Effects of Climate, Tectonism, and Variations in Sea Level on Formation of Cretaceous Coals of North America

Peter J. McCabe, Michael E. Brownfield, Dan E. Hansen, Robert D. Hettinger, Mark A. Kirschbaum, J. David Sanchez

Extensive deposits of Cretaceous coal-bearing strata are present in western North America, extending from the North Slope of Alaska to northern Mexico. Most of the Cretaceous sediments were derived from the active Cordillera region and were deposited in foreland basins on the western margin of the Western Interior seaway. A multidisciplinary study is in progress to document and attempt to explain the temporal and spatial distribution of the Cretaceous coals. The study examines the effects of variations of paleoclimate, tectonics, and relative sea level on a continentwide scale. In addition, coal quality is related to the regional depositional settings.

Many aspects of coal quality (for example, maceral composition, ash content, sulfur content) are determined by the flora and hydrology of the mire in which the original peat accumulated. The existence of Cretaceous coals throughout the length of the Western Cordillera provides a unique opportunity to determine variations in mire type with climate over a range of 50° of paleolatitude, and to examine the effects of these variations on coal quality. The relationships between coal beds and associated clastic facies should also be expected to change with varying mire types.

Recent developments in our understanding of foreland basin evolution, Cretaceous sea level changes, and peat-forming environments make this an optimal time to begin a regional synthesis of North America's Cretaceous coals. Results of this study should aid the development of better predictive models of coal quality and seam thickness. These models will take into account the effects of major controls on sedimentation (climate, tectonics, sea level changes) rather than just the local depositional environment. Many of the major coal deposits of the world lie within foreland basins, and we hope that the models derived from this study will be transferable to coal deposits of differing age in other areas.

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