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Stephen F. Greb1, Donald R. Chesnut2, Cortland F. Eble2
(1) Kentucky Geological Survey, Lexington, KY
(2) Kentucky Geological Survey

Abstract: Comparison of Coal-Bearing Sequences in Basins of Different Tectonic Styles-Pennsylvanian Strata of the Illinois and Appalachian Basins in Kentucky

The Western Kentucky Coal Field occurs in the southeastern part of the Illinois Basin, an intra-cratonic basin, whereas the Eastern Kentucky Coal Field is part of the central Appalachian Basin, a foreland basin. Differences in time-equivalent strata thicknesses and coal continuity between the two basins illustrates how different mechanisms and rates of tectonic subsidence influence coal distribution, although both basins show decreases in tectonic accommodation from the Morrowan into the Desmoinesian. Desmoinesian stability led to the classic, widespread cylothemic parasequences of the Illinois Basin.

In both basins, lowstand systems tracts (LST) are best developed in the early Morrowan, with deeply incised, bedrock paleovalleys filled by extra-basinal conglomeratic sands. In younger strata, the lack of valley confinement and a shift in clastic sources in both basins make differentiation of LST sands more complicated, especially in the foreland basin where channel-based prograding distributaries of the highstand systems tract (HST) can be confused with LST valley-cutting deposits. In parts of both basins, Morrowan coals may be restricted to paleovalley-influenced transgressive systems tracts (TST) and HST deposits. In the Atokan and Desmoinesian, distinctive carbonaceous shales with marine fossils and marine flooding surfaces become more widespread. Coals also become increasingly more continuous in cyclothemic parasequences. Morrowan and Atokan coals account for most of eastern Kentucky's production, while Desmoinesian coals account for most of western Kentucky's production.

In the foreland basin, increased accommodation space toward the basin axis causes thickening of individual parasequences, and splitting and development of coal zones. Basinward thickening and marginward truncation and pinching of individual parasequences suggests strong tectonic controls on sequence distribution and parasequence preservation.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana