EVALUATING FAUNAL ASSEMBLAGES OF THE CHESTERIAN ALONG THE EASTERN SHELF, ILLINOIS BASIN

Chesterian (Upper Mississippian) strata of the Illinois Basin yield a high abundance of well-preserved and highly diverse marine fossils. The Illinois Basin spans central and southern Illinois, southwestern Indiana, western Kentucky, and a small portion of eastern Missouri. The stratigraphic framework of the Illinois Basin has undergone rigorous study over the past two decades, but the associated fauna has been described in piecemeal rather than as a whole. During the Mississippian, there were several episodes of community reorganization that strongly affected suspension feeding benthic invertebrates. By the Late Mississippian, crinoid faunas common in the Early and Middle Mississippian were largely replaced by bryozoan and blastoid dominated communities. In the Illinois Basin the immediate aftermath of this transition is captured within the middle to upper Chesterian strata. We examined faunal differences and similarities in both the macro- and micro-communities by performing a series of Detrended Correspondence Analyses.

The faunal assemblages are superficially similar, including bryozoans, blastoids, brachiopods, corals, gastropods, bivalves, edrioasteroids, and crinoids as macroinvertebrates. Large faunal differences include variations in abundances and a strong presence of epibionts in several of the localities that are absent in others. The microfauna was largely similar including fragmented trilobites and echinoids as well as ostracodes, conodonts, foraminifera, serpulids, and juvenile echinoderms. We provide a more complete understanding of the community structure, of both micro­ and macrofauna, and assemble a framework alongside the sequence stratigraphic data to begin to understand the depositional environment and paleoenvironmental conditions.