GEOLOGICAL STRATEGIES FOR EXPLORING MARINE SAND RESOURCES ALONG DELTAIC COASTS IN LOUISIANA

Because large volumes of sand are required for beach renourishment, dredging from offshore borrows is a preferred method of sediment supply. Efforts to locate offshore sand bodies that can supply mixed sediments (sand, silt, and clay) to barrier-island restoration efforts in Louisiana depend on recognition of specific types of depositional environments on the continental shelf viz. shoreface deposits, inner shelf shoals, tidal and distributary channel fills, flood- and tidal-delta areas, and drowned beach ridges. Seismic reflection profiling verified by jet probes and vibracores provides a basis for geophysical and geotechnical interpretation of regional sand resources. Sediment volumes required for beach renourishment and marsh restoration are estimated to range in the extreme from 14 to 71 million cubic meters for one complete restoration of all barrier island chains. Sand search protocols broadly applicable in a conceptual sense for US East Coast sedimentary environments are adapted to deltaic sediment bodies in Louisiana in the form of procedures and protocols for the newly developed Delta Sand Search Model (DSSM). Bathymetric, geophysical, and geotechnical survey recommendations for the identification of targets, achieved via the DSSM, are proven out by detailed studies and cultural resource investigations. Development of a DSSM in place of generic sand search procedures has advantage because it is specifically adapted to coastal marine morphosedimentary units in different-aged lobes of the Mississippi Delta that have fine-grained (muddy) deposits that are interspersed by sandy deposits of paleo-distributaries and inter-distributaries.