Sequence stratigraphy, hydrostratigraphy, and mineralizing fluid

Sequence stratigraphy, hydrostratigraphy,
and mineralizing fluid flow in the Proterozoic
Manitou Falls Formation, eastern
Athabasca Basin, Saskatchewan
E.E. Hiatt1 and T.K. Kyser2
Hiatt, E.E. and Kyser, T.K., 2005: Sequence stratigraphy, hydrostratigraphy, and mineralizing
fluid flow in the Proterozoic Manitou Falls Formation, eastern Athabasca Basin, Saskatchewan;
in EXTECH IV: Geology and Uranium EXploration TECHnology of the Proterozoic Athabasca
Basin, Saskatchewan and Alberta, (ed.) C.W. Jefferson and G. Delaney; Geological Survey of
Canada, Bulletin 588 (also Saskatchewan Geological Society, Special Publication 17;
Geological Association of Canada, Mineral Deposits Division, Special Publication 4).
Abstract: The Manitou Falls Formation, deposited during the early evolution of the eastern Athabasca
Basin, is composed of flat-lying, unmetamorphosed sandstone and conglomerate that change
stratigraphically upward from polymictic pebble conglomerate to medium-grained quartz arenite. This succession has been subdivided into lithofacies that are diachronous by nature. Variations in lithofacies and
paleoenvironment are useful for lithostratigraphic correlation, but do not allow resolution of
chronostratigraphic horizons.
Drill cores along two transects were studied, thickness of fluvial fining-upward successions were
recorded, and these were plotted stratigraphically. Thickness of fining-upward intervals is used as a proxy
for accommodation. These show systematic changes from times of low accommodation marked by
coarse-grained intervals followed by gradual shifts to greater accommodation and finer-grained intervals. A
hydrostratigraphic model for the eastern Athabasca Basin is presented based on integration of
sedimentology, sequence stratigraphy, and diagenesis. The two basal sequences contain aquifers that onlap
basement rock units eastward and focused burial brines.
1
2
Department of Geology, University of Wisconsin, Oshkosh, Wisconsin, 54901 U.S.A.
Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario K7L 3N6
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GSC Bulletin 588
INTRODUCTION
The Athabasca Basin (Fig. 1) of northern Saskatchewan hosts
the world’s largest known high-grade unconformity-type
uranium deposits and has been the subject of many studies
(Kyser et al., 2000 and references therein). These include pioneering studies of basinwide lithostratigraphy by Ramaekers
(1990), and those concerning mineralogical and geochemical
characteristics of rocks within, and away from, uranium mineralization (Hoeve and Quirt, 1984; Wilson and Kyser, 1987;
Kotzer and Kyser, 1992, 1995; Fayek and Kyser, 1997; Holk
et al., 2003). Broad-based regional studies that have considered the evolution of the Athabasca Basin are rare, and stratigraphic relationships have not been documented in detail
until this bulletin (e.g. Ramaekers et al., 2005). The interconnected role that sedimentology, stratigraphy, and diagenesis
played in controlling mineralizing fluid flow has never been
adequately documented. The recognition that sedimentological
and stratigraphic variation, even in a thick, coarse-clastic
sediment-filled continental basin, can cause major differences in the subsequent hydraulic properties of the resulting
rock (e.g. Hiatt et al., 2003) suggests that the linkages between
sedimentology, stratigraphy, and diagenesis in the Athabasca
Basin need to be addressed.
There are many difficulties inherent in the investigation
of Proterozoic sedimentary successions; primary among
these are the absence of fossils to guide paleoenvironmental
interpretation, the dominance of braided fluvial systems in
terrestrial settings, and the paucity of exposures. In the
Phanerozoic, fossils provide the basis for both paleoenvironmental interpretation and regional correlation. Correlation in
Proterozoic sedimentary rocks, on the other hand, must rely
totally on physical and/or chemical characteristics. The dominance of braided fluvial systems also makes lithological
correlation difficult because without land plants to bind floodplain
sediments, very little mud is deposited, resulting in extensive,
thick, amalgamated sand and gravel-dominated, sheet-like
deposits (e.g. Schumm, 1968). These factors contributed to
the difficulties in understanding regional and even local
stratigraphic variation in clastic sediment-filled Proterozoic
terrestrial basins, like the Athabasca Basin. Rivers flowing
into the Athabasca Basin were sourced in the Trans-Hudson
Orogeny to the east and deposited most of the gravel to
medium-grained sand that comprises the Manitou Falls
Formation (Fig. 2). The Manitou Falls Formation, which is
the focus of this study, records the early dynamic history of
the eastern Athabasca Basin. Notwithstanding the new
lithostratigraphic nomenclature introduced by Ramaekers et
al. (2005), this paper is based on and utilizes the lithofacies of
Ramaekers (1990).
The ability to predict and project stratigraphic relationships
is essential for understanding sedimentary basin-hosted,
unconformity-type uranium mineralization in the Athabasca
Basin because fluid flow related to mineralization is
controlled by stratigraphic relationships (Holk et al., 2003).
Figure 1. Map showing the study area, general geology, and location (inset) of the Proterozoic
Athabasca Basin, Canada. The locations of some major unconformity-type uranium deposits are
shown by black dots. Athabasca Basin formations are: FP = Fair Point, S = Smart, RD = Read
(hereafter referred to as MFa), MF = Manitou Falls (members b (u = upper, l = lower), r, w, c
and d), LZ = Lazenby Lake, W = Wolverine Point, LL = Locker Lake, O = Otherside, D = Douglas,
C = Carswell). Modified from Ramaekers and Catuneanu (2004) and Ramaekers et al. (2005).
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E.E. Hiatt and T.K. Kyser
Figure 2. Stratigraphic subdivision, position of major unconformities and hiatuses
(grey), sedimentary environmental interpretations, sediment source areas, and
estimated relative base-level change for the subbasins of the Athabasca Basin
(modified from Ramaekers, 1990; Ramaekers et al., 2005; this study). The relative
base-level curve depicts major changes in basin dynamics, such as tectonic uplift,
subsidence, and eustasy. The dashed line represents the point at which base-level fall
could allow a marine transgression into the basin (based on data from this study for the
Manitou Falls Formation and Ramaekers (1990) for the entire Athabasca Group).
This suggests that stratigraphy played a role in determining
the hydrostratigraphy of the basin and thus in the mineralization process. Existing lithofacies correlation is useful for
regional correlation (up to tens of kilometres), but lithofacies
are a product of paleoenvironmental changes, which are
diachronous. For the most part, the lithofacies represent variations in energy of the river systems. Such changes can occur
both at local and regional scales and have no chronostratigraphic significance. To achieve a better understanding
of the hydrology of the basin, the present authors developed
a sequence stratigraphic model for the Manitou Falls
Formation to provide a spatial and temporal framework in
which to understand its hydrostratigraphic evolution. The
goal of this work is to identify and correlate time-equivalent
stratigraphic units and internal bounding surfaces that
controlled hydrological flow regimes (cf. Miall, 2000).
Mineralization processes in sedimentary basins are often
related to regional movement of chemically active fluids (e.g.
Garven and Freeze, 1984; Kotzer and Kyser, 1995; Fayek and
Kyser, 1997; Lee, 1997; Renac et al., 2002). Direct geochemical evidence for these processes is recorded in the coarsegrained conglomerate and sandstone units of the Manitou
Falls Formation where significant fluid (brine) flow in the
deep burial setting has occurred (e.g. Kotzer and Kyser, 1995;
Fayek and Kyser, 1997; Renac et al., 2002; Holk et al., 2003).
Isotopic, chemical, microthermometric, and petrological data
indicate that the Athabasca Basin has had a protracted fluid
history unlike that documented for any Phanerozoic sedimentary basin (Kyser et al., 2000). Therefore, understanding fluid
movement throughout the basin is of primary importance for
mineral exploration (e.g. Garven and Freeze, 1984; Bethke,
1986; Fayek and Kyser, 1997; Kyser et al., 2000).
