Shaking a methane fizz: Seismicity from the Araguainha impact event and the Permian–Triassic global carbon isotope record E. Tohver a, ⁎, P.A. Cawood a,b , C. Riccomini c , C. Lana d , R.I.F. Trindade c a School of Earth & Environment, University of Western Australia, Australia b St. Andrews University, Scotland, United Kingdom c Universidade de São Paulo, Brazil d Universidade Federal de Ouro Preto, Brazil abstract article info Article history: Received 22 May 2012 Received in revised form 8 July 2013 Accepted 11 July 2013 Available online 18 July 2013 Keywords: Permian–Triassic mass extinction Impact event Carbon isotope excursion Seismicity Methane The Late Permian and Early Triassic periods are marked by large fluctuations in the carbon isotope record, but the source(s) of the disturbance to the global carbon cycle and the link to the end-Permian mass extinction are wide- ly debated. This contribution explores the possible isotopic effects of an impact event into the hydrocarbon-rich rocks of the Paraná–Karoo Basin. Recent U–Pb and 40 Ar/ 39 Ar dating of the 40 km Araguainha impact structure of central Brazil reveals an age of 254.7 ± 2.5 Ma (2σ error) for this event. The calculated energy (10 5 –10 6 MT of TNT equivalent) released by this impact is less than threshold values of 10 7 –10 8 MT TNT equivalent for global mass extinctions. Thus, the Araguainha crater is unlikely to have been the cause of the end-Permian biotic crisis. However, the combined seismic effects from the impact itself and the post-impact collapse of the 20–25 km diameter transient crater to its present 40 km diameter would result in large magnitude earthquakes (M w 9.3–10.5) and tsunamis in the shallow marine Paraná–Karoo Basin. Slope failure and sediment liquefaction are predicted to have occurred within a 700–3000 km radius of the crater, causing large-scale release of methane from organic-rich sediments of this basin, including the oil shale horizons of the Iratí Formation. New geological evidence for seismicity in the Paraná Basin at the time of impact is presented, together with a compilation of existing carbon isotope data from the Paraná Basin, which demonstrate a widespread pattern of disturbance consistent with the release of methane. These two datasets suggest that both seismicity and methane release took place within ca.1000 km of the impact site, with mass balance calculations suggesting ca. 1600 GT of methane were released into the atmosphere at this time. Methane release at this scale would have significant climate effects and would contribute to a sharp (b 1 ka) negative shift in δ 13 C values at the time of the impact, which should be distinguishable from the more gradual shift over 0.5–1 Ma caused by contemporaneous intrusion of the Siberian traps. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The end-Permian mass extinction is the largest of the five mass extinctions that punctuate the Phanerozoic record of life on Earth (Raup and Sepkoski, 1982; Erwin et al., 2002; Alroy et al., 2008). The integration of U–Pb geochronology, isotope chemostratigraphy, and biostratigraphy have been critical in defining a globally synchronous Permian–Triassic horizon (e.g., Bowring et al., 1998), which is followed by the first appearance of the basal Triassic conodont Hindeodus parvus (Yin et al., 2001). High precision U–Pb analysis of zircon from volcanic ash layers establishes the 252.6 ± 0.2 Ma timing of the biotic crisis in the marine realm (Mundil et al., 2004), redefined by Shen et al. (2011) to 252.28 ± 0.06 Ma. The carbon isotope record demonstrates a large decrease in 13 δC of seawater at this time (Korte and Kozur, 2010), with perturbation continuing into Early Triassic times (Payne et al., 2004; Xie et al., 2007; Tanner, 2010). The global nature of the car- bon isotope record (Baud et al., 1989; Korte and Kozur, 2010) has been established by studies of high latitude, Gondwanan sites, e.g., New Zealand (Krull et al., 2000), Antarctica (Krull and Retallack, 2000), and South Africa (MacLeod et al., 2000), equatorial sites in the Panthalassan Ocean (e.g., Japan; Algeo et al., 2008), as well as middle to low latitude Tethyan sites including the European Alps, Iran, and the type section in Meishan, eastern China (Magaritz et al., 1992; Wang et al., 1994; Jin et al., 2000; Xie et al., 2007; Cao et al., 2009). The recent U–Pb and 40 Ar/ 39 Ar dating of the impact melts from the 40 km Araguainha structure at 254.7 ± 2.5 Ma establishes the Permian–Triassic age of a mid-sized impact event (Tohver et al., 2012). The most lethal effects of meteorite impacts are caused by the sun-blocking blanket of ejecta in the upper atmosphere, resulting in the catastrophic collapse of primary productivity, known as the “nuclear winter” scenario (Toon et al., 1997). Global die-off can ensue from im- pacts that release N 10 6 Mt TNT equivalent of energy, which is estimated from crater size; e.g., the 180 km diameter Chicxulub crater released Palaeogeography, Palaeoclimatology, Palaeoecology 387 (2013) 66–75 ⁎ Corresponding author. Tel.: +61 8 6488 2677. E-mail address: eric.tohver@uwa.edu.au (E. Tohver). 0031-0182/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.palaeo.2013.07.010 Contents lists available at SciVerse ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo