Overview of amino acid geochronology

Amino acid geochronology is an increasingly important chronostratigraphic tool than can be used in a wide range of Quaternary geologic settings. The technique has been applied to deep-sea and coastal marine deposits, terrestrial deposits and archeological sites. Although a wide variety of preserved organic remains have been used, most recent studies have focused on marine molluscs and foraminifera. Studies utilizing bone remain controversial. The most successful applications rely on d l ratios as relative-age indices that are independent of assumptions regarding post-depositional temperatures. As a relative-age tool, d l ratios provide a basis for identifying unconformities in stratigraphic sequences, resolving mixed populations of reworked material and evaluating stratigraphic correlations between disjunct exposures. d l ratios, combined with independent paleoenvironmental evidence, can be used to constrain the reasonable time/temperature range of a stratigraphic unit. Where the ages of units are known from independent determinations, d l ratios can be used to evaluate the overall temperature history of a deposit. A newly emerging and particularly promising application of the amino acid geochronology is in dating eggshell from archeological sites. The outstanding potential of this application is derived from the integrity of the eggshell carbonate matrix which, better than any other carbonate system, approximates a closed system for the retention of amino acids.