Using a Quality-Controlled Database of Holocene Relative Sea-Level Data from Louisiana to Assess Conflicting Hypotheses of Gulf Coast Sea-Level Change

A number of well constrained basal-peat sea level records from the Mississippi Delta in Louisiana provide evidence for a continuous flooding over the past ~8000 years along the Gulf Coast. However, this observation appears to be inconsistent with a proposed mid-Holocene relative sea-level (RSL) highstand up to 2 m above present, as derived from beach-ridge records in Texas, Alabama, and Florida. Most recently, the excavation and refilling history of the lower Mississippi Valley over the last glacial-interglacial cycle has been used to model the flexural uplift/subsidence effect in this area, suggesting that the two contrasting Holocene RSL records can potentially be reconciled. This modeling also predicts that the flexural effects of sediment loading and unloading mostly dissipate 100-150 km away from the edge of the Mississippi Delta. Considerable portions of the chenier plain in southwestern Louisiana are far enough away from the Mississippi Delta and thus they may provide a suitable testing ground for this hypothesis. Within the framework of a larger project that aims at establishing a RSL database for the Atlantic and Gulf Coasts of North America, we have compiled all published RSL data from Louisiana and subjected these data to a rigorous error assessment. Collectively, these results suggest that RSL data from the chenier plain are generally compatible with those from the Mississippi Delta, and the RSL there is significantly lower than the proposed RSL highstand elsewhere along the Gulf Coast. This finding reinforces the hypothesis that land subsidence caused by glacial forebulge collapse dominated the RSL rise along the Gulf Coast over the past ~7000 years. However, the resolution of older published data is limited and new, high-resolution RSL data are essential to substantiate these preliminary conclusions.