Bakken/Madison petroleum systems in the Canadian Williston Basin. Part 2: molecular markers diagnostic of Bakken and Lodgepole source rocks

The uppermost Devonian-Mississippian Bakken Formation black shale and the M ississippian Lodgepole Formation carbonate represent two of the most import ant source rocks in the Canadian Williston Basin. Quantitative analyses of both saturated and aromatic hydrocarbon fractions reveal significant differ ences in the relative distributions and absolute concentrations for a wide range of molecular markers between the extracts of the two source units. Am ong others, the Bakken shales are characterized by their high relative abun dance of trimethyl aryl and diaryl isoprenoids likely derived from green su lfur bacteria Chlorobiaceae. In contrast, the Lodgepole carbonates at simil ar maturity levels display a C-35 homohopane prominence and abundant benzoh opanes, ring-D monoaromatic 8,14-secohopanes and a tetracyclic monoaromatic hydrocarbon. The distinctive nature of molecular marker "fingerprints" dia gnostic of the two source rocks is clearly related to their different organ ic inputs and depositional environments. Additionally, the large difference in the absolute concentrations of these compounds observed in both Source units may potentially lead to biased geochemical interpretations if strictl y conventional, saturate-based biomarker approaches were used for oil-oil a nd oil-source correlation. Crown Copyright (C) 2001 Published by Elsevier S cience Ltd. All rights reserved.