Frontal Wedge Structures in the Flathead Creek Area, Northeast British Columbia

Paul A. MacKay and Oscar Jansen

The Flatbed Creek area in the central Foothills of the Canadian Cordillera has a structural style that is dominated by folding with minor associated thrust faults. The foreland edge of the deformed belt in this area is a series of ads that decrease in amplitude to the east. These folds root within the Paleozoic section and appear as detachment folds on seismic data. within this fold train a tectonic wedge has formed. This wedge has significant lateral extent and appears to have formed synchronously with the episode of folding.

The basal surface of the wedge is the Kinuseo Fault, a foreland-directed thrust fault that is blind. The Kinuseo Fault roots within the Triassic and ramps into the Upper Cretaceous Moosebar Formation. In the Moosebar Formation the Kinuseo Fault merges with a series of hinterland- directed thrust faults to form the tip of a wedge. The hinterland-directed thrust faults form the upper surface of the wedge. An anticline is carried within the hanging wall of the Kinuseo Fault. This fold is outlined on seismic data by the bright reflectors equivalent to the coals within the Gething

Formation. The bright reflectors are also observable in the footwall of the Kinuseo Fault and displacement at the Gething level is estimated to be approximately four kilometers. Within the footwall of the Kinuseo Fault are folds that appear to be a continuation of the folds within the hanging wall of the Kinuseo Fault. The bottom surface of the wedge associated with the Kinuseo Fault is folded harmonically with the folds in the footwall of the Kinuseo Faults. Thus it is interpreted that the Kinuseo Fault formed synchronously with the formation of the fold train in this area. The Lower Cretaceous Grizzly Field is a gas accumulation within one of these folds in the footwall of the Kinuseo Fault This field is a fractured enhanced sandstone reservoir. A clearer understanding into the stru tural style and timing in this area may lead to a greater understanding of fracture patterns and an increased ability to delineate these types of fracture enhanced gas reservoirs.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California