PALEOGEOGRAPHY AND SUBMERGED PREHISTORIC ARCHAEOLOGY IN DAMARISCOTTA RIVER, MAINE, USA

Marine geoarchaeology benefits from paleogeographic reconstruction informed by marine geophysics and vibracoring. We are currently investigating the potential for submerged archaeological sites adjacent to relict (5000 – 4000 yBp) oyster beds in Dodge Basin, Damariscotta River, USA. Late Holocene Native populations utilized a similar resource at Salt Bay after 2000 Bp, and we are confident that the same situation occurred in Dodge Basin during the mid-Holocene. Damariscotta River comprised a series of stair-step ponds at the sea-level lowstand. Dodge Basin was transgressed after 6300 yBp, and Salt Bay by 2000 yBp, allowing oyster colonization over confining sills. More than 80 km of seismic reflection profiles (SRP) and 14 vibracores provide data for interpretation. We exported and combined 2-dimensional SRP data as a series of xyz points to form 3-dimensional views of the modern bathymetry and structure contour maps for the oyster beds, glaciomarine mud, and bedrock. From this we computed volume for many lithologic units in ArcGIS including that of Holocene sediment, oyster beds, and Pleistocene sediment in the basin. We utilize the glaciomarine mud reflector to reconstruct paleogeography in the first order, under the assumption that the depth of paleoshorelines was not below the current depth of glaciomarine mud. A second-order reconstruction is facilitated by the correlation of vibracores to seismic stratigraphy. Vibracores provided data on subsurface lithology, including significant unconformities such as tidal ravinement surfaces and the ravinement unconformity. Fauna in cores imply changes in salinity through time from brackish to fully marine. Vibracores penetrated buried high marsh deposits at -7.80 to –7.90 mbsl. This deposit was submitted for radiocarbon dating, and we expect a date between 5000 and 5500 yBp. A buried terrestrial soil occurs at -13.40 to –13.60 mbsl, with preserved organics that are currently undergoing radiocarbon dating. We expect the age of this soil to be approximately 6000 yBp. Vibracore data in concert with SRP stratigraphy and data on rates of sea-level rise allow confident reconstruction of paleogeography for Dodge Basin around the time the oyster beds were active, and thus modeling of high potential locations for submerged archaeology.