LATE QUATERNARY STRATIGRAPHIC HISTORY OF THE SARATOGA CREEK SALT MARSH ROCKPORT, MA

The objective of this study is to reconstruct the post-glacial late Quaternary geologic history of Saratoga Creek Marsh (SCM), a back barrier marsh associated with Long Beach barrier, Rockport, MA. In August 2015 a Livingstone core, SCM15LC7, was recovered to refusal. Core lithologies and color corrected images were recorded on the split core. Wet and dry bulk densities (WBD, DBD) were measured at 2-cm resolution and volume magnetic susceptibility (MS) at 1-cm resolution down-core. CNS isotopic analysis was conducted at 2-cm resolution using a continuous flow Elemental Analyzer / Isotope Ratio Mass Spectrometer (EA/IRMS). SCM15LC7 contains 5 distinct lithofacies, penetrating 4.76 meters and terminating in 30cm of dense massive gray clay, Facies 1, with low organic carbon (OC %). Unconformably overlying the clay is Facies 2, a moderately dense black silty mud including pebble horizons indicating a transition zone. This unit is 80cm thick with increasing OC%. Above is Facies 3, a silty peat-rich brown mud 110cm thick with high OC%. The middle of the core, Facies 4, consists of dark gray coarse-grained sand 60cm thick. Facies 5 is 120cm that caps the core with peat-rich silty mud shifting from light to dark brown with high OC%. Facies 3 and 5 show sandy beds on the order of a few cm thick. The MS for the whole core ranges from -1.9*10^-5 SI to 159.3*10^-5 SI, with elevated values associated with sandy, pebbly, and clayey strata in Facies 1 and 4. Low MS corresponds with increasing organic matter (OM) that dilutes the siliciclastic signal in Facies 3 and 5. MS is significantly correlated with DBD (r=0.647, p<0.001). Facies 1 is interpreted as glaciomarine clay (Presumpscot Formation) and provides evidence that this region of MA was below the marine limit at the end of the Pleistocene. Lithologic variability suggests that since isostatic rebound, the environment has been occupied by a marsh that has experienced episodes of higher energy deposition evidenced by dense, magnetic, coarse sediments with little OM. Preliminary CNS data suggest that a freshwater marsh may have predated the modern salt marsh. Facies 4 may represent the transition associated with late Holocene transgression. Ongoing isotopic analysis and pending radiocarbon dates will provide further constraints on the environments of deposition and the timing of such shifts.