CORRELATION OF UPPER THREE RUNS AQUIFER TO THE EOCENE SANDERSVILLE LIMESTONE, COASTAL PLAIN GEORGIA

Atlantic Coastal Plain stratigraphy in Georgia is poorly correlated between updip outcrop exposures and subsurface downdip equivalents. Eocene subsurface units are identified by their hydrogeologic characteristics, whereas surface outcrops are better defined. Previous work has shown the Sandersville Limestone member of the Barnwell Group in central Georgia is a basal limestone within the Tobacco Road Sand and is age correlative to the Ocmulgee Formation. We examined 40 feet of core material of the Eocene Upper Three Runs Aquifer unit at Girard, Georgia to attempt to correlate it to the updip Late Eocene (middle Jacksonian) carbonate units.

The Upper Three Runs Aquifer is a partially lithified wackestone containing calcite, fine-grained quartz, and abraded pelecypods, gastropods, and bryozoa. Clay mineralogy determined by X-ray diffraction shows smectite, heulandite and opal-CT. Bryozoa species Ochetosella Jacksonica, of middle Jacksonian age in central Georgia, was identified by scanning electron microscopy (SEM). Heulandite is an authigenic phase based on SEM images.

Based on our results, the Upper Three Runs aquifer is age correlative to both the Middle Jacksonian Sandersville Limestone and to the Ocmulgee Formation in the western Georgia Coastal Plain. The low fossil abundance and diversity, fine-grained clastics, and the presence of smectite indicate the Upper Three Runs was deposited in a deeper marine setting relative to the shallow marine depositional environment of the fossiliferous Sandersville member and Ocmulgee Formation.