New insights from regional-scale mapping and modelling of the Paleozoic succession in northeast Alberta: Paleogeography, evaporite dissolution, and controls on Cretaceous depositional patterns on the sub-Cretaceous unconformity

Abstract

Abstract The distribution and extent of Paleozoic strata within an area encompassing 874 townships in northeast Alberta have been updated based on detailed regional-scale lithostratigraphic mapping and modelling. Precambrian basement paleotopography strongly influenced the distribution of Keg River Formation carbonate buildups and interbuildup basins, which in turn largely controlled the depositional patterns in the overlying Prairie Evaporite Formation. Keg River paleotopography controlled the type of evaporites that were deposited, particularly at the Whitkow Member level of the Prairie Evaporite Formation. Keg River paleotopography continued to have an effect on the overlying sedimentary succession including the Cretaceous strata in areas where evaporites in the Prairie Evaporite Formation were removed by intrastratal dissolution. East of the regional Prairie Evaporite halite dissolution scarp, enhanced structuring of the sub-Cretaceous unconformity occurs by the draping of Waterways strata over Keg River paleotopography, especially along the Athabasca Arch. Structural mapping and modelling of the Prairie Evaporite Formation, and isopach mapping of halite and anhydrite therein using modern well control, provide the basis for an updated version of the location and extent of the Prairie Evaporite halite dissolution scarp. A new regionally correlatable marker bed, the Conklin, is introduced within the Prairie Evaporite Formation. Detailed correlation of this marker bed, along with previously established member and marker bed stratigraphy from the Prairie Evaporite Formation, reveals a well-defined pattern of evaporite karst within the halite dissolution scarp, and provides evidence for the top-down removal of halite throughout the study area. A regional Devonian subcrop model, together with a paleogeographic reconstruction of the sub-Cretaceous unconformity, highlight the control that karst processes in the Prairie Evaporite Formation and resulting Devonian structure have had on accommodation space and depositional patterns in the overlying lowermost formations within the Mannville Group.