Reducing time-scale uncertainty for the Devonian by integrating astrochronology and Bayesian statistics

Abstract

Dealing with uncertainties is inherent to the scientific process. In the process of building geologic time scales, the reported uncertainties are at least as important as the estimates of the numerical ages. Currently all time scales for the Devonian are based on conventional age-depth models, constructed by linear or cubic interpolation between different dated positions. Unfortunately, such models tend to produce overoptimistic confidence intervals. In this study we apply Bayesian statistics to the Devonian time scale to better incorporate stratigraphic and radioisotopic uncertainty. This approach yields a Devonian time scale characterized by increasing uncertainty with growing stratigraphic distance from a radioisotopically dated sample. This feature is absent from The Geologic Time Scale 2012 ; therefore, that time scale is overoptimistic. We further constrain the obtained time scale by incorporating astrochronological duration estimates for the Givetian and Frasnian stages. The combination of radioisotopic dating and astrochronology results in a reduction of the uncertainty on the numerical age of the stage boundaries concerned by several million years. For example, we estimate the age of the Frasnian- Famennian boundary at 373.9 ± 1.4 Ma.