THE GEOLOGIC HISTORY OF SCARBOROUGH MARSH

The state of Maine is comprised of approximately 82 km² of coastal salt marsh. The largest of these marshes, Scarborough Marsh, covers ~ 12.2 km² and is located south of Portland, in the towns of Cape Elizabeth, Scarborough, and Old Orchard Beach. Scarborough Marsh is classified as a back barrier marsh in the southern region and a fluvial marsh in the center and northern regions. A preliminary study of marsh stratigraphy in 2013 revealed buried white pine stumps approximately 1 meter below the marsh surface. The stumps are in growth position and are associated with a ~5cm thick sand horizon. One of the stumps has a radiocarbon date of 3,000 years BP. The purpose of this project is to use stratigraphic principles, organic geochemistry, and additional radiocarbon dating to investigate the history of Scarborough Marsh, with a focus on understanding the nature of the stump horizon.

A total of 14 sediment cores have been collected and described; 7 of these cores have been analyzed for d13C, %C and C/N values. In the central and northern end of the marsh, silty intertidal and/or dune sands with the buried stumps are overlain by salt marsh peats. Multiple 1-5 cm thick sand layers are preserved in the marsh sediments, the thickest of which is associated with the 3,000 year old buried stump horizon. The grain size and spatial extent of these sand layers are being analyzed to determine if they are overwash deposits. Presently, we are exploring multiple working hypotheses to explain the death of the trees living just above sea level. Firstly, we hypothesize that a massive storm deposited salt water and sand and was followed by the gradual rise of sea level; or, a paleo-seismic event and resultant tsunami deposited salt water and sand and lowered land surface enough to facilitate the immediate colonization by salt marsh plants. Additional radiocarbon dates and stratigraphic and geochemical analyses are in progress and will be used to firm up the geologic history of the Scarborough Marsh.