Understanding sedimentary basin hydrodynamic systems
has long been a goal of petroleum geologists and has allowed
evolution of hydrological systems to be tracked through critical intervals during which fluid migration occurred in burial
settings (e.g. Tyler and Finley, 1991; Harrison and Tempel,
1993; Galloway and Hobday, 1996; Selley, 1998). These
concepts, however, have not been widely applied to sediment-hosted mineral systems. The purposes of this paper are: 1) to
present a stratigraphic model for the Mantiou Falls Formation
that may facilitate correlation of intraformational sequences,
and 2) to test whether there are sedimentological and stratigraphic controls over diagenesis, and if so, 3) to present an
integrated sequence stratigraphic and hydrostratigraphic
model for the eastern Athabasca Basin.
GEOLOGICAL SETTING
The Athabasca Basin began as a series of northeastsouthwest-oriented subbasins (Fig. 3A) at 1750–1700 Ma
(Ramaekers, 1980; Armstrong and Ramaekers, 1985; Kotzer
and Kyser, 1992, 1995; Ramaekers and Catuneanu, 2004).
These early subbasins were controlled by major northeastsouthwest faults associated with the Hudsonian Orogeny and
rooted in underlying Paleoproterozoic metasedimentary
rocks and Archean gneiss units (Ramaekers, 1990). The 1–2
km thick Athabasca Group (Fig. 2, 3) makes up the sedimentary basin fill, and consists of flat-lying, quartz-rich
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GSC Bulletin 588
The Athabasca Group sedimentary rocks and
the basement complex are cut by a series of northwest- and east-trending mafic dykes that were
emplaced along fractures reactivated during tectonic activity between 1350 Ma and 900 Ma, postdating the Athabasca Group deposition (Ey et al.,
1991). The dykes are believed to be related to the
Mackenzie dyke complex (Cumming and Kristic,
1992) and are the only preserved evidence of igneous activity throughout the evolution of the basin.
Temperature estimates derived from fluid inclusions indicate that the Manitou Falls Formation
was buried to about 5 km depth during the
peak diagenesis (Pagel et al., 1980). Uranium
mineralization occurred at 1700–1600 Ma with
remobilization events at ca. 900 Ma and earlier
than 400 Ma (Kyser et al., 2000).
Relation between tectonism and
formation of the Athabasca Basin
The Athabasca Basin is an intracratonic basin with
no direct evidence of rift-related igneous activity.
Cumming and Kristic (1992) reported U-Pb ages
of 1700–1650 Ma for fluorapatite from the
Athabasca Basin that they interpreted as a minimum age of deposition in the basin. The basin
probably formed at ca. 1750 Ma based on timing of
rapid uplift in the region of the Trans-Hudson
Orogen that was likely a major source of sediment
that comprises most of the Manitou Falls Formation
(Kyser et al., 2000; Ramaekers and Catuneanu,
2004).
Multiple fluid events, involving isotopically
and chemically distinct fluids that migrated laterally for considerable distances and along fault
zones, produced a paragenetically identifiable
assemblage of clay, silicate, and oxide minerals in
the basin and basement rocks (Kyser et al., 2000). Isotopic,
chemical, microthermometric, and petrological data indicate
that the major sandstone aquifers in the Athabasca Basin,
which were most pronounced in the coarse-grained basal
units, have been affected by widespread lateral flow of
diagenetic fluids over distances of hundreds of kilometres
(Kyser et al., 2000). These fluids appear to have been present
in the basinal conglomerate and sandstone units at temperatures in excess of 200oC for a minimum of 600 Ma (Kyser et
al., 2000). Circulation of these warm brines and their reactions with minerals in basin-filling clastic rocks occurred in
response to tectonic events, such as those associated with
intrusion of the Mackenzie dykes and the break-up of Rodinia
(Kyser et al., 2000). Fluid migration paths followed
stratigraphic units above unconformities (Holk et al.,
2003). The stratigraphic pathways, however, were modified
by crossformational fluid flow near active fault zones (Kyser
et al., 2000).
Figure 3. A) Locations of subbasins, major faults, and diabase dykes
(Mackenzie dykes) in the Athabasca Basin. B) Cross-section of the basin
showing the basic stratigraphic units. Modified from Ramaekers (1981).
sandstone and conglomerate interpreted to have been
deposited in major river systems and near-shore to shallow-shelf marine environments (Ramaekers and Dunn, 1977;
Ramaekers, 1990), recently reinterpreted as mostly fluvial
(Ramaekers and Catuneanu, 2004; Ramaekers et al., 2005).
Crystalline basement rocks underlying the Athabasca Group
are mantled by a well developed paleoregolith that extends to
a depth of several metres where it has not been removed by
erosion (Hoeve and Sibbald, 1978). The faults cutting the
Athabasca Group are major crustal lineaments that have
remained intermittently active to recent times (Hoeve and
Quirt, 1984). The Paleoproterozoic metasedimentary rocks
and Archean gneiss that comprise the basement are components of the Wollaston Domain of the Trans-Hudson Orogen
(Lewry and Sibbald, 1979, 1980; MacDonald, 1985).
Paleoproterozoic metasedimentary rocks that unconformably overlie the Archean granitoid gneiss units consist mostly
of quartz, plagioclase, biotite, cordierite, garnet, and tourmaline, with several anatectic and graphitic layers (Ey et al.,
1991; Marlatt et al., 1992). Quartzite units are locally
developed and are generally separated by intervals of
garnet-cordierite gneiss (Marlatt et al., 1992).
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E.E. Hiatt and T.K. Kyser
Sedimentology and stratigraphy
The basal sequence of the late Paleoproterozoic to
Mesoproterozoic Athabasca Group (Fair Point and Manitou
Falls formations) consists of quartz-rich conglomerate and
sandstone (Fig. 2) with paleocurrent indicators suggesting a
predominately east to west transport direction (Ramaekers,
1990; Ramaekers and Catuneanu, 2004). Most framework
grains in the Manitou Falls Formation are quartz, with very
minor muscovite, up to 15% lithic clasts (quartzite, gneiss,
schist, and sandstone), and rare heavy minerals, such as zircon and apatite. The absence of preserved feldspar and rarity
of other minerals further suggests relatively long transport,
intense weathering, and/or diagenetic alteration of remaining
feldspar during burial diagenesis.
The sandstone units of the Manitou Falls Formation are
overlain by a succession of less permeable marine sandstone,
phosphatic siltstone, and phosphatic mudstone (the Lazenby
Lake and Wolverine Point formations, respectively), which
are in turn overlain first by sandstone (Locker Lake and
Otherside formations), then by shale (Douglas Formation),
and finally by stromatolitic dolomite (Carswell Formation;
Fig. 2).
Lithofacies subdivision of the
Manitou Falls Formation
Ramaekers (1979) defined the Manitou Falls Formation and
informally subdivided it into members, based on lithofacies
characteristics (Ramaekers, 1980). This lithofacies classification has proven useful in the eastern Athabasca Basin
where correlation between closely spaced exploration drill
cores is needed; however, it is difficult to apply beyond the
eastern portion of the Athabasca Basin (Cree subbasin;
Fig. 4A; Ramaekers et al. (2005)). A brief summary of the
informal lithofacies subdivisions is given below.
The newly defined Read Formation (Ramaekers et al.,
2005) (MFa) lithofacies is composed of conglomerate,
sandstone, and minor sandy mudstone. It is thickest in the
east-central part of the basin, but it is absent throughout much
of the northeastern, northern, and western portions of the
basin (Fig. 4B; Ramaekers (1990)). The rapid thinning of
MFa to the north, east, and west suggests that, unlike the
overlying Manitou Falls Formation, MFa was sourced from
the south and may have been the result of tectonic uplift
during the initial stages of basin evolution. Ramaekers (1990)
interpreted this unit as having been bounded by unconformities, and deposited in marine and fluvial environments. Ramaekers and Catuneanu (2004) and Ramaekers et
al. (2005), however, interpreted all of the Manitou Falls
Formation as having been deposited in fluvial and possibly
large lake depositional systems.
