Mykotori

Timing and pacing of the Late Devonian mass extinction event regulated by eccentricity and obliquity

Abstract

The Late Devonian envelops one of Earth’s big five mass extinction events at the Frasnian–Famennian boundary (374 Ma). Environmental change across the extinction severely affected Devonian reef-builders, besides many other forms of marine life. Yet, cause-and-effect chains leading to the extinction remain poorly constrained as Late Devonian stratigraphy is poorly resolved, compared to younger cataclysmic intervals. In this study we present a global orbitally calibrated chronology across this momentous interval, applying cyclostratigraphic techniques. Our timescale stipulates that 600 kyr separate the lower and upper Kellwasser positive δ13C excursions. The latter excursion is paced by obliquity and is therein similar to Mesozoic intervals of environmental upheaval, like the Cretaceous Ocean-Anoxic-Event-2 (OAE-2). This obliquity signature implies coincidence with a minimum of the 2.4 Myr eccentricity cycle, during which obliquity prevails over precession, and highlights the decisive role of astronomically forced “Milankovitch” climate change in timing and pacing the Late Devonian mass extinction.

Introduction

Frasnian–Famennian (F–F) boundary sections around the world are often characterized by two horizons of dark bituminous shale, the so-called lower and upper Kellwasser horizons (LKW and UKW)1,2. Both layers coincide with a positive δ13C excursion, as recognized in North America, Morocco, Europe, Russia, western Australia, and southern China1,3,4,5,6,7,8,9,10. The worldwide incidence of Kellwasser horizons indicates a major perturbation of the global carbon cycle, and is associated with one of the most prominent mass extinction events in Earth history, primarily affecting tropical marine benthos11. Stromatoporoid and coral reefs were ubiquitous during the Middle to Late Devonian, but never truly recovered after the Late Devonian mass extinction. Despite this major reshuffling of the Earth’s system, the timing and pacing of the environmental changes responsible for the mass extinction remain poorly constrained. Recently, however, cyclostratigraphic efforts yielded constraints on the numerical ages of stage boundaries within the Devonian System12,13,14,15.

Read More: nature.com

DylanThomas

Add comment