TESTING FOR FAUNAL STABILITY ACROSS A REGIONAL BIOTIC TRANSITION: QUANTIFYING STASIS AND VARIATION AMONG RECURRING CORAL BIOFACIES IN THE MIDDLE DEVONIAN APPALACHIAN BASIN

The topics of ecologic assembly and long term biofacies persistence have been the focus of intense paleoecologic research over the past decade. Yet, questions central to these issues remain unresolved. In this study, recurring coral-rich biofacies were sampled from two stratigraphic horizons within the Middle Devonian Appalachian Basin in order to examine: (1) the extent to which biofacies are capable of persisting within a basin through time, and (2) whether ecological structure may be a viable mechanism for generating community stasis. Previous observations on the stable nature of Middle Devonian coral-rich assemblages from the Hamilton Group have led some researchers to invoke the primacy of ecological controls in maintaining biofacies structure through time. However, few analyses have quantified the degree to which recurring biofacies vary; in particular, none have assessed lateral variability as a benchmark for testing the significance of temporal variability. Thus, the extent to which Hamilton biofacies persist and the mechanism(s) responsible for their alleged stability remain contentious.

Here, species abundance variability was examined across multiple spatial scales within each of the sampled coral-rich horizons. This allowed for the establishment of a baseline against which to evaluate temporal differences in biofacies composition and structure. Although successive coral biofacies remained taxonomically stable, their dominances structures varied significantly through the 1.5 Myr study interval. This strongly suggests that an ecologic mechanism cannot be generating taxonomic stasis. Instead, these findings support a model in which taxa respond individually to fluctuations in the physical environment by altering their abundance distributions geographically and temporally.