Amino acid racemization and radiocarbon dating of interstadial marine strata (oxygen isotope stage 3), Gulf St. Vincent, South Australia

Concordant results for the extent of racemization of the amino acids, aspartic acid, leucine and valine and isoleucine epimerization in several mollusc genera support radiocarbon data that indicate an interstadial age (oxygen isotope stage 3: 45,000 to 30,000 yr B.P.) for a sequence of mollusc-rich, carbonate muds in Gulf St. Vincent, South Australia. A numeric age of 46,500 ± 9100 yr B.P. was obtained on marine molluscs from these sediments, using a model based on “apparent” parabolic racemization kinetics. In a global context, the sequence represents one of the few well documented occurrences of marine strata of this age from a tectonically quiescent setting. A sea level as high as −22 m is indicated for this interval. Amino acid racemization provides an important method for validating conventional, “finite” radiocarbon ages close to the practical limits of radiocarbon dating and in studies of reworking.