Microscopic studies of sedimentary organic matter: Key to understanding organic-rich strata, with Paleozoic examples from western Canada basin

Organic matter in sediments and sedimentary rocks provides data and interpr etations on biosphere-geosphere interactions. In modern and ancient deposit ional settings, a combination of anoxia and substantial bio-productivity le ads to the preservation of abundant organic matter, which in turn is transf ormed during subsequent burial into kerogen, the source of oil and gas depo sits. Kerogen can be evaluated by organic geochemistry and organic petrolog ical methods, whose parameters are used to define organic facies for fine-g rained, sedimentary rock sequences. Organic geochemistry uses Rock-Eval pyr olysis and elemental analysis to determine amounts of organic C, H, and O i n kerogen to assess petroleum potential and origin. Organic petrology uses reflected light microscopy to characterize dispersed organic matter in rock s, in terms of macerals and organic facies, which is then used to interpret the paleoenvironment and paleoecology of organic-rich sedimentary rocks. T his paper outlines the organic petrology of several hydrocarbon source rock s from western Canada, illustrating the success of this method in evaluatin g and understanding organic-rich rocks.