DISTRIBUTION AND TAPHONOMY OF CRINOIDS THROUGH THE ‘ROARING BROOK BUTTER SHALE’ INTERVAL OF THE WAYNESVILLE FORMATION (UPPER ORDOVICIAN: KATIAN, RICHMONDIAN), SOUTHEASTERN INDIANA

‘Butter shales’ are thin, widespread, poorly lithified intervals of pure siliciclastic clay that serve as distinctive marker beds within the mixed carbonate-siliciclastic Upper Ordovician (Katian) strata of the Cincinnati Arch region. Although ‘butter shales’ appear at first glance to be devoid of fossils, micropaleontological analysis has shown them to contain a rich fauna, including an unexpectedly abundant crinoid assemblage dominated by isolated ossicles. The ‘Roaring Brook butter shale,’ comprising the uppermost portion of the Richmondian-age Waynesville Formation, is well-exposed near St. Leon, Franklin County, southeastern Indiana, where it was sampled to assess the abundance, diversity, and preservation of crinoidal material. Bulk samples were collected from immediately below the erosional base of the overlying Liberty Formation, as well as 10 cm, 25 cm, 45 cm, and 90 cm below this surface. All samples contained crinoid material, although total abundance varied by an order of magnitude: the sparsest sample (25 cm below the base of the Liberty) yielded 163 ossicles/kg and the richest sample (45 cm below the base of the Liberty) yielded 1146 ossicles/kg. In all samples, arm material (isolated brachials and arm segments) was most common, followed by stem material (columnals and pluricolumnals), with calyx plates least common. No articulated cups or crowns were recovered, but arm segments and pluricolumnals occurred with a mean of 51 specimens/kg, demonstrating the dominance by isolated ossicles. Column material could, in most instances, be at least tentatively identified to genus, with Glyptocrinus, Plicodendrocrinus, Xenocrinus, and Cincinnaticrinus typically occurring in decreasing relative abundance. Collectively, these results indicate that crinoids represent an important component of the ‘Roaring Brook butter shale,’ although taxonomic and taphonomic variability can be detected throughout this interval, perhaps reflecting changes in sedimentation rate or degree of allochthonous vs. autochthonous material.