A MILLENNIAL RECORD OF MARSH ACCRETION IN THE TIDAL REACHES OF THE POTOMAC RIVER
Three marsh cores were collected from Mattox Creek, Rosiers Creek, and Wilkerson Creek; tidal creeks adjacent to the Potomac River that are just north or south of Colonial Beach, Virginia. The cores range in thickness from 5.0-6.7 meters in length and comprise two primary lithofacies of basal grey clay and an upper organic-rich peat and clay. The grey clay lithology ranges in Total Organic Matter (TOM) from 4-20%and has highlyvariable magnetic susceptibility intensity peaks. In contrast, the alternating organic rich peat and clay ranges in TOM from 14-82% and has negligible variability with respect to magnetic susceptibility values. Microfossils extracted from the cores include an association of marsh and estuarine foraminifera that include Ammoastuta inepta, Miliammina fusca, Trochammina inflata, Jadammina macrescens, and Ammobaculites. An age model is in preparation pending the results of AMS14C of woody matter, peat, and skeletal calcite.
Our prior work indicates that the tidal marshes record steadily deepening estuarine conditions transitioning to relatively rapid marsh progradation at the approximate onset of the medieval warm period. Marsh aggradation was initiated at this time due to increasing humidity and favorable conditions for higher marsh productivity. Alternations between peat and clay in the uppermost core record millennial and centennial-scale climate oscillations such as the Little Ice Age.