A STATISTICAL APPROACH TO UNDERSTANDING DIVERSITY IN AN UPPER MISSISSIPPIAN (CHESTERIAN) ECHINODERM-RICH UNIT ACROSS FOUR CONTIGUOUS LITHOFACIES, CARTER COUNTY, NORTHEASTERN KENTUCKY

The Upper Mississippian (Chesterian) Ramey Creek Mbr. of the Slade Fm. is an echinoderm-rich unit, interpreted to represent a shallow, open-marine environment, but closer analysis of lithologies and sedimentary structures from 136 fossiliferous slabs collected from the Valley Stone Quarry in northeastern Kentucky indicates four distinct lithofacies, each with varying fauna. To understand how depositional environments influenced faunal constituents, and exactly where and how the echinoderms fit into community structure, we performed census population counts of all species across each lithofacies, noting the area of each lithofacies. The lithofacies include: coarse, well-washed, shoal calcarenites (2.0 m², 724 individuals); coarse, shoal-margin, argillaceous calcarenites (0.9 m², 376 individuals); fine-grained calcarenites and interbedded calcilutites (0.6 m², 189 individuals); and basinal calcilutites (0.6 m², 610 individuals) for a total area of 4.1 m² and 1899 individuals, representing 64 species, of which 23 are echinoderms.

Examining richness (total individuals/area) and using Simpson’s Index of Diversity and Shannon’s Evenness Index, we derived richness (S), diversity (D) and evenness (E_H) data for each lithofacies. Then Pearson’s r, a value ranging from 0 (none) to 1 (strong), was adapted to show degree of strength or weakness of values for each index. On a gradient from shallow to deep, shoal calcarenites show that S=363/m², D=0.89 and E_H =0.71; shoal-margin calcarenites show that S=419/m², D=0.66 and evenness E_H =0.57; transitional calcarenties/calcilutites show that S=327/m², D=0.90 and E_H=0.84; and basinal calcilutites show that S=1024/m², D=0.92 and E_H =0.76. For the entire collection, S=467/m², D=0.90 and E_H =0.69. These data suggest that in the entire collection, richness is somewhat strong, diversity is strong, and taxa are uniformly abundant. Basinal environments are richest and most diverse, but taxa were not uniformly abundant. In contrast, the transitional environment shows the lowest richness, but strong diversity and uniform abundance of taxa. Although studying echinoderms was the original purpose of the study, derived statistical data like these provide context in which to understand the relative abundance and functions of echinoderms within their communities.