ± 4 Ma and 1493 ± 4 Ma for tuffaceous material from
Mainoru Formation in lower Roper Group (Jackson et al
1999) provide the most reliable estimate for age of lower part
of that group, and hence, for South Nicholson Group.
Correlatives: Roper Group (Dunn et al 1966, Plumb
and Derrick 1975), based on overall lithological and
tectonostratigraphic similarity. Renner Group also likely to
be largely equivalent (Hussey et al 2001).
Comments: Although main constituent units of group,
Constance Sandstone and Mullera Formation, were named by
Carter et al (1961) from LAWN HILL, the group was named
by Smith and Roberts (1963) and Roberts et al (1963) on
the basis of extension of these units westward into MOUNT
DRUMMOND and CALVERT HILLS, respectively.
Revision of the definition became desirable following
Second Edition remapping of MOUNT DRUMMOND,
which led to recognition that much of group in western
MOUNT DRUMMOND is older than formations previously
recognised by Carter et al (1961) and Carter and Zimmerman
(1960) in LAWN HILL. Older part of group, previously all
included in Constance Sandstone, is now designated Wild
Cow Subgroup. Additionally, several unnamed units of
Constance Sandstone, recognised by Sweet et al (1981) in
eastern outcrop areas, ie in areas first mapped by Carter et al
(1961), have been formally defined and named as members.
7916800mN (base) to 688100mE 7916100mN (top). In this
area, Tobacco Member conformably overlies lower Crow
Formation and is, in turn, conformably overlain by Mittiebah
Sandstone. However, base is not exposed in type section,
so lower boundary stratotype proposed at eastern end of
Mittiebah Range at 18°14'29"S, 136°52'49"E (698000mE
7917350mN).
Thickness: 300–600 m.
Lithology: Dominant facies resistant (ridge-forming),
shallow-water sandstone, with lesser recessive storm shelf
facies. In type section, shallow-water sandstone facies
comprises interbedded: (i) medium- to very thickly bedded,
diffusely bedded, quartzose to lithic, locally ferruginous and
micaceous (± glauconitic) fine ± medium-grained sandstone
with amalgamated low-angle trough and hummocky crossstratification; (ii) medium- to coarse-grained glauconitic
sandstone, containing small red-brown mudstone flakes,
pits after evaporites and trough cross-beds and; (iii) minor
decimetre-scale beds of very coarse to granular, pebbly
lithic sandstone with parallel lamination. Storm-shelf facies
composed of flaggy white, fawn, red-brown or purple,
micaceous siltstone and fine- to medium-grained quartzose
to sublithic (± micaceous) sandstone. Sedimentary structures
include wavy and lenticular bedding, hummocky crossstratification, symmetric ripples, mudclasts, flute moulds,
tool marks, current lineations, runzel marks, load casts and
convolute bedding.
Geomorphic expression: Moderately resistant with well
developed, banded white and dark brown phototones.
Relationships: Lies conformably on lower Crow Formation
and is, in turn, conformably overlain by Mittiebah Sandstone.
Member not differentiated in areas where Crow Formation
is overlain by Constance Sandstone.
Age: Maximum age of 1591 ± 10 Ma, based on reworked
tuffaceous material from underlying Lawn Hill Formation
(Page et al 2000) in LAWN HILL, or 1595 ± 6 Ma based on
tuffs in Lawn Hill Formation in same area (Page and Sweet
1998). Interpreted age range of 1500-1400 Ma for South
Nicholson Group based on correlation with Roper Group
of southern McArthur Basin (Dunn et al 1966; Plumb and
Derrick 1975). Ages of 1492 ± 4 Ma and 1493 ± 4 Ma for
tuffaceous material from Mainoru Formation in lower Roper
Group (Jackson et al 1999) provide the most reliable estimate
for age of that group, and hence, for Crow Formation,
including Tobacco Member.
Tobacco Member (new name)
Proposer: DJ Rawlings.
Derivation of name: Tobacco Waterhole along Playford
River at eastern end of Mittiebah Range, southern MOUNT
DRUMMOND, near 18°53'S, 137°5'E.
Synonymy: Encompasses narrow strip of moderately
resistant outcrop at northern edge of Mittiebah Range that
was formerly mapped as Mittiebah Sandstone by Smith and
Roberts (1963) in First Edition MOUNT DRUMMOND.
Also incorporates similar narrow strip of moderately resistant
outcrop along Canyon Range that was formerly mapped as
Mullera Formation.
Parent units: Crow Formation, Wild Cow Subgroup, South
Nicholson Group.
Distribution: Canyon Range and Mittiebah Range in
northwestern and southwestern MOUNT DRUMMOND,
respectively.
Type section: Central Mittiebah Range at 18°50'S, 136°47'E
in MOUNT DRUMMOND. Section extends from 687300mE
Top Lily Sandstone Member (new name)
Proposer: DJ Rawlings.
Derivation of name: Top Lily Waterhole, in Fish Hole Creek
at 18°26'S, 136°53'E, MOUNT DRUMMOND.
