An organic geochemical study of Cenomanian-Turonian sediments from the Western Interior Seaway, Canada

Bulk-geochemical and biomarker data were collected for three Cenomanian-Turonian (Late Cretaceous) sections in the Western Canada Sedimentary Basin (Western Interior Seaway, Canada). Rock-Eval and biomarker analyses indicate an east-west thermal maturity trend due to progressive deeper burial associated with the tectonic flexure of the foreland basin. The source of extractable organic matter is dominantly marine with a minor terrestrial contribution. A pseudohomologous family of 2,2-dimethylalkanes (2,2-DMAs), in the C16–C28 range with an even number of carbon atoms exclusively, was tentatively identified from mass spectral data in samples from the Pasquia Hills region (easternmost section). The specific origin of 2,2-dimethylalkanes remains unclear. The presence of isorenieratene derivatives indicates that the northern part of the Western Interior Seaway experienced photic zone euxinic events throughout the transgressive, highstand, and regressive phases of the Greenhorn Cycle. The differential occurrence of isorenieratane between the Canadian sections and the United States transect at maximum sea-level high stand indicates that the water column of the northern part of the WIS was less oxygenated, whereas the water column in the southern WIS was more dynamic and well-mixed.