SEAWATER SR ISOTOPE VARIATIONS THROUGH TIME - A PROCEDURE FOR CONSTRUCTING A REFERENCE CURVE TO DATE AND CORRELATE MARINE SEDIMENTARY-ROCKS

A new curve of seawater Sr-87/Sr-867 variation through the past approx imately 450 m.y. enables dating and correlation of marine sedimentary rocks with quantifiable uncertainties. We discuss the method by which this curve was constructed. Strictly standardized Sr-87/Sr-86 ratios a nd biostratigraphic data for approximately 1300 Sr-87/Sr-86 analyses o f marine minerals were input into a data base. Objective criteria were used to assign each data point a reliability score. These scores were used as initial weights in a robust nonparametric regression (LOWESS) to obtain a curve of seawater Sr-87/Sr-86 variation with rigorous 95% confidence intervals for prediction of age uncertainty. Precise datin g and stratigraphic correlation are feasible for much of the Phanerozo ic. The main problem with future Sr isotope stratigraphy is likely to be sample quality, we discuss guidelines for sample selection.