A DROWNED, FORMERLY INHABITED BAY/LAKE SHORELINE OFF MOUNT DESERT ISLAND, MAINE

Recovery of prehistoric stone tools south of Mt. Desert Island, ME (Bass Harbor), by scallop draggers in the 1990's led to a 2007-2008 survey of this area using swath bathymetric mapping, seismic reflection, side scan sonar, a towed video camera system and an underwater vibracorer. At 20-30 m depth, the survey documented two boulder-littered ridges with up to 3 m of relief, separated by a pockmarked basin. Two acoustic reflectors were detected in the upper 3 m of the ridges. Abrupt breaks-in-slopes at 22 and 23 m with associated terraces are cut into the ridges and into nearby materials. Seismic reflection data reveal the ridges to be moraines covered with reworked littoral deposits that extend as spits from moraine margins. Cores through the paleo-spits penetrated sandy gravel overlying mud deposits with abundant Zostera marina, and muddy sand deposits with numerous articulated Crassostrea virginica and Mya arenaria specimens. We correlate the contacts between these units with the seismic reflectors and interpret the deposits to represent lagoon and tidal flat deposits, respectively. One core from the bay side of a spit met refusal in a muddy, gravelly sand that contained organic-rich, peat-like material, dated to 8530 (cal) B.P. Most cores met refusal in glacial-marine mud, but in some cores lacking fossils, it is possible that early Holocene lacustrine sediment is present. The apparent time of deposition of the coastal deposits in Bass Harbor corresponds to the “slowstand”, or time between 11 ka and 7 ka and -25 m and – 15 m depth, respectively, when sea level rose very slowly. It seems likely that the slow rise in sea level permitted constructional landforms (spits) to form, significant estuarine deposits to accumulate, and potentially Early to Mid-Archaic Period Native Americans to inhabit the landscape. Our research suggests that this time/depth interval is the best candidate to preserve sedimentary deposits and associated prehistoric archaeological sites and artifacts along the Maine shelf.