The Manitou Falls Formation unit B (MFb; Fig. 4C)
lithofacies is defined as sandstone interbedded with
clast-supported conglomerate beds that are greater than or
equal to 2 cm thick (Ramaekers, 1980). Ramaekers (1990, p.
15) noted that the clast-supported conglomerate beds are best
preserved in drill core because their lack of matrix and paucity
of cement makes them friable and easily eroded in outcrop.
From these characteristics Ramaekers (1990) deduced that
the MFb lithofacies may have been much more widespread
than is suggested by preserved outcrops. In much of the study
area (and in much of the Cree subbasin; Fig. 4C) MFb directly
overlies the basal unconformity with metamorphic basement.
The Manitou Falls Formation unit C (MFc; Fig. 4D) lithofacies is defined as those units of the Manitou Falls Formation
with less than 1% mud intraclasts and that contain conglomerate layers that are less than 2 cm thick (Ramaekers, 1980).
The contact between MFc and the underlying MFb is
gradational and conformable (Ramaekers, 1990). In the central and western portion of the Athabasca Basin, MFc appears
to directly overlie paleohighs on the basal unconformity
underlying Manitou Falls Formation (Ramaekers, 1990). The
Manitou Falls Formation unit D (MFd; Fig. 4E) lithofacies is
composed of sandstone units that are generally well sorted
and make up beds with greater than 1% of mud intraclasts
(Ramaekers, 1990). The contact with the underlying MFc
lithofacies is gradational and conformable, but MFd is overlain disconformably both by the Lazenby Lake Formation in
the south and west, and by the Wolverine Point Formation in
the north (Ramaekers et al., 2005). The MFb, MFc, and MFd
lithofacies are all interpreted to represent braided fluvial
depositional systems with energy levels generally decreasing
through time. Ramaekers (1990, p. 20), however, discovered
a stratigraphic interval in the MFd lithofacies (west-central
Athabasca Basin; NTS map area 74 F) that he interpreted as a
possible marine shoreline facies in the upper Manitou Falls
Formation, although Ramaekers and Catuneanu (2004) and
Ramaekers et al. (2005) interpreted the entire Manitou Falls
Formation as representing fluvial and possibly lacustrine
deposition.
METHOD AND RESULTS
Six drill cores from two strategic locations in the eastern
Athabasca Basin were examined, described, and logged in
detail. Samples were collected from each major stratigraphic
unit, and 80 of these were analyzed petrographically in this
study (Fig. 5). Outcrop exposures are generally poor in the
eastern Athabasca Basin and provide only fragmentary
stratigraphic information due to their limited thickness.
Exploration drill cores provide extensive continuous stratigraphic records (e.g. more than 830 m of continuous core in
RL-51; Fig. 5; 6A, see colour folio). At each location a core
was chosen proximal to known mineralization and others
were chosen distal to mineralization as a means to test
whether stratigraphy affected fluid flow and diagenesis.
Lithological data collected for each drill core included mean
grain size, maximum clast size, sorting, sedimentary
structures, and framework grain composition. Sedimentary
structures are generalized on the lithological columns, and
stratigraphic changes in mean grain size are represented by
the width of the column profile (Fig. 6A, B). Abrupt changes
in grain size and facies associations, and lithofacies defined
by Ramaekers (1980), noted above, were recorded and are
also represented graphically in Figures 6A and B.
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GSC Bulletin 588
Figure 4. Maps of the Athabasca Basin showing: A) the position of subbasins, and B)–F)
isopach thicknesses of lithostratigraphic units defined by Ramaekers (1980). Modified
from Ramaekers (1990).
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E.E. Hiatt and T.K. Kyser
Figure 5.
Map of the study area showing the
McArthur River and Cigar Lake
uranium deposits and drill-core
transects used in the stratigraphic
analysis in this study. Base map
modified from Ramaekers et al.
(2005). Lithofacies in the Manitou
Falls Formation unit A, B, C, and
D are represented by MFa, MFb,
MFc, and MFd, respectively.
Facies associations
Five major lithofacies associations were identified in the
Manitou Falls Formation (Fig. 6A, B). Facies association 1
(alluvial fan association) consists of matrix-supported
polymictic lithic conglo}erate with matrix- and clast-suoported
fabrics, pebbly lithic wacke, and moderately sorted lithic
arenite. The pebbly to cobbly conglomerate and sandstone
are medium grey to tan, and contain abundant metamorphic
quartzite, gneiss, and schist clasts that locally make up more
than 15% of the rock. Trough crossbedding, scour surfaces,
mudcracks, and asymmetrical ripple crosslaminae are present. Many matrix-supported conglomerate units have angular
clasts, suggesting mass wasting and deposition by debris
flows associated with alluvial fans. Other units in this
coarse-grained, mud-rich, heterolithic lithofacies suggests
rapid deposition in high-energy, proximal braided river systems where seasonal rainfall resulted in rapid deposition of
both coarse- and fine-grained sediment, fine-grained
sediments were exposed, mudcracks formed, and were
periodically ripped up in high-energy stream-flow events.
Lithofacies association 2 (proximal braided stream
association) is composed of clast-supported lithic to
quartzose conglomerate that in most places grades
stratigraphically upward into very coarse- to coarse-grained,
moderately to well sorted, sublithic to quartz arenite. Lithic
clasts (primarily fragments of gneiss and schist, but including
some sandstone clasts) rest directly on major erosional surfaces, suggesting that episodes of downcutting and stream
rejuvenation punctuated this association. Beds fine upward
stratigraphically and are commonly pebbly at the base, but
grade upward into coarse-grained sandstone; trough crossbedding is abundant. This lithofacies is interpreted to represent high-energy, proximal, in-channel deposition of braided
stream gravel and sand bars (cf. Miall, 1996).
Lithofacies association 3 (distal braided stream association) is composed of thin granule to pebble beds that generally overlie scour surfaces and grade upward into coarse- to
medium-grained, moderately to well sorted quartz arenite.
This association is interpreted to represent moderate- to
low-energy conditions in distal braided stream systems
where much of the sand was transported in large sand bars,
subaqueous dunes and sand waves, and by sheet flow on
submerged braidplains (cf. Miall, 1996).
Lithofacies association 4 (estuarine–braid delta association) is marked by well sorted, well rounded, generally
medium-grained quartz arenite with thin, well rounded,
quartz granule laminae. Abundant mud intraclasts are concentrated on bedding surfaces. Current ripple marks and ripple crosslaminae are pervasive throughout this association.
Minor, thin mud laminae form mud drapes over ripple marks.
This association is interpreted to represent distal braided
stream, estuarine, and braid delta deposition (cf. McCormick
and Grotzinger, 1993).
Lithofacies association 5 (upper shoreface association) is
composed of medium-grained, well sorted quartz arenite
with small-scale trough crossbedding, heavy mineral bands,
and pervasive early quartz cementation. This lithofacies is
only found in the lower sequence in core MAC-224. An
unconformity separates this interval from the overlying
Manitou Falls Formation. This lithofacies is interpreted to
represent an upper shoreface setting in either a marine or
lacustrine paleoenvironment.
