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Reply to Comment by Ali, J.R. and Wignall, P. on Ota, A. and Isozaki, Y., 2006

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Reply to Comment by Ali, J.R. and Wignall, P. on Ota, A. and Isozaki, Y., 2006 Journal of Asian Earth Sciences 30 (2007) 201–203 www.elsevier.com/locate/jaes Reply to Comment by Ali, J.R. and Wignall, P. on Ota, A. and Isozaki, Y., 2006. Fusuline biotic turnover across the Guadalupian–Lopingian (Middle–Upper Permian) boundary in mid-oceanic carbonate buildups: Biostratigraphy of accreted limestone, Japan. Journal of Asian Earth Sciences 26, 353–368 Yukio Isozaki *, Ayano Ota Department of Earth Science and Astronomy, The University of Tokyo, Tokyo 153-8902, Japan Received 19 October 2006; accepted 15 November 2006 We appreciate the comment by Ali and Wignall, as it Wuchiapingian (Lower Lopingian) Wujiaping Formation provides us with an appropriate opportunity to explain in its type locality in Shaanxi (Lu, 1956; Isozaki et al., in the link between volcanism and extinction at the Guadalu- preparation), in Sichuan (Isozaki et al., 2004), and in pian–Lopingian boundary (G–LB) event that was not the Hunan (Li et al., 1991), indicating no survival of the Guad- main topic of the commented article (Ota and Isozaki, alupian fauna after the Wangpo volcanism. This unique 2006). Continental flood basalts (CFB) have often been bed is also recognized at Qingying and at Xinchang near regarded as the ultimate cause of mass extinctions on Mt. Emei(shan) in central Sichuan; above the Maokou account of their apparent chronological coincidence with Formation and below the Emeishan Traps (Fig. 1). As the extinction-related boundaries of the Phanerozoic (e.g., no other thick tuff occurs around the G–LB horizon in Courtillot, 1999; Wignall, 2001; Ernst and Buchan, 2003). South China, the Wangpo tuff represents a prime strati- For the Permo-Triassic boundary (P-TB), the Siberian graphical and chronological marker bed of the G–LB with Traps are the most popular candidate (e.g., Renne and high-precision synchronism. In addition, a 0.8 m-thick Basu, 1991; Campbell et al., 1992; Kamo et al., 2003; Saun- mudstone/sandstone with plant fossils (Pecopteris sp. iden- ders et al., 2005; Racki and Wignall, 2005). As to the G–LB tified by T. Ohana; unpublished data) occurs immediately extinction, the Emeishan Traps in western South China above the Wangpo bed and below the Emeishan basalt at and the Panjal Traps in northern India are likewise favored Qingying, suggesting an appreciable time-gap between the by many because of their apparent coincidence in timing termination of the Guadalupian fossiliferous carbonates (e.g., Chung et al., 1998; Zhou et al., 2002; Ali et al., 2002). and the basalt eruption. These stratigraphic relationships In our research focused on the G–LB extinction, we indicate that felsic volcanism of regional extent occurred have emphasized the geological significance of a felsic tuff considerably before the main eruption of the Emeishan called the Wangpo bed (1–2 m-thick) in South China and Traps, and that the G–LB extinction was caused unlikely its correlatives in the accretionary complexes in Japan (Iso- by the trap volcanism. zaki and Ota, 2001; Isozaki et al., 2004; Ota and Isozaki, Second, recent geochronology of the Emeishan Traps 2006; Isozaki, 2006). Here, we wish to disagree in four ways has identified that the main eruption age was at with the comment by Ali and Wignall who favor a direct 256–259 Ma (Zhou et al., 2002), whereas age constraints cause–effect link between the Emeishan volcanism and for the Panjal Traps are insufficient for precise correlation. the G–LB extinction. First, the Wangpo bed occurs The age of the G–LB mass extinction has not yet been between the Guadalupian Maokou Formation and the tightly constrained yet; however, an age of 260.4 ± 0.7 Ma was proposed by Gradstein et al. (2004). Thus, the current data indicate that the trap volcanism apparent- * Corresponding author. Tel.: +81 3 5454 6608. ly postdated the mass extinction by 1–4 Myr. This age gap E-mail address: [email protected] (Y. Isozaki). may have been much greater, because the G–LB horizon is 1367-9120/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2006.11.004 202 Y. Isozaki, A. Ota / Journal of Asian Earth Sciences 30 (2007) 201–203 Liangshan Chaotian Qingying Xinchang S. Shaanxi N. Sichuan C. Sichuan C. Sichuan Wujiaping Emeishan Fm Traps Lopingian 1.2 m shale 0.8 m 0.7 m 2.0 m 2.2 mWangpo tuff 0.7 m 0.8 m G-LB extinction Maokou Fm Maokou Fm Guadalupian Fig. 1. Schematic correlation diagram showing the stratigraphic horizon of the Wangpo ‘‘tuff’’ bed in South China with respect to the Maokou Formation, Wujiaping Formation, and the Emeishan Traps (compiled from Lu, 1956; Isozaki et al., 2004; unpublished data). Columnar sections are not to