Mineralogy and oxygen isotope geochemistry of clays ...

Mineralogy and oxygen isotope geochemistry of clays from surficial deposits in the Athabasca Tar Sands area G. A. SPIERS AND M. J. DUDAS Department of Soil Science, University of Alberta, Edmonton, Alta., Canada T6G 2E3

K. MUEHLENBACHS Department of Geology, University of Alberta, Edmonton, Alta., Canada T6G 2E3 AND

L. W. TURCHENEK

Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Hubei university on 06/04/13 For personal use only.

Soils Department, Alberta Research Council, Edmonton, Alta., Canada T6H 5R7

Received May 13, 1983 Revision accepted August 12, 1983 Detailed clay mineralogical characterization was completed on four major glaciogenic surficial deposits in northeastern Alberta. The mineral species identified and quantified were mica, montmorillonite, beidellite, kaolinite, chlorite, and vermiculite. Although there were quantitative differences in the amounts of mica, kaolinite, and chlorite in the Legend unit, the similarity of the mineral species in all deposits precluded their use for a definitive assessment of sediment provenance. Oxygen isotopic data for the clay separates served as a useful criterion for differentiation of deposits. Differences in isotopic signature were related to the inclusion of materials from the underlying Cretaceous marine sediments and to the admixture of materials from preweathered Shield sediments. The difference in isotopic signature of the clay separates was specifically related to the formation conditions of the micaceous component. Une etude dCtaillk de la minkralogie des argiles fut rkaliske pour caractkriser quatre dep6ts superficiels glaciogenCtiques du nord-est de I'Alberta. Les espirces minkralogiques prksentes et kvalukes quantitativement sont le mica, la montmorillonite, la beidellite, la kaolinite, la chlorite et la vermiculite. Bien que I'on obtient des diffkrences quantitatives dans la teneur en mica, kaolinite et chlorite pour I'unitk Legend, la trop grande similitude des espirces minkralogiques dans tous les autres dCp6ts nous empCche d'utiliser leur minkralogie pour trouver de faqon explicite la source des sediments. Les donnCes de I'oxygkne isotopique des skparations d'argile furent utiliskes comme critirre pour distinguer les dCp6ts. Les diffkrences de signature isotopique sont relikes avec l'addition de matkriaux provenant de skdiments marins sous-jacents du CrktacC et avec l'apport de matCriaux de skdiments dkja altkres du Bouclier. La difference de signature isotopique pour les skparations d'argile est spkcifiquement relike aux conditions de formation de la composante micacke. [Traduit par le journal] Can. J. Earth Sci. 21. 53-60 (1984)

Introduction A major question in studies of glaciogenic sediments is identification of the provenance of the sediment matrix, especially in regions of continental glaciation. Several major surficial deposits of glacial origin occur in the Athabasca Tar Sands region (Bayrock 1971; Bayrock and Reimchen 1974). Four of these deposits have been mapped as parent materials of the Kinosis, Legend, Horse River, and Dover soil units (Turchenek and Lindsay 1982). However, there is little information describing either provenance or mineralogical composition of these materials. The proximity of this area to the boundary between the Precambrian, Paleozoic, and Cretaceous bedrock formations (which strike perpendicularly to the regional Quaternary ice-flow directions) and the nature of the surficial deposits suggest there are multiple source lithologies for these materials. Methods of regional identification of till lobes or glacial events have been based on properties such as texture and lithologic composition (Twardy et al. 1974), mineralogic composition (Gwyn and Dreimanis 1979; Rieck et al. 1979), geochemical composition (May and Dreimanis 1973), and weathering characteristics (McGregor 1981). Application of isotopic analyses such as Rb/Sr dating of feldspar separates in tills in the Transantarctic Mountains to differentiate sediment provenance (Taylor and Faure 1981) has been infrequent. Previous work with the oxygen isotope geochemistry of diagenetic phyllosilicate clays has demonstrated that there is neg-

ligible isotopic exchange or re-equilibration with pore fluids at low temperatures (Savin and Epstein 1970; James and Baker 1976). This property has enabled clay separates to be utilized as tracer material in the determination of abyssal sediment provenance (Mokma et al. 1972; Lawrence 1979). Data for the oxygen isotope geochemistry of potential source materials of the surficial sediments in northeast Alberta are limited. Values of 13'1~0relative to standard mean ocean water (SMOW) have been reported for the clay fraction of the Athabasca Group metasediments (Hoeve et al. 1981) and values of 18'1~0for the Clearwater Formation were obtained in this laboratory. This latter value is similar to those documented for both the lateral extension of Cretaceous marine shales in central Alberta (Longstaffe 1983) and for marine shales elsewhere (Savin and Epstein 1970). The distinctness of these values indicates that isotopic analyses of clay fractions may provide a new and useful tool to identify the source of the glaciogenic sediments of the region. The objective of this study was to obtain basic clay mineralogical data for surficial units in northeastern Alberta, and to determine whether oxygen isotope geochemistry of either the individual mineral species or of the whole clay separates can be related to provenance of surficial deposits.

