AMINOSTRATIGRAPHY OF QUATERNARY COASTAL UNITS, NORTH CAROLINA COASTAL PLAIN

Amino acid racemization (AAR) methods have been applied to the chronostratigraphy of the North Carolina Coastal Plain for over two decades, in combination with independent calibration using radiocarbon and uranium-series dating. The earliest results were limited to one drilled section (Stetson Pit, Dare Co.) and a limited number of exposures, either excavated or natural (Ponzer, Flanner Beach, Lee Creek, Chowan River, James City). More recent work has involved additional samples from these sites, plus offshore vibracores and grab samples, beach samples derived from shoreface units of both Pleistocene and Holocene age, and 14 cored sections (drilled in 2001 and 2002) from the Outer Banks and mainland Dare County. During the history of this work, analytical methods have varied and current efforts involve the use of high-resolution gas chromatography on both new and existing collections to develop results with the best available methods that yield D/L values for at least six amino acids. AAR data for over 100 collections now exist, permitting statistical analysis to identify regional aminozones (clusters of D/L values). Superposed aminozones identified in several of the subsurface sections in Dare County (where the Quaternary section is particularly thick) serve as reference sections for the regional aminostratigraphy. In many cases distinctions between aminozones are subtle if based on statistics alone, but results from superposed sections reinforce the statistical interpretations. At least four aminozones (perhaps as many as seven) are evident in the time interval between the James City Formation (early Pleistocene) and the early Holocene. Although the age-resolution capabilities of AAR decrease with increasing extent of racemization, kinetic modeling suggests that most, if not all, the interglacials of the middle- and late-Pleistocene could be represented by the collective record of the NC Coastal Plain, and although no single section contains the complete record, the Dare County section appears most complete.