The Early Cretaceous Mannville Formation and its equivalents are widely distributed in the subsurface in the Western Canada basin east of the Rocky Mountains. The formation is divided into the lower Mannville, which ranges from marine in the north to non-marine in the south, and the upper Mannville, which is a mixture of marine and non-marine sediments. The Mannville Formation is of considerable economic importance, because the sandstone reservoirs contain substantial oil and gas reserves. This paper deals primarily with that part of southern Alberta from the International boundary to Twp. 30.

The surface on which the Mannville Formation was deposited developed during a long period of erosion. An angular unconformity separates the Mannville from the underlying Mississippian and Jurassic. The pre-Cretaceous erosion surface, though of low relief, influenced considerably the depositional pattern of the Mannville. Variations in the thickness of the Mannville are primarily the result of irregularities on this surface.

The lower Mannville of southern Alberta was deposited under fluvial conditions in a well-developed drainage system in which the streams flowed toward the north. Lower Mannville sediments are confined mostly to the channels of this drainage system. Production is from porous and permeable sandstone bodies which were deposited as the streams migrated across broad floodplains.

Lower Mannville sediments filled most of the low areas on the erosion surface, thereby leveling the surface by late Mannville time. By the end of this time, the filling of the drainage system was complete and uppermost Mannville sediments were distributed across the entire area. The lowermost unit in the upper Mannville is the "Glauconitic sandstone," which appears to be non-marine in southernmost Alberta, but becomes marine toward the north. The "Glauconitic sandstone" contains most of the upper Mannville hydrocarbons. The remainder of the upper Mannville appears to be non-marine.

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