11 International Conference and Meeting on Geology, Institute of

Comments

Transcription

11 International Conference and Meeting on Geology, Institute of
11th International Conference and Meeting on Geology, Institute of
Geosciences, University of Campinas, Brazil, 2016
11th International Conference and Meeting on Geology,
Institute of Geosciences, University of Campinas, Brazil, 2016
Proceeding Book
GEOCHEMISTRY OF MAMUNIYAT FORMATION, IDRI AREA, SW LIBYA
O.R. Shaltami1, F.F. Fares1 and I. Bustany2
1
2
Department of Earth Science, Faculty of Science, Benghazi University, Libya
Department of Geology, Faculty of Science, Federal University of Rio de Janeiro, Brazil
ABSTRACT
The geochemistry of the Mamuniyat Formation from the Upper Ordovician Gargaf group will be discussed about
the provenance, paleo-oxygenation condition and tectonic setting. The studied sandstones are mainly classified as
sublitharenites and quartz arenites. The negative correlation of SiO2 with most major oxides is due to most of the silica
being sequestered in quartz. Pb and Hg are basically controlled by the carbonate fraction, while Rb, Sr, Ni, Co, Cu and Zn
are contained in alumino-silicates. The prevailing well oxidizing environments are well expresses by the low Cu/Zn, V/Cr,
Ni/Co and U/Th ratios. The PAAS-normalized REE patterns and (La/Sm)N vs. (La/Yb)N bivariate plot indicate that the
lower and middle parts of the studied formation of marine origin, while the upper part of fluvial origin. La/Sc, Th/Sc,
Cr/Th and Th/Co ratios suggest that felsic rocks must be the probable source rocks for the sediments of the Mamuniyat
Formation. The ternary plots of La-Th-Sc show that the data fall between the field of granite and granitoids. The tectonic
discrimination diagram shows that the Mamuniyat Formation is classified between active continental margin and passive
margin. The K2O/Na2O and TiO2/Zr ratios indicate that the Mamuniyat Formation is typically mature sediments.
Keywords: Geochemistry, Sandstone, Mamuniyat Formation, Depositional Environment, Paleo-oxygenation, Provenance, Idri, Libya.
INTRODUCTION
having a variable grain size. The Mamuniyat Formation
The present paper describes the geochemistry of
overlies the Melaz Shuqran Formation disconformably.
Ordovician sandstones from the Mamuniyat Formation,
The upper boundary is disconformable with the Tanzuft
Idri area, SW Libya. The Idri area belongs to the western
Formation. A type section was selected by Parizek et al.,
part of the Gargaf uplift and to adjoining northern flank
(1984) in the Idri area, it has the largest outcrops of the
of the Murzuk basin, SW Libya (Fig. 1). The Mamuniyat
Paleozoic formations, and it is prevailing component of
Formation was defined by Massa and Collomb (1960) as
the Mamuniyat and Jabal ad Duwaysah. In the eastern
a unit consisting of sandstones, frequently cross-bedded,
part of the area it forms outliners upon the
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 88
Fig. 1: Location map of the study area and distribution of the Mamuniyat Formation in Libya
Hasawnah Formation. Also has a wide distribution in the
resent day Murzuk Basin was caused by Cambro-
Murzuk, Al Kufrah and Ghadamis
Ordovician transtensional movements along pre-existing
basins.
The
Mamuniyat Formation is a major oil reservoir in the
NW-N
striking
pre-pan-African
and
pan-African
northern Murzuk Basin.
basement structure. During the Early Paleozoic, the
North African area formed an extensive, northerly
GEOLOGICAL AND STRATIGRAPHIC SETTING
dipping, depositional platform extending from Morocco
The Murzuk Basin is one of several intracratonic
to Saudi Arabia. This platform was locally modified by
basins located on the North African Platform. The basin
early extensional movements that created a series of
2
covers an area of over 350,000 km , and has a
northerly trending grabens and horsts (Klizsch, 1971).
roughly triangular shape, narrowing towards the south
These
from Libya into Niger (Fig. 2). The present day borders
depositional systems from south to north. The present
of the Murzuk Basin defined by erosion resulting from
day basinal structure is a result of a combinational of
multiphased tectonic uplifts, the flanks comprising the
Paleozoic, Hercynian and Alpine deformation and does
Tihemboka High to the west, the Tibesti High to the east
not reflect the depositional basin which developed
and the Gargaf/Atshan Uplift to the north. These uplifts
during
were generated by various tectonic events ranging from
Paleozoic times, sediments was derived from a sub-
mid Palaeozoic through Tertiary times, but the main
Saharan source and transported in a north to north-
periods of uplift took place during mid- Cretaceous
westerly direction across the Saharan platform. The
(Austrian) and Early Tertiary (Alpine) movements. In
Mamuniyat Formation in the study area (Fig. 3) is
structures
effectively
Cambro-Ordovician
channelized
times.
