GEOLOGIC AND PALEOBOTANICAL EVOLUTION OF EARLY AND MIDDLE PENNSYLVANIAN STRATA IN THE WESTERN KENTUCKY COAL FIELD

The Western Kentucky Coal Field is the southern tip of the Eastern Interior, or Illinois Basin. Pennsylvanian rocks in this area, which include conglomerate, sandstone, siltstone, shale, limestone and coal, were deposited primarily in coastal-deltaic settings at a time when western Kentucky was located close to the equator. This paper discusses temporal changes in regional sedimentation patterns and coal-forming floras of Lower and Middle Pennsylvanian strata in the Western Kentucky Coal Field.

Lower Pennsylvanian strata of the Caseyville Formation (Morrowan) are characterized by paleovalley-filling sedimentation patterns and extrabasinal quartz pebbles. Caseyville Formation coals are characteristically thin and discontinuous and were strongly influenced by Lower Pennsylvanian paleotopography. Caseyville coals are commonly dominated by Lycospora, but can also have variable palynofloras, which probably reflects variable edaphic conditions and edge effects within small, patchy paleomires.

Tradewater Formation strata (Atokan) show increased marine influences and tidal-estuarine sedimentation, especially in the middle and upper parts. Coal beds in the lower part of the Tradewater typically are thin and discontinuous, although some economically important beds are present. Coals become thicker, more abundant and more laterally persistent towards the top of the formation. Palynologically, lower and middle Tradewater Formation coals are dominated by Lycospora, but begin to show increased amounts of tree fern spores. Middle and upper Tradewater coals are characterized by heterogeneous palynofloras, with high percentages of tree fern spores being a common attribute. In addition, cordaite pollen (Florinites) becomes locally abundant in this interval.

Carbondale and Shelburn strata (Desmoinesian) are much more laterally continuous, and occur within classic cyclothems that can be traced across the coal field. Cyclothems have long been interpreted as being eustatically-driven, and glacio-eustacy appears to have controlled not only Desmoinesian sedimentation patterns, but also the formation of Desmoinesian paleomires. Palynologically, Carbondale and Shelburn coals are either dominated by Lycospora, or have heterogeneous palynofloras.