JURASSIC AND CRETACEOUS LINKS BETWEEN THE BOWSER BASIN / SKEENA FOLD BELT AND THE ALBERTA FORELAND BASIN / ROCKY MOUNTAIN FOLD AND THRUST BELT, CANADIAN CORDILLERA

Depositional and structural histories of the Bowser and Sustut basins provide an unique record of the Mesozoic tectonic development of the Canadian Cordillera. These include Middle Jurassic to Jura-Cretaceous marine to nonmarine deposition in the Bowser Basin on the western margin of North America, mid- to latest Cretaceous nonmarine deposition primarily in the Sustut Basin, and Cretaceous horizontal shortening of the Bowser and southwest Sustut basin to form the Skeena Fold Belt. Sustut strata were derived from the fold belt and subsequently deformed. At least 150 km of horizontal shortening roots westerly in the Coast Belt; on the east the fold belt locally ends in a triangle zone within the Sustut Group. In addition to these elements illustrating a hinterland-fold belt-foreland basin relationship in the western Cordillera, they provide insight on broader orogenic development because they evolved outboard of, but coeval with, the Omineca Belt, Rocky Mountain Fold and Thrust Belt, and Alberta Foreland Basin. For example, rapid southwest migration of shallow marine and deltaic facies over more distal ones in the Bowser Basin in mid-Oxfordian and the Early Kimmeridgian was roughly coeval with initial west-derived sedimentation in parts of the Alberta Foreland Basin. The latter is an indication of crustal thickening in the Omineca Belt which may also be related to the Bowser facies migration. Detrital zircon geochronology provides constraints on relationships of the two regions. Sustut Basin responses to orogenesis include the first westerly derived clastics and a Late Cretaceous influx of conglomerate. Paleogeographic reconstruction to relate specific events in the two regions is hindered by poor constraints on intervening Mesozoic and Cenozoic transcurrent faults.

The Skeena Fold Belt and Rocky Mountain Fold and Thrust Belt are typified by northwest-trending folds and thrust faults which accommodated major horizontal shortening. The existence of two parallel and coeval fold belts, each kinematically related with plutonic/metamorphic belts, is atypical of orogens. The 2 belts may have been kinematically linked by a detachment which fed displacement from the active plate margin east to an upper level (Skeena Fold Belt) as well as continuing east at depth below the Skeena Fold Belt to reach the eastern regions.