STRATIGRAPHIC EVIDENCE OF SALT MARSH EROSION AND RECOVERY ALONG THE NORTH SHORE OF DELAWARE BAY

Stratigraphic investigation of salt marsh deposits in southern New Jersey reviled the presence of at least 5 transgressive-regressive mud and marsh-peat sequences deposited during the past 2200 years. The deepest sequence was observed at the depth of ~ 4 m below modern marsh surface and traced for almost 2 km along the shoreline. The bottom contact of the shallowest sequence documented at the depth of ~ 50 cm was mapped from the shoreline inland across the marsh platform. Lead-210 and Cs-137 analysis of core sediments document sedimentation rate of 11-8 mm/yr above 50 cm contact and 3.5 mm/yr below. The rate of salt marsh accretion below the contact is comparable to the instrumental record of sea level rise for the Delaware Bay. Abrupt environmental changes from high marsh peat to tidal mud over extended area suggest its occurrence under forcing conditions and could be attributed to storm erosion. Eroded marsh deposits were replaced by a regressive sequence of tidal mud, low marsh peat and high marsh peat. Tidal mud units that filled eroded accommodation space vary in thickness from 10-50 cm. Radiocarbon dates of salt marsh plants sampled immediately above mud units suggest that the deepest mud unit (units 1) was deposited around 2000 yr BP. Deposition of mud unit 2 was completed ~ 1660 +/-40 yr BP. Low marsh peat developed above mud in unit 3 between 1070-1040 +/- 40 yr BP. The first appearance of low marsh plant, Sp. Alterniflora rooted into mud unit 4 dates back to 1000 +/- yr BP. Most recent rapid mud deposition completed around 1963 A.D. Stratigraphic position and thickness of mud units, overall horizontal facies boundaries within the regressive sequences, rapid post-erosion infilling and marsh recovery suggest that erosion occurred under storm-surge conditions and may be a sedimentary record of pre-historical hurricane strikes.