ABSTRACT

This study uses an organic geochemical approach to reveal evidence of post-Devonian magmatic intrusions along the Tabbernor Fault in southeastern Saskatchewan. The detailed chemical compositions of some unusual crude oils in the Jedburgh well drilled on a small salt dissolution structure have been investigated and recent advances in petroleum migration tracers have been incorporated in the study. The well lies near the Cussed Creek structure, a complex feature involving both Phanerozoic faults that offset the Precambrian basement and the dissolution edge of the Middle Devonian Prairie Formation. The chemical compositions of crude oils recovered from cores of Devonian strata in this well are unique in the Williston Basin and unusual in a global perspective because they contain significant quantities of oc-olefins (with n-C17 alk-1-ene/n-alkane ratios ranging from 0.28 to 0.72). The gross chemical compositions and distributions of aliphatic biomarkers, aromatic hydrocarbons and pyrrolic nitrogen compounds in the oils indicate that they were generated by high-temperature, short-term pyrolysis of thermally immature organic matter. Their composition indicates that they were not generated in situ, but accumulated in the Jedburgh well after lateral migration from areas that were influenced by post-Devonian magmatic intrusions. The inferred migration distance (-10 km) suggests that such intrusions occur within the Cussed Creek structure. Results show how organic geochemistry can assist geological interpretation of seismic and lithologic data.