Sr-isotope stratigraphy: Assigning time in the campanian, pliensbachian, toarcian, and valanginian

The trend of marine⁸⁷Sr/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 comparing⁸⁷Sr/⁸⁶Sr profiles for different localities and comparing those to the⁸⁷Sr/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.