Petroleum geochemistry and hydrocarbon potential of Cambrian and Ordovician rocks of western Newfoundland

Hydrocarbon seeps associated with lower Paleozoic rocks of western Newfoundland have been known since 1812, and sporadic exploration has proceeded for 125 years. A thick late Proterozoic/Cambrian/Ordovician sedimentary succession includes shallow marine platformal clastic and carbonate facies and coeval deep marine mudstone-dominated facies, deposited on the lower Paleozoic passive margin of North America. Taconian, Salinic and Acadian plate convergence and deformation telescoped, and juxtaposed, excellent source rocks with potential reservoir rocks in the onshore and nearshore area. This study integrates extensive new geochemical data from oils and organic-rich rocks with all previous geological and geochemical information to more effectively assess the hydrocarbon potential of the area. All samples of oils collected from old wells, organic-rich shales and other bituminous rocks have similar geochemical characteristics. Chemistry of the oils is consistent with a pre-Devonian clastic source rock containing Type I/II organic matter of mostly algal (Gloeocapsomorpha prisca) origin. Shales of the Cambro-Ordovician Green Point Formation, and probable equivalents, include excellent source rock intervals (TOC up to 10.35%, HI up to 759). Tmax values range from 434 to 443, indicating the source rocks sampled at surface are marginally mature to mature. Biomarker distributions indicate that shales of the Green Point Formation, or rocks with very similar geochemical characteristics, are the source of the oils obtained from seeps and wells. Two maturity trends are evident in western Newfoundland: increasing maturity from the Port au Port area in the south to the Gros Morne area in the north and increasing maturity from west to east across the Port au Port area. Cambro-Ordovician dolomitized platform/shelf carbonates and deeper marine clastics and carbonates offer abundant good potential reservoir facies. Complex structural deformation allows numerous possibilities for thrust repetition of source rocks, juxtaposition of source and reservoir rocks, abundant trap situations and significant hydrocarbon accumulations at depth, in both onshore and offshore settings.