ABSTRACT

Marked facies changes occur in the Mission Canyon and lower part of the Charles formation (Mississippian) in southeastern Saskatchewan. Northeastward from the basinal area, four successive environments of deposition with characteristic rock types and fossils may be mapped as follows:

Basin: dark brown-gray argillaceous limestone containing scattered white crinoid columnals, black bituminous shale partings and brownish gray chert.

Open marine shelf: cream-white fossiliferous-fragmental and chalky limestones containing crinoids, bryozoans, brachiopods, and zaphrentid corals.

Barrier bank: Cream-white precipitated limestone including pisolitic, oolitic, pseudo-oolitic and lithographic types. Fossils include abundant algae and a few scattered gastropods.

Lagoon: cream-white chalky argillaceous limestone containing ostracodes, earthy to micro-sucrosic secondary dolomite and anhydrite.

Oil production within the Midale member is limited in part by the distribution of permeable calcarenites of both precipitated and bioclastic origin. The distribution of these calcarenites is believed to be related to depositional shoals. The permeability of basinal, inter-shoal and lagoonal type limestones is generally too low for commercial production of oil.

Petroleum prospects (including extensions of fields) may be outlined along the Midale trend by extending facies boundaries (based on texture and fossil content) into wildcat areas.