Lower-Middle Paleozoic Basins in Eastern Canada: A Largely Under-Explored and Under-Evaluated Potential

Denis Lavoie
Geological Survey of Canada, Quebec City, QC

The Cambrian to Middle Devonian successions at the continental margin of Laurentia consist of largely underexplored marine to continental sediments deposited during alternating passive margin and foreland basin episodes. Two significant orogenic pulses, the Middle-Upper Ordovician Taconian Orogeny and the Late Silurian-Middle Devonian Salinian-Acadian event controlled tectono-sedimentary patterns.

Good hydrocarbon source rocks are found in the Upper Ordovician foreland basin shales (TOC up to 14%), in the Middle Ordovician oceanic shales (TOC up to 10.7%) and in the Lower Ordovician passive margin shales (TOC up to 10.4%). Fair hydrocarbon source rocks are found in Lower Devonian foreland basin limestones and coals (TOC up to 2% and 14%, respectively).

Primary and secondary potential clastic reservoirs are found in Cambrian-Ordovician passive margin and foreland basin coarse sandstone and conglomerate slope facies and in Silurian-Devonian nearshore sandstones. The potential for secondary carbonate reservoirs is recognized in hydrothermally-altered carbonates (Lower to Upper Ordovician passive margin and foreland basin; Lower Silurian and Lower Devonian foreland basin), in Upper Silurian to lowermost Devonian reefal complexes and in Lower Devonian fracture-type reservoir.

Traps and seals are multiple and include various stratigraphic (pinch-out, impermeable layers and unconformities), tectonic (fault closures, anticlines, duplexes and triangle zones) and diagenetic (HTD) types.

Maturation suggests that the Cambrian-Ordovician St. Lawrence Platform has a gas (southern Quebec) to oil (western Newfoundland) potential; the coeval Humber Zone has a gas (Quebec) to gas and oil (western Newfoundland) potential. The Late Ordovician to Middle Devonian Gaspé Belt has both gas to oil potential.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005