GEOLOGY OF THE UPPER FLORIDAN AQUIFER, FORT PULASKI NATIONAL MONUMENT, SAVANNAH, GA

Fort Pulaski National Monument, Savannah, Georgia, coincides with one of the most productive carbonate aquifers in the eastern United States. The Floridan aquifer system of Paleogene age underlies portions of South Carolina, Georgia, Alabama, Mississippi, and most of Florida. The USGS in cooperation with the U.S. National Park Service (NPS) drilled a 300-meter continuous core hole at Fort Pulaski to further understand the hydrogeology of the Floridan aquifer system. The Upper Floridan aquifer portion (UF) of the core from the Fort Pulaski site is being examined as part of an undergraduate research project of the Northern Virginia Community College-USGS intern program. Core and thin sections are being examined to document framework grains, matrix, cement, and porosity. USGS geophysics indicates that within the UF at Fort Pulaski is a 15-meter thick, high transmissive unit (Flow Zone 1) approximately 20 meters below the top of the UF. Pump tests from wells 5 km to the east indicate that 60% of the total UF flow is from Zone 1. Preliminary data indicate that bryozoan-, foram-rich grainstones, with thin section porosities of 20% to 40%, characterize Flow Zone 1. Both above and below Zone 1 of the UF, mixed carbonate and siliciclastic units have porosities that range from 6.5% to 29%. The confining unit below the UF is a skeletal grainstone, however, pores and framework grains are greatly reduced in size. This presentation documents the on-going work of the student intern which will be summarized as both technical and outreach products for the NPS at Fort Pulaski National Monument.