Abstract During the last decade geophysical exploration in the foothills area of Alberta has aided considerably in arriving at rough approximations, and in some cases fairly reliable data, with respect to the nature of the structural conditions above and beneath major sole faults. The compilation of structural cross sections on the basis of such surveys, plus knowledge derived from previous subsurface drilling and surface geology, are the main theme of this contribution. Several examples of structures mapped and drilled are given, together with a hypothetical case wherein the difficulties of interpretations are discussed. The structures described are Turner Valley, Highwood uplift, Jumping Pound, Brazeau uplift, Stolberg, Coalspur, Savannah Creek, and the hypothetical “Alpha” structure. The tectonic forces which gave rise to the building of the Rocky Mountains and foothills of Western Canada were operative from west to east. There appear to be contradictions to this statement, but when the data are fully studied and analyzed, they generally fit into the picture and thus substantiate the original contention. Furthermore, the intensity of the resultant deformation decreases gradually from west to east, so that the less complicated structures are at the eastern edge of the foothills. A logical corollary to this is the observed fact that folded faults and folded overthrust sheets are more common in the interior or western part of the foothills nearer the mountains. The construction of idealized cross sections through the foothills is, in some respects, an enjoyable pastime, but detailed cross sections which indicate ultimate depths to prospective oil zones is another matter, and these must be attempted by the petroleum geologist. The object of this contribution is to present illustrations showing results of some of the recent findings in the foothills on the basis of surface geology, seismic-reflection surveys, and subsequent deep drilling.

Abstract The “Tar sands” of the Athabaska or “McMurray bituminous sands” of Lower Cretaceous age in northeastern Alberta, Canada, are believed to have derived their bituminous content from the underlying coral-reef reservoirs of Upper Devonian age which come in contact and near-contact with the overlying sands at the unconformity between the Lower Cretaceous and the Devonian. The white quartz sands were supplied from the pre-Cambrian “Athabaska sandstone” lying at the northeast on the Canadian shield, and it is suggested that the escape of oil and gas through fissures and fractures from the Devonian reservoirs into the “Tar sands” occurred primarily during, but also possibly subsequent to, the deposition of the Cretaceous “Tar sands.” It is also believed that the Lower Cretaceous heavy oil of Lloydminster, Alberta, has had a similar history.