During
local
Early
the study area the initial subsidence in the area of the
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 89
Fig.2: NNE-SSW trending geological cross section through the Murzuk Basin, constructed from outcrop, well and seismic
information (after Tim et al., 2000)
Fig. 3: (A) Composite columnar section through the Gargaf Group of central Libya and (after Tim et al., 2000) (B)
Composite columnar section of Mamuniyat Formation in the study area
divided into six units, these units composed mainly of
environment and paleo-oxygenation condition. As far as
sandstones with intercalations of a few siltstone beds.
the author is aware, the published chemical data on the
The present work discusses the chemical composition of
Mamuniyat Formation in the study area are very
the Mamuniyat Formation, Idri area, SW Libya, with
insufficient.
special
Mamuniyat Formation deal with the structural geology,
emphasis
on
provenance,
depositional
Most
geological
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
publications
on
the
Page 90
stratigraphy, sedimentology and petroleum geology in
Ghadames, Murzuq and Al Kufrah basins (e.g., Crook,
Major oxides
Tables
(1-2)
show
that
the
Mamuniyat
1974; Sikander, 2000; Fello and Litha 2003; El-ghali,
Formation has very high SiO2 contents (97.8%, in
2005).
average). The negative correlation of SiO2 with most
major oxides is due to most of the silica being
sequestered in quartz. Na2O and K2O are strongly
METHODOLOGY
About 18 samples were collected from the
correlated with Al2O3 (r = 0.74 and 0.81, respectively)
Mamuniyat Formation (three samples of each unit). Bulk
suggesting, in agreement with Nagarajan et al., (2007),
geochemical analyses for major oxides and trace
that they are bound to alumino-silicate minerals. The
elements were performed using the inductively coupled
K2O/Al2O3 ratios for clay minerals and feldspars are
plasma-mass spectrometry (ICP-MS) technique, which is
different (0.0 to 0.3, 0.3 to 0.9, respectively; Cox et al.,
widely used, at present, for determination of elements in
1995). The K2O/Al2O3 ratio ranges from 0.001 to 1.71,
various materials with high precision. The analytical
indicating that clay minerals and feldspars have a major
procedure depends on the decomposition of exact weight
role in the distribution of aluminum in the study area.
of 0.2 g powdered fine sand size sample in 50 ml Teflon
CaO correlates strongly with MgO (r = 0.98). This
beaker. Decomposition was done by 4 ml HNO3, 3 ml
relationship means that anorthite and calcite are the sole
HClO4 and 5 ml HF, and evaporated to dryness under
carriers of MgO. TiO2 is positively correlated to Fe2O3 (r
200C. The residue was dissolved with 5 ml (1:1) HNO3
= 0.94) suggesting that Ti is contained in iron-titanium
by heating and 5 ml of 4 ppm indium solution was added
oxyhydroxides.
as an internal standard. The sample, as well as reference,
solutions were introduced by peristaltic pump with 0.18
Chemical classification
rpm. Before each measurement, nebulizer and spray
Although the chemical classification of sediments
chamber were washed by introducing the solution for 3
is not well developed, various authors have proposed
min with 0.5 rpm and 30 seconds with 0.18 rpm. The
few classification schemes for clastic sedimentary rocks
analysis was done in the Nuclear Materials authority of
or sediments based on their chemical compositions (e.g.,
Egypt.
Pettijohn et al., 1972; Crook, 1974; Blatt et al., 1980;
Herron, 1988). According to the diagrams of Pettijohn et
al., (1972) and Herron (1988) the studied sandstones are
RESULTS AND DISCUSSION
The mineralogical data show that the detected
classified mainly as sublitharenites and quartz arenites
light minerals are quartz, orthoclase and anorthite with
(Figs. 4-5). According to the diagram of Crook (1974)
other minor minerals such as calcite, kaolinite and illite,
the Mamuniyat Formation data plot in the quartz rich
while the detected heavy minerals are rutile, magnetite,
field (Fig. 6). In agreement with Khanehbad et al.,
ilmenite, zircon, tourmaline, rutile, muscovite, biotite,
