A STRATIGRAPHIC INVESTIGATION OF THE GOLDTHWAIT RESERVE SALT MARSH, MARBLEHEAD, MA

The possible inundation of thousands of square kilometers of coastal land and areas of low elevation due to climate warming is a documented concern, and in order to project future changes in sea-level it is necessary to better understand past changes. New England salt marshes are important depositional environments that contain detailed records of Late Holocene sea level change that can be used to help reconstruct past changes. In this study a stratigraphic investigation of the Goldthwait Reserve Salt Marsh in Marblehead, MA was performed. The marsh is a back-barrier marsh that was connected to Marblehead harbor until 1669 when a causeway was built connecting Marblehead proper to Marblehead Neck. The building of the causeway and associated culvert restricted salt water replenishment to the marsh. The Livingstone coring technique was used to extract cores at three different locations that transect perpendicular to the shoreline. Overlapping core drives were taken at each location to provide continuous composite records. Magnetic susceptibility, lithologic core descriptions and weight loss on ignition were completed for each of the cores. The general lithology of the cores shows peat overlying silty-mud, overlying sand. Distal locations from the shoreline contain more and thicker sand layers intruding the peat layers, and the peat contains a higher silt fraction as compared to the proximal locations. This increase in siliciclastic material in distal locations suggests a primary source of sediment from the mainland instead of the barrier. In addition, distal locations contain alternating brown and black bands showing potential changes in the redox condition during deposition. The data obtained from weight loss on ignition and from magnetic susceptibility anti-correlate and distinct features coincide with lithologic transitions. A comparison of the Goldthwait Reserve stratigraphy to that of Romney Marsh in Revere, MA (Donnelly, 2006) reveals similar lithologies, suggesting a regional coherency between sites.