APPLICATION OF THE SOLUBILITY PROFILING TECHNIQUE TO RECENT AND FOSSIL FISH TEETH

Strontium isotope (Sr-87/Sr-86) signals and trace elements have been m easured in fossil fishes in order to evaluate their suitability as pa laeoenvironmental markers of their original habitats, while accounting for post-depositional alteration. Preliminary physical and chemical c haracterization of both Recent and fossil fish teeth from marine and f reshwater environments have demonstrated differences in their respecti ve biological properties, largely defined by their environment, and di fferences in post-depositional (diagenetic) alteration. A range of wel l-provenanced modern and fossil fish teeth dating back to the Eocene ( 55 Ma) have been subjected to a series of sequential washes in a mild acetic acid buffer in order to remove adsorbed and exchangeable ions o f diagenetic origin from mineral surfaces and exchange sites, and to d issolve calcite overgrowths. The leaching protocol is designed to sepa rate carbonate, hydroxy- and fluorapatites on the basis of differentia l solubility and relative crystallinity. The relative solubilities of enamel, dentine and whole tooth samples of fossil fishes would appear to correlate with those observed for modern biological apatites. Furth ermore, a highly soluble strontium rich phase is washed out of the maj ority of samples which may effect significant changes to their Sr-87/S r-86 signal. Studies have focused on Cenozoic fish material where the 87Sr/86Sr seawater curve is well-constrained, but there is little abso lute or quantitative congruence with this reference. However, relative or qualitative trends in Sr-87/Sr-86 signals of samples representing presumed marine-freshwater transitions suggest that biogenic signals c an potentially be recovered from palaeontological material with contin ued leaching to remove the diagenetic overprint.