INDIGENEITY OF ORGANIC-MATTER IN FOSSILS - A TEST USING STABLE-ISOTOPE ANALYSIS OF AMINO-ACID ENANTIOMERS IN QUATERNARY MOLLUSK SHELLS

Comparison of the delta(13)C values of D and L enantiomers of individu al amino acids was used to evaluate the presence of amino acid contami nants in Quaternary land snails. Measurements of delta(13)C values of amino acid D and L enantiomers determined by combined gas chromatograp hy, combustion, isotope-ratio mass spectrometry are reported. Conventi onal combustion techniques, following separation of aspartic acid and glutamic acid enantiomers by liquid chromatography, were also used to determine delta(13)C as well as delta(15)N values. Thoroughly cleaned samples ranging in age from 7000 to >100,000 yr B.P. are shown to have analytically identical delta(13)C values for the D and L enantiomers of each amino acid, thus confirming that the amino acids are indigenou s to the shells, even in Pleistocene samples. On the other hand, parti ally cleaned material shows divergence of isotopic values, thus indica ting the presence of amino acid contaminants and emphasizing the impor tance of proper cleaning procedures. This approach provides a powerful method for assessing the indigeneity of amino acids in fossils.