RECONSTRUCTING THE BIODIVERSITY AND PALEOECOLOGY OF THE LOWER MIOCENE CHIPOLA FORMATION OF FLORIDA

The Chipola Formation is a fossiliferous, near-shore marine unit from the Lower Miocene (~18.9 Ma) that is exposed along the Apalachicola River and its tributaries in Florida’s Panhandle. Despite a great deal of knowledge concerning the taxonomic composition of this formation’s fauna, relatively little work has gone into understanding how its diverse molluscan-rich fauna compares to younger paleocommunities in Florida, its faunal diversity, and its paleoecological setting. This study examines the faunal and paleoecological composition of the Chipola Formation using samples collected from reef-associated localities (i.e., Cooter Bluff and the Cooter Bluff Reef Site) and more open-shelf deposits (i.e., Alum Bluff and Farley Creek). The resulting data is compared with younger Pliocene and Pleistocene molluscan faunal data from peninsular Florida to understand how the diversity of shallow-marine settings in the Gulf of Mexico changed during the Neogene. Bulk samples from each locality were screened using two sieves measuring -2.0 and 0.0 phi. Specimens were identified to species level, and assigned to an ecological guild. Faunal data was then statistically analyzed using the program PAST 2.17c. Our results showed that the reef-associated faunas of the Cooter Bluff Reef Site has the lowest diversity levels, whereas the back-reef deposits at Cooter Bluff had the highest diversity levels The open-shelf deposits of Alum Bluff and Farley Creek had relatively moderate diversity. With the exception of the higher values for the Cooter Bluff Reef Site, all of the localities had comparable values for evenness. When compared to the Pliocene Pinecrest Bed fauna (its closest analogue in terms of overall diversity), both species richness and evenness values indicate that the Chipola Formation had a moderately diverse molluscan assemblage with a higher species evenness.