A Late Cretaceous‐Eocene Geomagnetic Polarity Time Scale (MM26) That Combines Marine Magnetic Anomaly Records, Radioisotopic Dates, and Astrochronology

Abstract

The Geomagnetic Polarity Time Scale (GPTS) is essential to date geological events in stratigraphic sequences and to reconstruct plate motions. The first GPTSs were based on the record of magnetic anomalies created by seafloor spreading, calibrated by a few radioisotopic dates. Recently, GPTS construction shifted to astrochronology, where magnetostratigraphy is dated from astronomical cycles recorded in selected sediment sequences. We construct here a MM26 GPTS for the Late Cretaceous‐Eocene (magnetochrons C33–C13, ∼83–33 Ma) based on three data sources: 20 radioisotopic dates, 97 magnetochron durations from astrochronology, and 154 ship tracks of magnetic anomalies from thirteen mid‐ocean ridge flank regions. Whereas current practice concentrates on the best records dated by astrochronology, we argue here that the combination of diverse types of data that have independent errors provides a better constrained GPTS. Starting from a Bayesian formulation, a Markov chain Monte Carlo (MCMC) algorithm generates a large sample of GPTSs that fit radioisotopic and astrochronology data while minimizing global spreading rate fluctuations. Best estimates of the GPTS ages and durations are the averages of the MCMC sampled values, and uncertainties are quantified by the sample standard deviations. Numerical experiments that use only some data sources to constrain the MCMC sampling show that time scale uncertainty is minimized when all data types are included. Finally, the GPTS confirms a global plate motion change at 50–45 Ma, when India‐Eurasia collision slowed spreading in the Indian Ocean while spreading rates concurrently increased in the Northern Pacific and South Atlantic.