INNER SHELF RECORD OF EARLY- TO MID-HOLOCENE COASTAL EVOLUTION ON THE NORTH CAROLINA CONTINENTAL MARGIN: WERE THERE BARRIER ISLANDS OR NOT?

Systematic geophysical mapping has furnished regional-scale, high-resolution information on the morphology and shallow stratigraphy of portions of the North Carolina continental shelf, over areas ranging from 100 km² to 4000 km². Supporting data include cores, sediment and rock samples, and radiocarbon and amino-acid racemization age estimates. The data reveal a remarkably well-preserved suite of Holocene coastal lithosomes that provide insight into the Late Quaternary evolution of coastal systems on this continental margin.

The inner shelf off Hatteras Island is comprised of a variety of Quaternary sediments that have been variably preserved through multiple regressions and transgressions. A network of tidal creek lithosomes up to 12 m thick is preserved in the shallow subsurface between Oregon Inlet and Cape Hatteras. Cores in the channels contain interbedded sand and mud, as well as thick sequences of oyster bioherms.

The inner shelf off Wrightsville Beach is underlain by unconsolidated, early Oligocene sandy silt that has been incised by late Tertiary and Quaternary fluvial channels. The uppermost sections of these channels retain a sedimentary record of early Holocene coastal lithosomes, which are mappable in the subsurface and occasionally crop out on the seafloor. Holocene lithosomes are also present outside of the incised fluvial systems as patchy veneers filling topographic lows on the ancient sediments. Cores in the Holocene sediments include open estuarine muddy sands, and shell-rich muds.

Radiocarbon ages on peats and mollusks from these locations are surprisingly continuous given the Holocene transgression of the continental shelf, but show a common chronologic discontinuity from ~7900-7400 cal yr BP. Possible explanations for this discontinuity include a brief but rapid rise in sea-level during this period, or erosional removal by shoreface incision during the relative stillstand of the past several millennia. The preservation of the lithosomes and spatial relations between them indicate some potential for the former possibility. This raises the interesting question of whether the North Carolina barrier islands migrated continuously across the shelf, or appeared and disappeared in response to changes in the rate of Late Quaternary sea-level rise.