CHARACTERIZING MAGNETIC SUSCEPTIBILITY SIGNATURES OF MODERN BARRIER ISLAND AND BACK BARRIER DEPOSITIONAL ENVIRONMENTS FROM ASSATEAGUE, CHINCOTEAGUE, AND WALLOPS ISLANDS, VIRGINIA

Magnetic Susceptibility (MS) is a geophysical method that has been used in economic geology to map Fe-Mn-bearing mineral deposits. It has also been used in stratigraphic studies where variations in MS values are attributed to changes in sediment composition due to climate and sea level change and/or tectonics. However, few studies have utilized this method for the investigation of sediments from modern coastal depositional environments. The main objective of this research is to fingerprint surface sediments from modern BI environments from the Eastern Shore of Virginia (Chincoteague Bay region) using a portable MS meter (TerraPlus KT-20). The goal is to enhance interpretation of vibracores from Assateague and Chincoteague islands. MS values depend on the Fe/Mn-bearing mineral concentrations in the sediment assemblage. These, in turn, are directly related to the depositional processes and environmental energy. Initial results from surface samples indicate that sediments collected from modern environments vary in their MS values. These are attributed to processes that affect detrital deposition (i.e. waves/tides/storms/wind) and diagenetic processes that result in authigenic sediment formation. Our initial study has revealed that MS values increase landward from oceanside BI beaches. Samples from wave-dominated sites (predominantly composed of quartz and carbonate) have low MS readings (average 0.022 m³kg^-1). Samples deposited by storm processes in the backshore and reworked by wind have a MS average of 0.032 m³kg^-1. Samples from dunes have values that averaged 0.046 m³kg^-1. MS readings from overwash deposits ranged from 0.023 to 0.090 m³kg^-1. Finally, 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 may be due to fine-grained detrital mineral deposition (i.e. Fe-rich clay minerals), or to the formation of authigenic minerals in the dysoxic/anoxic fine-grained sediments. Although the analysis is ongoing, preliminary measurements of vibracores from Assateague Island also 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 present in cores.