GEOLOGY OF THE FORTSON, GEORGIA, 7.5 MINUTE QUADRANGLE, UCHEE BELT, SOUTHERN APPALACHIANS

The Fortson, Georgia, 7.5 minute quadrangle includes amphibolite facies metamorphic rocks of the Georgia Piedmont province and sedimentary rocks of the Gulf-Atlantic Coastal Plain, thus straddling the Coastal Plain unconformity (“Fall Line”) in the vicinity of the city of Columbus, GA. Crystalline rocks of the Piedmont Uchee belt, including those of the North Columbus metamorphic complex, Moffits Mill Schist, and Phenix City Gneiss, dominate exposures in the northern portion of the quadrangle and are overlapped in the southern portion by sedimentary rocks of the Cretaceous-aged Tuscaloosa Formation, which dip gently to the south. Tuscaloosa Formation sedimentary rocks are predominantly poorly indurated kaolinitic quartzose conglomerates and coarse sandstones of probable fluvial origin. The Phenix City Gneiss, at the structural base of the crystalline strata, is dominated by amphibolitic gneiss and is exposed primarily in the southern portion of the quadrangle at and immediately north of the Coastal Plain unconformity. To the north-northwest, the Phenix City Gneiss gradually gives way to micaceous schists of the Moffits Mill Schist, interpreted as the metasedimentary component of a ca. 600 Ma volcanic basin which included Phenix City Gneiss metavolcanic rocks. The Moffits Mill Schist in turn transitions into gneiss and migmatite of the North Columbus metamorphic complex in the northernmost portions of the quadrangle. Limited data from geologic mapping by previous workers was used to establish a geologic framework for this project. During this field study, a concerted effort to collect fracture data, in addition to lithologic and basic structural information, was undertaken in order to provide a framework for understanding the potential influence of joints on groundwater flow in the region. Existing and new data was compiled into a digital database (Microsoft Access) and used to construct a digital geologic map in a GIS framework (AutoCAD Map 3D). This year-long research project investigating the geology of Columbus, GA, was supported by a grant from the U.S. Geological Survey’s EDMAP program.