Paleotopography of the Sub-Cretaceous Unconformity Surface, Lower Athabasca Region, Alberta (NTS 73M, 74D, 83P and 84A)

The sub-Cretaceous unconformity is an important regional surface across the Alberta Basin, which represents a significant period of non-deposition and erosion initiated after deposition of Upper Jurassic/lowermost Cretaceous sediments of the first foreland basin clastic wedge. In the investigated area, this major unconformity surface separates the basin into broad depositional sequences assigned to distinct tectonic phases: an early passive margin basin below and a subsequent foreland basin above.

The paleotopography of the passive-margin phase of strata at the sub-Cretaceous unconformity is an important control on the deposition and preservation of the overlying Cretaceous succession.  Major factors controlling this paleotopography include differential erosion, and intrastratal dissolution of evaporites of the Prairie Evaporite Formation along the eastern margin of the study area. These factors led to the development of sediment transport pathways and increased accommodation  for deposition of the overlying Lower Cretaceous Mannville Group of the Athabasca Oil Sands area.