SEDIMENTOLOGY AND GEOCHEMISTRY OF ESTUARINE SEDIMENTS FROM THE ALBEMARLE SOUND AND ADJACENT TRIBUTARIES IN EASTERN NORTH CAROLINA

Scientists from East Carolina University, the U.S. Geological Survey – Woods Hole, and the North Carolina Geological Survey are conducting geological and geochemical investigations of estuarine and barrier island systems in North Carolina. Data are being used to define the Quaternary evolution of the North Carolina coastal system and the response of the coastal environments to climate and sea-level changes. An important component of this investigation is to define the geology and geochemistry of the modern depositional systems in order to better evaluate depositional facies acquired in deep cores. This investigation is concerned with characterizing the sedimentology and geochemistry of estuarine sediments. Twenty-nine shallow push cores (13-73 cm in length) were acquired from the Albemarle, Currituck, Croatan, and Roanoke Sounds and adjacent tributaries. Core sediments are dominated by variable mixtures of terrigenous sands and muds, and organic matter (0.2-58%) from terrestrial, estuarine, and marine sources. The origin of organic matter (OM) deposited in the estuarine environment is being determined using a combination of stable isotopes (d¹³C and d¹⁵N) and C:N ratios. Grain size data are being determined to evaluate variations in sediment flux and as a potential correlation tool. Organic matter percentages have been determined using the loss-on-ignition method. Vertical variations are seen within individual estuaries and tributaries in the study area, showing corresponding inflections in OM, which are potentially correlative. Many cores show a decrease in %OM with depth, possibly due to in situ remineralization. Spatially, the data indicate there is a decrease in the percentage of organic matter from west to east. Preliminary d¹³C data show a range of values (-16.41 to -27.57 per mil), which may represent variations in the contributions of C3 and C4 plants and marine-derived OM. There appears to be a slight trend toward increasing d¹³C values eastward, possibly due to the increase in marine OM influence. These geochemical data, in conjunction with radio-dating techniques (Pb-210, Cs-137), are being correlated and interpreted to understand the variations in sediment flux and geochemical processes (including anthropogenic influences) occurring during the last 200 years.