(2012) the authors believe that the high K2O/Na2O ratio
garnet,
in the studied sandstones are due to the presence of K-
monazite,
hornblende,
anatase, pistachite and coronadite.
staurolite,
kyanite,
bearing minerals such as orthoclase, illite, biotite and
muscovite.
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 91
Table 1: Chemical analysis data (major oxides in wt. %, trace elements in ppm) of the Mamuniyat Formation
Formation
Unit
Sample No.
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K 2O
P2O5
Cl
SO3
L.O.I
Total
Rb
Sr
Ni
Co
V
Cr
Cu
Zn
Pb
Hg
Zr
Hf
Th
U
Sc
Y
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
1a
72.71
0.60
2.91
3.37
0.13
3.50
6.35
2.05
2.88
0.06
0.11
0.05
5.11
99.83
44.29
202.63
17.65
6.52
35.68
68.00
10.43
44.82
16.79
7.66
326.26
6.15
12.13
3.34
7.67
21.93
27.31
57.20
6.17
21.10
4.61
0.63
3.64
0.76
3.65
0.79
2.35
0.48
2.25
0.49
1
1b
71.32
0.73
1.88
3.46
0.17
3.67
7.41
1.93
2.70
0.09
0.09
0.05
6.00
99.50
44.11
201.60
16.54
5.41
34.02
66.34
8.77
43.16
16.82
7.69
326.00
5.89
11.24
2.94
7.21
21.77
26.88
56.77
5.74
20.67
4.18
0.54
3.21
0.67
3.23
0.71
2.00
0.37
2.12
0.37
1c
70.66
0.91
1.47
4.00
0.16
3.55
7.92
1.53
2.36
0.09
0.09
0.04
6.73
99.51
43.77
201.19
15.04
3.91
32.23
64.55
6.98
41.37
16.83
7.70
325.88
5.77
10.90
2.87
7.00
21.69
26.81
56.70
5.67
20.60
4.11
0.42
3.14
0.60
3.16
0.68
1.89
0.34
2.06
0.33
Mamuniya
2
2a
2b
2c
65.44 65.88 64.52
0.67
0.63
0.64
1.76
1.93
2.11
3.73
3.08
3.61
0.13
0.10
0.11
5.67
5.22
6.00
10.23 10.00 10.84
1.21
1.33
1.10
1.81
2.02
1.66
0.12
0.11
0.09
0.08
0.08
0.07
0.05
0.05
0.04
9.12
8.96
9.71
100.02 99.39 100.50
43.22 43.43 43.07
201.48 201.65 201.83
16.36 17.01 17.13
5.23
5.88
6.00
32.76 34.27 35.15
65.08 66.59 67.47
7.51
9.02
9.90
41.90 43.41 44.29
16.79 16.77 16.78
7.66
7.64
7.65
325.05 325.60 325.29
4.94
5.49
5.18
9.65 10.00 9.91
2.59
2.71
2.66
5.57
6.06
5.93
20.74 21.00 20.94
24.33 24.70 24.62
51.65 52.07 51.96
5.60
5.80
5.73
20.72 21.07 20.94
4.28
4.57
4.49
0.51
0.70
0.63
3.74
4.04
3.92
0.61
0.85
0.73
3.87
4.10
4.04
0.67
0.92
0.81
2.09
2.40
2.38
0.28
0.48
0.42
1.91
2.15
2.06
0.27
0.41
0.37
3a
98.00
0.12
0.37
0.07
0.01
0.10
0.19
0.13
0.09
0.04
0.05
0.08
0.90
100.15
41.50
200.09
14.41
3.28
30.90
63.22
5.65
40.04
16.77
7.64
333.23
13.12
16.69
5.51
10.63
28.41
41.86
86.21
9.38
34.24
5.78
0.86
5.78
0.98
5.27
1.02
2.96
0.45
2.75
0.53
3
3b
98.20
0.06
0.23
0.04
0.01
0.05
0.12
0.10
0.08
0.05
0.05
0.11
0.87
99.97
41.49
199.95
14.26
3.13
30.77
63.09
5.52
39.91
16.77
7.64
334.00
13.89
16.88
5.63
10.77
28.73
41.98
86.33
9.50
34.36
5.90
0.98
5.90
1.10
5.39
1.14
3.08
0.57
2.87
0.65
3c
97.27
0.08
0.24
0.07
0.01
0.10
0.18
0.11
0.08
0.06
0.05
0.10
1.10
99.45
41.49
199.96
14.23
3.10
30.68
63.00
5.43
39.82
16.78
7.65
332.90
12.79
16.00
5.00
10.50
28.00
41.75
86.10
9.27
34.13
5.67
0.75
5.67
0.87
5.16
0.91
2.85
0.34
2.64
0.42
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 92
Table 2: Chemical analysis data (major oxides in wt. %, trace elements in ppm) of the Mamuniyat Formation
Formation
Unit
Sample No.
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K 2O
P2O5
Cl
SO3
L.O.I
Total
Rb
Sr
Ni
Co
V
Cr
Cu
Zn
Pb
Hg
Zr
Hf
Th
U
Sc
Y
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
4a
78.68
0.93
1.90
7.11
0.06
1.09
1.20
3.32
3.89
0.12
0.06
0.07
1.33
99.76
45.30
201.62
16.93
5.80
34.08
66.40
8.83
43.22
16.78
7.65
328.92
8.81
14.11
4.13
9.00
23.20
30.72
62.53
6.63
25.46
5.35
0.66
4.47
0.89
4.42
0.82
2.43
0.36
2.18
0.37
4
4b
79.19
0.89
1.14
6.93
0.06
1.00
1.11
3.42
3.95
0.11
0.06
0.07
1.29
99.22
45.36
200.86
14.79
3.66
31.68
64.00
6.43
40.82
16.77
7.64
329.00
8.89
14.24
4.20
9.23
23.66
30.90
62.71
6.77
25.59
5.44
0.74
4.58
0.94
4.54
0.91
2.56
0.44
2.29
0.42
4c
79.36
0.80
2.33
6.25
0.04
1.11
1.27
3.51
4.00
0.08
0.04
0.05
1.31
100.15
45.41
202.05
17.23
6.10
35.29
67.61
10.04
44.43
16.76
7.63
329.81
9.70
14.30
4.27
9.64
23.95
31.00
62.84
6.92
25.71
5.58
0.80
4.70
1.00
4.61
0.98
2.64
0.53
2.31
0.44
Mamuniya
5
5a
5b
5c
97.08 97.23 97.88
0.11
0.17
0.13
0.80
0.71
0.66
0.10
0.09
0.07
0.03
0.03
0.03
0.09
0.08
0.10
0.19
0.26
0.21
0.11
0.21
0.16
0.08
0.09
0.09
0.05
0.04
0.05
