Abstract

Detailed mapping of Cretaceous strata in the southeastern Peace River Arch (PRA) area offers new insight into processes that may have influenced stratal patterns in this region. Three first-order abrupt changes of depositional stratal trends were observed on the isopach maps: (a) NW-SE trending in the Lower Mannville Group to NE-SW trending in the Upper Mannville (b) NE-SW trending in the Dunvegan Formation to NW-SE trending in the Pouce Coupe Formation, and (c) NW-SE trending in the Colorado Shale to E-W trending in the Lea Park and Belly River formations. Three syntectonic processes can be inferred from isopach patterns on maps of Cretaceous formations: progradational shifting of depositional centres, differential subsidence, and aggradation. Progradational shifting was observed on isopach maps of the Cardium and lower Shaftesbury-Dunvegan formations, where elongate depositional zones, parallel to the Cordilleran tectonic front, migrated perpendicularly to the tectonic front. These likely reflect the classic advance/retreat of depozones in a dynamic foredeep setting. Differential subsidence was observed on isopach maps of the upper Dunvegan and Doe Creek formations, where subsidence patterns reflect basement domain boundaries and faults. Isopach maps of the lower Pouce Coupe Formation serve as an example of aggradation, where the basement floor appears to have subsided as a uniform sheet. Both Cordilleran tectonic loading and PRA uplift and subsidence were intermittent and appear to have influenced stratal depositional trends in the PRA region during Cretaceous time.

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