Antecedent Geologic Control on the Evolution of Fetch-Limited Barrier Islands in the Mississippi Sound.

The Grande Batture Islands were fetch-limited marsh fringing barrier islands that previously fronted a late Pleistocene/ Holocene delta of the Pascagoula-Escatawpa fluvial system in the eastern Mississippi Sound. Historical maps and aerial imagery produced between 1848 and present indicate that the islands were initially formed by the reworking of the deltaic headland into two elongate shore-parallel flanking spits, which were subsequently fragmented and reduced in area until they became remnant shoals with an exclusively submarine expression by the mid-1980s. The focus of the research presented here is an analysis of the environmental factors contributing to the morphological evolution of the Grande Batture Islands and later shoals, with particular emphasis on the role of underlying framework geology. The stratigraphy and bathymetry of the Grande Batture Islands’ remnant shoals and adjacent seafloor were mapped with high-resolution geophysical instruments including single beam bathymetric sonar, side-scan-sonar, and chirp sub bottom profiling sonar. The resultant geophysical data were ground-truthed with surface sediment grab samples as well as vibracore sediment samples. Here, the spatial correlation between antecedent geology and surface morphological expression is characterized and a conceptual model for the evolution of the Grande Batture Islands is presented. Limited previous analysis has largely attributed the recent morphological evolution of the Grande Batture Islands to the combined influence of increased fetch, relative sea level rise, reduction in local sediment supply, and periodic tropical storm events. Results indicate that the underlying paleo-fluvial distributary ravinement surface contributes to morphological variability in the Grande Batture shoals and must also be accounted for in conceptual models of system evolution.