Paper No. 8
Presentation Time: 1:30 PM-5:30 PM
CRITERIA FOR DETERMINING LIVE VS. DEAD FAUNAL ELEMENTS AND FAUNAL INTERACTIONS ON AN OBRUTION SURFACE FROM THE UPPER ORDOVICIAN MIAMITOWN SHALE, SHARONVILLE, OHIO
A bivalve shell pavement collected from the Upper Ordovician (Maysvillian) Miamitown Shale at Trammel Industrial Park in Sharonville, Ohio, preserved various marine organisms that were smothered by a thick layer of siliclastic mud. Taxa found included two species of bivalves Ambonychia and Modiolopsus, two species of gastropods Loxoplocus and Cyrtolites, one species of orthonconic cephalopod, three species of brachiopods Zygospira, Dalmanella, and Rafinesquina, one species of tube worm Cornulites, two species of edioasteroids Isorophus and Carnyella, one trilobite species Flexicalymene and three species of bryozoans including encrusting globular trepostomes, thin ramose trepostomes, and dendritic cyclostomes. Evidence suggests that some of the taxa were part of the smothered community while others were skeletal debris on the sea floor prior to the obrution event. Criteria for the identification of living versus dead faunal elements include: faunal interactions, articulation of skeletal remains, preserved life position, preserved biological interaction, and nature of encrustation. Bivalves on the surface showed bryozoan encrustation on both internal and external surfaces clearly indicating they were debris. These shells form the substrate upon which the smothered community attached. The brachiopod Zygospira was found in life position in clusters around the bivalves suggesting live attachment at the time of burial. These brachiopods further showed biological interactions with Cornulites that were epibiotically attached to their valves with their apertures along the commissure where they fed parasitically from the brachiopod's feeding currents. The edrioasteroids were in life position and fully articulated indicating they were part of the live smothered community. Rafinesquina, Flexicalymene, thin ramose bryozoans, and cephalopods were preserved as broken and disarticulated skeletal debris suggesting that they were not part of the smothered community at least locally. Whether the encrusting trepostome and cyclostome bryozoans, and gastropods were alive or dead at the time of burial is equivocal.