THE GEOLOGIC AND ENVIRONMENTAL RECORD FROM CAVES AND SINKHOLES ON THE ATLANTIC COASTAL RIDGE OF SOUTHEAST FLORIDA

The late Pleistocene Atlantic Coastal Ridge of southeast Florida represents an ö-peloidal tidal sequence with a highly bioturbated lagoon facies overlain by cross-bedded shoals separated by tidal channels. A late-stage barrier bar accreted to the shoal complex. Following the end-Pleistocene sea level rise, the barrier bar complex held at bay ponded discharge from the Everglades ecosystem, creating seasonal wetlands in transverse glades. Underflow through the bioturbated facies along the glade margins, particularly at the closest approach to Biscayne Bay, led to the formation of stratiform caves. Respiration of accumulated organic matter and amassed tree roots at the water table contributed to cave development. Vertical cave entrances resulted from the enlargement of holes created by tree roots that penetrated the soft bedrock. 17 caves have been mapped since 2008.

Fauna and Native Americans have interacted with the Atlantic Coastal Ridge since sub-aerial exposure. The Cutler Fossil Site, a sinkhole located at the Deering Estate south of Miami, yielded late Pleistocene mega-fauna, ¹⁴C dates, and projectile points dating to 10-12 kybp. Recent archaeological investigations from midden and other material at the Deering Estates have produced evidence of habitation during the Paleo-Indian through Archaic periods (>9.5 kypb) as well as more recent Formative period (<3k kypb). Interestingly, recent sediment cores obtained from sinkholes at the glade margin at the Deering Estate have produced basal ¹⁴C ages from charcoal that are all post Spanish contact (>1513 CE). In the sinkhole entrance to one cave, more than 50 cm of quartz sand accumulated rapidly around the time of Spanish contact; a sinkhole adjacent to a mangrove delta in Biscayne Bay has incrementally accumulated peat on quartz sand. These data suggest charcoal production and mobilization of sediments into Deering Glade between 1485-1640 CE; the product of changing land use or environmental conditions.