ABSTRACT
Distribution of crinoids within a major shoaling-upward sequence of the Upper Ordovician in the Cincinnati, Ohio, region reveals association of taxa and morphotypes with distinct facies. The shale-rich Kope lithofacies, representing offshore deposition mostly below normal wave base, has a low-diversity crinoid fauna, typified by the small, slender inadunates Ectenocrinus and Cincinnaticrinus. Crinoid diversity increases in the overlying Fairview lithofacies which contains nearly equal propotions of thinbedded limestone and shale deposited in the transition between offshore and shoreface zones. Although slender inadunates (Ectenocrinus) are present, diminutive forms decline and larger, more robust inadunates (Iocrinus) and the multiplated camerate Glyptocrinus become dominant. Crinoid diversity drops in the overlying carbonate-rich Bellevue lithofacies, deposited above wave base at a regressive maximum. Here, a large, robust inadunate, Anomalocrinus, with a thick column up to 1 m long and a massive cemented holdfast occurs in association with hardgrounds. The faunal and morphologic transition from small, slender morphotypes in deeper-water, clastic-rich facies to more diverse assemblages characterized by larger, more robust, nonpinnulate inadunates and pinnulate camerates in shallower carbonate-rich facies suggests a relationship to a gradient of increasing energy of water movement and decreasing turbidity. These relationships between Late Ordovician crinoid morphology and paleoenvironment may represent early expressions of similar patterns recognized among Early Carboniferous crinoids.
