Rocks of Mississippian age in southwestern Saskatchewan consist of a sequence of relatively similar carbonate rocks ranging from 340 ft to 1,030 ft thick. A vertical change in lithologic character not generally reflected on a geophysical log permits an informal division of these rocks into a lower, generally sparsely fossiliferous argillaceous or bituminous limestone unit, and an upper, commonly fossiliferous nonargillaceous limestone unit. The lower unit shows some lateral variations from locally developed bituminous limestone to argillaceous limestone. Red ferric oxide coloration is common in the argillaceous rock, as is glauconite, particularly in the basal part. The upper unit is characterized by a preponderance of crinoid remains generally in the form of alternations of particle-supported crinoidal limestones and micritic limestones with varying percentages of crinoid columnals. Bryozoa, brachiopods, and solitary corals also are concentrated in this sequence of rocks.

The variable thickness of Mississippian rocks is probably related to the effects of regional erosion on the post-Mississippian-pre-Jurassic erosion surface which have resulted in removal of progressively older beds in a northwesterly direction. A paleotopography having a distinct northeast-southwest grain was developed on the erosion surface. Local paleotopographic relief is in the order of 100 ft and regional relief is approximately 400 ft from west to east.

At present oil in commercial quantities is obtained from only 1 well in the study area. This oil accumulated in a dolomitized crinoidal limestone that subcrops on the western slope of a paleotopographic ridge. The ridge is on the easterly plunging Battle Creek anticline. The prospects of discovering additional hydrocarbon accumulations in the Mississippian rocks of southwestern Saskatchewan are enhanced greatly by the presence of excellent local source rocks as represented by the bituminous limestones of the lower carbonate unit.

End_of_Article - Last_Page 538------------