Explosive eruption of coal and basalt and the end-Permian mass extinction

Abstract

The end-Permian extinction decimated up to 95% of carbonate shell-bearing marine species and 80% of land animals. Isotopic excursions, dissolution of shallow marine carbonates, and the demise of carbonate shell-bearing organisms suggest global warming and ocean acidification. The temporal association of the extinction with the Siberia flood basalts at approximately 250 Ma is well known, and recent evidence suggests these flood basalts may have mobilized carbon in thick deposits of organic-rich sediments. Large isotopic excursions recorded in this period are potentially explained by rapid venting of coal-derived methane, which has primarily been attributed to metamorphism of coal by basaltic intrusion. However, recently discovered contemporaneous deposits of fly ash in northern Canada suggest large-scale combustion of coal as an additional mechanism for rapid release of carbon. This massive coal combustion may have resulted from explosive interaction with basalt sills of the Siberian Traps. Here we present physical analysis of explosive eruption of coal and basalt, demonstrating that it is a viable mechanism for global extinction. We describe and constrain the physics of this process including necessary magnitudes of basaltic intrusion, mixing and mobilization of coal and basalt, ascent to the surface, explosive combustion, and the atmospheric rise necessary for global distribution.R ecent studies have brought the Great Dying at the end of the Permian Period into focus. Up to 95% of shell-bearing marine species and 80% of land animals perished (1, 2). The temporal association of the extinction with the Siberia flood basalts at approximately 250 Ma is well known (1-7), but a causal mechanism connecting the flood basalts to global extinction is not evident. The flows directly killed only those biota in their path, and basalt is not a massive source of greenhouse gases such as CO 2 (8). Recent studies suggest flood basalts may have mobilized carbon in thick deposits of organic-rich sediments, resulting in global climate change and extinction (4,5,7,(9)(10)(11)(12)(13). New work also suggests magmatic release of CO 2 from mantle-derived eclogite as a potential extinction mechanism (14). Svensen et al. (15) were the first to discuss the mechanism by which basaltic interaction with organic sediments may cause mass extinction through explosive release of methane. McElwain et al. (16) expanded on this idea by linking the intrusion of KarooFerrar magmas into coal with the 183 Ma Toarcian oceanic anoxic event. In this model, basaltic intrusions metamorphosed sediments driving off hydrocarbons, including methane, which quickly oxidized to carbon dioxide (CO 2 ) and water. This sudden release of organic carbon acidified the ocean and caused a ∂ 13 C excursion in the sedimentary record.Retallack and Jahren (5) applied a similar idea linking basaltic intrusion of coal seams in Siberia to the late Permian extinction. Their study focused on this mechanism as an explanation for the large, short-term carbon isotopic excursions ...

Methanogenic burst in the end-Permian carbon cycle

“…However, quantitative estimates of direct volcanic outgassing are much too small to account for the changes in the carbon cycle (9). Secondary effects of Siberian volcanism, such as the combustion of huge deposits of coal (10) or other forms of organic carbon (11), are more attractive quantitatively but still difficult to reconcile with observed geochemical changes (1)(2)(3)(4)(5)(6). Reports of marine anoxia in the Late Permian (5,12,13) also indicate changes in the carbon cycle.…”

A cold, hard look at ancient oxygen

“…In fact, diminished postglacial primary production was recently called upon to explain the large 17 O anomalies at 635 million years ago in an atmosphere not much more CO 2 -rich than today's (7). The basic argument is that if primary production were weaker, photosynthetic O 2 fluxes would be (7), very different from the CO 2 -rich postglacial atmosphere that had been originally proposed (5,6).…”

“…Although the identification of elevated atmospheric CO 2 levels as Earth exited a hypothesized snowball state was a compelling and notable achievement, the relative 17 O anomaly in atmospheric O 2 is not only a function of atmospheric CO 2 levels. Photosynthetic O 2 is characterized by isotopically "normal" oxygen sourced from the global hydrosphere (9).…”

“…Photosynthetic O 2 fluxes directly reflect global primary production (the amount of photosynthetically fixed carbon available for initial heterotrophic consumption in the global ecosystem). Primary production, therefore, was another potential control knob that could have amplified or suppressed postglacial 17 O anomalies.…”

“…The original isotopic work was motivated by an empirical correlation between CO 2 concentrations and deficiencies in the rarest oxygen stable isotope, 17 O, in O 2 in samples of ancient atmospheres preserved as bubbles in ice cores (9,10 O anomalies in unique post-Marinoan rocks are larger than at any other time in Earth history and, under the framework laid out above, originally seemed to require CO 2 levels ∼30-to 200-times larger than in the current atmosphere (5,6). Although the identification of elevated atmospheric CO 2 levels as Earth exited a hypothesized snowball state was a compelling and notable achievement, the relative 17 O anomaly in atmospheric O 2 is not only a function of atmospheric CO 2 levels.…”