NEW DATA ON THE STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE ANASTASIA FORMATION IN SOUTHEASTERN FLORIDA

The Anastasia Formation, the youngest lithified marine Pleistocene unit in the eastern coast of Florida, crops out along the east coast of Florida, from St. Augustine to Boca Raton. It has typically been viewed as single unit of marine sands interbedded with coquinoid limestone. It is dated as Illinoian – Sangamonian (130,000 – 100,000 ybp) by correlation with the Miami Limestone. The depositional environment for the Anastasia Formation was interpreted as a near shore sand bar deposit. Bioturbated sandy deposits rich in mollusk shells fragments had formed in the shallow water during the high sea-levels of the Sangamonian Interglacial. The bioturbated coquina is capped by a caliche crust with root impressions indicating a period of subaerial exposure and soil formation during Late Sangamonian – Early Wisconsian. New field observations in the Palm Beach and Martin counties and geophysical data from Ground Penetrating Radar (GPR) surveys revealed some previously unknown details about the stratigraphy and origin of the Anastasia Formation. These observations include: (1) The discovery of a well preserved complete shell of the gastropod Cittarium pica, living today in the Bahamas and locally extinct in Florida because of lack of rocky supratidal habitats indicating that the Anastasia Formation is of the same age as the Miami Limestone, where C. pica was found previously; and (2) GPR imaging of an erosional surface along existing subaerial Anastasia outcrops during the Sangamonian confirmed by the discovery of fragments of the coquinoid sandy limestone in large rocks washed on the shore after hurricanes in 2004 in Martin County. These observations indicate that the rocky or partially rocky coastline had existed during the Sangamonian, suggesting that partial exposure of the Anastasia Formation had occurred earlier than previously thought. Furthermore they indicate that the Anastasia Formation in West Palm Beach consists of two distinct units: a more common bioturbated marine coquina, and a cross-bedded dunal sand rich in small fragments of mollusk shells. Our observations also indicate that eolian sand is overlaying the caliche crust on top of bioturbated coquinoid limestone, suggesting that the age of the dunal coquinoid sand to be either Late Wisconsian or early Holocene.