Analysis of Magnetic Susceptibility Signatures of Modern Coastal Sediments and Vibracores, Assateague & Wallops Island, VA

Barrier islands (BI) are dynamic landforms controlled by nearshore processes and sea-level changes. They provide protection for coastal communities by dampening the impacts of SLR and storm events and serve as wildlife habitat. The understanding of BI evolution is critical for future coastal zone land use planning and management. The main objective of this research is to fingerprint surface sediments in modern BI depositional environments using a portable magnetic susceptibility (MS) meter (TerraPlus KT-20). MS values are based on the Fe/Mn-bearing mineral concentration in analyzed sediments. We are also testing the use of MS signatures in interpreting depositional environments in vibracores taken from Assateague and Wallops Islands. The overall goal is to contribute reliable data to aid in interpretation of cores used to develop refined BI evolution models. Initial results from surface samples indicate that sediments collected from diverse modern depositional environments vary in their concentrations of Fe/Mn-rich minerals. These variations are attributed to geoenvironmental processes that affect detrital sediment deposition (i.e. wave/tide/storm/aeolian processes) and diagenetic processes that result in authigenic sediment formation. MS values increase landward from barrier island beaches. Samples from wave-dominated sites (predominantly quartz and carbonates) have low MS readings (average 0.022 m³kg^-1). Samples from the backshore/berm, deposited by storm processes and reworked by wind, have a MS average of 0.032 m³kg^-1, while samples from dunes have values that averaged 0.046 m³kg^-1. MS readings from overwash fans ranged from 0.023 to 0.090 m³kg^-1. Overall, the salt marsh, coastal bay, and tidal creeks have the highest MS readings with averages of 0.170, 0.487, and 0.724 m³kg^-1, respectively. The reason for these higher values is uncertain and may be attributed to fine-grained detrital mineral deposition, or to the formation of authigenic minerals in the dysoxic/anoxic fine-grained sediments. Although analysis is ongoing, preliminary measurements of vibracores from AI demonstrate pronounced variability in MS values. MS signatures acquired from modern sediments will be compared to MS signatures from cores to refine our interpretation of paleo-environments represented downcore.