BIOSTRATIGRAPHY AND PALEOECOLOGY OF THE LATE MISSISSIPPIAN – EARLY PENNSYLVANIAN BOUNDARY IN WESTERN KENTUCKY

Late Mississippian and Early Pennsylvanian coal and shale samples from the Eastern Interior (Illinois) Basin have been analyzed primarily to identify the Mississippian - Pennsylvanian boundary in western Kentucky. Samples that were examined are from outcrop sections and drill core. Differentiating Late Mississippian from Early Pennsylvanian strata in western Kentucky, as well as the entire Illinois Basin, is often problematic because similar lithologies persist across the boundary. Another goal of this study was to see if the recovered palynomorphs could help in correlating, and reconstructing the paleoecology of the sampled interval with a similar interval in the Lublin Basin, Poland.

Unfortunately, Late Mississippian palynostratigraphy in the US is poorly defined in terms of miospore assemblage zonation. The stratigraphically oldest samples that were examined contained spore and pollen assemblages indicative of a Late Chesterian age, though further resolution was not possible. Diagnostic Late Mississippian palynomorph taxa in these samples include: Tripartites, Rotaspora, Grandispora, Schulzospora elongata, S. campyloptera, Endosporites micromanifestis, E. parvus, and Crassispora maculosa. None of these forms extend into the Pennsylvanian.

Ecologically, many of the samples are dominated, or co-dominated, by forms ascribed to lycopod trees (Lycospora),seed ferns (Schulzospora), small ferns (Granulatisporites, Leiotriletes, Stenozonotriletes and others), and calmites (Calamospora). Collectively, these samples are inferred to represent marsh-like, but not coal-forming, environments.

In contrast, younger samples usually include thin coal beds that yield an assemblage of Middle to Late Morrowan age. This indicates a substantial gap (unconformity) between Mississippian and Pennsylvanian strata in western Kentucky. Diagnostic Pennsylvanian taxa in this sample include: Laevigatosporites, Endosporites and Granasporites medius. Ecologically, Early Pennsylvanian coals are typically dominated by Lycospora pusilla, L. pellucida, and L. granulata, indicating that the lycopod trees Lepidodendron and Lepidophloios were the dominant vegetation in a mire (peat-forming) setting.