LATE HOLOCENE ESTUARINE PHYSICAL STRATIGRAPHY OF TOTUSKEY CREEK, VA, TRIBUTARY TO THE RAPPAHANNOCK RIVER

Estuaries are dynamic tidal systems at the interface of terrigenous and marine environments, and estuarine sediments have the potential to record evidence of climatic and biologic variability. The goal of this study is to quantify the physical stratigraphy and organic matter isotopic stratigraphy of Totuskey Creek, a tidal tributary to the Rappahannock River, VA. Sub bottom SONAR profiles were recorded in the creek using a CHIRP system in 2015. A 213.5 cm Kullenberg core was recovered at a location along one of these transects. The core was split, followed by initial core descriptions and color-calibrated imaging. The archive half was logged with a GEOTEK core logger for volume magnetic susceptibility (MS) and density through gamma ray attenuation porosity evaluation (GRAPE). Subsamples (1 cm³) were taken at 1 cm resolution from the working half of the core. These samples were weighed, freeze-dried, and reweighed to calculate wet and dry bulk densities. Ongoing analyses of subsamples using an elemental analyzer / isotope ratio mass spectrometer (EA/IRMS) are producing depth series of weight percent carbon, nitrogen, and sulfur, as well as stable isotope values (δ¹³C, δ¹⁵N and δ³⁴S). Sub bottom profiles reveal wipeout features consistent with gaseous sediments, likely due to decomposing organic matter. The core is composed of a continuous unit of dark grey silty clay with detrital grasses in the upper ~50 cm. The average MS is 5.6 x10^-5 SI, with a maximum of 19.4 x10^-5 SI at 20 cm and minimum of 2.0 x10^-5 SI at 63 cm. MS increases with depth, likely due to higher terrigenous input of siliciclastic material at depth. Similar cores taken in the Potomac River display a MS peak related to industrial activity at the top of cores, and the lack of such a peak here may suggest Totuskey Creek has not been subjected to apparent anthropogenic influence. Wet and dry bulk densities were calculated to be and 1.36 g/cm³ and 0.60 g/cm³ respectively, while wet bulk GRAPE density was measured at 1.45 g/cm³. These values also increased with depth. Completion of isotopic analysis will provide further constraints on organic matter sources and environmental variability.