ZEOLITES IN THE FLORIDAN AQUIFER SYSTEM AT FORT PULASKI NATIONAL MONUMENT, GEORGIA

Analysis of core from the U.S. Geological Survey Cockspur Island, Georgia core hole drilled in 2010 to a depth of 1,020 feet and penetrating the Upper and Lower Floridan carbonate aquifer indicates the presence of the zeolite clinoptilolite. Previous studies on the occurrence of clinoptilolite in the Floridan aquifer system are sparse and those that have documented its presence do not go into detail on the processes leading its formation. Studies of other Tertiary-aged rocks in the S.E. United States attribute clinoptilolite to diagenetic alteration of “glass”, with suggested sources ranging from volcanic ash to bolide impacts to biogenic silica, ponded in restricted marine basins. The absence of feldspars in this study suggests they have reacted with one of these precursor glasses to produce zeolite.

Rocks containing clinoptilolite have a low permeability (13-355mD) and high porosity (27-47%) when compared to surrounding non-zeolite bearing rocks. X-ray diffraction shows that zeolite bearing rocks only occur in the Avon Park formation, which is a confining unit of the Floridan aquifer system above the Lower Floridan aquifer. When zeolite occurrence is considered along with thin-section image analysis, mini-permeametry, and laboratory resistivity measurements, an underestimation of porosity determined from wire-line sonic logs results. These insights are important for salinity and water storage variations of the Floridan aquifer.