The Mississippian strata of Southern Alberta plains region, known only from the subsurface, are described as to lithology, thickness, rock units, their correlation with adjacent areas, and history of deposition.
The Mississippian section thins from west to east due to post-Paleozoic erosion and to a lesser degree by reason of depositional thinning. In the extreme western part of the map area, there remains approximately 1,500 feet which is one third of the total Mississippian exposed in the mountains.
The rock units and member names introduced and defined by Douglas in 1953 and the more recently amended subdivisions and new names being proposed by the Mississippian Committee for the foothills area in the vicinity of Turner Valley oil field are defined, for adjacent Plains region, in the Shell-Anglo Canadian Pine Creek well. The formation names, Bakken, Banff, Pekisko, Shunda, Turner Valley, and Mount Head, are used in this general area. It is further proposed to introduce the name Elkton for the commercial gas zone of the Great Plains, et al., Elkton No. 16–13 well. This zone is regarded as the correlative of the “Crystalline” and “Lower Porous” zones of Turner Valley field usage.
The correlation of these rock units is illustrated on cross sections from the Shell-Anglo Canadian Pine Creek well to the northeast, toward the Big Valley oil field, southeast to Saskatchewan, and south to Kevin-Sunburst area in Montana. The Banff strata of the Shell-Anglo Canadian Pine Creek well are correlated with the combined MC and MB2 (Lodgepole) of the Kevin-Sunburst area; the Pekisko and Shunda formations, plus Elkton member of Turner Valley formation, with MB1 (Mission Canyon) ; and the upper part of the Turner Valley with the MA unit as defined by Sloss and Laird (1945).
The typical lithological units of the Bakken formation of Montana and the Dakotas are present in the southeastern part of the map area. Pre-Mississippian epeirogenic uplift has caused thinning of the Bakken formation to near zero toward the west. To the north, only the lower black shale is present as a distinguishable rock unit to which the name Exshaw is applicable. The upper part of the formation changes to gray shale which is not readily distinguished from the overlying Banff shale.