PRELIMINARY STUDY OF THE PALEOSOLS OF THE MANNVILLE GROUP, LOWER CRETACEOUS, SASKATCHEWAN, CANADA

The Lower Cretaceous Mannville Group has been studied since the early 1940’s and is considered to be one of the most important hydrocarbon units in Canada. According to resource reports it has high economic potential and estimated to contain as much as three billion m³ barrels of oil in the Lloydminster area of Saskatchewan, Canada alone. Although there has been considerable academic and industry research on the unit, to our understanding, there has been no systematic study of paleosols tentatively identified in the unit. Paleosols have been identified mainly because their features do not fit into normal marine sediment descriptions and contained traces consistent with terrestrial environments. The purpose of this project is to identify, describe and classify paleosols in the Mannville Group in Saskatchewan cores to determine paleoenvironmental conditions in the Lower Cretaceous. The objectives include: detailed analysis of pedogenic features of the paleosols of the Mannville Group; establish key paleosol criteria; classify the paleosols to type; determine the paleoenvironments of the paleosols; and correlate paleosol units between cores to better delineate and understand formation boundaries and the stratigraphic framework of the Mannville in Saskatchewan. Initial criteria used to identify the paleosols include lack of structures (bedding, cross bedding, stratification), root related features (mainly rootlets), boundaries (wavy, irregular, tonguing), colours, any evidence of organic matter, grain size, structures/cracks, contacts, and staining. Seventeen of the 19 wells examined to date, show evidence of paleosols in the McLaren and Waseca formations of the Mannville Group. These paleosols are all topped with a coal unit, and underlain by a mudstone layer with an abundance of rootlets (5-20%). The mudstone units are generally massive and light gray (2.5Y7-1). Some of the cores have an additional dark gray (2.5Y4/1) mudstone layer underneath the coal and above the light gray unit. The Waseca paleosol is usually overlain and underlain by an oxidized mudstone, that is stratified and sometimes bioturbated. Whereas, the McLaren paleosol is typically overlain by a mudstone unit or oil-stained sand unit, and underlain by oil-stained sand that appears columnar and blocky.