Reflectance Studies on Organic Matter in Lower Paleozoic Sediments of Quebec

ABSTRACT Reflectance data from twelve wells (six in St. Lawrence Lowlands Cambrian-Ordovician rocks, three in Silurian rocks, and three in Devonian rocks of Gaspe Peninsula) are included in this paper. The observations were made on polished organic matter obtained by palynological preparations made from drill cuttings and cores. The organic matter in the Cambrian-Ordovician and Silurian rocks, and the Devonian carbonates, presumably consists of asphaltic pyrobitumen, which closely resembles vitrinite under the microscope. The organic matter in the Devonian clastics is characteristically coaly. The relatively undeformed platform rocks of the St. Lawrence Lowlands, despite a wide regional variation, generally attain an initial maturity (oil prone) stage of organic metamorphism to a depth of approximately 3,000 ft (900 m) and a mature (mainly gas-with-condensate prone) stage to an approximate depth of 6,000 ft (1,800 m). These maturation levels are shown by the Utica and Lorraine shales, silts and minor sandstones, and the Trenton carbonates. Rocks below 6,000 ft (1,800 m) contain mainly gas possibilities. The Silurian sediments, in the Gaspe Peninsula area, generally attain mature and postmature stages of maturation corresponding to gas potential. The maturation can be correlated with the total thickness of Silurian rocks but anomalous high maturation levels in the interior of Gaspe Peninsula are attributed to regional igneous activity. The Devonian carbonates and clastics are best preserved in a series of regional folds in eastern Gaspe. They are at the immature to postmature stages of organic metamorphism, suggesting both oil and gas possibilities. The metamorphism increases toward the interior of Gaspe Peninsula, where it may be related to basinal thickening and increased regional igneous activity.