Mode and provenance of sediment deposition on a transgressive marsh

In this study, we use foraminifera as environmental indicators to aid in computing the historical volumetric inputs of estuarine sediments to adjacent marsh. These data can help assess the importance of estuarine sediment inputs to marsh accretion. The Grand Bay system (GBS), located on the southern coast of Alabama and Mississippi, has been described as a “self-cannibalizing bay-marsh complex” due to the disproportionately large amount of suspended sediment exported from the GBS relative to the amount of sediment imported into tidal channels and available to the marsh. Despite this sediment limitation in the marshes, mass sediment budgets along shoreline-proximal marsh sites suggest depositional fluxes on the marsh are nearly equivalent to erosional losses at decadal scales. Geochronologies and foraminiferal census data for two shore-normal transects show that estuarine sediment contributes significant portions (28-65%) of this depositional flux. Contrast in shoreline morphology (i.e., orientation, irregularity, and exposure) and adjacent environments (i.e., tidal creeks and mud flats) may influence the proportion of estuarine sediment delivered to marsh. Improvements of sediment provenance tracers in these environments will continually improve the understanding of sediment reworking and transport in transgressive marsh-estuarine systems such as GBS and the role they play in marsh resiliency to sea-level change.