0.05
0.05
0.05
0.13
0.20
0.11
1.15
0.95
0.77
99.97 100.11 100.31
41.49 41.50 41.50
200.52 200.43 200.38
14.84 14.73 14.56
3.71
3.60
3.43
31.80 31.59 31.34
64.12 63.91 63.66
6.55
6.34
6.09
40.94 40.73 40.48
16.81 16.80 16.80
7.68
7.67
7.67
330.08 330.39 330.61
9.97 10.28 10.50
14.44 14.60 14.71
4.43
4.71
4.88
10.07 10.18 10.29
27.68 27.73 27.88
40.15 40.20 40.29
84.59 84.71 84.80
8.76
8.88
8.94
31.79 31.94 32.00
6.33
6.46
6.53
0.67
0.80
0.85
4.85
4.91
5.00
0.86
0.92
1.05
4.55
4.63
4.72
0.83
0.95
1.04
2.64
2.76
2.83
0.40
0.51
0.56
2.57
2.68
2.73
0.39
0.49
0.51
6a
78.62
0.61
2.09
3.95
0.10
2.33
3.23
2.22
2.94
0.05
0.09
0.06
4.11
100.40
44.35
201.81
17.03
5.90
34.68
67.00
9.43
43.82
16.80
7.67
328.12
8.01
13.00
3.55
8.09
22.88
30.20
61.89
6.39
23.48
4.81
0.52
3.91
0.40
2.56
0.45
1.60
0.21
2.53
0.40
6
6b
79.05
0.55
2.45
3.92
0.09
2.17
2.67
2.71
3.29
0.05
0.09
0.06
3.35
100.45
44.70
202.17
17.34
6.21
35.31
67.63
10.06
44.45
16.79
7.66
328.44
8.33
13.69
3.73
8.70
23.00
30.33
62.03
6.50
23.59
4.88
0.65
4.00
0.48
2.68
0.57
1.70
0.27
2.61
0.45
6c
79.27
0.50
2.78
3.90
0.08
1.91
2.11
3.00
3.68
0.05
0.08
0.06
2.94
100.36
45.09
202.50
17.53
6.40
35.55
67.87
10.30
44.69
16.78
7.65
328.56
8.45
13.81
3.92
8.88
23.11
30.41
62.09
6.64
23.71
5.00
0.73
4.16
0.56
2.77
0.60
1.77
0.30
2.66
0.48
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 93
10.0
Log (Na2O/K2O)
0.0
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5▲
Unit 6 ■
Quartz-rich
K2 O/Na2O = 1
1.0
Quartz-intermediate
K2O/Na2O = 0.4
Subarkose
Litharenite
Graywacke
0.4
K2 O %
0.8
Quartz-poor
0.1
0.1
Arkose
Quartzarenite
Sublitharenite
-0.4
10.0
Na2O %
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5 ▲
Unit 6 ■
-0.8
1.0
Fig. 6: Chemical classification of the Mamuniyat
Formation using K2O/Na2O ratio (fields after Crook,
1974)
-1.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Log (SiO2/Al2O3)
Trace element
Rb and Sr are strong correlated with K2O (r = 0.99
Fig. 4: Chemical classification of the Mamuniyat
Formation using log(SiO2/Al2O3)-log(Na2O/K2O)
and 0.81, respectively), suggesting that their distribution
is mainly controlled by K-rich minerals. Pb and Hg
diagram (fields after Pettijohn et al., 1972)
correlate positively with CaO (r = 0.72 and 0.62,
respectively), while Ni, Co, Cu and Zn are strongly
2.0
1.5
respectively), suggesting that anorthite and calcite are
the sole carriers of Pb and Hg, while Ni, Co, Cu and Zn
are contained in alumino-silicates. Th and U are strongly
Fe-sand
1.0
Fe-shale
Litharenite
Shale
0.5
correlated with Zr (r = 0.98 and 0.97, respectively)
Wacke
Log (Fe 2O3/K2O)
correlated with Al2O3 (r = 0.97, 0.97, 0.97 and 0.62,
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5 ▲
Unit 6 ■
suggesting that they are contained in zircon.
Sublitharenite
Rare earth elements
0.0
The REE
Arkose
Subarkose
-0.5
Quartzarenite
are normalized
to
Post-Archean
Australian Shale (PAAS, Taylor and McLennan, 1985,
Fig. 7). All units , except unit 6, show more or less flat
REE pattern, while unit 6 shows convex REE pattern,
-1.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Log (SiO2/Al2O3)
Fig. 5: Chemical classification of the Mamuniyat
Formation using log(SiO2/Al2O3)-log(Fe2O3/K2O)
diagram (fields after Herron, 1988)
indicating, in agreement with Fello and Litha (2003),
lower and middle parts of the studied formation of
marine origin, while the upper part of fluvial origin. This
interpretation is further supported by the (La/Sm)N vs.
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 94
(La/Yb)N and ΔLa vs. (La/Lu)N bivariate plots (Figs. 89).
Sorting and weathering effects
The Th/U ratio in most upper crustal rocks is
typically between 3.5 and 4.0 (McLennan et al., 1993).
In most cases, weathering and sedimentary recycling
Samples/PAAS
1.40
typically result in loss of U, leading to an elevation in
the Th/U ratio. Figs (10-11) show a typical distribution
0.70
similar to the average values of fine grained sedimentary
Unit 1 ■ Unit 2 O Unit 3 Δ Unit 4 ■ Unit 5▲ Unit 6 ■
rocks reported by Taylor and McLennan (1985), but do
not follow the normal weathering trend.
