MOLLUSKS OF THE LATE PLEISTOCENE OOLITIC FACIES OF THE MIAMI LIMESTONE

The oolitic limestone that makes up the bedrock of Miami-Dade and parts of Broward County is a highly studied formation, with poorly studied fossil content. No published systematic record of Pleistocene fossils in the Miami Limestone Formation is available. Besides the basic knowledge of taxonomy and biodiversity of the Miami Limestone mollusks, comparison with extant assemblages can yield important information about the biodiversity changes in southern Florida during the past ~130,000 years. This is important considering the environmental stresses the region has underwent during the past centuries. Preliminary survey of several localities, both previously described and new, within the Dade County yielded a record of diverse and well preserved mollusks from over 16 families, 17 genera and 23 species. Few of the species that have been found are either locally extinct to South Florida (Cittarium pica) or are a rare occurrence (i.e. Terebra floridana and Lucina muricata). The preliminary findings of molluscan fossils have led to a new, unstudied and unpublished fossil locality with the second discovery of a possible Strombus costatus in the Miami Limestone. These larger fossils of the Pleistocene are quickly being eroded away through colonization from algae and drilled by sponges and are not commonly preserved. The primary occurrences of the Miami Limestone mollusks are in the facies interpreted as proximal to the rocky shoreline, as indicated by taxa preferring attachment to hard substrate, such as Cittarium pica and Diodora listeri. Some current oriented bivalves were found in the active oolitic shoal facies at the Coral Gables Waterway, and few in the vegetated sand flats of Alice Wainwright Park and Miami Metro Zoo. Miami Limestone fossils are being compared to recent South Florida mollusks indicating patterns of local diversification and extinction related to the minor changes in sea level and disappearance of certain habitats such as the rocky island substrates that Cittarium pica once thrived on.