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GSC Bulletin 588
Fining-upward cycle thickness and
stratigraphic correlation
Abrupt changes from finer to coarser grain size are commonly accompanied by the appearance of lithic clasts (primarily metamorphic rock fragments). Such changes may be
followed by a gradual shift to finer grain sizes, and changes in
clast composition from polycrystalline to monocrystalline
quartz. These variations, along with changes in grain size and
position of erosional surfaces, were measured and plotted
stratigraphically for each drill core in both transects (Fig. 7A,
B, see colour folio). The data used in the stratigraphic plots
were smoothed by calculating a running average (window
size of two) to compensate for possible errors in measurement of fining-upward cycle thickness. These fining-upward
packages largely represent deposition of dunes and bars in
fluvial channels. Major rapid changes in fining-upward package thickness were used to correlate changes in accommodation (Fig. 7A, B). Correlation along each of the transects
suggests topographic relief was important early in the
depositional history of the Manitou Falls Formation. The
authors estimate that there was 85 m of relief over 15 km distance, or 6 m vertical change per kilometre in the McArthur
River transect, and 30 m relief over 1500 m, or 20 m vertical
change per kilometre in the Cigar Lake transect.
Petrography and diagenesis
Diagenesis varies with lithofacies and stratigraphy due to
such factors as: the variable amount of mud matrix present,
original clast composition, sorting, and grain size. Quartz
cement is a major diagenetic component in the Manitou Falls
Formation. Quartz cement is virtually absent in units that are
clay-rich, such as the matrix-supported conglomerate of the
alluvial fan lithofacies association (Fig. 8A). Quartz cement
becomes important where interstitial clay is less abundant,
such as in the grain-supported conglomerate units that characterize the proximal braided fluvial associations (Fig. 8B,
C). Early quartz cement and paleosol horizons characterize
the well sorted lithofacies of the basal sequence in core
MAC-224 (Fig. 8D, E). The paleosol interpretation is based
on primary textures such as mechanically infiltrated mud-filled
vugs with internal horizontal laminations. The early cement
phase filled pore space and prevented significant pressure
solution. In well sorted, interstitial clay-poor lithofacies,
pressure-solution–generated silica drives precipitation of
typical burial quartz cement (Fig. 9A, B). Most stratigrapic
units that did not experience early cementation commonly
experienced intense pressure solution creating sutured
grain-to-grain boundaries (Fig. 9C, D). Where matrix clay
was present, chemical compaction coupled with clay diagenesis commonly resulted in removal of earlier formed quartz
cement through replacement (Fig. 9E, F).
A detailed paragenesis for the Manitou Falls Formation
across the entire basin was developed by Kotzer and Kyser
(1992, 1995), refined by Fayek and Kyser (1997), and is here
updated in Figure 10. Early diagenetic events include
precipitation of pore-filling quartz cement in the MFa (Qa),
precipitation of pressure-solution–derived quartz cement
(Q1), chemical compaction, precipitation of authigenic
8
phosphate (crandalite), and crystallization of hematite on
dust rims of detrital grains. Overall, the hydraulic conductivity of the Manitou Falls Formation remained relatively high
where quartz cementation was either inhibited or earlierformed cement was replaced by clay minerals. These units
preferentially would have allowed fluid movement, and thus
were important for basin hydrology during burial diagenesis.
DISCUSSION
The coarse clastic rocks that make up the Manitou Falls
Formation represent deposition in a continental basin initially
marked by alluvial fans, braided rivers, and possible shallow-marine environments (Ramaekers, 1990). Ramaekers
and Catuneanu (2004), however, interpret the marine
environments as possible lake to eolian environments. The
Proterozoic age of this succession and the absence of interbedded volcanic rocks that can be traced regionally make
paleoenvironmental determination and correlation difficult
both because of the absence of fossils, and because without
land plants to trap and bind fine-grained alluvial plain sediments, braided streams would have dominated the landscape
in which mud was rarely deposited and preserved (e.g. Schumm,
1968). Without lithological or paleontological markers, a
new approach is needed to provide intraformational correlation and a means to understand the basic foundation for diagenesis, and the resulting hydrostratigraphy of the eastern
Athabasca Basin. The sequence stratigraphic model offers a
possible means to build such a stratigraphic framework, but
outcrop extent and quality of Proterozoic rocks are generally
not sufficient to allow lateral tracing of surfaces, the detection
of erosional truncation, or the recognition of incised valleys
and sequence boundaries. Therefore, any new approach to
understanding the stratigraphy of Proterozoic continental
deposits must include a means to recognize changes in basin
dynamics (uplift, subsidence, eustasy) within generally
monotonous lithofacies from limited outcrop exposures and
drill core. This requires an understanding of the relationship between lithofacies, paleoenvironments, and their
chronostratigraphic significance.
Lithofacies and paleoenvironments in the
Manitou Falls Formation
To clarify the relationship between lithofacies and stratigraphic changes due to basin-scale processes the authors
identified and recorded Ramaekers (1980) lithofacies and
recognized five broad lithofacies associations based on interpreted paleoenvironments (Fig. 6A, B). Ramaekers (1980)
subdivided the Manitou Falls Formation into the MFa, MFb,
MFc, and MFd lithofacies based on simple criteria that make
field classification easy, however, these subdivisions are
based on factors that were largely controlled by variations in
paleoenvironmental conditions (primarily changes in fluvial
flow-energy levels). It is important to recognize the relationships between lithofacies, paleoenvironments, and their
diachronous nature.
E.E. Hiatt and T.K. Kyser
The MFa lithofacies is heterolithic and contains facies
marked by angular pebbles and cobbles with a matrixsupported texture overlain by matrix-rich sandstone units
containing mudchips and mudcracks (Fig. 6A, B) that suggest an alluvial fan setting. In one location (MAC-224; Fig. 5,
6A) MFa is marked by paleosol horizons and an interval
of well sorted quartz arenite with small-scale crossbeds.
A)
The MFa in the westernmost core in this study (RL-51; Fig. 5,
6A) is marked by a thick interval of coarse sandstone and
moderately to well sorted quartzose clast-supported
conglomerate units that represent high-energy, proximal,
braided stream deposition.
E)
dq
dq
MC
dq
dq
Qa
dq
5 µm
2 mm
B)
dq
MC
Figure 8. A) Photomicrograph in planepolarized light showing angular quartz grains
(dq) supported by a clay-rich mud matrix
(MC) that, along with lack of interbedding
or fabric suggests that this unit of MFa was
deposited in a debris flow. B) Photomicrograph
in plane-polarized light showing quartz-pebble
conglomerate with angular to well rounded
sand and gravel grains (dq) with a poorly
sorted, clast-supported texture characteristic of
the proximal braided fluvial facies association.
Quartz cement (Qa) appears to predate
significant grain-to-grain compaction and,
although it effectively blocks pore throats,
the moderate amount of mud matrix (MC)
present inhibited cementation. C) Same field
of view as in Figure 8B, but in cross-polarized
light using the mica plate (1/4 wavelength) to
highlight subtle differences in birefringence.
D) Photomicrograph in plane-polarized light
that shows a well sorted, well rounded, mediumgrained quartz arenite from MFa lithofacies in
which detrital quartz grains (dq) are completely
surrounded by hematite inclusion-rich quartz
cement (Qa). The cement predates significant
compaction as indicated by the minor degree
to which grains have experienced pressure
solution. E) Same field of view as in Figure
8D, but in cross-polarized light with the
mica plate inserted.
Qa
dq
1 mm
C)
dq
MC
Qa
dq
1 mm
D)
dq
dq
dq
Qa
5 µm
9
GSC Bulletin 588
A)
B)
dq
dq
PS
PS
Q1
dq
250 µm
Q1
dq
250 µm
D)
C)
MC
dq
dq
dq
dq
sb
sb
sb
sb
500 µm
500 µm
E)
F)
dq
dq
Q1
Dk
50 µm
dq
Q1
50 µm
Dk
dq
Figure 9. A) Photomicrograph in plane-polarized light of a well sorted quartz arenite from
MFd lithofacies in which well rounded detrital grains (dq) have undergone pressure solution
(PS) as indicated by the abundance of convex-concave grain-to-grain contacts. Silica derived
from pressure solution is reprecipitated in remaining pores as blocky quartz cement
(Q1) indicating that this cement phase is contemporaneous with or postdates
chemical compaction. B) Same field of view as in Figure 9A, but in cross-polarized light.
