Black Shales of Southern Ontario and Their Petroleum Potential

Mark Obermajer, Martin G. Fowler, and Lloyd R. Snowdon
Geological Survey of Canada - Calgary, Calgary, AB

Paleozoic black shales of eastern north America are important sources of oil and gas. In southern Ontario, three distinct black shale horizons of that age include the Upper Ordovician Collingwood, Middle Devonian Marcellus and Upper Devonian Kettle Point strata. All three units contain high amounts of oil-prone predominantly marine organic matter and have good to excellent petroleum source rock potential. The organic matter consist of varying proportions of unstructured bituminite and unicellular alginite. Other organic components found within this bituminite-alginite network include zooclasts, acritarchs and solid bitumen. The biomarker distributions for all units are typical for marine derived organic matter and are characterized by smooth normal alkane and homohopane profiles. Geochemical (Tmax, biomarker data) and optical (reflectance, fluorescence) thermal maturity parameters indicate that the Ordovician Collingwood strata are mature with respect to hydrocarbon generation while the Devonian shales have either only reached the early stage of hydrocarbon generation and expulsion (Marcellus) or are immature (Kettle Point). In general, these shales were deposited in a low-energy, clastic-dominated environment, ranging from shelf to an open basinal depositional setting. The accumulation and preservation of high amounts of organic matter occurred as a result of high marine plankton productivity (algal blooms) and intense microbial interaction in the sediments and bottom waters under progressing anoxicity.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005