THERMAL MATURITY, ALGINITE-BITUMEN TRANSFORMATION, AND HYDROCARBON GENERATION IN UPPER ORDOVICIAN SOURCE ROCKS, SASKATCHEWAN, CANADA

Organic petrological techniques have been used to study the alginite-bitumen-oil transformation in Upper Ordovician Yeoman Formation kukersite source rocks of the northern Williston Basin, Saskatchewan, Canada. The kukersites are characterized by two distinct interlaminated microfacies, disseminated and stromatolitic, each representing a growth stage of the precursor to the alginite maceral Gloeocapsomorpha prisca. Different rates of thermal maturation and thresholds of petroleum generation for the two G. prisca maceral subvarieties are indicated by different rates of percent reflectance in oil increase and are verified by shifts in fluorescence spectra and observations on transformation into bitumen. With increasing thermal maturation, disseminated G. prisca reaches a softening stage, losing its primary morphological features as it is transformed from a primary to a secondary maceral (bitumen). The stromatolitic subvariety of G. prisca does not display comparable alteration in response to increasing thermal stress. Hot stage experiments conducted on doubly polished thin sections of the kukersites support the optical discrepancies observed between the two maceral subvarieties in the subsurface. These findings indicate that hydrocarbon generation from kukersites may involve two steps controlled largely by organic 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 to postgeneration of petroleum has occurred at a maximum temperature of 148-degrees-C, as suggested by homogenization temperatures for fluid inclusions.