0.00
La
Ce
Pr
Nd Sm Eu
Gd Tb
Dy
Ho
Er Tm
Yb
Lu
Fig. 7: PAAS normalized REE diagram for the studied
8
Unit 1 ■ Unit 2 O Unit 3 Δ
Unit 4 ■ Unit 5▲ Unit 6 ■ Weathering
trend
Upper continental
crust
samples
Th/U
6
10.00
Marine
environments
2
Unit 1
1.00
4
Depleted mantle
crust
(La/Yb)N
Unit 2
Unit 3
Terrestrial
environments
Aeolian-influenced
environments
0.10
0
Unit 4
0.1
1.0
Unit 5
Unit 6
0.01
0.01
10.0
100.0
Th ppm
Fig. 10: Plot of Th/U versus Th in the Mamuniyat
0.10
1.00
10.00
Formation
(La/Sm)N
100.00
Fig. 8: Bivariate plots between (La/Sm)N vs. (La/Yb)N in
Recycling/Zircon concentartion
10.00
Th/Sc
the Mamuniyat Formation (fields after Cook and
Trueman, 2009)
1.00
Upper continental crust
0.10
Mantle
10.0
Marine
environment
0.01
0
Unit 1
1.0
35
70
Zr/Sc
Unit 2
Continental
environment
ΔLa
Unit 1 ■ Unit 2 O Unit 3 Δ
Unit 4 ■ Unit 5▲ Unit 6 ■
Unit 3
Unit 4
Unit 5
0.1
Fig. 11: Plot of Zr/Sc versus Th/Sc in the Mamuniyat
Unit6
Formation
0.0
0.0
0.1
1.0
10.0
Provenance
(La/Lu)N
McLennan et al., (1993) have defined five distinct
Fig. 9: Bivariate plots between ΔLa vs. (La/Lu)N in the
Mamuniyat Formation (designed by the authors)
provenance components on the basis of geochemical
compositions. These components include the following:
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 95
Old
Upper
Continental
Crust
(OUC),
Recycled
authors believe that the granite of Tibesti Mountains
Sedimentary Rocks (RSR), Young Undifferentiated Arc
must be the probable source for the Mamuniyat
(YUA), Young Differentiated Arc (YDA) and Exotic
Formation. This interpretation is further supported by the
components (Table 3). The OUC components constitute
ΔEu vs.(Gd/Yb)N plot (Fig. 17). The (Gd/Yb)N ratio also
the old, well-differentiated upper continental crust that is
document the nature of source rocks and the composition
characterized by a substantial Eu anomaly. The RSR
of the continental crust (Taylor and McLennan, 1985).
component includes recycled sedimentary and meta-
Archean crust generally has higher (Gd/Yb)N ratio,
sedimentary rocks. The YUA component represents the
recording typically values above 2 in sedimentary rocks,
young (dominantly mantle derived) igneous arc material
whereas the Post-Archean rocks have (Gd/Yb)N values
(volcanic or plutonic) that has not undergone significant
commonly between 1 and 2 (McLennan and Taylor,
intracrustal differentiation (i.e., it has not undergone
1991).
plagioclase fractionation and therefore show no Eu
anomalies).
The
YDA
provenance
component
Paleo-oxygenation condition
constitutes the young (mantle derived) volcanic or
The Cu/Zn, V/Cr, Ni/Co and U/Th ratios are
plutonic igneous rocks from island and continental arcs
used as a redox parameter in many studies (e.g.,
that
intracrustal
Shaltami, 2012). According to Hallberg (1976) the
differentiation. The studied sandstone shows high Th/U
increasing value of the Cu/Zn ratio indicates a reducing
and Th/Sc ratios (3.44 and 1.56, in average, respectively)
depositional condition while decreasing Cu/Zn values
and negative Eu anomalies (0.68, in average), favor the
suggest increased oxidizing conditions. Ratio of V/Cr
RSR provenance for the Mamuniyat Formation.
above 2 indicates anoxic conditions, whereas values
have
undergone
significant
below 2 suggest more oxidizing conditions (Jones and
Ratios such as La/Sc, Th/Sc, Cr/Th and Th/Co
Manning, 1994). Ni/Co ratios below 5 indicate oxic
are significantly different in felsic and basic rocks and
environments, whereas ratios above 5 suggest suboxic
may allow constraints on the average provenance
and anoxic environments (Jones and Manning, 1994).
composition (Wronkiewicz and Condie, 1990). These
U/Th ratios below 1.25 suggest oxic conditions of
ratios of the studied samples are compared with those of
deposition, whereas values above 1.25 indicate suboxic
sediments derived from felsic and basic rocks as well as
and anoxic conditions (Nath et al., 1997). According to
to PAAS values (Table 4). This comparison suggests
Nagarajan et al., (2007), in the Arabian Sea, sediments
that felsic rocks must be the probable source rocks of the
below the oxygen minimum zone (OMZ) show high
Mamuniyat Formation. Figs (12-15) also show that the
U/Th (> 1.25) ratios, whereas the sediments above the
Mamuniyat Formation was derived from felsic sources.
OMZ exhibit low U/Th (< 1.25) ratios. The studied
Fig (16) shows that data of the studied samples fall
samples show low Cu/Zn, V/Cr, Ni/Co and U/Th ratios
between the field of granite and granitoids compositions,
(0.19, 0.51, 3.48 and 0.29, in average, respectively)
indicating that the studied sandstone is probably derived
which suggest that the Mamuniyat Formation was
from mixed source rocks of granite and granitoids. The
deposited in a well oxygenated environment.
