UPPER PALEOZOIC TECTONOSTRATIGRAPHIC FRAMEWORK AND BIOSTRATIGRAPHY ALONG THE ANCIENT NORTH AMERICAN CRATON IN WESTERN CANADA

The Upper Paleozoic succession varies spatially and temporally along the western North American cratonic margin and is punctuated by numerous unconformities. A complex, tectonically driven history is emerging from detailed stratigraphic studies in which conodont biostratigraphy plays an important role. Species of Rhachistognathus, Neognathodus, and Streptognathodus are used to recognize at least 7 zones in the Pennsylvanian and species of Sweetognathus, Neostreptognathodus and Mesogondolella define at least 13 zones in the Permian of western Canada. In this region, Pennsylvanian and Permian sediments were deposited in arid environments along the western margin of Pangea at approximately 20 to 30°N paleolatitude. The stratigraphic succession is thickest in two basins, the Ishbel Basin in southeast British Columbia and the Peace River Basin in west-central Alberta; between these basins the Upper Paleozoic succession is typically condensed and marked by major unconformities. Pennsylvanian rocks are dominated by warm-water carbonate, much of it dolomitic and sandy. In contrast, Permian rocks comprise cool-water siliciclastics, spiculitic chert, and minor silty dolostone. Cold thermohaline circulation may account for this significant lithofacies change during the Permian. However, the climate remained warm in the region as indicated by alluvial facies with caliche and braid delta deposits grading into mixed carbonate-siliciclastic marine successions in the semi-restricted Peace River Basin during the Kungurian and Roadian, which was apparently protected from the predominant cold-water influence along the margin. Shifting depocentres and active uplifts strongly controlled the stratigraphic succession and compartmentalized reservoir units in several oil and gas plays. Significant unconformities that at least locally display angular relationships are dated as Late Moscovian (Kasimovian-Lower Sakmarian rocks are very rare in the region), Early Artinskian, Early Kungurian, Early Roadian, and Late Permian. Tectonic stress buildup and release events associated with plate reorganizations or interaction between the cratonic margin and pericratonic and allochthonous terranes probably caused these NW Pangea sequence boundaries and influenced biotic extinction and migration patterns.