MARINE GEOPHYSICS AND VIBRACORING APPLIED TO THE SEARCH FOR SUBMERGED PREHISTORY IN DAMARISCOTTA RIVER, MAINE, USA

Damariscotta River is well known geologically (Shipp, 1989; Belknap et al., 1994) and archaeologically (Sanger and Sanger, 1986). Ceramic Period Crassostrea virginica oyster middens exist in the upper Damariscotta, including the famous Glidden and Whaleback middens and smaller oyster and clam middens. The inhabitants of these sites utilized a robust oyster population that can be seen in at least one relict reef in Salt Bay dated to 1325 +/- 40 radiocarbon YBP. In the middle Damariscotta River oyster shell middens are conspicuously absent, yet a massive (700m long, 3 thick) oyster bioherm exists at Dodge Basin, 3m below Holocene mud. We have conducted research to investigate whether human populations also utilized this earlier oyster resource. Shipp (1989) first identified this oyster bioherm upstream of Glidden Ledge in the middle Damariscotta River. This ledge acted as a barrier to saltwater intrusion prior to transgression. A dated salt marsh peat occurs below the bioherm, at 15 mbsl and 6340 +/- 55 BP. Oysters may have arrived shortly after, and at least by 4835 +/- 60 BP. If the oysters were used by humans, any existing archaeological sites would have been submerged by late Holocene sea-level rise. Our research design employs seismic reflection profiling, side-scan sonar, and vibracoring. Complete seismic reflection profiling coverage of Dodge Basin provided data on sub-surface lithologic units, as well as oyster reef configuration. Oyster bioherms have a unique, ‘chaotic’ reflector that is readily identifiable on seismic profiles. After examining the seismic data, nine vibracores were taken in order to: 1) collect a complete Holocene to Pleistocene stratigraphic sequence, 2) collect oyster bioherm deposits overlying salt-marsh peat, 3) investigate areas of high archaeological site potential, and 4) retrieve sufficient data to reconstruct the paleogeography of Dodge Basin. Through a combination of geophysical and geologic methods it may be possible to refine the search for submerged prehistoric sites by using a spatially restricted, easily identifiable, and geologically preserved biological resource. Given the broad geographic range of C. virginica, this methodology for refining the search for submerged prehistoric sites is pertinent to areas outside Damariscotta River.