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 96
Table 3: Geochemical characteristics of sediment derived from different provenance types (after McLennan et al., 1993)
Provenance type
Eu/Eu*
Th/Sc
Th/U
Old upper continental
crust
0.6-1.1
1.0
>3.8
Recycled sedimentary
rocks
0.6-1.1
≥ 1.0
>3.8
Young differentiated arc
0.5-0.9
1.0 to <0.01
<3.0
Evolved major element composition
(e.g. high Si/Al, CIA) high LILE
abundance variable compositions
<3.0
Unevolved major element
composition (e.g. low Si/Al, CIA) low
LILE abundance variable
compositions
Young undifferentiated
arc
1.0
1.0 to <0.01
Others
Evolved major element composition
(e.g. high Si/Al, CIA) high LILE
abundance, uniform compositions
Evidence of heavy minerals
concentration from trace elements
(e.g. Zr,Hf for zircon)
Table 4: Range of elemental ratios of the studied samples compared to the ratios derived from felsic rocks, mafic rocks
(after Cullers and Podkovyrov (2000)) and Post-Archean Australian shale (after Taylor and McLennan (1985))
Rocks
La/Sc
Th/Sc
Th/Co
Felsic rocks
2.5 - 16.3 0.84 - 20.5 0.67 - 19.4
Mafi c rocks
0.43 - 0.86 0.05 - 0.22 0.04 - 0.4
PAAS
2.40
0.90
0.63
Mamuniyat Formation
3.78
1.56
3.00
15.0
10.00
tholeiitic ocean island source
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5▲
Unit 6 ■
12.5
lower continental crust
0.10
andesitic arc source
▼
10.0
Silicic
rocks
La/Th
Th/Co
1.00
Cr/Th
4.00 - 15
25 - 500
7.53
5.07
mixed felsic/basic source
7.5
▼
2.5
upper continental crust
0.01
0.01
passive
margin
source
felsic source
5.0
Basic
rocks
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5▲
Unit 6 ■
increasing old sediment component
0.0
0.10
1.00
10.00
La/Sc
0.0
2.5
5.0
7.5
10.0
12.5
15.0
Hf ppm
Fig. 12: La/Sc versus Th/Co diagram for sandstone
Fig. 13: Source and composition discrimination of the
samples from the Mamuniyat Formation (fields after
Mamuniyat Formation using La/Th ratio and Hf
Cullers, 2002)
abundance (fields after Floyd and Leveridge, 1987)
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 97
1.6
3
Unit 1 ■ Unit 2 O Unit 3 Δ
Unit 4 ■ Unit 5▲ Unit 6 ■
Mafic
rocks
Archean
PAAS
ΔEu =0.85
1.2
TiO 2 %
2
ΔEu
1
Felsic
rocks
Unit 3
50
100
150
200
250
300
Unit 4
+
Archean
+
0
Unit 2
0.8
Unit 5
+
0.4
0
Unit 1
Graniotoids
Intermediate
rocks
Unit 6
Granitic gneisses
Post-Archean
350
0.0
Zr ppm
0
1
3
4
5
6
7
(Gd/Yb)N
Fig. 14: TiO2 versus Zr diagram of the Mamuniyat
Formation (fields after Hayashi et al., 1997)
2
Fig. 17: Bivariate plots between (Gd/Yb)N vs. ΔEu in the
Mamuniyat Formation (fields after McLennan and
TiO 2 %
1.0
Taylor, 1991)
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5▲
Unit 6 ■
0.5
Felsic
Intermediate
Paleoclimate
The K2O/Na2O and TiO2/Zr ratios are used as a
maturity parameter in many studies (e.g., Garcia et al.,
Mafic
0.0
0
40
80
1994, Asiedu et al., 2000; Shaltami, 2012; Malick and
120
Ni ppm
Ishiga, 2015). Mature sediments show a wide range of
Fig. 15: Ni versus TiO2 diagram of the Mamuniyat
Formation (fields after Floyd et al., 1989)
K2O/Na2O and TiO2/Zr variations whereas immature
sediments show a more limited range of K2O/Na2O and
TiO2/Zr variations. In the present study, the K2O/Na2O
and TiO2/Zr ratios range from 0.43 to 1.54 and 1.80 to
La
28.27, respectively, this is indicative of typically mature
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5▲
Unit 6 ■
Granite
Granitoids
sediments. Moreover, plot of SiO2 versus Al2O3+N2O3+
K2O proposed by Suttner and Dutta (1986) was used in
order to identify the chemical maturity of the studied
samples as a function of climate. The plotted samples
Granodiorite
Granite
revealed humid conditions for the samples but do not
follow the chemical maturity trend (Fig. 18).
Tectonic setting
Th
Sc
Several studies have shown that the chemical
Fig. 16: Ternary plots of La-Th-Sc of the Mamuniyat
compositions of siliciclastic sedimentary rocks are
Formation (fields after Hu and Yang, 2016)
significantly controlled by plate tectonic settings of their
provenances and depositional basins, and as a result, the
siliciclastic rocks from different tectonic settings posses
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 98
terrain-specific geochemical signatures (Bhatia, 1983;
10.0
Kroonenberg (1994) and Roser and Korsch (1986)
discriminate
between
Oceanic
island
Arc
(A),
K2O/Na2O
Roser and Korsch, 1986). The tectonic diagrams of
D
1.0
C
A
continental island Arc (B), active continental margin (C)
and passive margin (D). These diagrams classified the
Mamuniyat
Formation
between
active
0.1
50
60
70
80
90
100
110
SiO2 %
continental
margin and passive margin (Figs. 19-20).
