ABSTRACT
The Upper Devonian, Frasnian, of Alberta contains a large number of carbonate complexes bounded by shale. Both the argillaceous and the carbonate facies are exposed in the Rocky Mountains, where they are assigned to the Fairholme Group.
This study is concerned with a detailed stratigraphic and paleoecological examination of the carbonate facies of a portion of the Southesk-Cairn complex, in an attempt to document the complex’s depositional history.
The “Big Hill” section, located on the Banff-Jasper highway (No. 93), 20 mi northwest of Saskatchewan River Crossing, was chosen as a site for field study. Interpretations of depositional environment are based on detailed field and laboratory studies supplemented by the application of an established paleoecological model.
The Cairn biostrome was deposited in shallowing water over a locally elevated area. The biostrome is characterized by alternating barren and fossiliferous bedded units. This factor coupled with lateral faunal variation suggests the development of shallow-water banks or patch reefs with deeper interbank, or reef, quiet-water areas.
The Southesk Formation is divided into four members, each of which has a distinct depositional history. The lowermost Peechee Member represents further shallowing over the carbonate platform, and is interpreted as a carbonate-bank deposit displaying subtidal, intertidal and supratidal facies. The overlying Grotto Member marks a subsidence of the platform (or rise in sea-level?), as evidenced by the development of quiet-water disphyllid coral banks around the periphery of the complex. Subsequent shallowing took place over the complex, at which time the Arcs and Ronde Members were deposited. The shallowing continued until subareal exposure terminated Fairholme Group deposition, in Late Frasnian time.
The Fairholme Group, at the “Big Hill,” is completely dolomitized. Petrographic studies of the dolomite showed that there is no apparent relationship between the size of dolomite crystals and the postulated grain size of the original limestones. It is demonstrated that dolomite crystallinity appears to be related to the per cent, by weight, of insoluble residue.