C) Photomicrograph in plane-polarized light of a moderately sorted quartz arenite that has
undergone significant pressure solution as indicated by the well developed solution
boundaries (sb) at grain contacts. Quartz cementation may have been inhibited in this unit by
the presence of a small amount of clay (MC), perhaps carried by groundwater into the pores.
D) Same field of view as in Figure 9C, but in cross-polarized light and with the mica plate
inserted. E) Photomicrograph in plane-polarized light showing detrital quartz grains (dq),
burial quartz cement (Q1) and dickite clay (Dk). Dickite replaced the earlier-formed quartz
cement as indicated by the dickite-filled caries in the cement. F) Same field of view as in
Figure 9E, in cross-polarized light.
10
E.E. Hiatt and T.K. Kyser
Mineral
Precompaction qartz overgrowth
Stage E Hydrothermal
alteration
Late meteoric Temp
(°C)
events
<70
Qa
Quartz overgrowth
Q1
Chemical compaction
Cm
Hematite (A-mag.)
H1
Crandallite
P1
Chlorite basement
C1, C2
Illite + dickite diagenetic
I1, K1
Hematite (B-mag.)
H2
150–
170
Fluid
Low-latitude
meteroricwater
Pore-fluids
(10–25 wt % NaCl)
Basement
fluids (reducing)
Quartz+dravite alteration halo Q2,T1
Uranium
U1,U2
Fluorapatite
A2
X1
Xenotime
Cu-Ni-As-sulphides
S1
Rutile
R1
Hematite (C-mag.)
H3
Dravite fractures
T2
Kaolinite pervasive
K2
Pyrite fractures
S2
Uranium fractures
U3
Siderite vugs
S
Kaolinite fractures
K3
U1
U2
180–
240
<50
1.7
1.4
1.0
Mid-latitude
basinal brine
(oxidizing; 30–
33 wt % NaCl)
High-latitude
meteroric waters
(<5 wt % NaCl)
0.4
Age (Ga)
Figure 10. Paragenesis of minerals in the Athabasca Basin as a function of
time. E = early, near surface (< 2 km burial) stage of diagenesis. Major
diagenetic events that established the hydrostratigraphy of the basin, as well
as the primary uranium mineralization events are highlighted by
shade-filled boxes. The H1 hematite phase (A-mag.) occurs throughout the
Athabasca Basin and has been interpreted as a paleomagnetic direction that
occurred at 1600–1750 Ma (Kotzer and Kyser, 1992). H2 hematite is
coincident with peak diagenesis and a paleomagnetic age (B-mag.) of
1450–1600 Ma (Kotzer and Kyser, 1992). The H3 hematite (C-mag.) is
coincident with recrystallization of uraninite (U2) and is association with
final stages of the Grenville Orogeny and onset of Rodinia break up at ca.
900–1000 Ma (Kotzer and Kyser, 1992; Kyser et al., 2000). Modified from
Kyser et al. (2000).
The MFb lithofacies corresponds exclusively to our
high-energy, proximal, braided stream association (Fig. 6A,
B) and is marked by coarse-grained, clast-supported,
quartz-rich conglomerate and moderately to well sorted
quartz arenite that contain abundant trough crossbedding.
This initial interval of coarse sediment is overlain by a variably developed, finer, sandy interval that probably represents
subsidence in the basin and a decrease in overall stream
energy. As noted by Ramaekers (1990) the contact between
MFb and overlying MFc is gradational. The fact that MFc
reaches a maximum thickness over an interpreted paleohigh
(Fig. 4D), and comparison of MFb and MFc isopach maps
(Fig. 4C, D) suggest that the change from MFb to MFc simply
represents a decrease in energy level in the fluvial systems.
This paleoenvironmental change would have been diachronous
across the region.
The change from MFc to the overlying MFd lithofacies is
also gradational (Ramaekers, 1990) and represents another
diachronous paleoenvironmental change. The MFd lithofacies is marked by thicker beds of well sorted, generally
medium-grained quartz arenite with abundant current ripple
marks, mudstone intraclasts, and thin granule laminae on
scour surfaces (Fig. 6A, B). The presence of mud drapes,
exceptional textural and compositional maturity of the sand,
and stratigraphic relationships suggest that MFd represents
either a distal portion of a large braided stream, or an estuary
and possible braid delta setting. McCormick and Grotzinger
11
GSC Bulletin 588
(1993) defined a braid delta facies association as one where a
sand-dominated braided stream enters a marine shelf setting,
and is subsequently modified by marine processes. In their
study of a Proterozoic braid delta system, McCormick and
Grotzinger (1993) noted that abundant mud rip-up clasts are
characteristic of the braid delta platform and braid deltaplain
environments. Abundant rip-up clasts however, could be
associated with flash floods with minor reworking and rapid
burial — conditions that based on the thickness of the MFd
must have persisted for an extended time interval. It is
unlikely that these conditions were maintained over the
extended time required to accumulate the hundreds of metres
of sediment on a braidplain. This set of characteristics and the
greater thickness of the MFd in the Cree subbasin (Fig. 4E)
are consistent with aggradation and progradation of deltaic
sand; this interpretation is further supported by the presence
of a lithofacies that suggests a possible marine incursion
noted by Ramaekers (1990, p. 20) in the upper MFd in the
west-central part of the basin. Paleoestuaries and deltaic settings, however, can be very difficult to distinguish from
alluvial, lacustrine, and marine environments in strata that
predate the advent of macrofossils (McCormick and
Grotzinger, 1993). These regional-scale stratigraphic
relationships show that the lithofacies nomenclature developed by Ramaekers (1980, 1990) reflects variation in
energy levels in the paleoenvironments, and has little
chronostratigraphic significance.
Paleotopography and subbasins
The presence of an alluvial fan facies association that thins
basinward (cores RL-51 and RL-86; Fig. 6A) and the concentration of MFa deposition in the east-central portion of the
basin (Fig. 4B) suggest that significant relief existed early
during deposition of the Manitou Falls Formation. Overall
geometries of the Fair Point Formation and the MFa lithofacies along with the subbasins (Fig. 3, 4) recognized by
Ramaekers (1981) suggest a tectonically active early stage in
the development of the Athabasca Basin. These early,
coarse-grained basal units probably mark a period when subdivision of the overall Athabasca Basin was at its greatest
with alluvial fans adjacent to paleohighs, and high-energy
braided streams flowing in the deeper parts of the subbasins
mostly from the Ahenakew drainage area of Ramaekers and
Catuneanu (2004). Subsidence and possible development of
the Dufferin paleohigh during Manitou Falls Formation
deposition is suggested by absence of MFb lithofacies
beyond the western part of the Cree subbasin (Fig. 4C).
Proterozoic continental depositional systems
and stratigraphic correlation.
The controls over stratal architecture in continental basins are
primarily: subsidence, tectonic uplift, climate, and eustasy
(Shanley and McCabe, 1994). Prior to the rise of land plants
(before the Silurian) climate would have had a much simpler
effect on sedimentary systems without the complexities
inherent in vegetated landscapes. Overbank deposition of
muddy facies would have been rare due to the absence of terrestrial macrophytes (Schumm, 1968; Cotter, 1978; Long,
12
1978) and the resulting increased effectiveness of wind in the
removal of fine-grained sediments as loess (Dalrymple et al.,
1985). Therefore, without terrestrial vegetation all Proterozoic
rivers are widely believed to have been braided due of the
lack of mud-rich cohesive overbank sediments to stabilize the
stream banks (Schumm, 1968). Without overbank mud-rich
facies, fluvial channel deposits would have been stacked one
on another causing extensive channel amalgamation. The
result is what, at least initially, appears to be monotonous
thick successions of conglomerate and sandstone without any
stratigraphic marker beds, such as shale beds that are regional
in extent (e.g. Christie-Blick et al., 1988; McCormick and
Grotzinger, 1993; Eriksson et al., 1998).
