Sr isotopic compositions of single conodont elements were measured to investigate the potential usefulness of conodonts in defining the Sr isotope seawater curve. Analysed elements had very low colour alteration indices (CAI = 1) and were of the coniform species Drepanodus arcuatus (Pander, 1856), sampled from the Early Ordovician (early Bendigonian, ~490 - 492Ma) Emanuel Formation in the Canning Basin of Western Australia. 87Sr/86Sr ratios measured from single whole conodont elements were compared to those from mechanically separated cusp tissue and from the element base with attachment cone, showing significant isotopic heterogeneity within single elements. Cusps are characterised by significantly lower 87SR/86Sr ratios (0.708949 - 0.709056) than their associated base and attachment cone (0.709503 - 0.709829), and are well within the boundaries of the seawater curve. Single whole elements have 87Sr/86Sr ratios (0.709097 - 0.709282) intermediate between cusp and basal tissue. Host-rock limestone from the same horizon yielded high 87Sr/86Sr ratios (0.709368, 0.709454). A few small, thin-shelled articulate brachiopods recovered from elsewhere in the section have also suffered significant diagenetic alteration; the 87Sr/86Sr measurements of secondary shell material range from 0.709027 to 0.709430. These results indicate both carbonate and phosphate components have experienced significant diagenetic alteration, and that basal tissue appears to be a major source of secondary Sr in D. arcuatus. Despite the isotopic heterogeneity of conodont apatite, preliminary results suggest that the lowest, and perhaps primary, 87Sr/86Sr ratio (0.708750) is retained near the 'core' of cusp tissue, at the growth axis.
|Number of pages||8|
|Journal||Bollettino della Societa Paleontologica Italiana|
|Publication status||Published - 1 Dec 1998|