Dynamic Casting of a Graben Complex: Syn-Sedimentary Infill and Differential Subsidence during the Permo-Carboniferous; Peace River Embayment, Western Canada

BARCLAY, J. E., Geological Survey of Canada, Calgary, Alberta, Canada, and University of Calgary, Alberta, Canada, F. F. KRAUSE, University of Calgary, Alberta, Canada, and R. R. CAMPBELL, Geological Survey of Canada, Calgary, Alberta, Canada, and Calamity Resources, Calgary, Alberta, Canada

The Carboniferous Stoddart Group and Permian Belloy Formation record infill of a long-lived graben complex in the center of the Peace River Embayment. The "Dawson Creek Graben Complex" began down-dropping during deposition of the Rundle Group and Golata Formation and reached its maximum during Kiskatinaw time. The overlying Taylor Flat Formation shows graben filling and graben decay; whereas the flat Permian Belloy Formation beds within and beyond graben limits indicate tectonic stability.

The complex comprised the larger "Fort St. John Graben" and satellite "Hines Creek," "Whitelaw," and "Cindy" grabens. The grabens consist of kilometer-scale horst and graben blocks bounded by normal faults. The internal blocks subsided at various rates, with differential subsidence occurring in the form of horsts subsiding slower than neighboring grabens. Syn- and post-depositional growth-type normal faults controlled formation and bed thickness, as did inter- and intra-formation unconformities.

From these observations, a structural/stratigraphic model can be constructed that explains the complex stratigraphy and depositional interpretations. This model describes a basin dominated by tectonic controls rather than global sea-level events. Syn- and post-sedimentary growth-type block faulting, differential subsidence of fault blocks, sedimentary infill, and unconformity truncation were the major controls on the basin. The model provides an analog to grabens and block-faulted basins of growth-faulted basins occurring elsewhere.

The implications of the model to petroleum exploration are that all beds can be correlated by assuming that beds were essentially flat-lying prior to and during faulting. The combination of the block-faulted character and complex facies changes provides many structural and stratigraphic petroleum traps.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)