ORGANIZATION AND DISTRIBUTION OF MIDDLE DEVONIAN BIOFACIES WITHIN A SEQUENCE STRATIGRAPHIC FRAMEWORK, HUNTINGDON COUNTY, PENNSYLVANIA, USA

Understanding the controls on the distribution of fossils in time and space has been an important aspect of paleontological research in the last several decades. The Middle Devonian Hamilton Group of New York State has been identified as a unique period in geologic history, with virtually no taxonomic and ecological turnover throughout the interval. While this interval has been studied extensively in New York State using both qualitative and quantitative methodologies, virtually no studies have been conducted in other regions of the Appalachian Basin. Field collection from an extensive outcrop of Mahantango Formation (Hamilton Group) in Huntingdon, Pennsylvania was conducted to characterize ecological gradients and to identify biofacies. Cluster Analysis and detrended correspondence analysis (DCA) reveal seven distinct biofacies in the Hamilton Group of Central Pennsylvania that are distributed primarily by factors associated with water depth. Four biofacies identified in Pennsylvania (Tropidoleptus, Tropidoleptus-Devonochonetes, Devonochonetes, Ambocoelia) share taxonomic and life history traits with those previously identified in New York. Three novel biofacies have been identified in Pennsylvania (Pustulatia-Longispina, Rhipidomella, Rhipidomella-Devonochonetes), suggesting that additional undiscovered biofacies may exist within this paleontologically important interval. Quantitative comparison of niche parameters between Pennsylvania and New York study sites reveal that preferred environment (PE) is well correlated and statistically conserved at the intrabasinal spatial scale, while environmental tolerance (ET) and peak abundance (PA) are not.