Quaternary Evolution of North Core Sound Sound, North Carolina

Abstract

Northern Core Sound is a shallow lagoonal estuary located behind the Outer Banks barrier islands of eastern North Carolina. Thirty-two vibracores and 155 km of chirp and boomer seismic data have been used to define the geologic framework and establish the Holocene evolution of this back-barrier lagoon. Vibracores have been logged for lithology, and sampled to establish the distribution and abundance of foraminifera. The lithostratigraphy and biofacies could not be directly correlated but when related to the seismic data, apparent patterns could be recognized. The Quaternary stratigraphic framework of North Core Sound consists of five depositional sequences, comprising transgressive, highstand, and falling stage systems tracts. Seismic reflections are prominent and are correlated to the sequence stratigraphic surfaces within Pamlico Sound defined by Mallinson et al. (2010). The late Pleistocene paleotopographic surface dips slightly seaward and is characterized by two or three fluvial channels correlating to modern embayments. These channels are separated by a paleotopographic high that extends from Cedar Island seaward. The channels run northeast in the north and southwest in the south creating two different paleo-environments. The paleotopographic high may have contributed to differing foraminiferal assemblages found within Holocene unit. The Holocene unit is characterized by high salinity estuarine deposits dominated by the foraminifera Elphidium excavatum and Ammonia parkinsoniana. Three very similar biofacies were defined with more abundant Ammonia parkinsoniana where salinities may have been slightly lower. Only a salt marsh facies was significantly different. The biofacies may also represent the two paleo-environments illustrated in the seismic data as one is mainly found to the north of the paleotopographic high and the other to the south. Two seismic reflections, H30 and H60, are interpreted as tidal ravinement surfaces and divide the Holocene into three parasequences. Lithologically the units are coarsening upward, which may be a result of the transgressing barrier island (Core Banks) or increased tidal energy related to inlet activity. Radiocarbon age estimates place the lower surface, H30, older than 600 cal y BP, suggesting that this erosional surface is related to the segmentation of the Outer Banks during the Medieval Warm Period or the Little Ice Age, as defined by other workers.