--> Depositional Environment Map of the Canadian Cordilleran Foreland Basin in the Middle Aptian

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Depositional Environment Map of the Canadian Cordilleran Foreland Basin in the Middle Aptian

Abstract

The Aptian McMurray Formation is the reservoir for the Athabasca Oil Sands which contains the largest deposit of bitumen-in-place in the world. To better constrain basin-scale provenance data, sediment entry points, and facies patterns a full basin depositional environment map was created. Publically available well data was used to construct isopach maps which were combined with well based lithology data, geologic maps, and other published reports to build a restored gross depositional environment (GDE) map for the Aptian Stage of the Western Canada Sedimentary Basin (WCSB). The map extends from the position of the restored Columbian Thrust Front in the west to the onlap edge of Cretaceous rocks onto the Canadian Shield in the east. The northern limit of the map includes the Canadian Beaufort Basin and restored position of the Alaskan North Slope and extents south near the Canadian-US border. Major drainage basins and valley systems are recognized. The Spirit River Valley captured sediments derived from the Cordilleran orogenic wedge while in the east, major sediment depocenters include the Edmonton and Assiniboia valleys which transported sediments from the south and east. This map highlights the northern connection to the Beaufort Sea via a relatively narrow epicontinental seaway. A corresponding flexural analysis of the WCSB was conducted. The purpose of flexural modeling was to differentiate local sources of accommodation from regional sources. This helped to define sediment sinks such as the Assiniboia Valley, the depocenter for the McMurray Formation. Flexural models were matched to the total foreland basin isopach with the Sub-Mannville Unconformity serving as the base of the WCSB foreland basin phase. Estimates of eroded overburden were added in to produce a pre-erosional estimate of the basins geometry. Modelling assumed a lithosphere with variable elastic thickness, differing from previously published studies. Notable regional differences between the model and total sediment isopach exist that cannot be explained by differential weather along the Sub-Mannville Unconformity. These may relate to pre-existing topography or a different subsidence mechanism.