Abstract: Coal-Bench Architecture as a Means of Understanding Regional Changes in Coal Thickness and Quality

Stephen F. Greb, Cortland F. Eble, James C. Hower

Analysis of the Fire Creek (Westphalian B), Pond Creek (lower Westphalian B), and Stockton (Westphalian C) coals, three of the most heavily mined coals in the Central Appalachian Basin, shows that all have a similar multiple-bench architecture of at least two benches split by a regional clastic parting or durain. Coal benches beneath regionally extensive partings are generally less continuous, thinner, more palynologically variable, higher in ash yield, and higher in sulfur content than coal benches above regional partings in all three coals. Where thick, benches above regional partings tend to exhibit temporal palynological changes from lycopod- to fern-dominant. Where inertinite-rich/fern-dominant benches are overlain by additional benches, the upper benches are limited in extent, variable in thickness, high in sulfur content and ash yield, and split away from the coal.

The multiple-bench architecture exhibited by these coals is interpreted to represent a cyclic mire succession that was common in the Middle Pennsylvanian. Peats began as planar mires infilling an irregular topography during rising base level. When the topography was infilled, unconfined flooding was possible and resulted in widespread partings. Ponding above these clay-rich flood deposits led to re-establishment of new planar mires with greater continuity than the underlying mires. The extent of these mires provided buffers to clastic influx and, in many cases, allowed domed conditions to develop. Doming resulted in thick, high-quality coal benches. In some cases, a third stage of planar peats, with similar characteristics to the planar peats at the base of the beds, developed on the nevenly distributed clastics that buried underlying mires during continued base-level rise.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas