SEQUENCE STRATIGRAPHY OF THE ARCADIA FORMATION ALONG THE EASTERN COAST OF BROWARD, MIAMI-DADE, AND MONROE COUNTIES, FLORIDA

Four cores were used to correlate the lithofacies within the shallow marine deposits of the Arcadia Formation. Two cores down to approximately 420 meters are located on the Florida Keys in Monroe County, one down to approximately 200 meters in Miami-Dade County, and one down to approximately 396 meters in Broward County. The Arcadia Formation in Monroe County is composed mainly of limestone with subordinate amounts of dolomite. In the Miami-Dade County, the lithology transitions to interbedding of carbonate mudstone and packstone/wackestone with some intervals containing fine sand, silt, and clay. This lithologic transition may affect the hydrologic behavior of the formation. In areas where the formation is composed of fine-grained sediments, it behaves as a confining unit, but in areas where the formation is made of limestone and dolomite, it may behave in part as an aquifer. Lithological changes within the Arcadia Formation indicate four transgressive sequences. Each sequence in the Monroe and Miami-Dade Counties begins with a subaerial exposure surface and ends with offshore carbonate muds. The exposure surfaces may be traceable to the Broward County core where the drop in the sea level might not have resulted in the subaerial exposure. The change of primary lithology from limestone in the Florida Keys to very fine-grained sand, silt, and clay in Broward County may indicate that the Broward region may have been a paleotopographic low, with a lower energy environment than in the Florida Keys region. Each sequence has a characteristic system tract pattern that was correlated with biostratigraphic analysis, geophysical borehole logs, and seismic reflection data. Integration of these methods allowed for more accurate mapping of the paleotopography that existed during the Late Oligocene to Miocene Epochs, and for correlation of the sequences between all three counties.