Changes in grain size have been used to recognize
sequence boundaries in Proterozoic fluvial deposits (e.g.
Christie-Blick et al., 1988), but given the dynamic nature of
the Manitou Falls Formation, changes in grain size are insufficient to permit recognition of sequence boundaries, and a
multivariate approach is needed. The present authors developed a semiquantitative method for regional correlation that
reflects significant regional changes in basin dynamics by
carefully recording the thickness of fluvial fining-upward
successions, location of erosional surfaces, and changes in
framework grain composition within the Manitou Falls
Formation and plotting these data along with lithology, lithofacies, and paleoenvironmental interpretations for each drill
core (Fig. 7A, B). Fluvial fining-upward succession thickness is interpreted as a proxy for channel depth, and thus,
accommodation (i.e. the space available for sediment
accumulation or sedimentation capacity; e.g. Vail et al.
(1977); Posamentier et al. (1988); Van Wagoner et al. (1990).
Such space is created by base-level (i.e. sea- or lake-level)
rise, decreased sediment supply, and/or tectonic subsidence
(e.g. Shanley and McCabe, 1994). Changes in climate, however, can also affect accommodation by either increasing or
decreasing sediment supply.
In continental settings climate change can modify the
shape and/or position of the fluvial equilibrium profile (e.g.
Schumm, 1968; Shanley and McCabe, 1994). Lowering this
profile can cause streams to downcut and deposit coarsegrained sediments, whereas a climate change that causes the
equilibrium profile to rise rapidly can produce the same end
result as a base-level rise. It is the change in accommodation
through time that determines the nature of the stratigraphic
succession. These concepts can be applied to stratigraphic
successions even when the mechanism responsible for the
change is not known (Emery and Myers, 1996). There is an
inverse relationship between grain size and channel thickness
— coarse-grained beds represent times of low accommodation, sediment bypassing (mud and medium- to fine-grained
sand mostly), and stream-channel amalgamation (e.g.
Wright and Marriott, 1993; Shanley and McCabe, 1994).
Finer-grained beds (medium- to coarse-grained sand mostly)
represent times of relatively high accommodation, sediment
deposition, and a low degree of channel amalgamation
(e.g. Wright and Marriott, 1993; Shanley and McCabe,
1994).
E.E. Hiatt and T.K. Kyser
These principles can be used in isolated sections, such as
drill cores, and have potential as a regional correlation tool
(provided the accommodation changes responsible for the
changing degree of channel amalgamation are regional in
extent). This technique appears to work on the kilometre
scale and the linkage between fluvial fining-upward packages and accommodation provided the basis for correlating
sections along the two transects included in this study (Fig. 5,
7A, B). The limited data set included in this study may apply
to the immediate region, but may not be represent of the entire
basin. These correlations are based largely on major changes
in fining-upward succession thickness over intervals, major
erosional surfaces, and where possible, changes in clast
composition.
This technique, however, may not be applicable to stratigraphic changes within stratigraphic sections on a fine scale
because of the potential variable sizes of individual rivers and
the randomness of channel erosion and amalgamation. In
addition to variation within the fluvial depositional system,
alluvial fan deposition would have produced individual beds
that were very different in character and with very irregular
patterns of cycle bundling relative to braided streams. This
may explain why the patterns in fining-upward cycle thickness are more subtle in the Cigar Lake transect (Fig. 7B) relative to that of the McArthur River (Fig. 7A), and why the
cycle bundling in sequence 1 and the lower portion of
sequence 2 is difficult to cor elate from core to core.
Furthfsmore, this technique may not work in all circumstances, at least when the available stratigraphic database is
limited, and where absence of coarse channel-base deposits
(i.e. very uniform sediment textures) might lead to missing
amalgamation surfaces and an underestimate of the degree of
amalgamation. Conversely, stratigraphic change within
deposits created by individual flood events might be misinterpreted as amalgamation surfaces, causing an overestimate
of the degree of amalgamation.
Sequence stratigraphy
Based on these stratigraphic relationships, a sequence
stratigraphic model was developed for the Manitou Falls
Formation in which three depositional sequences are identified (Fig. 7A, B). Sequence 1 is bounded below by the basal
unconformity developed on older crystalline basement rocks,
and by an unconformity above that marks a major change in
depositional environment and paleoclimate. This basal
sequence in the eastern Athabasca Basin is composed dominantly of the MFa lithofacies. It contains paleosol horizons
and records alluvial fan and braided stream depositional environments (Fig. 7A). Sequence 1 thickens to the southwest in
the study area because it is composed mostly of sediments
shed directly off paleohighs rimming the eastern edge of the
basin. High-energy braided fluvial deposits of MFa and MFb,
and to a lesser degree, distal braided fluvial deposits of MFc
dominate sequence 2 (Fig. 7A) and mark a period of basin
subsidence and rapid filling. Gradually, channel depth and
accommodation increased, as inferred from thicker finingupward stratigraphic successions. Sequence 2 is terminated
by an unconformity marked by a sudden decrease in fluvial
fining-upward succession thickness suggesting a rapid drop
in base level that would have caused downcutting and channel amalgamation (Fig. 7A, B). The base-level fall that led to
the boundary between sequence 2 and sequence 3 caused a
rapid, regional-scale accommodation drop; active river systems downcut, channels would have become highly amalgamated, and finer-grained sediment bypassed the study area
(was flushed through in suspension) and was deposited to the
west. Sequence 3 is marked by a period of relatively low base
level as suggested by coarser grained sediments of the MFc
lithofacies and thin fining-upward cycles, followed by a
major increase in accommodation reflected in the finer
grained sediments and thick, fining-upward cycles of the
MFd lithofacies. The sequence boundary that caps sequence
3 was not captured in these drill cores in this study area. The
next reported sequence boundary is the contact between the
Manitou Falls Formation and the overlying units (Lazenby
Lake and Wolverine Point formations; Ramaekers and
Catuneanu (2004)), and may correspond to the top of
sequence 3 of this study.
Stratigraphic controls on diagenesis
In Proterozoic continental deposits diagenetic processes differed from those of the Phanerozoic because of the paucity of
muddy facies. In these matrix-poor rocks compaction (both
mechanical and chemical) and cementation play a more
important role in determining porosity and permeability than
do depositional processes relative to similar Phanerozoic
ones (Hiatt et al., 2003). Depositional aquitards (impermeable mud-rich facies) in these continental settings are virtually absent and the role of quartz cementation becomes more
important in establishing initial basin hydrology (Hiatt et al.,
2003). Because quartz cement preferentially formed in
quartz-rich, clay-poor, well sorted lithofacies, the porosity
and permeability relationships during the critical interval of
peak diagenesis (Fig. 10) in the burial setting in the Manitou
Falls Formation were opposite to those predicted on the basis
of lithofacies characteristics.
There is a predictable succession of facies within each of
the Manitou Falls Formation sequences (Fig. 7A, B). The
lower part of each sequence consists of the coarsest sediment
and thinnest fining-upward cycles, and the smallest amount
of quartz cement (Fig. 7A, B). These deposits commonly contain an interstitial clay component that is interpreted to have
formed either by depositional processes, the infiltration of
mud, sometimes associated with soil-forming processes,
because water tables were commonly low and variable during
lowstands, and/or by the diagenetic alteration of detrital aluminosilicate grains, such as feldspar. This clay inhibited later
quartz cementation during burial diagenesis (Fig. 8A, B, C).
Basal units in each sequence are overlain by finer grained,
quartz-rich, clay-poor facies composed of much more
compositionally and texturally mature sediments. The
absence of clay and excellent initial hydrological properties
permitted preferential development of quartz cementation in
these more quartz-rich facies (Fig. 8D, E, 9A, B).
