POTENTIAL STORM EVENT LAYER, SCARBOROUGH MARSH, SCARBOROUGH, ME

Scarborough Marsh is a 2,700-acre, back-barrier salt marsh located in Scarborough, Maine. Despite being the largest contiguous marsh system in the State, the geologic development of Scarborough Marsh and its potential to record past storm events have been little studied. In August 2013, a 10 m long, low-tide, tidal creek exposure was discovered and revealed a distinct and an uninterrupted sand horizon coincident with four in situ tree stumps, approximately 80 cm below the high marsh surface and approximately 4 km from the present-day inlet. Preliminary analyses reveal that the sand horizon varies in thickness from 1-4 cm and is comprised mostly of quartz and mica grains ranging in size from fine to very coarse sand. Dutch coring in the high marsh around the tidal creek shows that the sand layer extends at least 50 m to the southwest and 12 m to the northeast. In addition, microscopic identification of one of the tree stumps indicates it is Pinus strobus, Eastern white pine, from observed fenestration pits in the ray crossings and the lack of dentations on the ray tracheids. Stable carbon isotope analysis of the organic matter in the core sediments indicates that a distinct isotopic (and ecological) shift occurs at the sand layer. Upland C3 terrestrial vegetation is the dominant source of organic matter below the sand horizon, and a mix of C4 and C3 vegetation is the dominant source of organic matter above the sand horizon. Further stratigraphic analyses of the Dutch cores, carbon-14 dating of stump material, and foraminiferal analyses of the sand layer are used to better constrain the timing and nature of the sand horizon depositional event.