ABSTRACT: Thermal Maturity of Petroleum Source Rocks from Ontario as Determined from Reflectance and Fluorescence of Dispersed Organic Matter

OBERMAJER, MARK, STASIUK, LAVERN D. and GOODARZI, FARIBORZ, Geological Survey of Canada, Calgary, AB, Canada

Thermal maturity of Paleozoic strata in southern Ontario has long been a subject of scientific debate. Therefore, the origin of crude oils occurring in this area, despite their well-established geochemical affinity and relationship with oils found in more central parts of the Michigan, Appalachian and Illinois basins, remained unclear.

In the present study, optical properties of dispersed organic matter from organic-rich Paleozoic rocks of southern Ontario were examined to determine the level of thermal maturity of these potential petroleum source rocks. Lack of vitrinite in these rocks precluded the application of standard vitrinite reflectance technique. Instead, novel optical microscopy techniques such as reflectance (%Ro) of zooclast fragments (chitinozoa, graptolites, scolecodonts) and solid bitumen, as well as fluorescence properties (lmax and Q) of Prasinophyte telalginite (Leiosphaeridia, Tasmanites, G.prisca) and acritarchs were used to resolve burial temperatures in southern Ontario. All the investigated macerals occur as minor but persistent components within a dominantly Type II kerogen matrix. The results indicate that the source rocks within the Middle-Upper Ordovician Trenton - Blue Mountain interval reached the zone of prolific oil generation in the southernmost part of the province, in vicinity of the oil pools. The Middle Silurian Eramosa and Middle Devonian Marcellus strata have reached the early stages of oil generation and expulsion, whereas the Kettle Point Formation is immature with respect to oil generation. Thermal maturity assessment is supported by a number of standard geochemical maturity parameters. This conclusion allows a better understanding of oil-source rocks petroleum systems in Ontario.

Search and Discovery Article #90907©2000 AAPG Eastern Section Meeting, London, Ontario, Canada