ABSTRACT: Foreland Basin Oil and Gas Plays, Western Canada Jura-Cretaceous

BARCLAY, J. E., Geological Survey of Canada, Calgary, Alberta, Canada

Western Canada foreland basin tectonic stages are recorded as five distinct depositional assemblages. Each assemblage consists of regressing and transgressing proximal to distal facies belts composed of coarsening-upward progradational sequences. Most petroleums occur in higher-energy, porous shoreline-fluvial sandstones and conglomerates capping sequences. Orogen-induced subsidence, sea level, and sediment supply controlled sequence lithologies and reservoir-source-seal geometries. Variations in these controls caused each assemblage to have a unique set of traps and plays:

1. Fernie-Nikanassin Assemblage (shallow marine to continental Upper Jurassic/basal Cretaceous): Intra-Jurassic marine, shoreline, fluvial sandstones, and uppermost Jurassic sandstone erosional remnants (e.g., Swift, Success, and Nikanassin formations).
2. Mannville Assemblage (fluvio-deltaic-littoral Lower Cretaceous): Continental basal sandstones on the sub-Cretaceous unconformity and overlying deltaic-estuarine sands. Variety of stratigraphic traps (e.g., Basal Quartz, Dunlevy/Buick Creek. Athabasca and Peace River oil sands). Dominates foreland basin gas and heavy oil.
3. Colorado Assemblage (marine Middle Cretaceous): Thin, coarsening-upward sandstone-conglomerate sequences within marine shales (e.g., Viking and Cardium dominate foreland basin's oil. Medicine Hat shallow gas sands).
4. Saunders/Edmonton Assemblage (marine Upper Cretaceous to continental Lower Tertiary): Basal fluvio-deltaic sandstones representing the last marine stage (e.g., Milk River, Belly River). Overlying continental strata are petroleum-barren.
5. Cypress Hills/Hand Hills Assemblage (continental Upper Tertiary): Thick continental gravels representing proximal molasse. Channel reservoirs are too shallow, are thermally immature, and lack source-seals.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)