DETERMINING FAUNAL DIVERSITY AND THE ROLE OF KEY BIOTA FROM REEF-LIKE BUILDUPS IN THE LATE ORDOVICIAN (KATIAN) KIMMSWICK LIMESTONE, EAST-CENTRAL MISSOURI

The Kimmswick Formation of east-central Missouri is dominated by fossiliferous grainstones of Late Ordovician (Chatfieldian; Katian) age. The Kimmswick in eastern Missouri formed in a transitional shallow-water environment between the Ozark Plateau (now the Ozark Dome) and the deep-water Sebree Trough. The Kimmswick Limestone is relatively homogeneous in faunal composition and lithology throughout the midwest. Here, however, we report on a unique mound-related paleocommunity of encrusting stromatoporoids, cyathocystid edrioasteroids, camerate and cladid crinoids, paracrinoids, edrioblastoids, bryozoans, and tabulate and rugose corals, including many taxa that are rare elsewhere. Ongoing examination of the outcrop has identified that the initial and main stabilization of this buildup consisted primarily of stromatoporoid boundstones with minor echinoderm components. The colonization and diversification of the buildup consisted of various encrusting echinoderms intergrown with stromatoporoids and other undetermined binding organisms. Cyathocystid edrioasteroids, often in inverted life orientation, occur in dense aggregations pendant from cavity ceilings. Stalked echinoderms (crinoids, paracrinoids, and edrioblastoids) exploited higher tiers, and occur attached to and intergrown with stromatoporoids by root-like to lobate holdfasts.

The purpose of this study is to assess the faunal diversity and reef community structure at a greater resolution by analyzing richness and evenness at two different scales: bulk sample and thin section. Buildup diversity was evaluated at both the macro and microscales by conducting individual taxon counts as well as estimating biovolume. These methods allow for the identification and determining density of the key biota, dominantly echinoderms and stromatoporoids, and their structural role in each buildup phase of the reef-like structure. Establishing a detailed narrative of the community dynamics of this reef-like mound provides a unique opportunity to assess the paleoenvironment and ecological interactions during the Late Ordovician and can potentially add to our knowledge of atypical modern reef systems dominated by taxa other than corals, including crinoids and other echinoderms.