Fine-grained sedimentation on the Chenier Plain Coast and inner continental shelf, northern Gulf of Mexico

Abstract

Abstract : This thesis examines the evolution of a mud-dominated coastal sedimentary system on multiple time scales. Fine-grained systems exhibit different properties and behavior from sandy coasts, and have received relatively little research attention to date. Evidence is presented for shoreline accretion under energetic conditions associated with storms and winter cold fronts. The identification of energetic events as agents of coastal accretion stands in contrast to the traditional assumption that low-energy conditions are required for deposition of fine-grained sediment. Mudflat accretion is proposed to depend upon the presence of an unconsolidated mud sea floor immediately offshore, proximity to a fluvial sediment source, onshore winds, which generate waves that resuspend sediment and advect it shoreward, and a low tidal range. This study constrains the present influence of the Atchafalaya River on stratigraphic evolution of the inner continental shelf in western Louisiana. Sedimentary and acoustic data are used to identify the western limit of the distal Atchafalaya prodelta and to estimate the proportion of Atchafalaya River sediment that accumulates on the inner shelf seaward of Louisiana's chenier plain coast. The results demonstrate a link between sedimentary facies distribution on the inner shelf and patterns of accretion and shoreline retreat on the chenier plain coast.