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 individual amino acids was used to evaluate the presence of amino acid contaminants in Quaternary land snails. Measurements of delta(13)C values of amino acid D and L enantiomers determined by combined gas chromatography, combustion, isotope-ratio mass spectrometry are reported. Conventional 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 indigenous to the shells, even in Pleistocene samples. On the other hand, partially cleaned material shows divergence of isotopic values, thus indicating the presence of amino acid contaminants and emphasizing the importance of proper cleaning procedures. This approach provides a powerful method for assessing the indigeneity of amino acids in fossils.