Amino acid racemization dating of some coastal plain sites, southeastern Virginia and northeastern North Carolina
Date
1985
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware, Newark, DE
Abstract
Bivalve mollusks (g. Mercenaria and g. Anadara) have been analyzed
from 4 southeastern coastal plain sites using the amino acid racemization
(AAR) technique for correlation and age estimate purposes. As seen
previously (Wehmiller and Belknap, 1982), a conflict exists between age
estimates obtained by AAR and V-series methods at the Norris Bridge, VA
locality. Here, V-series dating of coral yields a 187 ±20 KA age, while AAR
methods suggest a 400 to 500 KA age. The following methods are employed
to understand this discrepancy at the Norris Bridge site: 1). Analysis of
standard samples to ensure uniform sample preparation and system operation;
2). Quantification of variation in Mercenari'a and Anadara samples for each
field site; 3). Qualitative comparison of AAR behavior between Mercenaria
and Anadara to assess suitability of Anadara for dating purposes; 4).
Aminostratigraphic correlation of field sites using both genera, and 5).
Estimation of AAR ages using the the non-linear model of Wehmiller and
Belknap (1982).
Standard samples analyzed for this study show relatively good
preCISIon. Coefficients of variation (CVs) of D/L leucine values are 5.7%
(ILC-A) and 9.1% (ILC-B). Overall, both ILC-A and -B show accuracy
within 6% when compared to other University of Delaware analyses. Several
valves of each genus were analyzed from all sites to determine field site
precision. CVs for multiple Mercenaria samples from each site are as follows:
Gomez Pit, VA (5.2%); New Light Pit, VA (7.0%); Moyock Pit, N.C. (8.8%)
and Norris Bridge, VA (4.4%). CVs for Anadara samples are slightly higher,
but comparable for each field site. No Anadara were analyzed from the New
Light Pit locality. On the basis of an identical order of racemization rates
(i.e. ASP2:ALA> LEU>VAL) and similar ASP/LEU values in both genera,
Mercenaria and Anadara qualitatively show similar racemization behavior.
3 clusters of DjL leucine values have been discerned from these field
site analyses. These D/L leucine values are used to correlate fossiliferous
strata in the southeastern Virginia and northeastern North Carolina Using the
non-linear kinetic model, these Coastal Plain. D/L values suggest the
following ages: 0.21 to 0.25 (75 KA) and 0.530 (approximately 400 KA).
D/L values ranging between 0.33 and 0.38 are tentatively estimated to be 100
to 200 KA in age.
Description
Keywords
Bivalve mollusks (g. Mercenaria and g. Anadara), Gomez Pit, Virginia, New Light Pit, Virginia, Moyock Pit, North Carolina, Norris Bridge, Virginia