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ABSTRACT: Geology and Petroleum Potential of the Gulf of St. Lawrence Region

B. V. Sanford, A. C. Grant

The Gulf of St. Lawrence is underlain by two large sedimentary basins: the lower Paleozoic foreland Anticosti basin on the north containing more than 6 km of strata; and the upper Paleozoic successor Magdalen basin to the south containing upwards of 10 km of strata. Initial deposits in the northern part of the Gulf (Cambrian to Lower Ordovician) were deposited on a broad continental shelf bordering a spreading proto-Atlantic Ocean to the southeast. Emergence of tectonic land along the shelf margins, accompanied by westward movement of allochthons in the early Middle to Late Ordovician, initiated the Anticosti basin and provided a source of fine and coarse clastics to intertongue with carbonates for much of the remainder of the early Paleozoic. Equivalent geosynclinal depo its to the south of Anticosti basin deformed, intruded, and locally metamorphosed during Taconian and Acadian orogenies formed a favorable tectonic setting for the inception and development of the Magdalen basin into which thick redbed clastics, carbonates, and evaporites accumulated during Carboniferous to Permian times.

In Anticosti basin, thick units of black shale are a potential source of hydrocarbons that may have accumulated in a variety of block-faulted structures and stratigraphic traps along the southern margins of the basin. Salt-cored structures comprised of ridges, walls, and diapirs occur in great abundance along the southern and eastern margins of the Magdalen basin and have been recently identified by the authors along the southwestern margin of the Anticosti basin north of Gaspe Peninsula. These undoubtedly offer potential for oil and gas, some of the more promising structures of which may have been hitherto overlooked by the petroleum industry.

AAPG Search and Discovery Article #90998 AAPG Eastern Section Meeting, London, Ontario, Canada, September 10-12, 1990