Estimation of the ages of Devonian and Cretaceous stage boundaries in the Geologic Time Scale

Abstract

Estimation of the ages of period and stage boundaries of the Geologic Time Scale (GTS) has a long history that commenced over a century ago with the pioneering work of Arthur Holmes. Frequencies, precision and accuracy of radiogenic isotope age determinations used for time scale construction continue to increase steadily. Later stage boundary age estimates are accompanied by error bars based on 2-sigma age dating errors with incorporation of stratigraphic uncertainty. Most GTS2004 and GTS2012 results involved spline-curve fitting. In GTS2012, Milankovitch-type orbital climate cyclicity was used to tune the Neogene geologic time scale while seafloor spreading was combined with sedimentary cycle scaling to construct the Paleogene time scale, and it also contributed to the construction of the Cretaceous and Jurassic time scales. Geomathematical procedures continue to be refined for the next GTS which is in Gradstein et al. (2020). In this study smoothing splines are used to construct Devonian and Late Jurassic - Early Cretaceous time scales. This methodology and its results are described and some estimates are refined by incorporating Milankovitch cycle durations.