Since 1968, absolute ages have been assigned to the Late Cretaceous–Cenozoic geomagnetic reversal time scale by fixing the ages of two or more calibration points in a composite marine magnetic-anomaly profile and interpolating between or extrapolating beyond these points, assuming constant spreading rates in each interval. Previously, no more than 4 calibration points were used, but it is now possible to specify 11 calibration points, in addition to the 0 m.y. datum. This improvement is based on magnetostratigraphic studies in Italian pelagic limestones; these studies closely tie the geomagnetic reversal sequence to the foraminiferal and coccolith zonations. Absolute ages of calibration points are provided by the best available dates on stage boundaries, which are located from the biostratigraphic zonation. The greatest changes from previous scales come in the late Paleocene–early Eocene, where the new ages are as much as 3 m.y. younger than in the 1977 scale of LaBrecque and others, and as much as 1.8 m.y. younger than in the 1980 scale of Ness and others.

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