TESTING FOR SUBMERGED PREHISTORIC ARCHAEOLOGICAL SITES ON THE OUTER CONTINENTAL SHELF, NORTHWESTERN GULF OF MEXICO, USA

Archaeologists have been actively engaged in the study of submerged prehistoric archaeological sites for over 30 years. Various combinations of diver investigations, side scan sonar, and multi-beam bathymetry data are commonly used to locate potential human habitation sites located at or near the seafloor in the underwater environment. These data sets are most successful when applied in areas with minimal sediment overburden, but are insufficient for locating targets in areas with significant modern sediment deposition such as the northwestern Gulf of Mexico. The recent geology of the northwestern Gulf of Mexico Outer Continental Shelf (OCS) is dominated by sediment deposition from the Mississippi River since the Last Glacial Maximum. Holocene sediment thickness offshore can range from 1 to greater than 50 meters depending on water depth and proximity to sediment sources, effectively eliminating the possibility of visually identifying a prehistoric archaeological site at the seafloor. In response, models have been developed that delineate high probability areas for site occurrence by the spatial relationship between human activity areas and relict landforms that were subaerially exposed prior to sea-level rise, and protected from erosion during sea-level transgression. Shallow, high resolution seismic sources are the primary method used to locate these now-buried landforms and can help identify areas for further investigation. This data, however, can not be used to verify discrete archaeological deposits. Despite the identification of “high probability areas” for archaeological sites little ground-truthing has been conducted to determine the accuracy of predictive models in this region. An immediate problem for archaeologists and land managers in the Northwestern Gulf is reconciling numerous sea-level curves to determine the age of imaged land-forms and determine how far offshore interpreted “high probability” landforms could be located. Only by reconciling offshore geology with archaeological potential can we identify, research, and manage prehistoric archaeological sites on the OCS.