Synonymy: Previously mapped as Constance Sandstone in
First Edition MOUNT DRUMMOND (Smith and Roberts
1963) and in Carrara Range region (Sweet 1984).
Parent unit: Playford Sandstone.
Distribution: Forms west- to west-southwest-trending
outcrop belt in central to southwestern MOUNT
DRUMMOND, from headwaters of Moloney Creek in east,
to Waterfall Creek in southwest. Outcrops most extensively
99
in ranges forming watershed of Eight Mile, Ten Mile and
Waterfall creeks. An isolated outcrop occurs in northwest,
east of headwaters of Benmara Creek.
Type section: Upper part of Playford Sandstone type
section, 4 km southeast of Mitchiebo Waterhole, MOUNT
DRUMMOND. Section extends from south to north: base
at 18°39'39"S, 137°7'29"E (724130mE 7935360mN), top
about 500 m to north, at 18°39'25"S, 137°7'33"E (724230mE
7935810mN). Section easily accessed from Mittiebah
homestead–Wangalinji track.
Thickness: 143 m in type section, 750 m in Playford Anticline
17 km to west-northwest, and 1100 m in westernmost
outcrops of Ten Mile Anticline.
Lithology: White to pink or darker pink-red, thickly to very
thickly bedded, very fine- to fine-grained, well sorted lithic
sandstone; scattered granules and pebbles; trough crossbedded on large to giant scale; current ripples and primary
current lineations common.
Geomorphic expression: Series of low ridges and plateaux.
Relationships: Lower contact conformable and gradational
with Wangalinji Member and placed where shale and
siltstone give way to pink, fine-grained lithic sandstone
over 10–15 m. Upper contact, with No Mans Sandstone
Member, sharp and locally erosive in type section, but
essentially conformable. In outcrops other than type section
and environs, No Mans Sandstone Member is absent,
and Top Lily Sandstone Member is overlain, apparently
conformably, by Crow Formation. Boundary placed at
an abrupt transition from fine-grained lithic and quartz
sandstone into shale.
Age: Maximum age of 1591 ± 10 Ma, based on reworked
tuffaceous material from underlying Lawn Hill Formation
(Page et al 2000) in LAWN HILL, or 1595 ± 6 Ma based on
tuffs in Lawn Hill Formation in same area (Page and Sweet
1998). Interpreted age range of 1500–1400 Ma for South
Nicholson Group based on correlation with Roper Group
of southern McArthur Basin (Dunn et al 1966; Plumb and
Derrick 1975). Ages of 1492 ± 4 Ma and 1493 ± 4 Ma for
tuffaceous material from Mainoru Formation in lower Roper
Group (Jackson et al 1999) provide the most reliable estimate
for age of that group, and hence, for Playford Sandstone and
its members.
Correlatives: None known, but likely that sandstones low
in Renner Group (Hussey et al 2001) and Roper Group
(Jackson et al 1999) are in part correlative, given overall
correlation between these groups.
Comments: Middle of three members comprising Playford
Sandstone in its type section.
Wangalinji Member (new name)
Proposer: DJ Rawlings.
Derivation of name: Wangalinji Outstation, an Aboriginal
settlement in Waanyi/Garawa (Nicholson River) Land Trust,
at 18°23'41", 137°28'04", MOUNT DRUMMOND.
Synonymy: Previously mapped as Constance Sandstone in
First Edition MOUNT DRUMMOND (Smith and Roberts
1963) and in Carrara Range region (Sweet 1984). Some
outcrops included in Lawn Hill Formation by Sweet (1984).
Parent unit: Playford Sandstone.
Distribution: Forms west- to west-southwest-trending outcrop
belt in central to southwestern MOUNT DRUMMOND,
from headwaters of Moloney Creek in east, to Waterfall
Creek in southwest. An isolated outcrop occurs in northwest,
east of headwaters of Benmara Creek.
Type section: 4 km southeast of Mitchiebo Waterhole,
MOUNT DRUMMOND. Section extends from south
to north: base at 18°39'57"S, 137°7'38"E (724360mE
7934820mN); top about 300 m to north, at 18°39'34"S,
137°7'34"E (724130mE 7935360mN).
Thickness: 390 m in type section, 750 m in Playford Anticline
11 km to northwest.
Lithology: Basal white, thickly bedded, medium- to coarsegrained cross-bedded sandstone, with current ripples and
primary current lineations, scattered mudstone intraclasts,
and granule and pebbly layers; clasts mainly of quartz.
Remainder of formation laminated shale with thinly bedded
siltstone and very fine-grained lithic sandstone interbeds,
interbedded with medium to thick beds of white, crossbedded, sublithic, medium- to coarse-grained sandstone;
minor purple-red mudstone with discontinuous disrupted
laminae, ubiquitous mudflakes and desiccation cracks, and
rare stromatolitic chert and carbonate rocks.
Geomorphic expression: Low ridge or rubble-strewn rise
corresponding to basal sandstone and an adjacent valley or
undulating terrain corresponding to upper, finer-grained part.
