Geology of Coal Resources in Alberta Plains

Dennis Nikols, Rudolph Strobl, Richard Richardson, Donald MacDonald

In the plains region of Alberta, major deposits of mineable coal are present in three geological units: the Paskapoo Formation (lower Tertiary), the lower Horseshoe Canyon Formation and the Belly River Group (both Upper Cretaceous in age). Coal-resource studies of each unit were recently completed by the Coal Geology Group of the Alberta Research Council. The size of the study areas ranged from 474 to 490 to 1,202 townships, respectively. Data from 2-3 wells per township provided a comprehensive basinwide coal-resource data base. A series of maps describing the cumulative coal, structure on major markers, number of seams, and maximum seam thickness for each coal zone were generated and provided a framework for a basinwide evaluation of these coals.

Results of these investigations show that the distribution of coals and coal quality are controlled by the depositional environment and the tectonic setting. For the Cretaceous of Alberta, relative sea level fluctuation appears to be the dominant control on coal development. These coals were formed in a coastal-plain setting, parallel to north-south oriented paleoshorelines. Cretaceous coals generally have a maximum seam thickness of 1-2 m, are laterally discontinuous, and exhibit significant variation in coal quality regionally and locally. Tertiary coals were formed in an alluvial-plain setting well removed from marine influences. The dominant control on coal development was regional subsidence associated with loading along the western basin margin. The best coal resources of the Te tiary are associated with areas that underwent relatively rapid subsidence and isolation from western-derived clastics. These coal seams commonly have a maximum seam thickness of 4 m, can be correlated over distances of 100 km or more, and exhibit less variation in coal quality than the Cretaceous coals. Application of these differences and understanding the major controls on coal deposition play an important role in current coal-quality studies by the Alberta Research Council. Tertiary age coals are reviewed as an example.

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988