GEOLOGICAL EVOLUTION OF NORTH CORE SOUND, NORTH CAROLINA, IN RESPONSE TO HOLOCENE SEA-LEVEL RISE

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. Cores have been logged for lithology, and sampled to establish the distribution and abundance of foraminifera. Foraminiferal distributions are being used to identify environmental changes. Radiocarbon ages are providing the temporal context. This data will provide an understanding of the response of this coastal system to Holocene sea-level change and storm impacts.

Prior studies have shown that Pleistocene sediment is found at the surface of Cedar Island and roughly 10-12 meters below sea level on Core Banks. Data from this investigation has indicated that the Pleistocene surface dips slightly seaward and is characterized by numerous fluvial channels correlating to modern embayments. At least four other erosional surfaces were identified within the seismic data. Two of these surfaces were within the Holocene record and provided evidence for high energy events that modified the geomorphology of the system.

Lithologic data were correlated to the seismic data to produce a stratigraphic framework. Six lithofacies that were determined include massive sand, muddy sand, shelly sand, sandy mud, clay, and peat. Dark grey-green clay was observed within some cores which have been determined to immediately underlie the Pleistocene surface.

Two radiocarbon dates were acquired from bivalve shells found in two different cores ~ 800 meters apart in a shore perpendicular transect. A Mercenaria mercenaria shell, found in massive sand, was sampled at 3 meters below sea level and provided a conventional age of 1390 +/- 40 yrs B.P. A pecten shell, found in sandy mud, was sampled at 5 meters below sea level and provided a conventional age of 930 +/- 40 yrs B.P. Additional dates are pending that will help to constrain the paleoenvironmental evolution of this coastal system in response to Holocene sea-level rise.