Bioerosion of the Pleistocene Key Largo Limestone In the Florida Keys

Bioeroders (organisms that excavate and remove lithified substrate) are important contributors to the diversity of coral reef communities and major producers of carbonate sediment in these environments. Borings made by sponges (Entobia), bivalves (Gastrochaenolites), and worms (Trypanites) are the most common types of macroborings found in carbonate substrates in the Bermuda-Bahamas-Caribbean region today, but their occurrences in the Pleistocene of Florida are poorly known. Recent observations reveal that bioerosion trace fossils, mainly macroborings, are abundant in the Pleistocene Key Largo and Miami Limestones, the two main stratigraphic units of southern Florida and the Florida Keys. The Key Largo Limestone is a coralline framestone with many large coral colonies preserved in life position. The formation interfingers with the bryozoan facies of the Miami Limestone. Preliminary research demonstrates that the Key Largo Limestone is bored by a diversity of endolithic organisms, represented by the ichnotaxa Gastrochaenolites, Trypanites, Entobia, and other unidentified borings (likely made by worms). It appears that bivalve borings (Gastrochaenolites) are restricted mainly to corals, while sponge borings (Entobia) are seen primarily in calcarenite. This study of the occurrence and distribution of bioerosion trace fossils in the Florida Keys enhances our understanding of the general geologic history of the Keys and gives a more complete ichnologic picture of the Pleistocene paleoecology in this region.