ABSTRACT: Geological mapping of mesozoic strata in southeastern Saskatchewan, northwestern North Dakota, and northeastern Montana, and regional effects of deformation by glacial-Ice loading (IEA Weyburn CO2 Monitoring and Storage Project).

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Abstract

Recent subsurface geological mapping of Mesozoic strata, part of the IEA Weyburn CO2 Monitoring and Storage Project, has indicated that deformation under loading by Pleistocene continental ice sheets may have impacted clay-rich and sandy, weakly consolidated formations as deep as 350 m below ground level. Because of post-Eocene erosion across the southward-dipping sedimentary strata, the formations affected are younger toward the south. Thus Colorado Group formations are affected in east-central Saskatchewan, and the Lea Park and Bearpaw formations farther south. Antecedent landforms probably influenced glacial-ice flow, erosion and deposition, and topographic highs likely impeded and deflected basal ice motion until sufficient ice mass developed to overcome them. Factors contributing to deformation were: 1) the weight of the ice (which was approximately 1.5 km thick), 2) repetitive glaciation and accompanying meteoric formation-water over-pressures, and 3) permafrost and thawing. Bentonite may have acted as a lubricant in the deformation process under loading. However, for the rocks to have deformed at depth, even by plastic flowage, accommodation space would have been required. Under glacial-ice loading, there would have been little free space. Formations below the Lea Park are increasingly indurated with depth, and the Jurassic and Paleozoic beds are all competent, except for the Middle Devonian salt beds of the Prairie Evaporite Formation at a depth of about 2400 m, which could have yielded to differentially applied compressional stress. This is suggested to have occurred.

Bibliography of Canadian Geomorphology