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5▲
Unit 6 ■
Fig. 20: Tectonic discrimination diagram of major
oxides for the Mamuniyat Formation (fields after Roser
and Korsch, 1986)
110
Humid
100
Increasing
chemical
maturity
SiO2 %
90
Unit 1 ■
Unit 2 O
Unit 3 Δ
Unit 4 ■
Unit 5▲
Unit 6 ■
80
70
60
CONCLUSIONS
The present work aims to characterize the
geochemistry of the Mamuniyat Formation, Idri area,
Arid
SW Libya. The studied sandstones have very high SiO2
50
0
5
10
15
Al2O3 + K2O + Na 2O (%)
contents. The negative correlation of SiO2 with most
major oxides is due to most of the silica being
Fig. 18: Bivariate plot of SiO2 vs. (Al2O3 + K2O + Na2O)
sequestered in quartz. The studied sandstones are mainly
to discriminate paleoclimatic condition during the
classified as sublitharenites and quartz arenites. Rb and
deposition of the Mamuniyat Formation (fields after
Sr are strongly correlated with K2O suggests that that
Suttner and Dutta, 1986)
their distribution is mainly controlled by potassium-rich
minerals. Pb and Hg correlate positively with CaO,
SiO2/20
while Ni, Co, Cu and Zn are strongly correlated with
Unit 1 ■
Unit 2 Ο
Unit 3 ∆
Unit 4 ■
Unit 5 ▲
Unit 6 ■
Al2O3 .These relationships mean that anorthite and
calcite are the sole carriers of Pb and Hg, while Ni, Co,
Cu and Zn are contained in alumino-silicates. The
studied samples Th and U are strongly correlated with
D
Zr, suggesting that they are contained in zircon. Units 1,
2, 3, 4 and 5 show more or less flat REE pattern with
C
positive Ce and negative Eu anomalies, while unit 6
B
A
(Na2O + K2O) %
shows convex REE pattern with positive Ce and
(TiO2 + Fe2O3 + MgO) %
negative Eu anomalies, suggesting that the lower and
Fig. 19: Ternary plots of SiO2/20 – (Na2O + K2O) –
middle parts of the studied formation of marine origin,
(TiO2 + Fe2O3 + MgO) for sandstone samples from the
while the upper part of fluvial origin. This interpretation
Mamuniyat Formation (fields after Kroonenberg, 1994)
is further supported by the (La/Sm)N vs. (La/Yb)N and
ΔLa vs. (La/Lu)N bivariate plots. The Mamuniyat
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 99
Formation sandstone shows high Th/U and Th/Sc ratios
Massa, D. and Collomb, G.R. (1960): Observations
and negative Eu anomalies; favor the RSR provenance
nouvelles sur la Region d, Aouinet Quenine et du Djebel
for the Mamuniyat Formation. La/Sc, Th/Sc, Cr/Th and
Fezzan (Libye). Report of the Twenty-First Session
Th/Co ratios show that the Mamuniyat Formation was
Norden, 12: 65-73.
derived from felsic source rocks. The ternary plots of
La-Th-Sc show that the studied samples fall between the
Cook, E. and Trueman, C. (2009): Taphonomy and
field of granite and granitoids compositions, indicating
geochemistry of a vertebrate microremains assemblage
that the Mamuniyat Formation is probably derived from
from the Early Triassic karst deposits at Czatkowice 1,
mixed source rocks of granite and granitoids. The
southern Poland. Palaeontologia Polonica; 65: 17–30.
authors believe that the granite of Tibesti Mountains
must be the probable source for the Mamuniyat
Cox, R.; Low, D.R. and Cullers, R.L. (1995): The
Formation. This interpretation is further supported by the
influence
ΔEu vs.(Gd/Yb)N plot. The studied sandstone shows low
composition on evolution of mudrock chemistry in the
Cu/Zn, V/Cr, V/Ni and Ni/Co and U/Th ratios which
southwestern
suggest that these sediments were deposited in a well
Cosmochimica Acta; 59: 2919–2940.
of
sediment
United
recycling
and
States.
basement
Geochimica
et
oxygenated environment. The climatic discrimination
diagram suggests that the humid conditions for the
Crook K.A.W. (1974): Lithogenesis and geotectonics:
source area of the Mamuniyat Formation. The tectonic
The significance of compositional variation in flysch
discrimination
arenites
diagrams
show
that
data
of
the
(greywackes).
Society
of
Economical,
Mamuniyat Formation fall in the field between active
Paleontological and Mineralogical Special Publications;
continental margin and passive margin.
19: 304-310.
REFERENCES
Cullers,
Asiedu D.K.; Suzuki S.; Nogami K. and Shibata T.
concentrations for provenance, redox conditions, and
(2000): Geochemistry of Lower Cretaceous sediments,
metamorphic studies of shales and limestones near
Inner Zone of Southwest Japan: Constraints
Pueblo, CO, USA. Chemical Geology; 191(4): 305-327.
provenance
and
tectonic
on
R.L.
(2002):
Implications
of
elemental
environment. Geochemical
Journal; 34: 155–173.
Cullers,
R.L.
and
Podkovyrov,
V.N.
(2000):
Geochemistry of the Mesoproterozoic Lakhanda shales
Bhatia M.R. (1983): Plate tectonics and geochemical
in southeastern Yakutia, Russia: implications for
composition of sandstones. Journal of Geology; 92: 181–
mineralogical and provenance control, and recycling.
193.
Precambrian Research; 104(1-2): 77-93.
Blatt H.; Middleton G. and Murray R. (1980): Origin of
El-ghali T.M.A. (2005): Depositional environments and
Sedimentary Rocks. pp.782. 2nd edition, Prentice-Hall,
sequence stratigraphy of paralic glacial, paraglacial and
New Jersey.
postglacial Upper Ordovician siliciclastic deposits in the
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 100
Murzuq Basin, SW Libya. Departm ent of Earth Science,
Herron, M.M. (1988): Geochemical classification of
Uppsala University, Villavagen 16, SE 75236 Uppsala,
terrigenous sandstone and shale from core and log data.
Sweden, p. 145 – 173.
J. Sediment. Petrol.; 5(8): 820-829.
Fello,
N.
and Litha
A.M.
(2003):
Depositional
Hu, F. and Yang, X. (2016): Geochemical and
environments of the Upper Ordovician Mamuniyat
geomorphological evidence for the provenance of
Formation, NW Murzuk Basin, Libya. AAPG Search
aeolian
and Discovery Article.P.2
northwestern China. Quaternary Science Reviews; 131:
deposits
in
the
Badain
Jaran
Desert,
179-192.
