PIs will investigate patterns and rates of late Holocene fluviodeltaic sedimentation with the aid of optically stimulated luminescence (OSL) dating, and explore the potential of land building and organic carbon (OC) sequestration using field data collected from one of the largest clastic depocenters: the Mississippi Delta. This research is not only important scientifically, but also for coastal restoration in the Mississippi Delta that suffers continuous wetland loss. PIs will collect stratigraphic and geochronologic data from overbank deposits along a recently abandoned major distributary of the Mississippi River to test the hypothesis that the clastic stratigraphic record in fluviodeltaic settings consists of a patchwork of discrete sediment bodies that accumulate in an episodic fashion over relatively short time periods. This hypothesis is rooted in a long-standing geological debate that traces back to the early 19th century, centering on the question whether the Earth's stratigraphic record primarily reflects gradual deposition or catastrophic events. This debate is important because understanding the nature of the preserved sedimentary record is critical to interpret changes in the Earth system over geological timescales. Furthermore, they will measure the content and age spectra of OC within fluviodeltaic deposits. The OC content will be used, in combination with the chronologic data, to calculate rates of OC sequestration to test the hypothesis that rates of OC sequestration by clastic overbank deposition can equal or exceed those by swamp peat accretion. Consequently, floodplains and delta plains may constitute an important OC pool that is to date poorly quantified and commonly ignored. The age spectra of the OC will be compared with the OSL dating results to investigate the effect of human activity on OC transport by large rivers. Finally, stratigraphic data will be used to estimate the sediment trapping efficiency of crevasse-splay deposition, a natural analog to artificial river diversions that are currently proposed for coastal restoration. Studying sediment trapping efficiency in the Mississippi Delta, in concert with numerical modeling, will provide critical information to assist in the better estimation of land-building potential by Mississippi River diversions. In addition, the OC sequestration data will provide new insights about potential ecosystem services of restored wetlands.
