Influence of the Atchafalaya River on Stratigraphic Evolution of the Chenier Plain Inner Shelf, Northern Gulf of Mexico

This study provides new constraints on the influence of the Atchafalaya River, a major distributary of the Mississippi River, on stratigraphic evolution of the Northern Gulf of Mexico inner continental shelf. Sedimentary, geochemical, and shallow acoustic data have been used to identify the western limit of the distal Atchafalaya subaqueous delta, and to estimate the proportion of Atchafalaya River sediment that accumulates seaward of Louisiana's chenier plain coast. The results demonstrate a link between facies distribution on the inner shelf and geomorphic variation on the chenier plain. A zone of coastal mudflat progradation corresponds to the location of Atchafalaya sediment accumulation on the inner shelf. West (downdrift) of the subaqueous delta, relict sediment is exposed that was originally deposited between ~1200 and 600 years BP during activity of the Lafourche lobe of the Mississippi Delta complex. Mass balance calculations indicate that the eastern chenier plain inner shelf and coastal zone form a sink for 7 +/- 2% of the Atchafalaya River sediment load.