THRUST FAULTS, FALSE STRATIGRAPHY, AND FALSE FACING CRITERIA IN THE BLUE RIDGE IN GEORGIA AND ALABAMA, SOUTHERNMOST APPALACHIANS

In many areas in the Blue Ridge in Georgia and Alabama the “accepted” stratigraphy is based upon false facing criteria and upon the notion that thrust faults are uncommon in these rocks, despite the widespread presence of mylonites. The common presence of tight to isoclinal folds at all scales in nearly every layer in nearly every unit raises questions about the use of graded bedding and cross bedding as facing criteria in most places. Thus, the “stratigraphic” successions in many areas are based on questionable criteria and may not constitute valid depositional sequences. In many places five generations of folds have affected these rocks, making stratigraphic interpretations of straight-trending contacts suspect. Many straight-trending contacts have mylonites along them, indicating ductile faulting, and kinematic features above and below these contacts indicate that many are thrust faults. Thrusting is especially common in graphitic units where the graphite appears to have lubricated the faults. This is especially true of the lower contacts of these units where sheath folds are common above the faulted contacts. Moreover, metamorphic discontinuities have been overlooked in many places, such as in parts of the Murphy “syncline,” where chlorite zone rocks have been juxtaposed against staurolite zone rocks. Therefore, well-known “stratigraphic” sequences such as those in the Murphy “syncline” and in the eastern Talladega belt are probably tectonostratigraphic sequences instead. Interpretations of the geologic history of the Blue Ridge in Georgia and Alabama may need to be revised and reinterpreted to fully consider the tectonic and metamorphic as well as the stratigraphic history, taking the numerous thrust faults into account.