FLOOD HISTORY FROM PALEOFLOOD DEPOSITS IN CUT BANK SOIL PROFILES IN CHICKAMAUGA RESERVOIR, TENNESSEE RIVER, U.S.A

Unveiling the flood history of a river beyond what historical records indicate can be achieved by analyzing floodplain deposits, which can contain successions of flood deposits and buried soils. Dating these sequences and analyzing proxy indicators within them can reveal flood chronologies and conditions. Here we focus on flood history of the Tennessee River near Decatur, Tennessee, in the upper portion of Chickamauga Reservoir. Building on ongoing analysis of a 3.5 m profile with 15 flood layers deposited over the last 1000 years, we describe evidence from five nearby cut banks. These profiles vary in depth from 1.35 m to 2.50 m and consist of 8 to 21 stratified flood deposits with interbedded paleosols. An initial radiocarbon date indicates that one profile reaches back to 4300 ¹⁴C yr BP. Flood layers are composed mainly of silt and very fine to fine sand. Soil layers are composed of silt with small amounts of clay and are weakly to moderately developed. Soil development is a function of landscape stability between flood episodes. Some of the buried soils exhibit redoximorphic characteristics such as mottling, insect burrows extending to underlying strata, and other evidence of soil processes. Micromorphological analysis using thin sections shows abundant pedogenic clay that accumulated in pores and as coatings on mineral grains. Pedogenic clays are thought to require several hundred years to form, and the abundance of clay and the thicknesses of clay layers or cutans can provide an indicator of sample age, complementing radiocarbon and other dating methods. Visually distinctive flood layers are present in all profiles, suggesting the potential to correlate deposits and identify events that were only recorded in certain profiles. Laboratory analyses that will facilitate correlation and synthesis include grain size, magnetic susceptibility, AMS radiocarbon dating, loss on ignition to estimate organic matter content, quantification of pedogenic clay abundance, and analysis of micromorphological features such as the thicknesses of clay cutans and mineral weathering. The study of these five new paleoflood profiles will allow for a better understanding of the past behavior of the Tennessee River, which is important for risk assessment in nuclear power plants and dams.