EVENT STRATIGRAPHY OF CONTRASTING BACKBARRIER SEQUENCES ALONG THE EASTERN SHORE OF DELAWARE BAY, NEW JERSEY: LITHOLOGICAL AND GEOCHEMICAL SIGNATURES OF PRE-HISTORIC ANOMALIES

In addition to its impact on open-ocean coastlines, rising sea level has induced dramatic changes in estuarine environments on the Atlantic Seaboard over the past 2000-3000 years. This period of decelerated sea-level rise has been punctuated by large-magnitude events, such as intense storms (hurricanes and extra-tropical cyclones) and floods. Whereas some events leave diagnostic signatures, such as distinct sand layers in marsh sequences, other indicators are more subtle and require an analytical approach to complement the traditional geological methods. The present study combines x-ray fluorescence (XRF) and low-field magnetic susceptibility (MS) measurements with lithological and stratigraphic analyses of sediment cores at two sites in coastal New Jersey: 1) Sea Breeze (a tide-dominated saltmarsh within the Delaware Bay) and 2) Sewell Point (mixed-energy backbarrier wetland adjacent to Cape May). Multiple sediment cores from Sea Breeze reveal at least four distinct lithological shifts in the pre-historic part of the sequence (2,500-400 BP), interpreted as erosion/drowning events punctuating marsh accretion in response to sea-level rise. XRF analyses revealed four anomalies in Fe and Ti concentrations that correlate with these shifts. MS measurements ranged from 1-6 (x10^-5 SI units), with a prominent peak in the uppermost part of the sequence. To assess the regional extent of these events and their potential use as a regional correlation tool, a Cape May location was chosen as an intermediate site between wave-dominated central NJ barrier coast and tide-dominated Delaware Bay estuary. High-resolution georadar imaging and historical data were used to ensure an undisturbed backbarrier setting with at least 5-6-m-thick sand-rich fill capped by a supratidal Phragmites wetland. Based on regional sea-level history and the depth interval of in-situ Spartina rhizomes and intertidal gastropods, the lagoonal fill at Sewell Point dates back to at least 2500 years BP. Bulk MS measurements obtained in the field range from 8-10, with several peaks exceeding 12. The ongoing research will integrate high-resolution lithological and geochemical analyses with detailed AMS radiocarbon chronology to constrain backbarrier sedimentation rates and estimate the ages of pre-historic coastal events.