TRACE METALS AS A TOOL FOR CHRONOSTRATIGRAPHY IN SEDIMENT CORES FROM SOUTH SHORE BARRIER BEACH MARSHES IN LONG ISLAND, NY

Sediment cores through overwash lobes deposited in barrier beach marshes can reveal information about past storms. Trace metal concentrations can be used to constrain key tie points in the sediment core chronology. Two sediment cores collected from the Tiana Beach area near Hampton Bays, NY, were analyzed for lead (Pb) concentrations. Pb reached its highest concentrations in one core (TB1D) at 19cm below the surce in a buried peaty layer, while Pb peaked at 57.5cm in the other core (TB1A) in a similar buried peaty layer. These peaks of Pb most likely occur in the same old marsh surface that was subsequently covered by coarser material. Aerial photographs suggest that this layer of coarse material may correspond to an overwash lobe deposited by a hurricane that struck the area in 1954, or possibly the Ash Wednesday nor'easter of 1962. This timing is consistent with the timing of peak Pb deposition reported in previous studies: peak atmospheric (fuel combustion sources) and sewage deposition of Pb in a Rhode Island marsh reached their highest levels about 1950 (Bricker 1993), and between 1970-1980 in marshes on Long Island's North Shore (Cochran et al. 1998). Grain size data from this particular coarse layer, however, do not share the grain size characteristics of Superstorm Sandy overwash deposits. The relatively large proportion of pebble-sized material suggests that perhaps this layer is not an overwash deposit after all. The two cores were collected about 5m apart, and about 15m from the end of a gravel access road. Aerial photographs suggest this road was built between 1962 and 1972, raising the possibility that the coarse layer above the buried marsh surface was deposited by the road-building process. Aerial photographs taken before the 1938 hurricane that struck Long Island indicate that the location of the cores was covered by bay bottom, which is consistent with the muddy sand present at the bottom of the cores. These bay bottom sediments are overlain by sands which are likely subaqueously deposited overwash from the 1938 hurricane. The chronology implied by the Pb levels is still consistent with this inferred history of the sedimentation.