Developing a quality-controlled postglacial sea-level database for coastal Louisiana to assess conflicting hypotheses of Gulf Coast sea-level change
A sea-level database following a new protocol of quality evaluation standards has been constructed and is used for a comparative analysis to reconcile conflicting hypotheses about Holocene relative sea-level change in the Gulf of Mexico. Sea-level data are assessed quantitatively by assigning errors to both sample elevation and radiocarbon age. Sources of elevation uncertainty include sample thickness, indicative range, sampling errors, and surveying errors. Radiocarbon ages are corrected for bulk peat contamination, reservoir effects, and isotopic fractionation. Error calculations are performed as conservatively as possible. Furthermore, other variables such as sediment compaction are considered, in part relying on descriptive and semi-quantitative information that can prove useful for future studies. Overall, this database is valuable as a guideline for sea-level database standardization. A relative sea-level database has been compiled for coastal Louisiana following the proposed protocol. Comparing relative sea-level records from the Mississippi Delta and the southwest Louisiana Chenier Plain reveals that local sea-level change in both areas exhibits the same trend. This result challenges a recent model used to reconcile the smooth trend of rising sea level in the Mississippi Delta with a mid-Holocene highstand elsewhere along the US Gulf Coast, which advocated cyclic uplift and subsidence of the Mississippi Delta caused by sediment excavation and filling of the Lower Mississippi Valley, respectively. Therefore, it is concluded that vertical crustal movements in coastal Louisiana (i.e., subsidence) are mainly controlled by glacio-isostasy, associated with the melting of the Laurentide Ice Sheet.