Journal of Asian Earth Sciences 135 (2017) 70–79 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Multiple sulfur isotope records at the end-Guadalupian (Permian) at Chaotian, China: Implications for a role of bioturbation in the Phanerozoic sulfur cycle ⇑ Masafumi Saitoh a, , Yuichiro Ueno b,c, Fumihiro Matsu’ura b, Tetsuya Kawamura b, Yukio Isozaki d, Jianxin Yao e, Zhansheng Ji e, Naohiro Yoshida c,f a Research and Development (R&D) Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Natsushima-cho, Yokosuka 237-0061, Japan b Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan c Earth-Life Science Institute, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan d Department of Earth Science and Astronomy, The University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan e Geology Institute, Chinese Academy of Geological Science, Beijing 100037, China f Department of Chemical Science and Engineering, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan article info abstract Article history: A recent study on quadruple sulfur isotopes (32S, 33S, 34S, and 36S) of sedimentary pyrite suggested that Received 28 May 2016 the end-Guadalupian extinction was caused by shoaling of the sulfidic deep-water. This scenario is based Received in revised form 9 December 2016 on the assumption that sulfur isotopic compositions of pyrite from hosting sediments were controlled by Accepted 9 December 2016 benthos activities, thus by the redox conditions of the sedimentary environments. Nonetheless, the rela- Available online 18 December 2016 tionship between the sulfur isotope records and redox conditions, reconstructed from litho- and bio- facies, are poorly known. In order to examine the effect of bioturbation in sediments, quadruple sulfur Keywords: isotopic compositions of sedimentary pyrite from the end-Guadalupian succession in Chaotian, South Guadalupian China, were analyzed. Black mudstones of deep-water facies immediately below the extinction horizon Extinction D33 ‰ Quadruple sulfur isotope records have consistently high S values of ca. +0.079 , clearly suggesting a sulfate reduction in the anoxic Bioturbation water column. Our new data are consistent with the emergence of a sulfidic deep-water mass prior to Sulfate supply into sediments the end-Guadalupian extinction; the upwelling of the toxic deep-water may have contributed to the Sulfide burial extinction. In contrast, shallow-marine bioclastic limestones with burrows deposited under oxic condi- tions have negative D33S values. This anomalous isotopic signal indicates the mixing of two distinct types of pyrite; one generated during the sulfate reduction in an open system and the other in a closed system. We interpret that bioturbation supplied sulfate in the sediments and promoted sulfate reduction and in- situ sulfide precipitation within the sediments. The negative D33S values of oxic sediments in Chaotian are inconsistent with the previous model and demonstrate that the sedimentary sulfur cycle associated with bioturbation was more complicated than previously thought. Our study also implies that, more gen- erally, the role of bioturbation in increasing seawater sulfate concentration in the Phanerozoic may have been overestimated in the previous studies, because bioturbation may have enhanced sulfide burial or sulfur output from the oceans. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Around the Guadalupian-Lopingian (Late Permian) boundary (G- LB), several global-scale geologic phenomena occurred, such as The end-Paleozoic mass extinction was one of the largest biodi- the eruption of the Emeishan flood basalts in South China (Chung versity crises in the Phanerozoic (e.g., Erwin, 2006; Alroy, 2010) and Jahn, 1995; Zhou et al., 2002), the onset of prolonged deep- and had two phases: the biodiversity decline at the end- sea anoxia (Isozaki, 1997), a substantial global sea-level fall (Jin Guadalupian (ca. 260 Ma) and the abrupt extinction at the latest et al., 1994; Haq and Schutter, 2008; Kofukuda et al., 2014), the Permian (ca. 252 Ma) (Jin et al., 1994; Stanley and Yang, 1994). ‘Kamura’ cooling event (Isozaki et al., 2007, 2011), and authigenic carbonate precipitation (Grotzinger and Knoll, 1995; Saitoh et al., 2015). Many researchers have considered the Emeishan volcanism ⇑ Corresponding author at: 2-15 Natsushima-cho, Yokosuka 237-0061, Japan. as the leading candidate for the cause of the end-Guadalupian E-mail address: [email protected] (M. Saitoh). http://dx.doi.org/10.1016/j.jseaes.2016.12.009 1367-9120/Ó 2016 Elsevier Ltd. All rights reserved. M. Saitoh et al. / Journal of Asian Earth Sciences 135 (2017) 70–79 71 extinction (e.g., Wignall et al., 2009). However, the causal link cycle in the end-Guadalupian oceans at Chaotian, focusing on the between the global environmental changes and the extinction at redox conditions of the sedimentary environments and benthos the end-Guadalupian remains a topic of discussion (e.g., Clapham activity, and examines