STIRRED NOT SHAKEN: USING TAPHONOMY TO RECONSTRUCT PALEOECOLOGICAL SUCCESSION AND TAPHONOMIC FEEDBACK IN A CINCINNATIAN (ORDOVICIAN, OHIO) STORM-DISTURBED SHELL BED

Walker and Alberstadt’s 1975 idea that a single shell bed contains a record of ecological succession has seemingly been refuted through stratinomic studies. These studies suggest that fossils are destroyed and accumulations are reworked by storms to the point of obliterating any record of successional-scale changes in faunas. Therefore storm-disturbed shell beds are not considered ideal for reconstruction of paleoecological succession.

Nevertheless, a storm-winnowed shell bed from the Fairview Formation, Ohio preserves a wide variety of shells in a range of taphonomic conditions that reveal succession-like changes. Exceptionally-preserved lingulid brachiopods found as intact pyrite-lined spar-filled shells rule out the final storm as the cause of shell fragmentation within the bed. Therefore, shell damage accrued over time and can be used to reconstruct not only the paleoecological structure of the pre-storm community, but also to assess the role of taphonomic feedback in community succession.

Fossils within the shell bed are identified and classified by taphonomic condition. The more complete specimens are primarily epibenthic forms, many of which attached to the substrate. Disarticulated Rafinesquina are abundant and served as a pioneer species, allowing epibenthos to recruit into the community. Abundant small, intensively fragmented recrystallized shells, presumably originally aragonite, indicate that molluscs were a more important component of the community structure in the past than at the time of the storm. Preserved whole bivalves are generally epibyssate forms. Some bivalves are found as fragments only and may represent early stages of community succession. The accumulation of Rafinesquina shells provided positive taphonomic feedback that allowed the development of a diverse epifaunal community, while at the same time exerting negative taphonomic feedback that may have increasingly excluded the larger infauna.

This Ordovician storm deposit offers evidence of changing community structure through time facilitated through both positive and negative feedback. It also suggests that existing assumptions about the fidelity of original community structure preserved in storm-disturbed shell beds may not be true in all cases.