PALEOECOLOGICAL ANALYSIS OF THE GEOLOGICAL SURVEY OF ALABAMA'S RIPLEY FORMATION FOSSIL COLLECTION

During the summer and fall of 2007, Ripley Formation fossils from the Geological Survey of Alabama's (GSA's) invertebrate paleontology collection were inventoried and studied for a paleoecological analysis of the Ripley Formation, a Late Cretaceous marine sand. GSA's Ripley collection (over 1,150 specimens collected in Alabama) was inventoried with taxonomic breakdown and provenance information entered into a database for each fossil specimen. After specimen information was recorded, fossil genera of which five or more specimens were present in the collection were compared with modern marine genera. Biological attributes including taxonomy, general morphology, and biogeographic ranges were used to identify closest extant relatives living in today's Gulf of Mexico, Atlantic Ocean, and Caribbean Sea. For each modern relative, taxonomy, substrate, water depth range, and life habit were recorded. Paleoecological analysis included descriptive statistics for taxonomic distribution of fossils in the collection, sedimentological comparison of modern substrates to Ripley matrix, and statistics of multiple biological and ecological attributes of the extant relatives. Statistics show more than 90% of the Ripley collection to be molluscan, with 70% of the mollusk specimens belonging to the class Bivalvia. Approximately 80% of the related modern genera have habitats in sandy substrate and live in water depths shallower than 50 feet deep. When compared with a similar assemblage of modern genera, the paleomolluscan assemblage in GSA's collection appears to suggest the Ripley Formation is a near-shore, subtidal, shallow marine deposit. Additional fossils in the Ripley collection that may support this interpretation, but warrant further investigation, include preserved plant material, trace fossils, sea urchin spines, and crabs.