HOLOCENE PALEOENVIRONMENTAL CHANGE IN PAMLICO SOUND, NORTH CAROLINA: EPISODIC BREACHING OF THE OUTER BANKS

Foraminiferal assemblages were identified in contiguous samples taken every 2 cm from an 8.2 m core from the deepest part (6.5 m water depth) southeastern Pamlico Sound, North Carolina. The bottom of the core has been dated (bulk organic-rich sediment) at 7010-7285 cal yr BP. The upper 1.1 m of estuarine sediment was deposited behind a barrier island cut only by two inlets, and consists of organic-rich mud. However, down core the sediments alternate twice between estuarine and open shelf faunas each with distinct foraminiferal taxa. Estuarine assemblages are dominated by the benthic foraminifer Elphidium excavatum with Ammonia parkinsoniana and Ammotium salsum as important subsidiary species. Open shelf assemblages are also dominated by E. excavatum but contain benthic species (e.g., Hanzawaia strattoni, Nonionella atlantica) found only in the open shelf today and planktonic species (e.g., Globigerinoides ruber and Globorotalia menardii) that inhabit Gulf Stream waters. Calibrated radiocarbon AMS ages (each on 1,000 specimens of E. excavatum) from the top and bottom of the youngest open shelf sand bed are 430-530 cal yr BP and 960-1160 cal yr BP. During this 500 year interval fully marine conditions extended into Pamlico Sound probably due to the breaching of an extensive section of barrier island. The presence of two open marine sand-rich beds and their foraminiferal assemblages in the muddy, basinal part of Pamlico Sound indicate that the Outer Banks barrier islands had extensive breaches twice at least twice during the past 7,000 years and that at times of breaching southern Pamlico Sound had the aspect of a bay with fully marine salinity, open to Gulf Stream eddies containing warm water planktonic foraminifera. This interval corresponds to the Medieval Warm Period and may indicate increased Gulf Stream vigor and/or regional storminess.