Abstract: Depositional Models in Coal Exploration and Mine Planning

J. C. Horne, J. C. Ferm, A. D. Cohen

Geologic studies in the Appalachian region have shown that many parameters of coal beds (thickness, continuity, roof and floor rock, sulfur and trace-element content, and ash) can be attributed to the depositional environment in which the peat beds formed and to the tectonic setting at the time of deposition. With an understanding of the depositional setting of the coal seam and contemporaneous tectonic influences, the characteristics and variability of many of these parameters can be predicted.

Coals formed in "back-barrier" environments tend to be thin, laterally discontinuous, high in sulfur, and to have severe roof problems. For these reasons, they are not generally important as minable coals. Coal beds deposited in the "lower delta-plain" environment are relatively widespread with fewer roof problems but tend to be thin and have a highly irregular pattern of sulfur and trace-element distribution. Conversely, "upper delta plain-fluvial" coals are low in sulfur and are locally thick but usually are laterally discontinuous. Despite these problems, some "lower delta-plain" and "upper delta plain-fluvial" coals are mined successfully. However, most important seams in the Appalachian area are in the transitional zone between these two environmental facies. In this transition z ne, thick coals attain a relatively high degree of lateral continuity and usually are low in sulfur.

Superposed on changes in seam character attributed to variations in environments of deposition are contemporaneous tectonic influences. Rapid subsidence during sedimentation generally results in rapid variation in coal seams but favors lower sulfur and trace-element content, whereas slower subsidence favors greater lateral continuity but higher content of chemically precipitated material.

Knowledge of depositional environments and of their modification by tectonic setting is a valid and viable tool in the search for and development of solid-hydrocarbon resources.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC