GEOCHRONOLOGY METHODS TO DATE HOLOCENE SEDIMENTS FOR PALEOFLOOD STUDIES IN THE TENNESSEE RIVER, USA

Floods are one of the most dangerous hazards on Earth, causing major economic losses and impacting billions of people. Managing flood risk requires knowledge on the processes as well as information on frequency and magnitude of previous floods. One of the main uncertainties is the lack of long-term records of floods. Paleoflood hydrology provides a valuable tool that uses geological indicators to reconstruct frequency and magnitude of major flood events that occurred before the time of human records. Obtaining accurate ages for paleofloods has proven difficult in many cases. Early paleoflood studies relied mostly on radiocarbon dating of organic fragments in buried soils overlain by flood deposits for determining the age of flood sediments. Since the early 2000s, Optical Stimulated Luminescence (OSL) has been used as an alternative technique to date Quaternary deposits. Several paleoflood sites in the middle section of the Tennessee River are being studied to provide information on major floods recorded in geologic deposits over the past several thousand years. The study sites comprise six profiles in cut bank locations along the river, with an interlayering of flood and buried soil deposits. Charcoal pieces found in the sediments have been used for AMS radiocarbon analysis to determine ages of the sediments. Time of deposition is also being determined using OSL analysis of quartz grains from the flood deposits. Many factors can affect age estimation of flood deposits, such as degree of soil development, biological activity in the sediments, water content history, and the possibility of older charcoal being transported from other sites and deposited by the floods. Using both radiocarbon and OSL to date the sediments will provide a more robust geochronology of flood events for the study site. Comparison will allow evaluation of the advantages and shortcomings of each method for dating fluvial deposits found in soil profiles such as the ones in the middle Tennessee River.