PALYNOLOGY, STRATIGRAPHY AND PALEOECOLOGY OF LATE ATOKAN COALS IN SOUTHWESTERN INDIANA AND WESTERN KENTUCKY

Coal beds of Late Atokan (Late Bolsovian, Westphalian C) age in southwestern Indiana and western Kentucky include the Mariah Hill to Buffaloville/Minshall coal interval in Indiana, and the Dunbar to Mannington coal interval in Kentucky. Coal beds in this interval are of economic value as they tend to be low in ash yield and sulfur content. However, regional correlation has proven to be problematic because they occur in a stratigraphic interval where conventional lithostratigraphy is hampered by discontinuous coal distribution, and a lack of distinctive marker beds. As such, palynologic analysis has proven to be very helpful in correlating these coal beds, a factor that ultimately helps to provide for more accurate resource assessments.

All of the coal beds are co-dominated by Lycospora, which was produced by many of the large lycopsid trees (e.g., Lepidodendron, Lepidophloios) that were prevalent in Middle Pennsylvanian mires, and tree fern spores (mainly Punctatisporites minutus and Punctatosporites spp.). Spores ascribed to small lycopsids (Densosporites, Radiizonates), small ferns (e.g., Granulatisporites) and calamites (Laevigatosporites spp. and Calamospora), as well as cordaite pollen (Florinites) are locally abundant. Ecologically, a co-dominance of tree lycopsids and tree ferns is typical of Late Atokan coal beds. Local floral variation appears to be associated with the ephemeral nature of these coals, which results in a large amount of peripheral area relative to the overall paleomire size.

Palynology indicates that all but the very top of the Late Atokan in this area conforms to the Radiizonates difformis (RD) miospore assemblage zone. The Mariah Hill and Dunbar coals mark the first appearance of Radiizonates difformis, which is last seen in the Buffaloville/Minshall coal of Indiana and the top of the Elm Lick coal zone in Kentucky. Individual coal bed nomenclature is inconsistent and problematic; this will be a focal point of discussion.