Reconstructing the Holocene history of the Tennessee River using paleosols and paleoflood sediments

This dissertation presents the results of chronological, pedological, and paleohydrological studies of five Holocene soil profiles exposed along the floodplain of the Tennessee River in the Chickamauga Reservoir. Fluvial deposits and landforms are important archives of information for reconstructing paleoclimate, paleoenvironments, tectonics, and ancient floods that were not recorded directly by instruments or human observation.

In the first study, radiocarbon and optically stimulated luminescence (OSL) ages are compared for two soil profiles, and soil micromorphology is used as a tool to assess the reliability of each geochronological method. Results indicate that OSL performed well in fluvial sediments, as evidenced by illuvial clay accumulations observed as a common pedofeature in the soil profiles. Some of the radiocarbon ages appear to be too old owing to redeposition, but other dates are consistent with soil development and micromorphology.

In the second study, age determinations obtained from the first study and quantification of illuvial clay accumulation were used to construct a soil chronofunction. Quantification of illuvial clay accumulations as clay coatings was done by analyzing digital images of thin sections in ImageJ. Results from this study show that accumulation of illuvial clay increases with age and follows a linear relationship. Results yielded a new soil chronofunction that can be used to date other Holocene fluvial deposits in the floodplain of the Tennessee River. The use of ImageJ for clay quantification demonstrates the potential of using image analysis on large 2-D thin sections to improve quantitative analysis of soil properties.

In the third study, five soil profiles were examined to identify possible paleoflood deposits within soil horizons. Results from this study indicate that paleoflood deposits occur as coarser grain size intervals within soil horizons that present lower magnetic susceptibility and lower organic matter content. Geochemical analysis indicates that paleofloods present lower concentrations of Al, Fe, K, Mn, Rb, and Ti, and higher concentrations of Si and Zr. Radiocarbon and OSL ages indicate the intervals when the paleofloods occurred. This investigation shows that floodplain deposits can provide valuable information in areas where no other records are readily available.