LACUSTRINE SHALES AND OIL SHALES FROM STELLARTON-BASIN, NOVA-SCOTIA, CANADA - ORGANOFACIES VARIATIONS AND USE OF POLYAROMATIC HYDROCARBONS AS MATURITY INDICATORS

The Post-Acadian Stellarton Basin is a small pull-apart basin in north ern Nova Scotia. The Coal Brook Member, which is the main focus of thi s study, contains the thickest and most extensive development of oil s hales within the Late Carboniferous Stellarton Formation. Bulk and mol ecular geochemistry indicate that the organic-rich oil shales and blac k shales contain Type I/II kerogen with a mixed assemblage of aquatic and terrestrial organic matter that is dominated by the former. Biomar ker evidence indicates that these sediments were deposited under deep, anoxic and fresh-to-brackish water lake conditions. Organofacies dist inctions were made on the basis of several parameters that are indepen dent of maturity and therefore suggest organic matter changes. The org anofacies identified are the result of water-level fluctuations that a re climate controlled. All of the aromatic compounds evaluated as matu rity parameters were seen to experience alterations in proportion to t emperature in the form of either depth or geologic age, that can be co rrelated with maturity. These alterations are believed to result from changes in molecular composition. Maturity parameters based on the alk ylbenzothiophenic and alkylnaphthalenic compounds are shown to be effe ctive maturity parameters in lacustrine sequences, particularly over t he higher maturity ranges where standard maturity parameters based on steranes and hopanes are not effective.