The study region The location of the study region and sampling sites and the bedrock geology are depicted in Figs. 1 and 2. The uplands

CAN. 1. EARTH SCI. VOL, 21, 1984


1 1 1"

FrG. 1. Location and generalized surficial geology of the study area. L = glaciolacustrine clay and silt; Tg = Gypsy till; Tk = Kinosis till; Th = Horse River till; TI = Legend till. V = erosional gullies and river valleys; C = colluvial mixed bedrock and glacial material; E = eolian sand; Ff = fluvial fan deposits; Fg = glaciofluvial outwash sand; K = glaciofluvial ice-contact sand and gravel. Adapted from Bayrock and Reimchen (1974), Bayrock (197 I), and Turchenek and Lindsay (198 1).

of the region are mantled by glacial till deposited by the late Wisconsinan glaciation. These were mapped by Bayrock (1971) and Bayrock and Reimchen (1974) as three distinct units. The Legend till found on Birch Mountain has a loamy to clayey matrix and forms the parent material of the Legend soil

unit, and the till on the Stoney and Muskeg mountain areas forms the parent material of the Kinosis soil unit. The clayey calcareous till of the region forms the parent material of the Horse River soil unit (Turchenek and Lindsay 1982). During deglaciation Glacial Lake McConnell was formed when the ice

SPIERS ET AL.


UPPER CRETACEOUS Ks Smoky Group shale Kd Dunvegan Fm - sandstone shale Ksh Shattesbury Fm - shale Klb Lablche Fm - shale LOWER CRETACEOUS

FIG. 2. Generalized bedrock geology of the study area. Adapted from original map in Green (1972).

front retreated north beyond Fort McMurray (Christiansen 1979). The lacustrine sediments of Glacial Lake McConnell form the parent material of the Dover unit. Sites 4 and 14, at the southern limits of the lacustrine sediments, were taken from

isolated till "islands" that had no surf~ciallacustrine veneer (Fig. 1). Textural data describing these four surficial units are listed in Table 1. Precambrian metasediments, granite gneisses, and porphy-.

TABLE 1. Modal textural data for the major surficial units of the study region

Kinosis Horse River Legend Dover


I

CAN. 1. EARTH SCI.

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Number of samples

Sand

Silt

Clay

(%)

(%)

(%I

12 11 12 II

48 36 32 29

30 34 34 36

22 30 34

35

ritic granites subcrop and outcrop to the northeast of the region (Fig. 2). The clay minerals of the Athabasca Group are kaolinite and illite in varying proportions with or without chlorite as a significant third component (Hoeve et al. 1981). These are bounded to the southeast by Devonian evaporites and carbonates. The Lower Cretaceous formations outcrop in the Athabasca River valley in the centre of the region, and Upper Cretaceous formations form the remnants of the Alberta Plateau uplands in the northwest and southeast of the study area. Carrigy (1959) described the clay component of the Devonian rocks of the region as a mixture of kaolinite, illite, and chlorite. The Lower Cretaceous formations have a similar clay suite (Carrigy and Kramers 1973). The Upper Cretaceous formations of the Alberta Plateau remnants forming the Birch and Stoney mountains and the Thickwood Hills have a different clay suite: smectites are the major species, with lesser amounts of illite and kaolinite and trace amounts of chlorite and vermiculite (Carrigy and Mellon 1964). There is no published information on the clay mineral assemblages of the surficial deposits.

Materials and methods Forty-six sites representative of the Kinosis, Legend, Horse River, and Dover soil units were sampled for the characterization and geochemical phase of the study after detailed field mapping. Single bulk samples (2 kg) were collected from the C horizons (100- 150 cm) of soils at all sites except 1 and 16 (Fig. 1, Table 3), where five and six samples, respectively, were taken at approximately 25 cm intervals from a 1.5 m section. The samples were then air dried and ground to pass a 2 mm sieve. Clay (