Relationships: Overlies Widdallion Sandstone Member of
Lawn Hill Formation disconformably in outcrops between
Mitchiebo Waterhole and Western Creek, a distance
of about 50 km. Southwest of Mitchiebo Waterhole,
an angular unconformity exists between the two units.
Boundary marked by abrupt change from purple-brown,
highly micaceous and lithic sandstones of Widdallion
Sandstone Member to lighter coloured (white, light brown
or pink), more quartz-rich granule to pebbly sandstone
of Wangalinji Member. Upper boundary, with Top Lily
Sandstone Member, conformable, marked by rapid
transition from interbedded siltstone and shale to thickly
bedded, pink to brown, fine-grained lithic sandstone of Top
Lily Sandstone Member.
Age: Maximum age of 1591 ± 10 Ma, based on reworked
tuffaceous material from underlying Lawn Hill Formation
(Page et al 2000) in LAWN HILL, or 1595 ± 6 Ma based on
tuffs in Lawn Hill Formation in same area (Page and Sweet
1998). Interpreted age range of 1500–1400 Ma for South
Nicholson Group based on correlation with Roper Group
of southern McArthur Basin (Dunn et al 1966, Plumb and
Derrick 1975). Ages of 1492 ± 4 Ma and 1493 ± 4 Ma for
tuffaceous material from Mainoru Formation in lower Roper
Group (Jackson et al 1999) provide the most reliable estimate
for age of that group, and hence, for Playford Sandstone and
its members.
Correlatives: None known, but likely that sandstones low
in Renner Group (Hussey et al 2001) and Roper Group
(Jackson et al 1999) are in part correlative, given overall
correlation between these groups.
Comments: The concordant nature of the contact led Sweet
(1984) to include the member in the underlying Widdallion
100
Relationships:
Unconformably
overlies
Murphy
Metamorphics, and McNamara and Benmara groups. Contact
with Benmara Group poorly exposed and relationship
cannot be resolved with any certainty, but partly reactivated
unconformity favoured. Disconformably overlain by
Accident Subgroup, except in west, where contact with
Mittiebah Sandstone may be conformable. Locally,
unconformably overlain by Georgina Basin succession.
Age: Meaningful radiometric dating currently unavailable
for any part of South Nicholson Group and its age therefore
internally unconstrained. Maximum age of 1595 ± 6 Ma
is that of Lawn Hill Formation at top of immediately
underlying McNamara Group (Page and Sweet 1998). No
minimum age constraints imposed by overlying units, apart
from late Neoproterozoic to Phanerozoic Georgina Basin.
Interpreted age range of whole South Nicholson Group, and
by default for Wild Cow Subgroup, of 1500-1400 Ma, based
on correlation of South Nicholson Group with Roper Group
of southern McArthur Basin. These two groups, combined,
comprise Roper Superbasin (Jackson et al 1999, Abbott et al
2001).
Correlatives: Lower Roper and Renner groups and possibly
Caulfield beds.
Comments: This package of rocks has been accorded
subgroup status because a disconformity, locally an angular
unconformity, has been recognised within the South
Nicholson Group. The Wild Cow Subgroup constitutes all
of the South Nicholson Group below that unconformity. The
upper South Nicholson Group (Accident Creek Subgroup)
also has distinctly different facies patterns and depocentres
from the Wild Cow Subgroup.
Sandstone Member in eastern outcrops, adjacent to Western
Creek.
Wild Cow Subgroup (new name)
Proposer: DJ Rawlings.
Derivation of name: Wild Cow Creek (18°38'S, 137°25'E),
which drains southward from western Carrara Range in
MOUNT DRUMMOND.
Synonymy: Parts of Constance Sandstone and Mullera
Formation as mapped by Smith and Roberts (1963), and
subsequently by Sweet (1984). These two formations
substantially revised in Second Edition MOUNT
DRUMMOND.
Parent/constituent units: Lower of two subgroups forming
South Nicholson Group. Includes Playford and Bowgan
sandstones, and overlying Crow Formation.
Distribution: Western half of MOUNT DRUMMOND.
Type locality: As defined for each constituent formation.
Reference section provides convenient location for overview
of subgroup.
Reference section: Composite section from south to north in
Mitchiebo Waterhole area, around 18°39'S, 137°6'E: from
Mitchiebo Waterhole, at 721222mE 7937170mN (base),
thence 1.8 km to northeast to 722522mE 7938570mN (top);
this includes Playford Sandstone type section and separate
segment covering Crow Formation and is convenient
representation of subgroup.
Thickness: Up to 4500 m in western MOUNT
DRUMMOND.
Lithology: Mixed succession of sandstone, siltstone, shale
and minor conglomerate and rare carbonate rocks.
Geomorphic expression: Resistant ridge-forming basal
part (sandstone-dominated units) and recessive upper part
(siltstone and shale-dominated unit).
Appendix 2 – Whole-rock geochemistry
Appendix 3 – Stream sediment
geochemistry
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