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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Devonian of the World: Proceedings of the 2nd International Symposium on the Devonian System — Memoir 14, Volume III: Paleontology, Paleoecology and Biostratigraphy, 1988
Pages 29-34
Global Events and Boundaries

Late Devonian Mass Extinction: Episodic Climatic Cooling or Warming?

J. B. Thompson, C. R. Newton

Abstract

Many studies in physiological ecology of tropical to subtropical organisms have demonstrated an asymmetric thermal distribution, in which these marine organisms can tolerate a greater temperature drop than temperature rise. Climatic cooling, which has previously been hypothesized as the mechanism of the Frasnian-Famennian mass extinction, is not supported by existing δ18O data from the stratigraphic record. Therefore, we propose the alternative hypothesis that episodic climatic warming may have been responsible for the Frasnian-Famennian mass extinction. We propose that episodic climatic warming may have contributed to Late Devonian diversity losses via 1) direct thermal effects and 2) intensification and amplification of oxygenminimum zones during an extreme polytaxic oceanic mode.

The proposed model can explain both the protracted and the catastrophic elements of the Late Devonian marine crisis. Our model calls for an extreme polytaxic oceanic mode which includes a sea level highstand, widespread anoxia, and warm sea surface temperatures that are driven even higher over the short term into the upper lethal limits of many organisms via a climatic event (oceanic-atmospheric connection). Oxygen isotope studies of reported primary isotopic signals indicate markedly negative δ18O values for Late Devonian time; therefore present isotopic evidence is suggestive of warm seas, though it lacks detailed sampling across the boundary. Detailed primary isotopic sampling is needed from Givetian through Lower Carboniferous rocks to resolve this question.


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