13
GSC Bulletin 588
Quartz cementation
Grain-to-grain spatial relationships give a first-order indication of relative timing of quartz cementation with respect to
burial-driven compaction (e.g. Pittman, 1979). In stratigraphic units that experienced early quartz cementation,
grain-to-grain relationships show few signs of compaction
before emplacement of cement. The earliest such quartz
cement in the Athabasca Basin is a blocky cement phase that
is found only in the well sorted lithofacies in sequence 1
(Fig. 8D, E). Based on isotopic analysis, Hiatt et al. (in press)
determined that this cement phase formed at temperatures
that correspond to burial depths of less than 1 km. This
cement phase appears to have formed before the onset of
pressure solution, and therefore required an external source
of dissolved silica. Its close association with a paleosol horizon (Fig. 6A) suggests intense weathering may have provided the silica. Where some matrix clay was present, quartz
cementation was patchy, but because it preferentially formed
at grain contacts it effectively lowered the permeability of the
rock (Fig. 8B, C).
The next stage of cementation occurred during burial
compaction with silica derived through compaction-driven,
grain-to-grain pressure solution. This burial-cement phase
precipitated in open pores adjacent to pressure-solution
points (Fig. 9A, B). Quartz cement with this morphology is
common in sandstone in general and is well developed in
clay-free units of lithofacies associations 3 and 4, and to a
lesser extent lithofacies association 2. Pressure solution can
also occur with little cement precipitation and, in the absence
of clay matrix, can result in ‘welded’, interlocking grain fabrics (Fig. 9C, D). Where clay was present, compaction, along
with replacement reactions, often resulted in dissolution of
earlier-formed quartz cement (Fig. 9E, F). Although this
matrix clay occludes porosity to varying degrees, some permeability remains and such units can allow fluid movement
in the burial realm (cf. Hiatt et al., 2003).
Athabasca Basin hydrostratigraphy
Changes in sedimentary environments are ultimately driven
by basin-scale processes that control the internal fabric and
lateral and vertical extents of rock types that fill sedimentary
basins (e.g. Hiatt, 2000). Depositional environments not only
determine internal aquifer properties, but on a basin scale
(tens to hundreds of kilometres) their geometries are one of
the major factors that determine the degree of aquifer
compartmentalization. The sequence stratigraphic model for
the Manitou Falls Formation presented above provides a
means of understanding the degree of aquifer heterogeneity
and compartmentalization in the eastern portion of the basin.
Figure 11 summarizes the possible relationships between
sequences, lithofacies, and geometries of the fluvial basinfilling succession. During times of lowered base level, fluvial
channels incise into pre-existing sequences, show a high
degree of amalgamation, and are typically very coarse
grained. These conditions characterize the porous and permeable lower portions of the MFa, MFb, and to a lesser extent,
the MFc lithofacies. The juxtaposition of a major aquifer over
14
the paleoweathering surface on the basal unconformity may
have channellized flow along the unconformity, and established a flow system that delivered basinal fluids to sites of
mineralization. Indeed, Holk et al. (2003) showed that fluids
associated with uranium mineralization moved preferentially
along the basal unconformity in both transects included in
this study. Based on lithological and diagenetic characteristics, the lower portion of the upper sequence should have
been favorable for fluid flow also; although due to limited
stratigraphic thickness and greater textural and compositional maturity, this aquifer would have played a lesser role
than that of the underlying sequences. The overlying
clay-rich Wolverine Point Formation would have been a
regional aquitard; it shows little evidence of diagenetic alteration relative to the underlying Manitou Falls Formation,
suggesting that it was indeed a barrier to fluid flow (Sibbald
and Quirt, 1987).
The authors developed a hydrostratigraphic model based
on the integration of sedimentology, diagenesis, and the
sequence stratigraphic model presented above (Fig. 12). This
hydrostratigraphic subdivision shows that aquifers thin and
onlap onto the basal unconformity in the eastern portion of
the basin. This geometry would have focused diagenetic fluid
flow toward the underlying basement in the eastern portion of
the basin (Fig. 12) and could have established a flow system
that delivered basinal fluids to sites favorable for mineralization (rocks in the underlying basement that contain graphite,
amphibole, etc. drive reduction reactions).
Possible mechanisms driving fluid movement include:
thermal convection, tectonic uplift and/or subsidence, and
compaction-driven expulsion of pore fluid (e.g. Raffensperger,
1997; Einsele, 2000). It may be impossible to identify the
exact mechanism(s) controlling fluid flow in the Athabasca
Basin. The choice of mechanism has profound implications
for basin evaluation and exploration strategy. For example, if
compartmentalization produced by the development of
diagenetic aquitards directed or focused fluid flow, as proposed here, then aquifer intersections with paleotopographic
highs become important targets. If on the other hand, the thermal convection model is adopted, then uranium mineralization is predicted to occur throughout the basin where these
convection cells intersect reducing rock types (graphitic
schist units are the most common in the Athabasca Basin) in
the underlying basement rocks (Raffensperger, 1997). This
model, however, requires that the flow of convection cells
was uninterrupted in a sedimentary succession that is greater
than 2 km thick (Raffensperger, 1997).
Subtle differences between sequences in the Athabasca
Basin, coupled with stratigraphic control over later diagenesis, led to the development of distinct diagenetic pathways for
fluid flow (Fig. 12). As a result, permeabilities would not
have been uniform stratigraphically at the time when the uranium mineralizing fluids were flowing in the basin. Thus, it is
unlikely that the thermal convection mechanism could
operate given the complexity of the hydrostratigraphy.
Furthermore, chemostratigraphic analysis of lead isotopes in
the Athabasca Basin shows that fluids associated with uranium mineralization flowed laterally along the main aquifer
SB-1
SB-2
SB-3
SB-4
Dufferin
Paleohigh
Virgin
River Domain
Mudjatik Domain
Cree subbasin
Wollastin Domain
Virgin
River Domain
Cree subbasin
Mudjatik Domain
MFc
Wollaston
Mineralization
MFd
Figure 12. Interpreted hydrostratigraphy of the Athabasca Basin. Aquifers represent stratigraphic units that could
have conducted burial brines associated with uranium mineralization along the eastern portion of the basin.
Aquitards represent stratigraphic intervals that were preferentially cemented with quartz prior to major mineralization events, and intermediate aquifers were units that would have allowed a small amount of fluid movement, but were
not major conduits for mineralizing fluids. Lithofacies in the Manitou Falls Formation unit A, B, C, and D are
represented by MFa, MFb, MFc, and MFd, respectively.
Mirror subbasin
Western Craton
MFa
Lazenby Lake Fm
Wolverine Point Fm
MFb
MFc
Mineralisation
MFb
Figure 11. Generalized east-west cross-section of the eastern Athabasca Basin showing interrelationships between lithofacies,
lithostratigraphy, and sequence boundaries (SB-1, SB-2, and SB-3). Lithofacies in the Manitou Falls Formation unit A, B, C, and
D are represented by MFa, MFb, MFc, and MFd, respectively. Note that the MFb, MFc, and MFd lithofacies are diachronous and
interfinger stratigraphically.
Mirror subbasin
Western Craton
MFa
MFc
MFd
Lazenby Lake Fm
500 m
Wolverine Point Fm
SB-1
&
SB-2
SB-3
SB-4
500 m
Crossbedding
Pebbles
Current ripple marks
Wave ripple marks
Heavy minerals
Mud rip-up clasts
E.E. Hiatt and T.K. Kyser
15
GSC Bulletin 588
unit identified in this study (Holk et al. (2003); Fig. 12), and
not vertically, as would have been the case if thermal
convection had occurred.
