In western Saskatchewan the Mississippian carbonate rocks may be categorized into 5 lithofacies, which individually or collectively can be used to assist the interpretation of the various environments of deposition. The five categories are: (1) impoverished calcareous mudstone, (2) skeletal calcareous mudstone, (3) micritic skeletal or nonskeletal sandstone, (4) poorly washed skeletal sandstone, and (5) calcite-cemented skeletal or nonskeletal sandstone.

The impoverished calcareous mudstones dominate the lower part of the Mississippian succession, particularly in the southern part of the study area, where they are composed of bituminous and argillaceous materials as well as nonargillaceous calcareous mudstones. The impoverished calcareous mudstones probably represent sediments deposited in water below wave base on the seaward side of the shelf edge.

Collectively, the skeletal lithofacies probably represent shelf-edge deposits. Calcite-cemented crinoidal sandstones accumulated as thick, elongate banks. The poorly washed sandstones are generally at the top and bottom of the banks and the interbank areas show outward gradations from micrite skeletal sandstones on the flanks of the banks to skeletal calcareous mudstones in the centers of the interbank areas. Micritic skeletal sandstones also form blanket deposits that commonly act as platforms upon which the crinoidal banks were built.

The nonskeletal sandstones (primarily composed of oolites) probably represent subtidal deposits on the shoreward side of the shelf edge. In the central part of western Saskatchewan they are present in the lower part of the succession and pass laterally southward into shelf-edge deposits. Farther south they are found at higher stratigraphic levels, and they are in lateral continuity with and overlie shelf-edge deposits. The relationships suggest a regression of open marine conditions from north to south.

If the Mississippian sequence of southeastern Saskatchewan is used as an analogy, a dolomite-evaporite facies representing a supratidal environment probably existed north of the subtidal deposits, that is, beyond the present subcrop edge of the Mississippian in western Saskatchewan.

This postulated distribution of facies suggests that possible hydrocarbon reservoirs similar to those of the Virden area of Manitoba are present in subtidal and shelf-edge deposits along the Mississippian subcrop in Saskatchewan.

End_of_Article - Last_Page 959------------