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The trace-element content and strontium isotope ratio have been determined for twelve requienid rudists from SE France. Fromthese data the seawater ratio of eight stratigraphic intervals was determined. The biostratigraphy of the associated platform carbonates, ranging from Berriasian to Lower Aptian, was derived from shallow-water benthic organisms, including calcareous algae (Dasycladales), large foraminifera (mainly Orbitolinidae), and rudists. Isotope ratios of well preserved rudist shells were compared to secular variationsof the 87Sr/86Sr ratio of seawater as derived from belemnites and calibrated to the Boreal ammonite zonation (McArthur et al., 2001).Stratigraphic mismatches between the values measured on requieniid rudists and the Boreal Sr-isotope reference curve appear to resultmainly from the fact that the reference curve is resolved rather as a band. A few larger discrepancies may be due to weaknesses in the original correlation of biostratigraphic markers and isotope values for some time intervals (e.g., upper Barremian).

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