the main role of bioturbation in the oceanic et al., 2009; Bond et al., 2010; Jost et al., 2014). Recently, several sulfur cycle in the Phanerozoic. studies reported anoxic/sulfidic conditions in the oceans along the continental margins on a global scale at the end-Guadalupian (Schoepfer et al., 2012, 2013; Saitoh et al., 2013a, 2013b; Yan 2. Geological setting and stratigraphy et al., 2013; Zhang et al., 2015; Shi et al., 2016). The upwelling of the anoxic/sulfidic deep-waters may have contributed to the South China was located on the eastern side of Pangea at low end-Guadalupian biodiversity decline (Saitoh et al., 2014a). latitudes during the Permian (Fig. 1c; Scotese and Langford, Measurements of all four stable sulfur isotopes (32S, 33S, 34S, and 1995). On its extensive platform, shallow-marine carbonates and 36S) in geologic records are useful for understanding the evolution- terrigenous clastics with abundant fossils were thickly accumu- ary history of the ocean/atmosphere system (e.g., Farquhar et al., lated (Fig. 1d; Zhao et al., 1981; Jin et al., 1998). On a slope/basin 2000; Johnston, 2011). Coupled with photochemical experiments, setting in northern Sichuan along the northwestern edge of South this method has shed light on the characteristic sulfur cycle in China, carbonates and mudstones of relatively deep-water facies the Archean atmosphere (e.g., Ono et al., 2003; Ueno et al., 2008, were accumulated (Fig. 1d; Wang and Jin, 2000). The Chaotian sec- 2009, 2015). Moreover, the quadruple sulfur isotopic analysis of tion in northern Sichuan is located nearly 20 km north of the city of geologic records and products of microbial incubation experiments Guangyuan (32°370N, 105°510E; Fig. 1a; Isozaki et al., 2004, 2008; is useful for detecting the biogeochemical processes in the oceans Saitoh et al., 2013a, 2013b). At Chaotian, we mapped the eastern from the Proterozoic to the present (e.g., Farquhar et al., 2003; bank of the Jialingjiang River at a narrow gorge called Mingyuexia, Johnston et al., 2005; Aoyama et al., 2014). Shen et al. (2011) first where Middle Permian to lowermost Triassic carbonates are con- applied the analysis of quadruple sulfur isotopes to the end- tinuously exposed (Fig. 1b). Paleozoic mass extinction event. They analyzed carbonate rocks The Permo-Triassic rocks at Chaotian (>300 m thick in total) are across the Permian-Triassic boundary (P-TB) at the Meishan sec- composed of the Guadalupian Maokou Formation, Lopingian Wuji- tion, the Global Stratotype Section and Point (GSSP) for the P-TB, aping and Dalong formations, and lowermost Triassic Feixianguan in South China and suggested that the episodic shoaling of anoxic Formation, in ascending order (Fig. 3; Isozaki et al., 2008; Saitoh deep-water caused the latest Permian extinction. Recently, Zhang et al., 2013a, 2013b, 2014b). The Maokou Formation (>150 m thick) et al. (2015) analyzed the quadruple sulfur isotopic compositions consists mainly of massive dark gray bioclastic limestone with of carbonates across the G-LB at two sections in South China, diverse shallow-marine fossils such as calcareous algae, bra- including the Penglaitan section in Guangxi, the GSSP for the G- chiopods, crinoids, rugosa corals, and fusulines. The uppermost LB, and the EF section in west Texas, USA. Based on the results, part (11 m thick) of the formation is composed of thinly bedded Zhang et al. (2015) used the upwelling scenario proposed by black mudstone and chert with radiolarians and ammonoids. The Shen et al. (2011) to the end-Guadalupian case and suggested that Wujiaping Formation (70 m thick) is composed of massive dark the shoaling of sulfidic deep-waters contributed to the end- gray bioclastic limestone containing shallow-marine fossils such Guadalupian extinction. as fusulines, rugosa corals, and algae. The Dalong Formation The common and critical isotopic signal in Shen et al. (2011) (25 m thick) is dominated by bedded black siliceous mudstone 33 33 32 and Zhang et al. (2015) are negative D S (={( S/ S)sample/ with radiolarians and bedded limestone with ammonoids. The 33 32 34 32 34 32 0.515 ( S/ S)reference À [( S/ S)sample/( S/ S)reference] }) values of Feixianguan Formation (>30 m thick) is composed mainly of thinly pyrites in the analyzed rocks. This anomalous evidence indicates bedded light gray micritic limestone, which contains few con- the mixing of 34S-enriched and 34S-depleted sulfur (Ono et al., odonts and ammonoids. 2006). Both Shen et al. (2011) and Zhang et al. (2015) interpreted In the present study, we focus particularly on the 60 m thick that the negative D33S values of pyrites, and thus the mixing of sul- Middle–Upper Permian rocks, which are composed of the three fur from two different sources, recorded the shutdown of bioturba- stratigraphic units in the following ascending order: (1) the early tion in the sediments caused by shoaling of toxic (anoxic/sulfidic) Capitanian (Late Guadalupian) Limestone Unit of the Maokou For- deep-waters.