HOLOCENE PALEOENVIRONMENTAL CHANGE IN PAMLICO SOUND, NORTH CAROLINA: FORAMINIFERAL AND STABLE ISOTOPIC EVIDENCE

High-resolution foraminiferal, sedimentologic, and stable isotopic data from an 8.2 m long vibracore (PS03) taken from a 6.5 m water depth in Pamlico Sound, North Carolina, are used to reconstruct Holocene paleoenvironmental change. Four hundred and four contiguous 2 cm samples were processed, of which two hundred and fifty-nine contained foraminifera. Cluster analysis of foraminiferal data defined four biofacies, A to D. Comparison of the foraminiferal assemblages characterizing each group with the distribution of modern foraminifera led to the following paleoenvironmental interpretations: Biofacies A (Normal Marine Salinity Bay), Biofacies B (High Brackish Estuary), Biofacies C (Low to Mid-Brackish Estuary), and Biofacies D (Indeterminate-probably estuary). The foraminiferal data indicate that the generally estuarine southern Pamlico Basin was exposed to normal marine salinity conditions twice during the Holocene. Changes in δ¹³C and C/N (along with δ¹⁵N) confirm the occurrence of normal marine salinity conditions within the Pamlico basin. AMS dates (on ca. 1,000 specimens of Elphidium excavatum) taken near lithologic contacts reveal the older normal salinity episode occurred between 4340-4070 to 3750-3450 cal. yr. BP. The younger normal salinity episode occurred between 1170-950 to 550-440 cal. yr. BP. It is proposed that the older episode resulted from the flooding of a late Pleistocene topographic high, the Hatteras Flats Interstream Divide, during the Mid-Holocene Hypsithermal. The younger normal salinity episode is interpreted as resulting from a collapse of portions of the southern Outer Banks barrier island system during the Medieval Warm Period. This collapse could have been due to a large hurricane, a combination of relative sea-level rise and a large storm, or multiple, closely spaced, perhaps smaller, storm events. The southern Outer Banks suffered significant breakdown and the southern Pamlico Basin remained open to normal salinity marine waters for approximately 500 years, just prior to the arrival of Europeans, by which time the barrier islands had reformed to their present general configuration.