THE LATE QUATERNARY GEOCHRONOLOGY OF NORTH CAROLINA'S OUTER BANKS DERIVED FROM AMINOSTRATIGRAPHIC STUDY OF BEACH AND INNER SHELF CORE SAMPLES

Aminostratigraphic data for Mercenaria from 10 Outer Banks beach collection sites between Oregon Inlet and Cape Point identify at least four Pleistocene aminozones. Infinite AMS radiocarbon dates confirm the Pleistocene age of these specimens, and additional finite AMS dates paired with amino acid analyses allow aminozones for Holocene samples to be defined. Collection sites north of Rodanthe are dominated by Holocene shells; Pleistocene shells become much more abundant between Rodanthe and Cape Point. Oregon Inlet dredge spoil also contains a mixture of Pleistocene and Holocene shells. Where whole Pleistocene shells are found on beaches, close proximity to a source is inferred; Rodanthe and Cape Point being two prime examples. The source units for these aminozones are recognized by analysis of Mercenaria specimens from inner shelf vibracores obtained at sites between the mouth of Chesapeake Bay and Diamond Shoals. Equivalent aminozones are also recognized in mollusk racemization data from subsurface sections in Dare County and from outcrops of Pleistocene units along the western margin of Pamlico Sound. Although the beach specimens and perhaps some of the inner shelf samples have been transported, these regional aminostratigraphic data help to refine the chronology for the geologic framework of the North Carolina coastal plain. We interpret these aminozones to represent deposition during each of the marine isotope stages of the past million years, although model racemization kinetics and typical analytical uncertainties do not allow resolution of individual isotope stages. Age estimates are dependent upon choice of kinetic model. The oldest aminozone recognized from beach specimens is estimated to be equivalent to stage 11; older aminozones are recognized only in onshore subsurface sections.