Alberta Geological Survey
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The Famennian subsurface strata of Saskatchewan, Alberta and British Columbia consist of a series of stacked cyclical ramp and shelf carbonates and associated evaporites of the Wabamun Group. These rocks are coeval with Palliser Formation strata exposed in the Rocky Mountain Front Ranges. In northeastern British Columbia the ramp carbonates shale out into the Besa River shales of the Liard Basin. There is some evidence of a shale-out of the Palliser to the west in southeastern British Columbia (Richards, 1989), although stratigraphic relations have been obscured by later tectonic deformation. The eastern and northern margins of the Wabamun Group are defined by pre-Mesozoic erosion. Famennian sedimentary rocks subcrop beneath Mesozoic clastic rocks from Alberta to Manitoba along a belt extending some 700 km (Fig. 13.1).
The outcropping Palliser Formation is subdivided into two members: the Morro and the overlying Costigan. These correspond respectively to the Stettler and Big Valley formations of the subsurface Wabamun Group (Fig. 13.2). A major unconformity separates these units in both surface outcrops and the subsurface. Morro carbonates overlie Famennian Sassenach sandstones in the southern Rocky Mountains and Frasnian Simla limestones in the northern outcrop areas. Subsurface Wabamun strata overlie the Famennian upper Graminia Formation. Contact between the Famennian upper Graminia silt and the Wabamun carbonates is gradational, a result of reworking of upper Graminia strata during the Wabamun transgression (see Switzer et al., this volume, Chapter 12).
In the Liard Basin the Famennian part of the Besa River shales grades eastward into carbonates and shales of the Tetcho and overlying Kotcho formations (Fig. 13.2). These sediments interfinger with shallow-water shelf carbonates of the Stettler Formation via a ramp relationship. Stettler cyclic shelf carbonates grade southeastward into evaporite-dominated sediments. In Saskatchewan, equivalent strata are siliciclastics and dolomites of the Torquay Formation, and in Manitoba, redbed strata of the Lyleton Formation (Fig. 13.2).
Sediments of the overlying Costigan-Big Valley interval are less widespread than those of the Stettler Formation. A shallow sea spread northward across the shelf from Montana through southwestern Saskatchewan and southern Alberta into north-central Alberta. Open-marine fossiliferous limestones and shales were deposited, with restricted sediments occurring locally; for example, in the Coleville Basin in Saskatchewan. The northern and eastern present-day limits of Costigan and Big Valley sediments are erosional (Fig. 13.1).
Costigan-Big Valley carbonates and shales are overlain by the Exshaw/Bakken shales and the Banff siliciclastics and carbonates.
The regional distribution and geology of Palliser-Wabamun strata was described in the previous atlas - Geological History of Western Canada (Belyea, 1964). Much of the knowledge at that time came from the work of Beales (1956) and Sutterlin (1958), and the regional work of Andrichuk (1960) in west-central Alberta, and Christopher (1961) in Saskatchewan.
More recently, regional aspects of Palliser sedimentation were discussed by Morrow and Geldsetzer (1988) and regional Wabamun stratigraphy by Moore (1989). Their work complements work on equivalent strata in the Western United States by Sandberg et al. (1988). Recently, Richards et al. (1991) published significant conodont data, which improved correlations from the United States into Canada.
The early work by Andrichuk (1960) was extended by Metherell and Workman (1969) and Workman and Metherell (1969), with a detailed study of the Crossfield Member in the Stettler Formation of central Alberta. A depositional model for the Crossfield was developed by Eliuk (1984). The concept of sequence stratigraphy was applied to the Palliser Formation in the Moose Mountain area by Styan (1984).
Halbertsma and Meijer Drees (1987) subdivided Stettler-equivalent carbonates in the Peace River Arch area of north central Alberta into four mappable units. Nishida (1987) published on Wabamun patch reefs. Possible hydrothermal dolomitization was discussed by Stoakes (1987) and Packard and Pellegrin (1989). Churcher and Majid (1989) compared fault-bounded reservoirs in the Tangent area with the Ordovician Albion-Scipio play in the Michigan basin. Workum (1991) suggested that localized dolomite reservoirs may have been formed in association with subaerial karst.
Stratigraphic units in Palliser/Wabamun strata are illustrated in the correlation chart (Fig. 13.2).
Major unconformities, apparently equivalent in age, separate the outcropping Palliser Formation into the Morro and Costigan members and the subsurface Wabamun into the Stettler and Big Valley formations (Wonfor and Andrichuk, 1956; Richards et al., 1991).
The Tetcho Formation and overlying Kotcho Formation of northeastern British Columbia are coeval with the Stettler Formation of Alberta. In north-central Alberta, Stettler carbonates are subdivided into four members. In ascending order they are: the Dixonville, Whitelaw, Normandville and Cardinal Lake members (Halbertsma and Meijer Drees, 1987). The Crossfield Member is developed as a wedge in the middle of the evaporitic facies of the Stettler Formation in central and southern Alberta. It is considered equivalent to the combined Whitelaw and Normandville members of north-central Alberta. The Torquay Formation in Saskatchewan is the equivalent of the Stettler succession and can be subdivided into six units, of which the middle unit (No. 3) is possibly the equivalent of the Normandville Member of Alberta (Christopher, 1961).
The Big Valley Formation is eroded over and north of the Peace River Arch. It is, however, widely developed over central and southern Alberta and overlies the Stettler-equivalent Torquay Formation in Saskatchewan. The Torquay, Big Valley and Bakken formations of Saskatchewan together comprise the Three Forks Group.
Famennian Palliser/Wabamun cratonic basins can be subdivided into several major elements, reflecting their varied structural history (Fig. 13.1). The farthest basinward sediments are contained in the Liard Basin and in outer shelf or basin slope settings in northeastern British Columbia. Shelf sediments occur on the Hay River and Alberta inner shelf areas, separated by the Peace River Arch. The Smoky River Sub-basin is developed on the Alberta inner shelf area just south of the Peace River Arch. Infilling carbonates reflect a slight deepening of the environment. Along the deformed belt, the Sukunka Uplift in the northern Rocky Mountains separates deeper sediments of the Liard Basin from those of the Sassenach Sub-basin in southeastern British Columbia. Inner shelf carbonates, evaporites (Sweetgrass Arch area) and clastics occur to the southeast and east in a more landward position. More restricted clastics occur in the eastern-most Coleville1 Sub-basin, which is developed on the Saskatchewan inner shelf.
Onlapping relations show that the Peace River Arch remained high-standing but relatively inactive during Stettler sedimentation. This tectonic stability during Stettler deposition holds true for much of the shelf areas.
Relative sea-level changes during Stettler deposition appear to be mostly eustatic. This is particularly the case for transgressive upper Morro/Normandville patch reef and mud-mound carbonates, which can be correlated with similar age mud-mounds in Utah-Nevada and Belgium.
A major erosional unconformity, however, separates the Costigan/Big Valley and Morro/Stettler strata (Fig. 13.2) and very likely represents the onset of a period of structural instability. This tectonism, which continued well into the Carboniferous (Antler Orogeny), is evidenced by post-Stettler uplift and erosion of the Costigan/Big Valley section in the northern Rocky Mountains, the Liard Basin and the Peace River Arch. Geldsetzer (1982) reported erosional removal of the entire Palliser section north of latitude 54°N and west of longitude 121°W. Bentonites in Big Valley mudstones in Saskatchewan, and volcanic ash interbedded with Exshaw shales in southeastern and northeastern British Columbia indicate volcanism.
Alberta Geological Survey
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