The new reverse-phase HPLC procedure enabled amino acid geochronology to be applied to microfossils, including ostracodes. Ostracodes inhabit a wide range of environments, including deep-lake settings. Their shells are often present in sediment cores, especially from hardwater lakes, allowing amino acid geochronology to be integrated into the study of lake cores. The temperature history of ostracodes recovered from below the thermocline of stratified lakes can confidently be assumed to have remained close to 4°C, the temperature of maximum-density fresh water. Because the rate of amino acid enantiomers from racemization is dependent upon temperature, a stable and predictable temperature history lends confidence to ages derived using amino acid geochronology. I used independently dated sediment cores from multiple lakes to calibrate the rate of racemization for aspartic and glutamic acid in the common ostracode genus, Candona (Kaufman, 2003; Fig. 1). This calibrated age equation can be applied to ostracodes from other hypolimnic core sites; it yields ages with realistic uncertainties of ~20% for samples up to 100,000 years . The sample size required for an analysis is an order of magnitude less than for AMS 14C dating and presents a new opportunity to derive ages for deposits that are organic poor, or suffer from large 14C reservoir effects.
Reference
Kaufman, D.S., 2003, Dating deep-lake sediments by using amino acid racemization in fossil ostracodes: Geology 31, 1049-1052.
