BASIN-SCALE STRATIGRAPHIC ARCHITECTURE AND PALEOCENE DISTRIBUTARY FLUVIAL SYSTEMS OF THE CORDILLERAN FORELAND BASIN, ALBERTA, CANADA

The Paleocene Paskapoo Formation in Alberta, Canada is composed of several hundred meters of fluvial strata deposited 60 million years ago in the actively subsiding foreland basin of the Canadian Cordillera. The Paskapoo Formation is the major groundwater aquifer system in western Alberta, and covers approximately 65,000 km² and is divided into the upper Dalehurst Member, the mud dominated Lacombe Member and the basal Haynes Member. This heterogeneous fluvial unit comprises the youngest preserved bed rock of the western Canadian sedimentary basin. Here, we utilize newly available subsurface data from down-hole gamma-ray well logs to reconstruct the large-scale fluvial architecture and depositional history of the Paskapoo Formation in the northern portion of the Alberta Basin. These new data indicate the Paleocene fluvial strata in this region contain several notable features, including variable degrees of channel sandstone amalgamation, regionally-variable stratigraphic architecture, and an ancient distributary fluvial system that emanated from the adjacent fold-thrust belt. Fluvial channel sandstone bodies are abundant and amalgamated near the base of the formation in the southern portion of the study area, but become significantly less robust in the northern 100 km of the basin. The middle interval of the Paskapoo Formation is characterized by abundant mudstone with isolated channel sandstone bodies and is prevalent across the entire study area. The upper portion of Paskapoo Formation is dominated by a large (5000 km² area), laterally continuous sandstone in the northern portion of the basin that abuts against the fold-thrust belt and fans outward into the basin trending north-northwest. This feature is interpreted as a distributive fluvial system, or fluvial megafan, similar to those identified in many modern foreland basins. The correspondence between the location of this feature and the modern-day Athabasca River outlet suggests this area of the fold-thrust belt may be the site of a long-lived fluvial outlet.