Abstract

Marine geophysical surveys confirmed by deep exploratory drilling have indicated that the bulk of the Scotian Shelf, Grand Banks and continental slope beyond form the submerged extension of the Atlantic Coastal Plain. The Plain in this area comprises a wedge of Cenozoic and Mesozoic strata covering an area of 350,000 square miles and reaching a maximum thickness of over 30,000 feet, and is therefore one of Canada’s deepest and most extensive sedimentary basins.

Oil exploration began in this region in 1959, and since that time federal oil and gas permits have been issued for more than 200 million acres, over 100 crew-months of seismic work have been carried out, and 34 exploratory wells have been drilled to the end of 1971, including 28 on the Scotian Shelf and six on the Grand Banks. Data from five of these wells which have been released indicate that Jurassic and Cretaceous strata form the major part of the stratigraphic sequence, and include a probably widespread lower salt unit which may be correlative with the Louann Salt of the U.S. Gulf Coast basin, a carbonate unit not unlike the Smackover and Norphlet Formations of the same area, and a prograding, coastal marine or deltaic sequence of sand and shale which may reach its greatest development and thickness near the effluence of the ancestral St. Lawrence River. Tertiary clastics generally form a relatively thin veneer over the Cretaceous on all but the outer edge of the continental shelf, but thicken appreciably over the shelf break due to progradation across a clinoform surface of deposition, and appear to be very thick beneath the slope and rise where turbidite sands may eventually assume commercial significance, particularly beneath the Laurentian Fan.

The geological history and pattern of deposition reflect the influence of rifting and seafloor spreading in the North Atlantic Ocean basin since Late Triassic time. The Mesozoic and Cenozoic structural history is marked by stability and controlled by epeirogenic and tensional forces only. Local structures, including halokinetic features, normal basement faults and down-to-the-basin growth faults are abundant.

The region appears to have all the essential ingredients for a major hydrocarbon province. Offsetting these indications are a number of adverse factors involving operational, economic, and geologic considerations which add a touch of reality to what would otherwise be an unusually attractive exploration area. Although no commercial discoveries have been confirmed to date, numerous oil and gas shows have been encountered in wells and give promise of ultimate success. The area is compared with several productive basins throughout the world which have temporal, stratigraphic and structural affinities, and an estimate is made of potential hydrocarbon reserves based on weighted volumetric criteria. The Sydney and Acadian basins, beneath the Laurentian Channel and Bay of Fundy respectively, contain older sedimentary sequences and are considered to be less attractive than the submerged Atlantic Coastal Plain because of their lower proportion of reservoir and source rocks.