UPDATED GEOLOGIC MAP OF SWEETWATER CREEK STATE PARK, GEORGIA

Definitions and interpretations of the Brevard Zone and associated shear splays have long been debated in the geologic literature, particularly where these structures have been described in and around Sweetwater Creek State Park along the southern and eastern margin of the Austell-Frolona Anticlinorium. Previous workers have presented conflicting interpretations of the stratigraphic and structural relationships of lithologies related to the Brevard within and around the northwestern terminus of the Austell-Frolona Anticlinorium. The interpretations presented by these workers are based on regional, reconnaissance-scale geologic mapping in and around this area. Unpublished mapping in this area indicates that one of the more north-south trending shear splays trends into the northern part of the Park. In this area, the stratigraphic units from northeast of the park enter into a complex shear zone along the southern margin of the Austell-Frolona structure. These units are attenuated and generally thin to the southwest.

To better understand the complex stratigraphic and structural relationships within the Park and along the northern boundary, detailed geologic mapping was conducted on parts of the Austell, Ben Hill, Campbellton, and Mableton 7.5-minute quadrangles. Based on this mapping, greater structural and lithologic variability was observed within the Park and adjacent to the Austell-Frolona structure than previously depicted. Previous workers described interlayered muscovite schist and meta-greywacke within the Park with a through-going hornblende gneiss/amphibolite occurring at the old mill’s raceway and two quartzite layers further north near the old bridge. Topography was likely used to delineate these quartzites in lieu of detailed geologic mapping.

Based on our mapping, the hornblende gneiss/amphibolite does not occur as a continuous mappable unit; rather, it occurs as discontinuous layers/lenses within other lithologic packages. The best marker units within the park are thin quartzites and quartz-rich schists. These units generally grade into and out of each other along strike. They are easily identified through the mapping area and can be used as excellent marker horizons to delineate map-scale regional geologic structure.