Calibration of the geologic time scale: Cenozoic and Late Cretaceous glauconite and nonglauconite dates compared

Revision of the 1982 time scale of Harland et al. has led to the compilation of 377 isotopic dates for calibration of the Cenozoic to Cretaceous time interval. The results show that the ages of stage boundaries based on glauconite dates are on average about 2 m.y. younger than those based on nonglauconite dates, but for many Cenozoic and Late Cretaceous stages the differences are too small to require special consideration of glauconite dates. Future work may reveal an irreducible systematic difference between glauconite and nonglauconite time scales, but the progress made so far in recognizing those glauconites likely to yield reliable dates for the Cenozoic to Late Cretaceous interval may continue to provide useful time-scale calibration points.