STATISTICS FOR STRONTIUM ISOTOPE STRATIGRAPHY - A ROBUST LOWESS FIT TO THE MARINE SR-ISOTOPE CURVE FOR 0 TO 206 MA, WITH LOOK-UP TABLE FOR DERIVATION OF NUMERIC AGE

We provide a best-fit curve to 1849 strontium isotope data for the per iod 0 to 206 Ma using the LOcally-WEighted regression Scatterplot Smoo ther (LOWESS) method. This is a robust, nonparametric modem regression technique. Since it does not yield an explicit mathematical equation relating Sr-87/Sr-86 to time, a look-up table to determine numeric age has been generated in steps of 1 x 10(-6) in Sr-87/Sr-86. The calibra tion uses the timescales of Shackleton and coworkers for 0-7 Ma; Cande and Kent for 7-72 Ma; Obradovich for 72-95 Ma and Gradstein and cowor kers for >95 Ma. The look-up table includes 95% confidence intervals o n the predictions of numeric age. When using this table, the uncertain ty on the Sr-87/Sr-86 of the sample whose age is sought must be added to that inherent in the LOWESS regression. We show how to determine th e uncertainty in Sr-87/(86), i.e., how best to obtain the 95% confiden ce bounds on a single measurement of Sr-87/(86) for a sample, and on t he mean Sr-87/(86) value for 2 or more replicate measurements of Sr-87 /(86) in the sample; these confidence intervals reflect analytical-sys tem reproducibility for routine samples (as opposed to that of standar d control materials, e.g., NIST 987) and are necessary to establish th e final upper and lower bounds on predicted numeric age.