PALEOGEOGRAPHIC RECONSTRUCTION OF UPPER CRETACEOUS SOUTHWEST GEORGIA AND EASTCENTRAL ALABAMA USING THE GIS METHOD (DIGGH) TO ANALYZE THE DISCONFORMITY SEPARATING TUSCALOOSA SEDIMENTS FROM THE EUTAW FORMATION

Digital integration of georeferenced geologic maps with hypsography (DIGGH), a new technique for rapidly acquiring elevation data at the boundaries of geologic formations, was combined with elevation data recorded using a non-differential handheld GPS unit to develop a digital paleoelevation model (DPEM) of the eroded upper surface of the Tuscaloosa Formation. The disconformity between the Eutaw Formation and the Tuscaloosa Formation surface is the most significant in the Upper Cretaceous section of the Eastern Gulf Coastal Plain and reflects long term erosion. Spatial analysis of elevation data collected at the boundary between marine sediments of the Eutaw Formation and fluvial sediments of the Tuscaloosa Formation, using ESRI GIS software, allowed construction of a paleohydrographic map that was combined with the DPEM to produce a paleogeographic reconstruction of southwest Georgia and east-central Alabama.

In the paleogeographic reconstruction of the post-Tuscaloosa Chattahoochee Valley, the eroded Tuscaloosa Formation surface displays a distinct slope from the northwest toward the south/southeast consistent with the geology of the fall line dividing the Piedmont from the Coastal Plain. Upper Cretaceous stream locations and stream flow directions were found to be similar to modern stream locations and stream flow directions. Analysis of the paleogeographic reconstruction of the eroded Tuscaloosa Formation surface demonstrates the effectiveness of combining DIGGH with GPS to extract useable data from disconformities.