LATE HOLOCENE BACK-BARRIER EVOLUTION OF OCRACOKE ISLAND, OUTER BANKS, NORTH CAROLINA

Lithologic, geophysical, and foraminiferal data are being used to reconstruct the Holocene geologic evolution of Ocracoke Island on the Outer Banks of North Carolina. Nineteen vibracores were collected in three shore-perpendicular transects in the summers of 2004 and 2005. Four litho/biofacies have been identified in these cores. Facies A occurs at depths from 0 to +1m msl and is a medium to coarse grained, very mature quartz sand, mainly barren of foraminifera. Facies A is interpreted as Hurricane Isabel overwash sand. Facies B is an organic rich, fine grained, muddy sand, often rooted, that occurs at depths of 0 to -1m msl. This facies is interpreted as a salt marsh and contains typical salt marsh foraminifera. Facies C occurs from -1 to -4m msl, and is a slightly muddy, fine to medium grained, well sorted, gray sand with occasional root structures, bioturbation, organic matter, and fine shell hash, and is dominated by Elphidium excavatum. Facies C is interpreted as a back-barrier sand flat environment. Facies D occurs from -2 to -7m msl and is a medium to coarse grained quartz sand dominated by shell hash, interbedded with occasional coarse shell lenses. The foraminiferal assemblages that characterize this unit contain Buccella inusitata and Hanzawaia strattoni and are indicative of open inner shelf conditions. The modern Ocracoke Island is dominated by overwash processes. Facies D supports previous studies at Hatteras Village, Portsmouth Island and in southeastern Pamlico Sound that demonstrate that the southern Outer Banks collapsed approximately 1200 cal yr B.P., resulting in the southern portion of Pamlico Sound having full marine conditions until approximately 500 cal yr B.P.