CONCLUSIONS
Understanding paleohydrological systems during basin evolution requires integration of sedimentology, stratigraphy,
diagenesis, and geology of basin-filling successions. The
semiquantitative method to arrive at a sequence stratigraphic
model presented here utilizes fluvial fining-upward succession thickness in the Manitou Falls Formation as a proxy for
changes in channel thickness, and thus accommodation. The
authors’ data from the eastern Athabasca Basin may not be
completely representative of the entire basin, but the results
may provide a possible tool for correlation with chronostratigraphic significance in the absence of alternate stratigraphic markers. It allows the recognition of stratigraphic
sequences in the Athabasca Basin and should be applicable to
other Proterozoic (and younger) fluvial deposits where
changes in accommodation are caused by changes in basin
dynamics. These results confirm theoretical models wherein
the influence of changing accommodation affects the stratigraphic architecture of fluvial deposits; this technique should
be further tested regionally in the Athabasca Basin and in
other younger basins where independent means exist to
generate a sequence-stratigraphic subdivision.
There is a systematic relationship between diagenesis and
stratigraphy in the Manitou Falls Formation. During periods
of low accommodation, fluvial channels were highly amalgamated, experienced downcutting, and most finer grained
sediment was bypassed to distal settings. These intervals are
marked by variable amounts of clay due to depositional and
diagenetic processes, subsequently experienced little quartz
cementation, and thus, were highly permeable during mineralization-related burial diagenesis. During periods of high
accommodation, fluvial channel amalgamation was at a
minimum, channels were large, and migrated across the
braidplains, and extensive medium-grained, texturally and
compositionally mature sandstone units were deposited.
These clay-poor units experienced extensive quartz cementation, and thus became diagenetic aquitards at the time of
mineralization. This relationship is important where the stratigraphic sequences onlap to the east onto paleotopographic
highs. Burial brines, possibly driven by tectonic tilting of the
basin toward the east, moved laterally within aquifer units
that are concentrated, but not limited to, the lower sequences.
This lateral flow was a direct result of the hydrostratigraphy
of the Athabasca Basin; it lends support for hydrostratigraphic focusing of basinal fluids into zones where
diagenetic aquifers onlap basement rock types. These factors
should be taken into account in development of exploration
strategies.
16
ACKNOWLEDGMENTS
The authors would like to thank the staff at Cameco
Corporation, including Dave Thomas, Vlad Sopuck, Scott
McHardy, and Ken Wysluk for providing logistical, technical, and geological assistance and advice. Thanks to Paul
Ramaekers and Grant Young for thoughtful reviews that
improved the final version of this manuscript. The authors
also thank colleagues at Queen’s University including Bob
Dalrymple for discussions that led to the development of
the stratigraphic model, and Paul Polito and Kyle Durocher
for helping further the authors’ understanding of basin
analysis. This project was funded by a Natural Science
and Engineering Research Council of Canada (NSERC)
operating grant and an NSERC–Cameco Corporation
Collaborative Research and Development grant to T.K. Kyser.
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Depth (m)
800
700
600
500
400
300
200
100
0
A)
MFa
MFb
MFc
MFd
Gneiss
F M C G P Cb
RL-51
Proximal braided stream
Alluvial fan
1
500
400
300
200
100
0
MFa
MFb
MFc
MFd
F M C G P Cb
Quartzite
2.5 km
Depth (m)
Depth (m)
600
500
400
300
200
100
0
MFa?
MFa
MFb
MFc
MFd
Paleosol
F M C G P Cb
Gneiss
MAC-224
Figure 6. A) Lithological logs for the drill cores in the McArthur River transect: RL-51, RL-86, and
MAC-224 (Fig. 5). B) Lithological logs for drill cores near the Cigar Lake deposit: CL-182, CL-185, and
CL-229 (Fig. 5). Lithofacies associations and sedimentary structures are shown on the logs. The position
of each right edge of the log shows the mean grain size: F = fine-grained sand, M = medium-grained
sand, C = coarse-grained sand, G = granules, P = pebbles, Cb = cobbles. Lithofacies in the
Manitou Falls Formation unit A, B, C, and D are represented by MFa, MFb, MFc, and MFd, respectively.
Mudcracks
Mud rip-up clasts
Heavy minerals
Wave ripple marks
Current ripple marks
Pebbles
Crossbedding
Distal braided stream
Estuarine–braid delta
Upper shoreface–marine
Interpretation
5
4
3
2
Lithofacies
Key:
15 km
RL-86
From: Article by E.E. Hiatt and T.K. Kyser
19
20
Depth (m)
MFa
MFb
MFc
MFd
Metapelite
1.5 km
F M C G P Cb
Figure 6. (cont.)
600
500
400
300
200
100
0
B) CL-182
500
400
300
200
100
0
MFa
MFb
MFc
MFd
0.5 km
F M C G P Cb
Metapelite
CL-185
500
400
300
200
100
0
MFa
MFb
MFc
MFd
F M C G P Cb
Schist
CL-229
Proximal braided stream
Alluvial fan
1
Mudcracks
Mud rip-up clasts
Heavy minerals
Wave ripple marks
Current ripple marks
Pebbles
Crossbedding
Distal braided stream
Estuarine–braid delta
Upper shoreface–marine
Interpretation
5
4
3
2
Lithofacies
Key:
From: Article by E.E. Hiatt and T.K. Kyser
Depth (m)
Depth (m)
Depth (m)
800
700
600
500
400
300
200
100
0
A)
MFa
MFb
MFc
MFd
F M C G P Cb
Gneiss
RL-51
0
20
15 km
500
400
300
200
100
0
MFa
MFb
MFc
MFd
0
10
20
Apparent accommodation
(thickness in metres)
F M C G P Cb
Quartzite
RL-86
SB-1
Sequence 1
SB-2
Sequence 2
2.5 km
SB-3
Sequence 3
600
500
400
300
200
100
0
MFa?
MFa
MFb
MFc
MFd
0
10
20
Apparent accommodation
(thickness in metres)
Paleosol
F M C G P Cb
Gneiss
MAC-224
Figure 7. A) Correlation diagram for the McArthur transect drill cores, RL-51, RL-86, and MAC-224 (Fig.
5). B) Correlation diagram for the Cigar Lake transect drill cores CL-182, CL-185, and CL-229 (Fig. 5).
Lithofacies associations and sedimentary structures are shown on the logs. The position of each right edge
of the log shows the mean grain size: F = fine-grained sand, M = medium-grained sand, C =
coarse-grained sand, G = granules, P = pebbles, Cb = cobbles. Lithofacies in the Manitou Falls Formation
unit A, B, C, and D are represented by MFa, MFb, MFc, and MFd, respectively. For each diagram, the bar
graph to the right of each lithological log is the thickness of a single depositional cycle in its correct stratigraphic position. Depositional cycles are dominantly expressed as fining-upward successions caused by
fluvial processes and represent apparent accommodation. The shaded areas around the thickness data
highlight major trends in accommodation. Dashed lines represent interpreted correlations of fining-upward
cycle bundles. Sequence boundaries (SB-1, SB-2, and SB-3) were identified based on sedimentological
characteristics and major stratigraphic changes in accommodation.
10
Apparent accommodation
(thickness in metres)
From: Article by E.E. Hiatt and T.K. Kyser
21
22
MFa
MFb
MFc
MFd
0
5
10
Apparent accommodation
(thickness in metres)
F M C G P Cb
Metapelite
Figure 7. (cont.)
600
500
400
300
200
100
0
B) CL-182
SB-1 & SB-2
Sequence 2
SB-3
Sequence 3
1.5 km
500
400
300
200
100
0
MFa
MFb
MFc
MFd
0
5
10
Apparent accommodation
(thickness in metres)
F M C G P Cb
Metapelite
CL-185
0.5 km
500
400
300
200
100
0
MFa
MFb
MFc
MFd
0
5
10
Apparent accommodation
(thickness in metres)
F M C G P Cb
Schist
CL-229
From: Article by E.E. Hiatt and T.K. Kyser
Depth (m)