Stratigraphic Investigations into the Genesis of Anomalously Thick Coal Deposits in East-Central Saskatchewan

Abstract

The discovery of anonymously thick Cretaceous-age coal deposits in east-central Saskatchewan in 2008 generated a great deal of interest in the province and raised a number of geologic questions. Unlike other parts of the Saskatchewan where Mannville coals are laterally extensive and restricted to a few metres of thickness, these deposits appeared to be hosted in isolated ‘sub-basins’ with coal thicknesses exceeding 100 m. Coal accumulating in these thicknesses is exceptionally rare, comprising less than 1% of global deposits. The remarkable nature of these deposits provided the impetus for this study, with the aim of unravelling the geologic processes responsible for their development. A reconstruction of the depositional history in east-central Saskatchewan, within the context of the development of the Western Canada Sedimentary Basin, showed that the study area was subject to a unique mixture of marginal marine and terrestrial sedimentary environments at various stages through the Devonian to Cretaceous periods. These settings exposed the project area to a number of geologic processes that facilitated the development of these coal deposits. Seventeen separate deposits have been discovered in the study area, and are delineated by over 140 drillholes. Detailed logging was conducted on 103 of these drillholes and the results were used to correlate the lithologic units with documented regional stratigraphy. Stratigraphic correlations across the sub-basins revealed abrupt changes in elevations of Paleozoic strata, over horizontal distances of less than 100 m. These changes reflect paleotopographic lows which appear to have developed on the Paleozoic carbonates by karsting or erosion, or a combination of the two.