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Improving the reliability of amino acid geochronology

The importance of a robust chronology for Quaternary sediments cannot be underestimated.

In recent years advances have been made in Amino Acid Racemization (AAR; Penkman, 2005), combining the isolation of an 'intra-crystalline' fraction of amino acids by exhaustive bleach treatment of ground shell carbonate (Sykes et al., 1995) with a new Reverse-Phase High Pressure Liquid Chromatography (RP-HPLC) method (Kaufman & Manley, 1998).

This combination of techniques results in the analysis of D/L values of multiple amino acids from the chemically-protected protein within the biomineral, enabling both decreased sample sizes and increased reliability. The intra-crystalline protein occurs within a 'closed system' during the burial history of the shell, vital for the application of this technique for geochronological purposes. Amino acid data obtained from the intra-crystalline fraction of calcitic biominerals indicate this to be a particularly robust repository for the original protein, with this coherent system maintained as far back as the Pliocene.