Abstract

Five Major Stratigraphic Sequences Represent the Principal Chapters in the Devonian geohistory of Western Canada. Overall, the history is one of pulsatory advance of the sea over the craton. Thus the locus of carbonate platform construction moves from the Northwest Territories and Yukon in Early Devonian, to northern Alberta in mid-Eifelian and to southern Alberta in Frasnian time. A regression took place in the Famennian, while synorogenic clastics entered the northern region from the Ellesmerian Orogeny. Each sequence starts with some siliciclastic sediment overlying a discontinuity surface and continues with the deposition of extensive platform carbonates flanking the craton and emergent arches. Shale was deposited at the same time in open seas to the west and in shale basins formed between prograding carbonate platforms. The region lay in sub-tropical climes and reefs flourished, growing with particular vigor during periods of rapid sea-level rise. Other reefs grew on the foreslopes of prograding carbonate platforms when the rate of autochthonous sedimentation overcame the rise in sea level. Where circulation was restricted within the platformal areas thick and extensive evaporites were deposited. The region is traversed by a number of important tectonic features that controlled local sedimentation. In general sedimentation reflects cyclic eustatic changes but there is a strong local tectonic overprint.