scale. defined by the first appearance datum (FAD) of a new Siberian Traps was defined as 251.7 ± 0.4 Ma by Kamo conodont taxon that belongs to the Wuchiapingian fauna et al. (2003), whereas the age of the P-TB extinction was in Guanxi (Jin et al., 1998). Judging from the information dated as 252.4 ± 0.3 Ma at Meishan or 252.6 ± 0.2 Ma at in mid-oceanic paleo-atoll carbonates (Ota and Isozaki, Shangsi (Mundil et al., 2004). We admit that there is still 2006), the main extinction horizon of the Guadalupian fau- an appreciable gap between the extinction and CFB volca- na is located at a much lower stratigraphic horizon below a nism with respect to the error range, and that the extinction post-extinction barren interval. Our current dating project apparently predated the basalt volcanism by 1–2 Myr. will define the precise eruption age of the Wangpo tuff. Even though the Siberian Traps are associated with felsic Third, we did not ignore that some andesitic basalt and volcanics in hig1her stratigraphic horizons, they also could rhyolite units occur within the Emeishan traps. Their not be the source of the P-TB tuffs in South China. occurrence is confined, however, to the middle–upper part In all previous proposals on possible cause–effect rela- of the traps, not to the basal parts (e.g., Xu et al., 2001)as tionships, the absence of material-based hard evidence that Ali and Wignall mentioned. This higher stratigraphic por- directly links the extinction with the CFB volcanism tion of the felsic units within the traps contradicts with the remains a major obstacle regardless of the credibility of above-mentioned tuff stratigraphy. Moreover, these felsic coincidence in mutual timing. The boundary felsic tuffs in units are too small in volume to account for the entire wide South China and Panthalassa represent the only available extent of the regional ash fall (the Wangpo tephra) over hard evidence that can link volcanism with the two major South China (e.g., 1–2 m in thickness in Shaanxi, Sichuan, mass extinctions at the end of the Paleozoic; therefore, Hunan) and western Panthalassa (1 cm). their unique felsic composition needs a more detailed scru- Fourth, as to the main basaltic volcanism of the Emei- tiny. The petrological characteristics and geochronology of shan Traps, a global warming appears like the most prom- the Wangpo tuff will be reported elsewhere shortly (Isozaki ising kill mechanism (Wignall, 2001; Racki and Wignall, et al., in preparation). 2005) when we assume the cause–effect link between volca- nism and extinction. In this case, the expected volcanogenic Acknowledgements greenhouse effect should have started in the main phase of the volcanism, however, this contradicts with the lately The research in South China was funded by a grant-in- documented fusuline extinction pattern during a cool peri- aid of Japan Society of Promoting Sciences (No. od (Kamura event) in the low-latitude Panthalassa prior to 16204040). Jianxin Yao, Noriei Shimizu, and Zhansheng a warming (Isozaki et al., 2007) and with low sea-level in Ji collaborated in fieldwork in South China. Tami Ohana the late Guadalupian (Hallam and Wignall, 1999). identifed the plant fossil. The language was checked by According to the above discussion, the Emeishan Traps Brian F. Windley. were neither a likely source of the G–LB felsic tuff nor the ultimate cause of the G–LB extinction. This suggests that References we must identify another source for the volcanism, a felsic one in particular, at the end of the Guadalupian. A similar Ali, J.R., Thompson, G.M., Song, X.Y., Wang, Y.L., 2002. Emeishan situation exists at the P-TB. The initial eruption age of the basalts (SW China) and the ‘end-Guadalupian’ crisis: magnetobio- Y. Isozaki, A. Ota / Journal of Asian Earth Sciences 30 (2007) 201–203 203 stratigraphic constraints. Journal of Geological Society, London 159, Kamo, S.L., Czamanske, G.K., Amelin, Y., Fedorenko, V.A., Davis, 21–29. D.W., Trofimov, V.R., 2003. Rapid eruption of Siberian flood- Campbell, I., Czamanske, G.K., Fedorenko, V.A., Hill, R.I., Stepanov, volcanic rocks and evidence for coincidence with the Permian–Triassic V., 1992. Synchronism of the Siberian traps and the Permian–Triassic boundary and mass extinction at 251 Ma. Earth and Planetary Science boundary. Science 258, 1760–1763. Letters 214, 75–91. Chung, S.L., Jahn, B.M., Wu, G.Y., Lo, C.H., Cong, B.L., 1998. The Li, Z.S., Zhan, L.P., Yao, J.X., Zhou, Y.Q., 1991. On the Permian– Emeishan flood basalt in SW China: a mantle plume initiation model Triassic events in South China – probe into the end-Permian abrupt and its connection with continental breakup and mass extinction at the extinction and its possible causes. Proceeding of Shallow Tethys Permian–Triassic boundary. American Geophysical Union Geody- (Sendai) 3, 371–385.
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