Recognition and analysis of secondary depositional crusts in the surficial aquifer system of southeast Florida

This investigation identified, analyzed, characterized and correlated observed geophysical log "deflections" occurring at distinct depths in the sedimentary sequence and varying systematically with reference to the coastline. The deflections correspond to dense, hard crusts within the upper portions of the Surficial Aquifer System (SAS) of Southeast Florida. These crusts are proposed as zones of paleo-freshwater fluctuations within the aquifer. The secondary depositional crusts (SDC) have migrated vertically in response to sea level changes over thousands of years. Detailed continuous geological samples were collected from three boreholes in a contamination investigation in Delray Beach, Florida. These disturbed but representative samples were analyzed at the gamma log geophysical deflection points. Samples from each of the extant crusts were examined for grain characteristics; chemical analysis of adsorbed elements was performed, as well as stratigraphic and petrographic analyses (scanning electron and petrographic microscopy). Physical laboratory characteristics were calculated and sand/carbonate composition determined.