Geology of Northwestern Alberta and Adjacent Areas

Abstract

The area forms part of the Interior Plains of Canada. Cretaceous shales thicken from nothing in the northeast to 3,000 feet in the southwest where they rest unconformably on wedges of Triassic shales and sandstones underlain by Permian or Pennsylvanian sandstones and dolomites. The latter in turn rest unconformably on Mississippian limestones and shales. The Upper Devonian is truncated in the east, where it is overlain by the Cretaceous, but attains a thickness of 3,200 feet in the west. The upper part consists of limestones for which the use of the group name Wabamun is extended from central Alberta. This group overlies silty limestones. The lower part of the series consists of interbedded shales, siltstones, and limestones; a thick limestone section occurs in the east a d a reef complex is present in the southeast. The Middle Devonian has maximum thickness of 1,600 feet and consists of the Slave Point formation and Elk Point group. The former consists of limestone with an anhydritic member and rests, probably disconformably, on the Elk Point, which can be subdivided into a clastic unit, an upper evaporitic unit, a carbonate unit, and a lower evaporitic unit. The formational names, Watt Mountain, Muskeg, Keg River, and Chinchaga, are proposed for these units. The upper evaporitic unit passes northward into the Presqu'ile dolomite of the Great Slave Lake area. This dolomite is interpreted as forming a barrier reef. A barrier reef was also present in northwestern Alberta. The Middle Devonian rests on redbeds of doubtful age which in turn overlie Precambria granite. The regional structure is homoclinal with gentle dips west or southwest, but there is some evidence of local structure. Facies studies were used to forecast areas of favorable reservoir rock. Oil and gas showings occur in the northern part of the area where there are chances of commercial production.