CRITERIA FOR THE RETENTION OF ORIGINAL SEAWATER SR-87 SR-86 IN ANCIENT SHELF LIMESTONES/

A suite of 40 Pennsylvanian and Permian shelf limestones from Kansas a nd Oklahoma has been analyzed for major and trace elements and for C, O and Sr isotopes. The chemistry and C and 0 isotope ratios were compa red to the difference between the measured Sr-87/Sr-86 and original se awater ratio. Concentrations of Mn, Sr and Fe varied most systematical ly with the change in the seawater Sr ratio. All samples containing < 300 ppm Mn yielded correct ratios. All samples with > 700 ppm Mn yield ed altered ratios. Fe and Sr contents were also found to have a less w ell-defined correlation with the retention of the original Sr ratio. A ll limestones with > 900 ppm Sr and 20 of 22 samples with a Sr/Mn > 2. 0 yielded correct ratios. The geochemical guidelines were applied to t he chemical and isotopic results from 76 shelf limestones, mostly of P ennsylvanian age, from Texas and Oklahoma. More than 92% of the sample s that contain < 300 ppm Mn, or with a Sr/Mn > 2.0 yielded correct sea water ratios. Every sample with < 3000 ppm Fe and a Sr/Mn > 2.0 retain ed the original seawater ratio.