Strontium-isotope composition in the Tethys Sea, Euboea, Greece

The 37Sr/36Sr ratios of the Tethys Sea have been determined by analyzing limestones of Permian to Late Cretaceous age from the overthrusted sequence of central and northern Euboea. The results are in satisfactory agreement with ratios obtained by other investigators on unreplaced fossil shells of similar age collected elsewhere. The 37Sr/36Sr ratios of Mesozoic marbles from the autochtone metamorphic rocks of southern Euboea are more variable, perhaps because of increases in this ratio during regional metamorphism. Nevertheless, the lowest values of suites of isochronous samples may approach the correct ratio. Four samples of the Argyron Marble taken at different localities in southern Euboea and on the Attic peninsula have a concordant 87Sr/86Sr ratio of 0.70688+-0.00006 relative to 0.7080 for the Eimer and Amend isotope standard. This value indicates a Jurassic age for this formation even though the fragmentary fossil evidence favors a Late Cretaceous (Turonian) age