HOLOCENE GEOLOGIC FRAMEWORK AND EVOLUTION OF THE NORTHERN OUTER BANKS: RESULTS OF GROUND PENETRATING RADAR AND SEDIMENTOLOGICAL INVESTIGATIONS

The Pleistocene and Holocene geologic framework of the North Carolina Outer Banks exerts a fundamental control on modern patterns of shoreline erosion and barrier island dynamics. This abstract presents the results of ground penetrating radar (GPR) and sedimentological investigations from the northern Outer Banks, between Duck and Oregon Inlet. GPR and core data indicate that Holocene barrier island sands average 6-7 meters thick and are deposited upon Holocene estuarine sediments that range in age from ~6500 to ~2600 cal y BP. Southern Kitty Hawk and northern Kill Devil Hills are underlain by a major incised fluvial valley complex, backfilled with late Pleistocene to Holocene fluvial, bay, and estuarine sediments. 100 MHz GPR data resolve the final fill of this valley. In the Duck and Kitty Hawk area, GPR data resolve relict beach ridges buried beneath dune deposits, and eroding at the present shoreline, indicating Holocene shoreline progradation to some point east of the present shoreline, then erosion to its present position. North of Nags Head Woods, progradation is toward the south. This pattern is interrupted at Nags Head Woods by a significant inlet channel identified in GPR data. The preserved inlet channel-fill facies is approximately 300 meters wide by at least 8 meters deep, and appears to have closed by beach-ridge and spit progradation from the south. Southward of the inlet channel-fill, beach ridge clinoforms prograde north and occur in the subsurface to the southern edge of Jockey’s Ridge. Two paleo-fluvial channels are recognized in seismic and GPR data south of Jockey’s Ridge. Channel-fill facies have been cored and dated in the estuary, and exhibit fill from at least 5200 to 4400 cal y BP, a hiatus from 4400 to ~2200 cal y BP, then estuarine fill from ~2200 to 800 cal y BP. Data indicate an evolution of the barrier islands from a beach ridge dominated, progradational shoreline to a dune-field dominated retreating shoreline. This transition may be related to changes in sediment flux, climate change, minor sea level changes, or changes in the frequency and intensity of storms in the North Atlantic.