GEOLOGY OF THE BREWERSVILLE 7.5-MINUTE QUADRANGLE, GREENE AND SUMTER COUNTIES, ALABAMA: MAPPING AND DETRITAL ZIRCON U-PB RESULTS FROM THE USGS EDMAP PROGRAM
Detrital zircon U-Pb geochronology results from the Ripley Formation prohibit a maximum depositional age estimate because of the lack of syn-depositional grains. Previously reported calcareous nannofossil age determination (reaffirmed here) for the Demopolis Chalk brackets the Ripley Formation to Maastrichtian (< 72 Ma). Detrital U-Pb ages yield Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Devonian, Mississippian, and Pennsylvanian populations, which suggests a southern Appalachian Piedmont sediment source. We interpret these results to indicate that along the western Gulf Coastal Plain the Ripley Formation was sourced by the paleo-Alabama river only and did not receive any detritus from the north or west.