DOWN-VALLEY STRATIGRAPHIC RECORDS OF HUMAN-INDUCED CANYONS IN SOUTHWEST GEORGIA

Several large canyons (>60m deep) within Providence Canyon State Park (PCSP) in southwest Georgia were initiated by land clearing and enhanced erosion following European settlement. Eroded Cretaceous sediments moved down-valley from canyon headlands by colluvial and alluvial processes creating spatially variable sedimentary records of change in places >6 meters thick. Seven vibracore samples collected at headlands, confined-valley and open-valley locations are used to construct a stratigraphic model of sedimentation. Three units are identified from visible and physical properties including: basal unit I, which consists of in situ Cretaceous sediments of the Perote member and Providence Sand formations. These sediments predate canyon formation and are composed of finely laminated clay and cross-bedded sand associated with marine and near-shore depositional paleoenvironments. Stratigraphically higher deposits display vibrant colors due to groundwater staining of coarse grained sands. Unit II consists of colluvium with capping paleosols at down-gradient sites where the valley is open, but lack buried soil profiles at the up-gradient confined-valley locations. Contacts between units I and II are sharp in cores at confined-valley settings, suggesting erosion and undercutting of the canyon walls preceded deposition of overlying alluvium. Unit III, present in all cores, consists of recent alluvial deposits that contain large kaolin ball clasts which mark cut and fill sequences. Radiocarbon ages, although problematic due to the recent age of the canyons, indicate very recent unit I-II transitions (post 1950) at confined-valley locations, but a European settlement age for the transition at open-valley locations. The absence of buried soil horizons at confined-valley locations suggest that many deposits laid down immediately following canyon formation have been eroded away.