Reconstruction of Early Triassic ocean redox conditions based on framboidal pyrite from the Nanpanjiang Basin, South China Li Tian a,b , Jinnan Tong a, ⁎, Thomas J. Algeo a,c,d, ⁎⁎, Haijun Song a , Huyue Song a , Daoliang Chu a , Lei Shi a , David J. Bottjer b a State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, 430074, China b Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, USA c Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA d State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China abstract article info Article history: Received 4 February 2014 Received in revised form 30 June 2014 Accepted 15 July 2014 Available online 23 July 2014 Keywords: Early Triassic Redox conditions Ocean ventilation Marine productivity Recovery Widespread oceanic anoxia has been implicated as an important factor in the PTB (Permian Triassic boundary) mass extinction and the delayed recovery of Early Triassic marine ecosystems. An investigation of framboidal pyrite in the Bianyang section (Nanpanjiang Basin, South China) suggests that euxinia/dysoxia peaked during the Induan, late Smithian to earliest Spathian and late Spathian. These anoxic episodes show a relationship, albeit imperfect, to major episodes of climatic warming during the Early Triassic that were associated with intensified oceanic stratification, reduced marine productivity and organic carbon sinking fluxes, as well as diminished burial fluxes of organic carbon and reduced sulfur. In contrast, intervals of better-oxygenated marine conditions were associated with episodes of relative climatic cooling during the early to middle Smithian and mid-Spathian. The degree of ventilation of the thermocline region, in particular, had a profound effect on marine biotas, with intervals of improved ventilation resulting in increased global diversity among ammonoids and conodonts and increased local abundance of foraminifera in the Nanpanjiang Basin. These observations suggest that oceanic redox fluctuations played an important role in the delayed recovery of Early Triassic marine ecosystems, and, specifically, that episodic expansion of oceanic oxygen-minimum zones (OMZs) resulted in repeated setbacks to the recovery process, a pattern that persisted until the late Spathian. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Marine ecosystems are estimated to have taken ~ 5 Myr for recovery from the PTB mass extinction, the largest biocrisis of the Phanerozoic (Erwin, 1994; Bottjer et al., 2008; Chen and Benton, 2012; H.J. Song et al., 2013). The aftermath of this mass extinction was marked by unusual biotic and environmental consequences, including delayed marine ecosystem rebuilding, the Lilliput effect of reduced body size, the global spread of microbialites and other ‘anachronistic’ facies, and large perturbations of the global carbon cycle (Payne et al., 2004; Payne, 2005; Pruss et al., 2006; Baud et al., 2007; Tong et al., 2007a, b; Twitchett, 2007; Bottjer et al., 2008; Xie et al., 2010; Song et al., 2011a; Chen and Benton, 2012; H.J. Song et al., 2013). All of these developments are thought to have been triggered by the eruption of the Siberian Traps large igneous province (Campbell et al., 1992; Korte et al., 2010), whose attendant effects included volcanic gas emissions, high seawater surface temperatures, strong terrestrial weathering, oceanic anoxia/dysoxia, low seawater sulfate concentrations and ocean acidification (Wignall and Twitchett, 1996, 2002; Isozaki, 1997; Payne et al., 2007, 2010; Svensen et al., 2009; Algeo and Twitchett, 2010; Luo et al., 2010; Wignall et al., 2010; Algeo et al., 2011a; Black et al., 2012; Song et al., 2012a, 2012b; Sun et al., 2012; Romano et al., 2013; H.Y. Song et al., 2014; Pietsch and Bottjer, in press). Changes in marine redox conditions, especially the development of prolonged oceanic anoxia, are thought to have played a significant role in the PTB mass extinction and subsequent protracted recovery of marine ecosys- tems during the Early Triassic (Isozaki, 1997; Knoll et al., 2007; Algeo et al., 2011a; H.J. Song et al., 2014; Pietsch and Bottjer, in press). A number of studies have attempted to reconstruct changes in marine redox conditions during the crisis interval, mostly focusing on the PTB transition, based on biomarkers, carbon isotopes, sulfur isotopes, U isotopes and Mo isotopes (Wignall and Newton, 2003; Newton et al., 2004; Grice et al., 2005; Kaiho et al., 2006, 2012; Riccardi et al., 2006; Algeo et al., 2007, 2008; Gorjan et al., 2007; Gorjan et al., 2007; Riccardi et al., 2007; Xie et al., 2007; Liao et al., 2010; Nielson et al., 2010; Brennecka et al., 2011; Y.A. Shen et al., Palaeogeography, Palaeoclimatology, Palaeoecology 412 (2014) 68–79 ⁎ Correspondence to: J.N. Tong, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, 430074, China. Tel.: +86 27 67883450. ⁎⁎ Correspondence to: T.J. Algeo, Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA. Tel.: +1 513 556 4195. E-mail addresses: jntong@cug.edu.cn (J. Tong), algeot@ucmail.uc.edu (T.J. Algeo). http://dx.doi.org/10.1016/j.palaeo.2014.07.018 0031-0182/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo