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The trend of marine 87Sr/86Sr against stratigraphic level through sections, whether linear or not, can identify hiatuses and changing rates of sedimentation through those sections and so be a valuable constraint on attempts to assign numerical ages to sediments on the basis of astrochronology or U/Pb dating of zircons. Here we illustrate that value for the Campanian, Pliensbachian, Toarcian, and Valanginian ages by comparing 87Sr/86Sr profiles for different localities and comparing those to the 87Sr/86Sr profile through time. The analysis reveals possible problems both with current time scales and with some astrochronological calibrations. Our analysis is neither comprehensive nor final; rather, with a few examples, we show how Sr-isotope stratigraphy can be used to moderate other methods of assigning numerical ages to sediments.

An improved and updated version of the statistical LOWESS fit to the marine 87Sr/86Sr record and a revised look-up table (V3:10/99; available from j.mcarthur@ucl.ac.uk) based upon it enables straightforward conversion of 87Sr/86Sr to numerical age, and vice versa, for use in strontium isotope stratigraphy (SIS). The table includes 95% confidence intervals on predictions of numerical age from 87Sr/86Sr. This version includes the Triassic and Paleozoic record (0509 Ma) omitted from previous versions because of the paucity of adequate data at the time of preparation. We highlight differences between the previous versions of the table and the current version and discuss some aspects of the 87Sr/86Sr record that may have geological significance. We give examples of how the table can be used and where it has proven useful.

New 87Sr/86Sr analyses of macrofossils from 13 key marker horizons on James Ross and Vega Islands, Antarctica, allow the integration of the Antarctic Late Cretaceous succession into the standard biostratigraphic zonation schemes of the Northern Hemisphere. The 87Sr/86Sr data enable Late Cretaceous stage boundaries to be physically located with accuracy for the first time in a composite Southern Hemisphere reference section and so make the area one of global importance for documenting Late Cretaceous biotic evolution, particularly radiation and extinction events. The 87Sr/86Sr values allow the stage boundaries of the Turonian/Coniacian, Coniacian/Santonian, Santonian/Campanian, and Campanian/Maastrichtian, as well as other levels, to be correlated with both the United Kingdom and United States. These correlations show that current stratigraphic ages in Antarctica are too young by as much as a stage. Immediate implications of our new ages include the fact that Inoceramus madagascariensis, a useful ...

We provide a best‐fit curve to 1849 strontium isotope data for the period 0 to 206 Ma using the LOcally‐WEighted regression Scatterplot Smoother (LOWESS) method. This is a robust, nonparametric modern regression technique. Since it does not yield an explicit mathematical equation relating 87Sr/86Sr to time, a look‐up table to determine numeric age has been generated in steps of 1 × 10−6 in 87Sr/86Sr. The calibration 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 coworkers for >95 Ma. The look‐up table includes 95% confidence intervals on the predictions of numeric age. When using this table, the uncertainty on the 87Sr/86Sr of the sample whose age is sought must be added to that inherent in the LOWESS regression. We show how to determine the uncertainty in 87Sr/86, i.e., how best to obtain the 95% confidence bounds on a single measurement of 87Sr/86 for a sample, and on the mean 87Sr/86 value for 2 or more replicate measure...