ASSESSING THE MAGNITUDE AND HABITAT DIVERSITY OF MARINE TRANSGRESSIONS IN THE PENNSYLVANIAN BREATHITT GROUP USING RAREFACTION ANALYSIS OF FOSSIL COLLECTIONS

The Middle Pennsylvanian Breathitt Group of the Central Appalachian Basin, USA includes a number of marine stratigraphic intervals deposited at highstands during third and fourth order sea level cycles. Four of these marine intervals, the Elkins Fork, Kendrick, Magoffin, and Stony Fork members, have been quantitatively sampled for marine macroinvertebrates across their outcrop region in Kentucky, West Virginia, and Virginia. Results from this study suggest that the Magoffin marine interval was deposited by the largest transgression because it has the highest sampled species richness and the greatest range of sampled marine habitats. The Stony Fork has similar species richness as the Magoffin, but fewer sampled marine habitats. The Kendrick has intermediate species richness and habitat diversity, and the Elkins Fork has low species richness and only a single sampled habitat. However, direct comparisons are unreliable because of sampling bias caused by the variable stratigraphic position and outcrop accessibility of the different marine intervals. The Magoffin appears to be the most extensive marine transgression, but it was sampled at twice as many localities and is represented by over twice as many specimens as any of the other three. Rarefaction analysis was used to control for sampling bias in comparisons of species richness between marine intervals. Based on comparisons of rarefaction curves, the Kendrick, Magoffin, and Stony Fork do not appear to significantly differ in total species richness. The Elkins Fork does have a significantly lower overall species richness (gamma diversity), but its within-habitat species richness (alpha diversity) is comparable to similar habitats in the other marine intervals. These results suggest that the Elkins Fork transgression was a significantly smaller event than the Kendrick, Magoffin, and Stony Fork transgressions, which were of comparable magnitude and developed a comparable range of habitats and overall gamma diversity. The apparent greater development of the Magoffin transgression may simply be a sampling effect caused by its widespread accessibility within the Pennsylvanian outcrop belt in the study region.