AMINOSTRATIGRAPHIC MAPPING OF QUATERNARY COASTAL UNITS, CAROLINA COASTAL PLAIN

Amino acid racemization (AAR) data from the US Mid- and Southeast Atlantic coastal system have been used for correlation and age estimation of mollusks from Quaternary coastal units from ~400 onshore sites (excavations, natural exposures, or cores) and ~100 offshore cores or grab samples. More than a dozen investigators from academia, USGS and state surveys have contributed to this dataset, now being compiled in a series of on-line ArcGIS maps. Independent geochronologic (U-series, 14C, OSL) and stratigraphic data provide both local and regional frameworks for interpretation of AAR results, the long Quaternary record of the Albemarle Embayment being particularly useful. AAR results for beach shells are related to both offshore and onshore units, thereby identifying likely sediment sources, and supplementing local aminostratigraphic sequences.

Four local study regions in the Carolinas include the Albemarle Embayment (36-35^oN), Cape Lookout to Cape Fear (34.8-33.8 ^oN), Cape Fear to Cape Romain (33.8-33.1 ^oN), and the Sea Islands section of the SC-GA coast (33.1-31.9 ^oN). AAR data within each region identify multiple Pleistocene aminozones (between two and five, depending on the region), some being associated with named (mapped) units. Correlation of aminozones between these regions is challenging for many reasons, including limited numbers of quality samples, lack of in-place samples (particularly in the Cape Fear region), inter-method differences, and debates about the stratigraphic terminology of the host units. The combined results from NC to GA identify one or two late Pleistocene aminozones representing MIS5e-MIS5a, both onshore and offshore, with possible evidence of a younger (pre-Holocene) offshore zone. Older aminozones (both offshore and onshore) represent middle and early Pleistocene intervals. The region between Cape Fear and Cape Lookout, with few onshore collections, contains an offshore suite of age-mixed mollusks representing most of the Quaternary.

Analytical methods used in this research have evolved substantially over the past 40 years. Future work should focus on systematic application of current methods to both existing and new collections to refine these inter-regional correlations and improve our understanding of geochemical factors affecting these interpretations.