Precisely dating the Frasnian\u2013Famennian boundary: implications for the cause of the Late Devonian mass extinction

L M E Percival,D De Vleeschouwer,U Schaltegger,A.-C Da Silva,J H F L Davies,K B Föllmi

doi:10.1038/s41598-018-27847-7

Abstract

The Frasnian–Famennian boundary records one of the most catastrophic mass extinctions of the Phanerozoic Eon. Several possible causes for this extinction have been suggested, including extra-terrestrial impacts and large-scale volcanism. However, linking the extinction with these potential causes is hindered by the lack of precise dating of either the extinction or volcanic/impact events. In this study, a bentonite layer in uppermost-Frasnian sediments from Steinbruch Schmidt (Germany) is re-analysed using CA-ID-TIMS U-Pb zircon geochronology in order to constrain the date of the Frasnian–Famennian extinction. A new age of 372.36 ± 0.053 Ma is determined for this bentonite, confirming a date no older than 372.4 Ma for the Frasnian–Famennian boundary, which can be further constrained to 371.93–371.78 Ma using a pre-existing Late Devonian age model. This age is consistent with previous dates, but is significantly more precise. When compared with published ages of the Siljan impact crater and basalts produced by large-scale volcanism, there is no apparent correlation between the extinction and either phenomenon, not clearly supporting them as a direct cause for the Frasnian–Famennian event. This result highlights an urgent need for further Late Devonian geochronological and chemostratigraphic work to better understand the cause(s) of this extinction.

Highlights

The Late Devonian (∼383–359 Ma) marked a time of repeated environmental upheaval, featuring numerous carbon-cycle perturbations and local- to global-scale periods of marine anoxia during the Givetian (e.g., Frasnes Event), Frasnian (e.g., Punctata Event), and Famennian (e.g., Annulata Event) Stages
Microtektite layers have been reported from lower Famennian strata of both Belgian and Chinese records; a Late Devonian impact crater is well known from Sweden, with another in North America indicated by an impact breccia in Upper Devonian strata of Nevada (e.g.,33)
Constraining the timing of the Frasnian–Famennian (FF) mass extinction represents a crucial step in understanding the influence of external phenomena such as large-scale volcanism and meteor impacts in causing that event

Summary

Introduction

The Late Devonian (∼383–359 Ma) marked a time of repeated environmental upheaval, featuring numerous carbon-cycle perturbations and local- to global-scale periods of marine anoxia during the Givetian (e.g., Frasnes Event), Frasnian (e.g., Punctata Event), and Famennian (e.g., Annulata Event) Stages Two such episodes of environmental perturbation featured major faunal extinctions, documented at the Frasnian–Famennian and Famennian–Tournasian Stage Boundaries (reviewed by e.g.1,2). An excellent correlation between the determined ages of LIP volcanic events and times of mass extinction and major environmental perturbation has been established for latest-Palaeozoic through to early Cenozoic times (e.g.,35,38,39), and the end-Cretaceous extinction has been linked with a large extra-terrestrial impact (e.g.,40) In this context, the record of both large-scale volcanism and extra-terrestrial impacts occurring in the Late Devonian is intriguingly suggestive of a potential causal relationship between those phenomena and the many Late Devonian biotic and environmental crises, including the FF extinction. Because major LIP magmatic events and extra-terrestrial impacts can influence the Earth’s environment on the time scale of tens of millennia or less, a much greater degree of precision is desired for the age of the FF extinction, ideally to within

Results

Discussion

Conclusion