Latest Permian chars may derive from wildfires, not coal combustion

Abstract

7The Permian-Triassic extinction event was the largest biocrisis of the Phanerozoic. One 8 of the principle triggers for the 'big dying' is thought to be greenhouse warming resulting from 9 the release of CH 4 from basalt-coal interaction during the extensive Siberian Trap eruptions. 10Observations of organic matter interpreted to be coal combustion products (fly ash) in latest 11Permian marine sediments have been used to support this hypothesis. However, this 12 interpretation is dependent upon vesicular chars being fly ash (coal combustion-derived) and not 13 formed by alternative mechanisms. Here we present reflectance microscopy images of vesicular 14 chars from Russian Permian coals, as well as chars from modern tundra, peatland and boreal 15forest fires, to demonstrate that despite a difference in precursor fuels, wildfires are capable of 16 generating vesicular chars that are morphologically comparable to end Permian 'fly ash'. These 17 observations, coupled with extensive global evidence of wildfires during this time interval calls 18 into question the contribution of coal combustion to the end Permian extinction event. 19 INTRODUCTION 20The Permian-Triassic boundary event decimated 80-96% of marine and 70% of terrestrial 21 life and is marked in the geological record by a significant 2-8‰ negative organic and carbonate 22Publisher: GSA Journal: GEOL: Geology Article ID: G35920Page 2 of 15 δ 13 C excursion (Chen and Benton, 2012). One suggestion is that massive greenhouse warming 23 (Erwin, 1994) led to the most significant mass extinction event ever to occur on our planet. One 24 of the greenhouse contributors is thought to have been extensive CH 4 release from the 25 combustion of coals and organic-rich shales, during the emplacement of shallow intrusions, as 26 part of the Siberian Trap eruptions (Retallack and Jahren, 2008; Grasby et al., 2011; Ogden and 27 Sleep, 2012). 28In modern coal-fired power stations char is produced during high temperature 29 combustion of pulverized coal. The coals undergo complex physical and chemical 30 transformations, giving off volatiles and producing solid residues (char). The resulting char 31 (termed 'coal fly ash' in Grasby et al. (2011)) is highly variable depending on the organic 32 constituents of the precursor coal (Bailey et al., 1990; Yu et al., 2007; Lester et al., 2010), and 33 the morphology of the char ranges from solid to vesicular. Vesicular chars in particular, in Late 34Permian sediments from Lake Buchanan in Arctic Canada have been interpreted as definitive 35 evidence of coal combustion. These chars represent the only physical indicator of coal 36 combustion outside of Siberia and have been used extensively as evidence for global dispersal of 37 coal fly ash at the end Permian extinction event (Grasby et al., 2011; Ogden and Sleep, 2012; 38 Sanei et al., 2012; Knies et al., 2013; Kerr, 2013). In order to transport these coal combustion 39 chars 20,000 km from the Siberian Trap source, models imply that explosive interactions of coal ...

Transition into a Hothouse World at the Permian–Triassic boundary—A model study

“…The lower cloud optical depth as simulated in this study leads to a global average temperature increase of 4.5 °C, with extreme regional temperatures of >38 °C in the Tethys Ocean (Joachimski et al, 2012;2014) and >50 °C on land and an increase in vertical stratification in the ocean, resulting in an expansion of the oxygen minimum zone and low oxygen environments (Hallam and Wignall, 1997;Isosaki et al, 1997;Knollet al, 1996;Ward et al,2001;Wignall et al, 1996;Hallam, 1992, 1993;Wignall and Newton, 2003;Wignall and Twitchett, 2002). The processes described above act on relatively short timescales,with low productivity during the early Triassic (in the aftermath of the PTB extinction) resulting in reduced DMS emissions, thus favoring lower CCN concentrationsand hothouse conditions during that time.On longer timescales,however, an increase in the marine nutrient inventory due to weathering intensification by global warming, increased rain fall, and acid rain (Black et al, 2014), followed by soil erosion (Sephton et al, 2005) that is also enhanced by forest fires (Hudspith et al, 2014),would ultimately lead to enhanced marine productivity (Algeo et al, 2011)and anoxia (Meyer et al, 2008;Winguth and Winguth, 2012;Grasby et al, 2013).An associated rise in DMS emissions from the ocean and the resulting increase in cloud albedo by higher CCN concentrations would counteract the warming and weathering (Fig. 10).…”

A tale of two extinctions: converging end-Permian and end-Triassic scenarios

“…At Meishan the most dominant PAH are the 3- and 4-ring unsubstituted PAHs such as phenantrene, chrysene and benzo(e)pyrene, while the HMW PAHs (including coronene) occur in very low abundance. A volcanic link for fly-ash occurrences in Arctic Canada (Grasby, Sanei & Beauchamp, 2011) has recently been called into question by Hudspith, Rimmer & Belcher (2014) based on observations that peat-burning can also produce similar vesiculated chars. It should however be stressed that massive flood basalt volcanism producing pyrogenic substances (PAH, soot) does not exclude the simultaneous raging of forest fires; in some instances, volcanism is in fact the likely trigger for widespread forest fires.…”

Fires in the mire: repeated fire events in Early Permian ‘peat forming’ vegetation of India

“…Since Scott (2000) published a seminal review of the up to then accumulated knowledge about pre-Quaternary palaeowildfires, in which was reported that only scattered data would hint at Permian fires, many studies on Permian wildfires, primarily with a focus on the northern hemisphere, have added a lot of knowledge about the issue (e.g. Wang and Chen, 2001;Uhl and Kerp, 2003;Noll et al, 2003;Uhl et al, 2004Uhl et al, , 2008Uhl et al, , 2012DiMichele et al, 2004;Shen et al, 2011Shen et al, , 2012Shao et al, 2012;Hudspith et al, 2012Hudspith et al, , 2014.…”