The area examined is located in the northern part of the Williston Basin in southeastern Saskatchewan. The lithology and stratigraphy of the Mississippian strata of this area (excluding the Bakken formation) are discussed. Emphasis is given to the clarification of correlation problems which exist in certain parts of the succession. For the purpose of illustration, subcrop maps, cross-sections and isopach maps of the various Mississippian units are presented.

The Mississippian strata consist mainly of limestone and dolomites with several interbedded evaporite beds in the upper part of the succession. At the present time these Mississippian rocks are the most important oil- producing strata in Saskatchewan. The oil reservoirs occur in porous limestones or dolomites. Reservoir cap-rocks may be divided into 3 distinct categories--(1) those crested by primary evaporites in the normal Mississippian succession; (2) those caused by secondary infilling of normally porous and permeable rocks by anhydrite and dolomite, giving rise to dense non-porous layers at the erosion surface; (3) those formed by the argillaceous beds of the overlying Watrous formation of Jura-Triassic age. Combinations of these types of caprocks occur in certain locations.

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