Abstract

Most Devonian strata in the Canadian Cordillera accumulated in two major tectonic provinces, the western “continental shelf” and the eastern “cratonic platform”. During Early and Middle Devonian time the Porcupine Platform, Selwyn Basin, Mackenzie Shelf and MacDonald Shelf were the major subdivisions of the continental shelf, whereas the Peel Shelf, part of the Mackenzie Shelf, Elk Point Basin, Peace River Arch, West Alberta Ridge and Golden Embayment occupied the cratonic platform. Exposure of all shelf areas in Late Silurian time was followed by the Kaskaskia Transgression, beginning with deposition of the evaporitic Delorme Assemblage in isolated intra-shelf basins during Gedinnian-Siegenian time. The overlying Emsian Bear Rock-Stone and upper Eifelian-lower Givetian Hume-Dunedin Assemblages blanketed shelf regions with continuous and uniformly thick carbonates and evaporites. This progressive increase in tectonic stability was interrupted by the brief, but regional early Eifelian Headless-Chinchaga regression (Ebbutt Break), when the Peace River Arch and the West Alberta Ridge were formed.

In early Givetian time carbonate deposition shifted to the southern part of the MacDonald Shelf and to the Elk Point Basin, whereas the northern shelf and platform realms were covered by fine siliciclastics. These may have been derived from uplifts in the Selwyn Basin and farther north, coinciding with the onset of the regional Watt Mountain Regression.

During the late Givetian several new tectono-sedimentologic elements evolved which were represented on the “continental shelf” by starved basins (Mackenzie and Liard Basins) and by active source areas (Borovian and Selwyn Highlands). The “cratonic platform” was occupied by extensive shelf areas, the Peel and Mackenzie to the north and the Hay River and Alberta to the south, and by two passive (non-source) positive areas, the Peace River Arch and Central Montana Uplift.

Late Givetian marks the first transgressive pulse of the Taghanic Onlap, culminating in the middle Frasnian and waning in late Famennian. This craton-wide transgression was punctuated by periods of reef development (Ramparts, Swan Hills, Leduc and Nisku) and a brief regression during the late Frasnian (Graminia-Ronde peritidal sediments). The West Alberta Ridge was buried during the early Frasnian, whereas the Peace River Arch remained positive into Famennian time, effectively separating siliciclastic deposition to the north from dominantly carbonate deposition to the south. Widespread upper Famennian black shales (Exshaw) terminated carbonate deposition on the southern “cratonic platform” and northerly derived siliciclastic wedges started to infill the starved basins of the northern “continental shelf”.