Rapid and widespread response of the Lower Mississippi River to eustatic forcing during the last glacial-interglacial cycle
The Lower Mississippi Valley provides an exceptional fi eld example for studying the response of a continental-scale alluvial system to upstream and downstream forcing associated with the large, orbitally controlled glacialinter glacial cycles of the late Quaternary. However, the lack of a numerical chronology for the widespread Pleistocene strata assemblage known as the Prairie Complex, which borders the Holocene fl oodplain of the Lower Mississippi River, has so far precluded such an analysis. Here, we apply optically stimulated luminescence (OSL) dating, mainly on silt-sized quartz from Prairie Complex strata. In total, 27 OSL ages indicate that the Prairie Complex consists of multiple allostratigraphic units that formed mainly during marine isotope stages 7, 5e, and 5a. Thus, the aggradation of the Prairie Complex is strongly correlated with the sea-level highstands of the last two glacialinterglacial cycles. Fluvial incision during the sea-level fall associated with the MIS 5a–MIS 4 transition extended as far inland as ~600 km from the present-day shoreline, testifying to the dominant downstream control of fl stratigraphic architecture in the Lower Mississippi Valley. In addition, the short reaction time of the Lower Mississippi River suggests that large fl uvial systems can respond much more rapidly to allogenic forcing than is commonly believed.