Optical Chronology of Late Pleistocene Strata In the Lower Mississippi Valley: Implications for Fluvial Response to Relative Sea-Level Change

The Lower Mississippi Valley (LMV) is an exceptional field example for studying the response of a continental-scale fluvial system to relative sea-level (RSL) changes, tectonic movements, and climate changes. However, the relatively poorly understood chronology of the widespread late Pleistocene strata (Prairie Complex) in the LMV has hampered such studies. Here, we attempt to establish a numerical chronology for the Prairie Complex using optically-stimulated luminescence (OSL) dating. Fine silt quartz was mostly used due to the predominantly fine-grained nature of the sediments. A standard single-aliquot regenerative (SAR) protocol was employed. The LMV quartz has a very strong fast component, but an unstable slow component. The growth curve of the LMV quartz can be best fitted with a linear plus exponential function. Natural doses of the samples are usually in the linear dose response region. The optical chronology suggests that the formation of the Prairie Complex mainly occurred during the last interglacial (MIS 5) and may have terminated at ~80 ka. The formation of the Prairie Complex sediments is a multi-phase process. Phases of fluvial aggradation are tentatively correlated with RSL highstands (notably MIS 5e and 5a). In the mid-LMV, MIS 4 braided-river deposits cross-cut MIS 5a Prairie Complex meander-belt sediments, suggesting that fluvial incision occurred immediately following the eustatic sea-level fall at the end of MIS 5a. The correlation between Prairie Complex formation and RSL history suggests that fluvial aggradation and incision in the southern LMV are dominantly controlled by RSL change during the last interglacial.