GLACIOEUSTATIC SEA LEVEL, GAS HYDRATE STABILITY, AND A LATE PLEISTOCENE SHELF-EDGE DELTA IN THE NORTHEAST GULF OF MEXICO: ENVIRONMENTAL FACTORS CONTROLLING SHELF-MARGIN STABILITY AND THE PROBABLE RECORD OF PRE-CLOVIS MAN IN NORTH AMERICA

Gas hydrates form as frozen mixtures of water and gas along continental margins, providing considerable strength to slope sediments. The top of the gas hydrate stability zone, however, is sensitive to Quaternary environmental change. In the worst-case scenario, hydrate decomposition in low permeability sediments causes loss of shear strength triggering catastrophic slope failure (eg. Storrega Slide, Norway) and tsunamis. The worst-case scenario however is not easily studied beyond documenting its after effects. In cases of higher permeability sediments where the produced gas can escape along capillary seal-limited permeable pathways, e.g., in turbidites, slope stability is less impacted. Our study of the late Pleistocene Lagniappe Delta focuses on a shelf margin depositional and gas hydrate system, which has survived the latest glacioeustatic sea level cycle.

Of importance from a paleo-anthropological perspective, is the period during which the Lagniappe delta establishes attractive coastal environments at the shelf-edge, i.e., shortly before and during the last glacial maximum. This is a time for testing outer continental shelf habitats for evidence of pre-Clovis populations in North America. The oldest Clovis corrected radiocarbon dates are about 13 ka BP. Possible pre-Clovis artifacts have been reported in the U.S. and elsewhere in the Americas.

Drowned anthropogenic shell middens are observed along the Louisiana coast. Middens in bays and lakes have been detected by side-scan sonar and divers. We suggest that shell middens are the most easily identified targets for studying early humans in drowned deltaic paleo-environments of the outer continental shelf that have not been disrupted by hydrate dissociation. Stable shelf-edge delta systems of the Gulf of Mexico, like the Lagniappe, provide optimal settings in which to search for evidence of early man.