Use of strontium isotope ratios and rare earth elements in apatite microphenocrysts for characterization and correlation of Silurian metabentonites: a Scandinavian case study
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The Sr isotope ratio (87Sr/86Sr) metabentonites from the Garntangen Member, Vik Formation, Oslo, Norway, and two samples from the Lower Visby Formation, Gotland, Sweden. The results for the Norwegian group show a bimodal distribution: a 'low' group (0.7041-0.7043) and a 'high' group (0.7061-0.7065). These groups correspond to the 'primitive' and 'evolved' associations, respectively, as defined by previous work on these same samples based on REE and trace element distribution in bulk rock and apatite. The two Swedish samples gave values of 0.70413 and 0.70638, values that correspond to the two geochemical divisions in Norway. In conjunction with previously published REE and other trace element data for apatite, these data suggest a direct comparison between the Telychian metabentonites of Norway and Sweden. The application of Sr isotope ratios in apatite lends additional support to the conclusion that one pair of Telychian metabentonites from Gotland and Norway represent the same fall-out event. Using the biostratigraphic control of Gotland, which is more robust than that of Garntangen, it is proposed that the Lower Visby Formation in Gotland and the Garntangen Member, Vik Formation in Norway can both be assigned to the M. spiralis Biozone.

Richard A. Batchelor, School of Geography & Geosciences, University of St. Andrews, North Haugh, St. Andrews, Fife KYJ6 9ST, Scotland
Jane Evans, N.E.R.C. Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG ,England