The coal-bearing strata of the Lower Cretaceous Mannville Group (Western Canadian Sedimentary Basin, South Central Alberta). Part 1: Stratigraphic architecture and coal distribution controlling factors

Abstract

This study aims to reconstruct the stratigraphic architecture of the subsurface coal bearing Mannville Group deposits (Lower Cretaceous, Western Canada Sedimentary Basin, South and Central Alberta), in order to characterize the occurrence of coal strata within this interval, by focusing on their geometry, extension and distribution. Two regional well correlation transects, calibrated by core sedimentological analysis, were established. The Mannville Group was subdivided into system tracts: a lowstand system tract (LST), which corresponds to the Lower Mannville Fm., a transgressive system tract (TST), corresponding to a backstepping phase of marine transgression, and finally, a highstand system tract (HST) that corresponds to the “undivided” Upper Mannville.The geometry, distribution and extension of the coal layers are examined within the sequential framework previously reconstructed. Four different zones where coal seams have occurred have been identified: LST-TST, early HST, middle HST and late HST. Thinner and more restricted coal layers are formed during the lowstand and transgressive system tracts and also during the late highstand system tract. Thicker, more extensive coal layers are accumulated during early highstand, as a result of the interaction with the topography, which is partly smoothed during the deposition of the Mannville Group, and the changes to the accommodation space through time.