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Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction


During the latest Permian extinction about 250 Myr ago, more than 90% of marine species went extinct, and biogeochemical cycles were disrupted globally1. The cause of the disruption is unclear, but a link between the eruption of the Siberian Trap flood basalts and the extinction has been suggested on the basis of the rough coincidence of the two events2,3. The flood basalt volcanism released CO2. In addition, related thermal metamorphism of Siberian coal measures and organic-rich shales led to the emission of methane, which would have affected global climate and carbon cycling, according to model simulations2,3,4,5,6. This scenario is supported by evidence for volcanic eruptions and gas release in the Siberian Tunguska Basin6, but direct indicators of coal combustion have not been detected. Here we present analyses of terrestrial carbon in marine sediments that suggest a substantial amount of char was deposited in Permian aged rocks from the Canadian High Arctic immediately before the mass extinction. Based on the geochemistry and petrology of the char, we propose that the char was derived from the combustion of Siberian coal and organic-rich sediments by flood basalts, which was then dispersed globally. The char is remarkably similar to modern coal fly ash, which can create toxic aquatic conditions when released as slurries. We therefore speculate that the global distribution of ash could have created toxic marine conditions.

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Figure 1: Late Permian paleogeographic map showing location of the Buchanan Lake section and Siberian Traps volcanics.
Figure 2: Photomicrographs of combustion-derived isotropic chars.
Figure 3: Plot of S3 versus %TOC showing three distinct trends that relate to organic matter type.
Figure 4: Plot of vertical trends in key geochemical parameters across the LPE event at Buchanan Lake along with a lithostratigraphic column.

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L. Stasiuk and J. Potter provided valuable scientific input. Helpful comments from Norm Sleep are appreciated. Geological Survey of Canada GCS Contribution 20100284.

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S.E.G. collected field samples and conducted geochemical analyses, H.S. performed organic petrography, B.B. provided regional stratigraphic context.

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Correspondence to Stephen E. Grasby.

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The authors declare no competing financial interests.

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Grasby, S., Sanei, H. & Beauchamp, B. Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction. Nature Geosci 4, 104–107 (2011).

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