Organic petrology and petroleum formation in Paleozoic rocks of northern Williston Basin, Canada

Conventional and innovative techniques were used to elucidate the depositional environment and thermal maturity of potential hydrocarbon source rocks in southern Saskatchewan and Manitoba. The study has resulted in an improved understanding of the formation of petroleum from organic-rich strata in the Yeoman (Upper Ordovician), Winnipegosis (Middle Devonian) and Bakken (Upper Devonian-Lower Mississippian) Formations.;Yeoman Formation kukersites are dominated by Gloeocapsomorpha prisca alginite, derived from a photosynthetic cyanophyte. Two distinct organic microfacies suggest a three-stage life cycle for the alga: (1) a disseminated microfacies indicates an early non-motile, coccoidal stage and a later palmella stage, and (2) a stromatolitic microfacies indicates a sessile stage with phototactic textures. Different rates of thermal maturation and thresholds of petroleum generation for the two alginite varieties are indicated by different rates of alginite %Ro increase and are verified by shifts in fluorescence spectra and observations on transformation into bitumen. Hot stage experiments support the optical discrepancies observed between the two microfacies. Inception of petroleum generation appears to occur at a depth of 3000 m for the disseminated alginite. Bitumen has been cracked to anisotropic "coke" on a local thermal anomaly and peak generation of petroleum has occurred at a maximum temperature of 148;Organic microfacies in the Winnipegosis Formation indicate sub-oxic to anoxic paleoenvironments in basinal (inter-reef), platform and platform-margin rocks. Basinal microfacies, which have abundant bituminite III and unicellular alginate, were influenced by algal blooms. Platform carbonates comprise photosynthetic filamentous alginite stromatolites and rocks rich in bituminite II. Platform margin microfacies are dominated by alternating fluorescing and non-fluorescing bituminite laminae. Hydrocarbon generation from Winnipegosis platform microfacies occurred at a vitrinite reflectance of 0.70 %Ro. A second indicator of generation is a conspicuous red shift in the fluorescence of unicellular alginite.;Bakken black shales are dominated by microfacies rich in bituminite III. The size and distribution of unicellular alginite, acritarchs and sporinite define both shelf and deep basin depositional settings. Algal blooms, recorded by akinete cells, alginite cell lysis and bacterial remains, contributed to the bituminite. Thermal maturity of the Bakken Formation is within the late diagenetic stage. Hydrocarbons have been generated only where macerals in contact with phosphate particles have been damaged by radiation.