Floyd, P.A. and Leveridge, B.E. (1987): Tectonic
environment of the Devonian Gramscatho Basin, south
Jones, B. and Manning, D.C. (1994): Comparison of
Cornwall: framework mode and geochemical evidence
geochemical indices used for the interpretation of paleo-
from turbiditic sandstones. Journal of the Geological
redox conditions in Ancient mudstones: Chemical
Society; 144(4): 531-542.
Geology; 111(1-4): 111-129.
Floyd, P.A.; Winchester, J.A. and Park, R.G. (1989):
Khanehbad, M.; Moussavi-Harami, R.; Mahboubi, A.;
Geochemistry and tectonic setting of Lewisian clastic
Nadjafi, M. and Mahmudy Gharaie, M.H. (2012):
metasediments from the Early Proterozoic Loch Maree
Geochemistry of Carboniferous sandstones (Sardar
Group of Gairloch, N.W. Scotland.
Formation),
Precambrian
Research; 45(1-3): 203-214.
East-Central
Iran:
Implication
for
provenance and tectonic setting. Act Geologica Sinica;
86(5): 1200-1210.
Garcia, D.; Fonteilles, M. and Moutte, J. (1994):
Sedimentary fractionation between Al, Ti, and Zr and
Klitzsch, E. (1971): The structure development of part of
genesis of strongly peraluminous granites. Journal of
North Africa since Cambrian time. First symposium on
Geology; 102: 411–422.
the geology of Libya (ed. C. Gray). Faculty of Science,
University of Libya, Tripoli.
Hallberg, R.O. (1976): A geochemical method for
investigation of palaeoredox conditions in sediments:
Kroonenberg, S.B. (1994): Effects of provenance,
Ambio, Special Report; 4: 139-147.
sorting and weathering on the geochemistry of fluvial
sands from different tectonic and climatic environments.
Hayashi, K.; Fujisawa, H.; Holland, H. and Ohmoto, H.
Proceedings
of
the 29th International
(1997): Geochemistry of ~1.9 Ga sedimentary rocks
Congress, Part A, 69–81.
Geological
from northeastern Labrador, Canada. Geochimica et
Cosmochimica Acta; 61(19): 4115-4137.
Malick, B.M.L. and Ishiga, H. (2015): Geochemical
maturity of pocket beach sands from the Sanin region of
southwest Japan. Earth Science Research; 4(2): 45-61.
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 101
McLennan, S.M. Hemming, S. McDaniel, D.K. and
SiO2 content and K2O/Na2O ratio. Journal of Geology;
Hanson, G.N. (1993): Geochemical approaches to
94: 635 – 650.
sedimentation, provenance, and tectonics, in Johnson,
M.J., Basu, A. (eds.), Processes Controlling the
Shaltami, O.R. (2012): Mineral composition and
Composition of Clastic Sediments: Geological Society
environmental geochemistry of the beach sediments
of America, Special Paper; 284: 21-40.
along the Mediterranean Coast from Benghazi to Bin
Jawwad, Northeast Libya. PhD. Thesis. Cairo Univ.
McLennan, S.M. and Taylor, S.R. (1991): Sedimentary
Cairo, Egypt.
rocks and crustal evolution: tectonic setting and secular
trends. Journal of Geology; 99: 1-21.
Sikander, A.H. (2000): The geology, structure and
hydrocarbon potential of the Ghadamis and Murzuq
Nagarajan, R. Madhavaraju, J. Nagendra, R. Armstrong-
basins an overview (Abstract). Second symposium on
Altrin, J.S. and Moutte, J. (2007): Geochemistry of
the sedimentary basins of Libya. The Geology of
Neoproterozoic shales of the Rabanpalli Formation,
Northwest Libya. Book of abstracts, p. 81.
Bhima Basin, Northern Karnataka, southern India:
implications for provenance and paleoredox conditions.
Suttner, L.J. and Dutta, P.K. (1986): Alluvial sandstone
Revista Mexicana de Ciencias Geológicas; 24 (2): 150-
composition and paleoclimate. Framework mineralogy.
160.
Journal of Sedimentary Petrology; 56: 326–345.
Nath, B.N.; Bau, M.; Ramlingeswara Rao, B. and Rao,
Taylor, S.R. and McLennan, S.M. (1985): The
C.M. (1997): Trace and rare earth elemental variation in
Continental Crust: its composition and evolution.
Arabian Sea sediments through a transect across the
Blackwell Scientific Publishers, Oxford.
oxygen minimum zone. Geochimica et Cosmochimica
Acta; 61: 2375-2388.
Tim, G.; Keith, A.; Robert, W.; Bill, F. and Jonathan, C.
(2000): Evidence for soft sediment the Duwaysah slide
Parizek, A.; Klen, L. and Rolich, P. (1984): Geological
of the Garagaf Archm, central Libya. Geological
Map of Libya; 1:250,000 sheet: Idri NG 33-1.
Exploration in Murzuk Basin, 418P.
Explanatory Booklet, Ind. Res. Centre, Tripoli.
Wronkiewicz,
D.J.
and
Condie,
K.C.
(1990):
Pettijohn, F.J.; Potter, P.E. and Siever, R. (1972): Sand
Geochemistry and mineralogy of sediments from the
and Sandstone. Plate motions inferred from major
Ventersdorp and Transvaal Supergroups, South Africa:
element chemistry of lutites. Precam-brian Research;
Cratonic
147: 124–147.
Geochim. Cosmochim. Acta; 54, 343–354.
evolution during the Early
Proterozoic.
Roser, B.P. and Korsch, R.J. (1986): Determination of
tectonic setting of sandstone. Mudstone suites using
th
Page
88
11
International
Conference and Meeting on Geology, Institute of Geosciences, University of Campinas, Brazil, 2016
Page 102

Similar documents