POPULATION ANALYSIS OF A LATE MISSISSIPPIAN (CHESTERIAN) ECHINODERM FAUNULE ACROSS FOUR CONTIGUOUS DEPOSITIONAL ENVIRONMENTS, CARTER COUNTY, EAST-CENTRAL KENTUCKY

Mississippian echinoderms are well-known, but few studies attempt detailed population analysis across contiguous depositional environments. A “crinoid garden” was collected from the shallow open-marine Ramey Creek Mbr. (Chester, Hombergian) of the Slade Fm. in northeastern Kentucky. The “garden” was collected from a quarry in Carter Co., KY. Four contiguous facies were recognized: coarse shoal calcarenites; coarse, shoal-margin, shaly calcarenites; fine-grained calcarenites and calcisiltites from a shoal-basin transition; and basinal calcilutites. Fifty-one species were recognized; crinoids were most abundant, followed by brachiopods and bryozoans. Eighteen crinoid, 13 brachiopod and 10 bryozoan species were present; in addition, two edrioasteroids, a blastoid, an echinoid, an ophiuroid, a pelecypod, two scyphozoans, a sponge, and a tabulate coral were also present. Assuming that specimens are in place, we make some inferences about community structure. Shoal-top environments (37 species) were dominated by low-level sponge and brachiopod filter feeders; intermediate-level crinoid filter feeders were next in abundance. In shoal-margin environments (25 species), low-level filter-feeding brachiopods predominated; a few intermediate-level crinoids were present. In the basin-shoal transition (21 species), low-level brachiopod filter feeders predominated, but intermediate-level crinoids grew in abundance; numbers of ophiuroids and echinoids also increased. In the basinal environment (38 species), low-level brachiopod, sponge, and bryozoan filter-feeders predominated, but low-level and intermediate-level crinoids and blastoids approach abundances observed in the shoal-top setting. Ophiuroids declined in abundance here, while echinoids dramatically increased. Low-level filter-feeding brachiopods predominated in every environment. Intermediate-level filter-feeding crinoids were prominent parts of shoal-top and basinal settings and were largely dominated by one heavily constructed species. Ophiuroids and echinoids became prominent in the deeper environments where they were not buffeted by waves. Although patterns are not always clear, it appears that energy levels largely controlled diversity and the distribution of echinoderms across the environments.