NEW PERSPECTIVES ON US ATLANTIC COASTAL PLAIN AMINOSTRATIGRAPHY GLEANED FROM EXTENSIVE ANALYSES OF SHELL SPECIMENS FROM INNER CONTINENTAL SHELF VIBRACORES

Amino acid racemization (AAR) has been used in studies of Quaternary stratigraphy and geochronology of US Atlantic coastal plain sites for over 50 years. Several analytical methods have been employed (IE, GC, and RP) depending on available technology, sample size, or other criteria. Over the past three years, a campaign of coring to assess inner shelf sand resources from New Jersey (~ 40^o N) to Georgia (~ 30^o N) has been conducted by the Bureau of Ocean Energy Management (BOEM) and several state agencies. AAR results for ~900 mollusk specimens from >50 cores are now available. RP analyses were done at Northern Arizona University after initial sample preparation at the Delaware Geological Survey. New results for previously analyzed offshore and onshore samples (or sites) are included for comparison, including those with independent MIS-5a age calibration. Taxa employed in the offshore studies include Astarte, Chione, Spisula, Ensis, Mulinia, and Mercenaria, the latter two being the taxa most commonly used in prior studies (Wehmiller, 2013a).

In those instances where multiple methods are compared for specific shells (or collections from the same site), agreement is usually within 10%, although exact equivalence of D/L values from multiple methods should not be expected (Wehmiller 2013b; Whitacre et al., 2017). Nevertheless, multiple methods always lead to the same relative age interpretations.

Analytical results and related independent chronologic data are maintained in an ArcGIS database. Over 50 of the AAR results are for shells with paired ¹⁴C analyses, providing intergeneric calibration for Holocene samples and confirmation of Pleistocene AAR age estimates. The latitudinal distribution of results provides a broad perspective for the regional aminostratigraphic framework, which is further constrained by associated seismic trackline data. At least two Pleistocene units are identified at one or more shelf sites, and several examples of age-mixing on a variety of time scales are observed. The age distribution of mollusks, on the inner shelf and nearby beaches, is influenced by local and regional sediment supply and reworking during late Pleistocene sea-level transgression-regression cycles. Combined with geophysical and core data, age estimates aid in assessment of the volume of potential sand resources.