MULTIPLE PHASES IN THE MARINE TRANSGRESSION OF COASTAL ARCHAEOLOGICAL SITES IN MAINE AND DELAWARE

This paper focuses on the preservation potential of coastal archaeological sites during different phases of marine transgression: erosion, burial, and preservation. Two site locations in Maine and one in Delaware are discussed, with each representing one fundamental phase. The Glidden Point shell midden in Maine represents the erosion phase of marine transgression. The 2200 to 1500 yBP midden is located directly along the banks of the upper Damariscotta River estuary. In this setting, low rates of relative sea-level rise and a lack of topographic or geologic armoring have lead to severe erosion and a low probability for preservation during submergence. In Delaware, a large-scale cultural resource management (CRM) coring survey recently identified four prehistoric archaeological sites below 50 to 200 cm of tidal freshwater marsh mud. These sites represent the burial phase of transgression, where archaeological sites are preserved during the first stages of submergence. Finally, in Maine, shallow marine geophysical methods and vibracoring identified a well-preserved, 6300 yBP upland landscape at 12.67 meters below MHW representing the final preservation phase. The landscape is buried by Holocene estuarine sediment and overlies glaciomarine mud. Rapid rates of relative sea-level rise, coupled with indirect armoring by bedrock and oyster bed-derived biodeposition of a large sediment package contributed to the preservation of the buried landscape during and after submergence.

The geomorphic evolution of archaeological site settings from coastal to submerged contexts is highly variable in the persistence and magnitude of associated processes. Tidal channel migration, current scour, and anthropogenic influences contribute to the destruction of sites during and after submergence. Factors that enhance preservation potential of include high rates of relative sea-level rise, sediment supply, and antecedent conditions resulting in sheltered or armored settings that can protect sites during transgression. The study locations in Maine and Delaware represent three phases in site preservation and identify key processes that are fundamental to the understanding of preservation potential by marine transgression.