Stratal reorientation, depositional processes, and sequence evolution of the Cretaceous in the Peace River Arch region of the Western Canada Sedimentary Basin

Detailed mapping of Cretaceous strata in the southeastern Peace River Arch (PRA) area offers new insight into processes that may have influenced strat al patterns in this region. Three first-order abrupt changes of depositiona l stratal trends were observed on the isopach maps: (a) NW-SE trending in t he 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 Fo rmation, and (c) NW-SE trending in the Colorado Shale to E-W trending in th e Lea Park and Belly River formations. Three syntectonic processes can be inferred from isopach patterns on maps o f Cretaceous formations: progradation al shifting of depositional centres, differential subsidence, and aggradation. Progradational shifting was obser ved on isopach maps of the Cardium and lower Shaftesbury-Dunvegan formation s, 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. Di fferential subsidence was observed on isopach maps of the upper Dunvegan an d Doe Creek formations, where subsidence patterns reflect basement domain b oundaries and faults. Isopach maps of the lower Pouce Coupe Formation serve as an example of aggradation, where the basement floor appears to have sub sided as a uniform sheet. Both Cordilleran tectonic loading and PRA uplift and subsidence were intermittent and appear to have influenced stratal depo sitional trends in the PRA region during Cretaceous time.