The Guadalupian–Lopingian boundary mudstones at Chaotian (SW China) are clastic rocks rather than acidic tuffs: Implication for a temporal coincidence between the end-Guadalupian mass extinction and the Emeishan volcanism Bin He a , Yi-Gang Xu a, ⁎, Yu-Ting Zhong a,b , Jun-Peng Guan a,b a Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China b Graduate University of Chinese Academy of Sciences, Beijing, China abstract article info Article history: Received 31 October 2009 Accepted 6 June 2010 Available online 12 June 2010 Keywords: Geochemistry Mineralogy XRD Mudstone, Chaotian The ELIP, end-Guadalupian mass extinction Previous studies on the temporal link between the end-Guadalupian mass extinction event and Emeishan flood volcanism were mainly based on geochronological and bio- and chemostratigraphic correlation techniques (Wignall et al., 2009). The absence of material-based hard evidence that directly links the extinction with the Emeishan volcanism remains a major obstacle regardless of the indication of coincidence in timing (Isozaki et al., 2007). The Emeishan basalts overlie Permian platform carbonates that may contain a record of the end- Guadalupian mass extinction and erosional product of this province. This paper presents mineralogy and geochemistry of mudstones from the Guadalupian–Lopingian Boundary (G–LB) at Chaotian, SW China. Results indicate that these G–LB mudstones are not air-fall acidic tuff as previously thought, but likely represent clastic rocks derived from erosional deposits of the Emeishan large igneous province (ELIP). Mudstones of the lower part (Group 1) have a geochemical affinity to the Emeishan felsic volcanic rocks, whereas mudstones of the upper part (Group 2) are compositionally akin to mafic components of the Emeishan traps. This chemostratigraphic sequence resembles the Xuanwei Formation which sits on the Emeishan basalts (He et al., 2007). These data therefore indicate that the lower part of the mudstones at the Chaotian G–LB section, the lowermost part of Xuanwei and Longtan Formations and the Emeishan felsic extrusives broadly constitute an isochron horizon throughout the ELIP and adjacent region, suggesting a short duration for the Emeishan volcanism. A temporal coincidence between Emeishan volcanism and the end-Guadalupian mass extinction are therefore inferred thus providing support for a cause-and-effect relationship. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The temporal link between mass extinction events and large igneous province (LIP) volcanism is one of the most intriguing relationships in Earth's history (Courtillot et al., 1999; Wignall, 2001), with the end-Permian extinction–Siberian Traps association being the most examined (Wignall et al., 2009). In recent years the end- Guadalupian event, at the Middle–Late Permian boundary, has become a subject of great interest. Based on stratigraphic constraints, Courtillot et al. (1999) and Hallam and Wignall (1999) independently proposed that the end-Guadalupian mass extinction coincided with the ELIP in SW China. This notion gained support from a number of geochronological data from mafic dykes (Zhou et al., 2002; Guo et al., 2004; Zhong and Zhu, 2006), mafic lavas (Fan et al., 2004), felsic and alkaline intrusives (Zhong et al., 2007; Luo et al., 2007; Xu et al., 2008) and felsic extrusives and their erosional products (He et al., 2007). However, the temporal link between the end-Guadalupian mass extinction and the ELIP is still a matter of debate (Ali et al., 2005). Former geochronological correlation techniques with inherent timing inaccuracies make this link uncertain (Isozaki and Ota, 2007; Wignall et al., 2009). Secondly, this absence of material-based hard evidence that directly links the extinction with the LIP volcanism remains a major obstacle regardless of the credibility of the coincidence in timing (Isozaki et al., 2007, Isozaki and Ota, 2007). Isozaki's group recently argued, based on the study of the Guadalupian–Lopingian Boundary (G–LB) mudstones and its regional correlation, that the Emeishan flood volcanism postdated the end-Guadalupian mass extinction (Ota and Isozaki, 2006; Isozaki et al., 2007; Isozaki, 2007; Isozaki and Ota, 2007). One key point for this argument is the interpretation of an altered, acidic volcanic ash layer as the origin for the G–LB mudstones (Isozaki et al., 2004). However firm evidence has not yet been demon- strated. The ELIP in southwest China was emplaced on a Permian carbonate platform, which may have preserved the marine bio- extinction record and the erosional products of the ELIP. Sections of the platform along the margins of the ELIP thus may provide an oppor- tunity to evaluate the temporal relationship between the extinction and the Emeishan volcanism. To clarify these relations, we have examined the mineralogy and geochemistry of mudstones at Chaotian Lithos 119 (2010) 10–19 ⁎ Corresponding author. E-mail address: yigangxu@gig.ac.cn (Y.-G. Xu). 0024-4937/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2010.06.001 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos