LITHOFACIES AND ELEMENTAL STRATIGRAPHY OF A 1500-YEAR TIDAL MARSH CORE, BENEDICT MD

This research focuses on a tidal marsh core collected near Benedict Maryland off the Patuxent River. The sediment core was collected in August of 2023 and is divided into three sections each about 1 meter long. Tidal marshes are sensitive to changes in sea level and sediment influx. The purpose of this research is to characterize the lithologic facies and elemental stratigraphy present in the core, with interest in the environmental and depositional changes through time. The core was described using the Troels-Smith method, and scanned for magnetic susceptibility, color reflectance, and XRF at the Reston USGS. Four lithologic facies (Units) were identified: (Unit 1) a very dark grey to olive brown marsh peat with organic muds, (Unit 2) similarly colored estuarine muds (silts and clays), (Unit 3) a transitional black organic-rich mud, and (Unit 4) an older black marsh peat. These lithofacies were determined based on composition, color, and grain size. Magnetic susceptibility (MS) displays some correlation to iron in the XRF data, and is most variable in Unit 1. Color reflectance (L*) does not show any clear trend or correlation to lithological facies changes. L* values increase slightly in Unit 4, but is likely an artifact of core quality and orientation during scanning. Unit boundaries and changes within facies can be correlated to XRF data. For example, silicon and aluminum are in highest abundance in Units 2 and 3, likely reflecting the mineralogical composition of the core as the setting transitioned from being a peat rich marsh to a more clay and silt dominated estuary. A broad suite of XRF data will be used to infer changes in sediment supply and draw conclusions about the environmental changes that were taking place during the time. An age model was created using 3 carbon dates and an excursion in the lead XRF data which serves as a marker for the year 1974. The 3-meter core records approximately the last 1500 years. By looking at specific elements associated industrialization, changes in land use and other anthropogenic impacts will also be evaluated.