The Triassic of the Western Canada sedimentary basin; tectonic and stratigraphic framework, paleogeography, paleoclimate and biota

The Triassic of the Western Canada Sedimentary Basin records the transition from carbonate-dominant facies of the Paleozoic to siliciclastic-dominant facies of the Jurassic-Cretaceous in a tectonic setting preceding the onset of extensive terrane accretion and formation of a foreland basin in western Canada. Triassic sedimentation in western Canada was centred on four basins or subbasins: the extensional or transtensional Peace River Basin, the transtensional Liard Basin, an unnamed continental margin sag basin, and the Williston Basin. This paper covers only the Peace River Basin and its western extension into the continental margin sag basin. The Triassic basin occupied a midlatitudinal, west-facing position on the western margin of the Supercontinent Pangea. In this setting, climatic aridity, influence of prevailing northeast trade winds, offshore coastal upwelling, and other conditions resulted in limited fluvial influx, dominantly fine-grained siliciclastic sedimentation, significant aeolian processes, low-productivity carbonate shelves and ramps, extensive evaporites, and early-diagenetic dolomitization. Underlying Devonian reefs, reactivation of graben fault systems in the Peace River area, localized Paleozoic highs, and other tectonic elements, exerted strong influence on Triassic basin topography and facies, including localization of sediment gravity flows and turbidites. Collectively, these tectonic, paleogeographic and paleoclimatic conditions in western Canada in Triassic time have left a relatively unique sedimentological record with a wide range of facies and reservoir types. Ongoing discoveries of gas in Upper Triassic carbonates in northeastern British Columbia, new discoveries and extensions of play trends in the Lower Triassic in Alberta, and ongoing exploration in Middle Triassic units in both areas, are contributing to the growing reserves of oil and gas in the Triassic of western Canada. An understanding of some of the unique or different sedimentological aspects of the Triassic, as reflected by its tectonic setting, paleogeography and paleoclimate, is a necessary step in evaluating its reservoir potential.