GEOLOGIC AND BIOSTRATIGRAPHIC FRAMEWORK OF THE UPPER FLORIDAN AQUIFER IN THE GREATER SAVANNAH AREA, GEORGIA AND SOUTH CAROLINA

The Floridan aquifer system extends over an area of 260,000 km² in portions of South Carolina, Georgia, Alabama, Mississippi, and Florida. The Upper Floridan aquifer (UFA) is considered to be a continuous stratigraphic sequence of Eocene to Miocene carbonate strata with documented unconformities, based on lithology and biostratigraphy. As part of an on-going investigation of regional subsurface geologic framework in the Atlantic Coastal Plain Province, three deep cores (Pineora core in Effingham County, Georgia; Cockspur Island core in Chatham County, Georgia; and Palm Dunes core in Beaufort County, South Carolina), were drilled by the U.S. Geological Survey. The UFA in the Pineora core occurs at a depth of 50.6-118.0 m (166-387 ft) below land surface, in the Cockspur Island core at a depth of 34.1-105.5 m (112-346 ft), and in the Palm Dunes core at a depth of 24.7-82.6 m (81- 271 ft). Point counts of 120 stained thin sections identified 11 microfacies (Pineora: dolomitic-chert, echinoderm-bryozoan-red algal packstone, echinoderm-foraminiferal-red algal packstone, and echinoderm-red algal-foraminiferal grainstone; Cockspur Island: calcareous-quartz arenite, molluscan-bryozoan-foraminiferal grainstone, foraminiferal-bryozoan grainstone, and molluscan-wackestone; Palm Dunes: arenaceous limestone, foraminiferal-echinoderm-bryozoan grainstone, and foraminiferal packstone). Calcareous nannofossil biostratigraphy was used to provide age control between cores. Major disconformities are identified from the Pineora and Palm Dunes cores and channeling is documented at the top of the UFA in the Palm Dunes core. The age of the UFA ranges from early Oligocene to early Miocene in Pineora, late Eocene to late Oligocene in Cockspur Island, and late Eocene to questionably Miocene in Palm Dunes. The goal was to understand how geologic parameters are related to the Floridan aquifer system in an area where the hydrology has been extensively described. This study clearly documents how existing formation and time stratigraphic boundaries cross hydrologic units, the complex geologic nature of the Floridan aquifer across a relatively limited area, and allows for a better understanding of how lateral and vertical changes in the lithologic units of the UFA affect subsurface hydrologic flow across the region.