--> ABSTRACT: Coals Formed in Coastal Environments Within Upper Cretaceous of Alberta Basin, by Don E. MacDonald, Peter J. McCabe, and Rudy S. Strobl; #91040 (2010)

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Coals Formed in Coastal Environments Within Upper Cretaceous of Alberta Basin

Don E. MacDonald, Peter J. McCabe, Rudy S. Strobl

Coal resources in the Upper Cretaceous of the Alberta basin were studied using logs from 4,406 oil and gas wells and 331 shallow coal wells. Coal resources were determined to a depth of 400 m.

During the Upper Cretaceous, two major clastic wedge sequences prograded eastward into the Western Interior Cretaceous seaway of western Canada--the Judith River Formation and the Horseshoe Canyon Formation. Within these sequences, three coal zones are found in overall regressive settings and a fourth zone is found in a transgressive setting. The thickest coal development is presently close to zones where terrestrial sediments interfinger with marine sediments.

The coals are generally low in ash (< 15%) and sulfur (0.5%) and range from lignites to high-volatile bituminous C in rank. On a regional scale, the coal zones form broad belts paralleling the inferred north-south paleoshoreline. Coal seams thin seaward, and thicken in a landward direction. The thickest seams are up to 4 m and are found 30-50 km landward of the position of the paleoshorelines at times of maximum progradation.

These coals are thought to have formed in a broad coastal plain setting, but not in close proximity to the shoreline. The mires formed far enough inland not to be affected by coastal erosional and clastic processes. Better drained conditions farther inland may have restricted mire development in the west. The Okefenokee Swamp, located 70-100 km landward of the southeastern United States coastline (Georgia-Florida), is suggested as a modern-day analogue. This depositional model, and the implied stratigraphic architecture, can help guide coal exploration.

AAPG Search and Discovery Article #91040©1987 AAPG Rocky Mountain Section Meeting, Boise, Idaho, September 13-16, 1987.