Accommodation, Sediment Provenance and Paleo-Drainage on the Basal Cretaceous Unconformity Across the Canadian Western Interior Basin

Abstract

Jurassic-Paleogene strata of the Alberta basin are divided into a series of sedimentary wedges that have been linked to major uplift and denudation events in the North American Cordillera. A foreland setting has been interpreted for the entirety of the stratigraphic succession; however, well-established foreland characteristics are not prevalent through all intervals. We hypothesize that the Lower Mannville Group, which mantles the basal Cretaceous unconformity across the basin and contains a majority of western Canada's hydrocarbon resources, is not a foreland basin deposit. During the Aptian, the Western Interior basin of Alberta was dominated by a series of large-scale channel belts that were confined within elongate topographic lows that paralleled the incipient Cordillera to the west. The basin axial drainage networks intersected the Western Interior Seaway, which inundated the basin to the north. Topography on the depositional surface, the sub-Cretaceous unconformity, was controlled by differential erosion of underlying westerly dipping Devonian-Jurassic strata. Foreland basins are defined by numerous characteristics. Their fill is notably asymmetric, thinning away from the orogenic load. Sediment is dominantly derived from the uplifting, or recently uplifted mountain belt. The thickness of Lower Mannville Group strata measured from thousands of well bores across the Western Interior basin, a measure of accommodation, does not show a pronounced asymmetry. Furthermore, detrital zircon analysis from channel-belt deposits across the basin indicates limited Mesozoic grain input from the adjacent Cordillera (in contrast to younger foreland basin units). Recent results have lead to interpretations that the basin captured continental rivers, deriving sediment from as far away as the Appalachian Orogen and the southwestern United States. Although sediment accumulated adjacent to a mountain belt in a foreland position, accommodation was limited and the region was dominated by: (1) net erosion during formation of the sub-Cretaceous unconformity; and (2) subsequent Lower Mannville fluvial sediment transfer across the topographically complex landscape. Our observations challenge a long-accepted paradigm for Mesozoic basin evolution in western Canada, and emphasize variation in foreland basin history with implications for basin-scale sediment distribution and reservoir prediction.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016