BAHAMIAN COASTAL GEOARCHAEOLOGY AT LIGHT SPEED: INSIGHTS FROM HIGH-FREQUENCY GPR IMAGING

Geoarchaeological context of coastal sites relies on accurate reconstruction of paleogeography (paleo-shoreline extent and orientation, paleo-channels, dune topography) and identification and mapping of local cultural remains (dwellings, middens, hearths, graves, anthropogenic landscape alteration, large artifacts). Over the past five years, high-resolution subsurface imaging using 800 MHz ground-penetrating radar (GPR) has contributed to several advances in the coastal archaeological research of the Bahamian Archipelago, with sub-decimeter vertical resolution and typical penetration depth of up to 2.5-3.0 m. We present examples of 2D and quasi-3D images of classic Lucayan sites (AD 800-1500) on Eleuthera and San Salvador Islands: Rock Sound, Hatchet Bay, Pigeon Creek (SS1), Minnis-Ward (SS3), and Sugarloaf/Three Dog Sites (SS09/21). Complications arise in areas where high-amplitude (>10 dB) hyperbolic diffractions from archaeological remains are cluttered by point-source signal return from buried vegetation and burrows. However these limitations can be used to advantage as indicators of vegetation density and biogenically induced site reworking. For example, at Rock Sound, where excavation is prohibited due to amalgamated pre-historic and modern ocean-view burial sites, GPR imaging of bioturbated cemetery margins was used to complement surface collection of Taino-style pottery around land crab spoil piles. At one of the largest sites on the archipelago (SS1), surveys revealed possible dune-top gravesites, cultural soil horizons, and bioturbation-induced topography. Where sections of cultural sites have been partially lithified through hydrochemical interactions with carbonate matrix, GPR may prove to be the only means of identifying truncations in aeolianite cross-bedding. Imaging experiments with known (re-buried) targets and attribute analysis of 2D radargrams (amplitude and velocity structure) improves interpretation and helps discriminate between diffractions of diverse origin. Our findings show widespread applications of georadar to archeological research of Lucayan and post-contact sites in the Bahamas and similar carbonate coastal sites. This rapid non-invasive method can also aid in delineating cultural sites threatened by coastal erosion.