Holocene molluscan aminochronology and time averaging in Chesapeake Bay sediments

The present study is the first to establish a radiocarbon-calibrated amino acid racemization (AAR) chronology for the Chesapeake Bay. The aminochronology of Mulinia shells from two Chesapeake Bay sediment cores was created using several techniques to calibrate AAR with radiocarbon. Direct calibration methods included AAR and radiocarbon dating portions of 16 individual shells. The indirect calibration was accomplished by performing AAR analyses on 328 shells from 25 core intervals with independent radiocarbon dates. The direct and indirect calibration techniques yielded comparable results.; To approximate time averaging, each shell from the indirect calibration dataset was assigned an age based on the equation derived from the direct calibration. Following conventional methods of estimating time averaging using average standard deviation and range, the data from this study suggest time averaging on the order of 720 to 2600 years. These are likely to be overestimates, however, because conventional methods do not consider the influences of nonlinear racemization kinetics and inherent variability. Therefore, a new conceptual model was created based on the combined effects of analytical error, inherent variability, and ordinary time averaging.