Carmichael, Sarah K., Waters, Johnny A., Königshof, Peter, Suttner, Thomas J. and Kido, Erika (2019) Paleogeography and paleoenvironments of the Late Devonian Kellwasser event: A review of its sedimentological and geochemical expression. Global and Planetary Change, 183 . Art.Nr. 102984. DOI 10.1016/j.gloplacha.2019.102984.

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Abstract

The Late Devonian (383-359 Ma) was a time of prolonged climate instability with catastrophic perturbation of global marine ecosystems at the Frasnian-Famennian (F-F) and the Devonian-Carboniferous (D-C) boundaries. The causes and mechanisms of anoxia and extinction at the F-F interval are not clearly delineated, and alternative explanations for virtually every aspect of this interval are still intensely debated. In many (but not all) locations, the F-F interval is characterized by two dark, organic-rich lithologies: the Lower and Upper Kellwasser beds (as originally described in Germany) that represent a stepwise ocean anoxia and extinction sequence. The Upper and Lower Kellwasser anoxia event beds are often collectively termed the Kellwasser Event, and the termination of this sequence is within the Upper Kellwasser Event at the F-F boundary. Current knowledge is limited by significant sampling bias, as most previous studies sampled epicontinental seaways or passive continental shelves, primarily from localities across Europe and North America. Together these formed a single equatorial continent with a rising mountain chain during the Late Devonian. Our understanding of the Kellwasser Event is thus based on data and observations from a restricted set of paleoenvironments that may not represent the complete range of Late Devonian environments and oceanic conditions. In the last decade, new methodologies and research in additional paleoenvironments around the world confirm that the Kellwasser Event was global in scope, but also that its expression varies with both paleoenvironment and paleogeography. Studying the many differing geochemical and lithological expressions of the Kellwasser Event using a) a wide variety of paleoenvironments, b) a multiproxy approach, and c) placement of results into the broader context of Late Devonian marine biodiversity patterns is vital for understanding the true scope of ocean anoxia, and determining the causes of the marine biodiversity crisis at the F-F boundary.

Highlights

• Bias in existing samples limits understanding of the Frasnian-Famennian biodiversity crisis and the Kellwasser anoxia event.

• The Kellwasser Event was global but its expression is highly dependent on paleoenvironment and paleogeography.

• The Kellwasser Event was due to "top-down" climate forcing with surface eutrophication not upwelling anoxic bottom water.

• The F-F crisis was a lack of species origination in environments with climate stress and changes in sediment/nutrient supply.

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