Amino acid dating of Pleistocene mammalian enamel from the River Thames terrace sequence: a multi-taxon approach

Abstract

Amino acid geochronology can provide effective relative dating frameworks for the Pleistocene and has enabled correlation of terrestrial deposits to the global climatic fluctuations described by the marine oxygen isotope record. Using methods developed for the analysis of intra-crystalline amino acids in tooth enamel, we aimed to construct an enamel-based amino acid geochronology for the terrace deposits in the valley of the River Thames in southern Britain using different mammalian taxonomic groups: elephant, horse and bison. To achieve this, chiral amino acid analysis was applied to 58 elephantid, 21 horse and 15 bison teeth from 10 horizons in the Upper Thames Valley, three in the Lower Thames Valley and one from a Thames tributary in the Lea Valley. We evaluate differences in the rates of amino acid breakdown between the taxa and establish which species are similar enough to enable comparison for relative dating purposes. The relative dating of the river terrace deposits is in good agreement with the terrace stratigraphy, biostratigraphy, and other independent estimates of age for all three taxonomic groups. These frameworks demonstrate the potential of enamel-based amino acid geochronologies for relative dating of Middle–Late Pleistocene deposits in the UK, and establish an aminostratigraphic framework from which the dating of other tooth material can be refined. Enamel offers an opportunity to evaluate the age of sites where shell material is absent or poorly preserved. It can also, crucially, provide direct relative dating of mammalian fossils, which are often the focus of study in terms of their evolution, distributional changes or extinction. Direct dating negates the risk that the mammal fossils themselves might be reworked, or of different ages to shell, sediments or other dated material in the same deposits; it also enables archived samples with insecure provenance (e.g. from early 17th-19th century collections) to be directly dated.