This is a repository copy of Seawater carbon and strontium isotope variations through the late Ediacaran to late Cambrian in the Tarim Basin. White Rose Research Online URL for this paper: https://eprints.whiterose.ac.uk/160491/ Version: Accepted Version Article: Zhang, Y, Yang, T, Hohl, SV et al. (6 more authors) (2020) Seawater carbon and strontium isotope variations through the late Ediacaran to late Cambrian in the Tarim Basin. Precambrian Research. 105769. p. 105769. ISSN 0301-9268 https://doi.org/10.1016/j.precamres.2020.105769 © 2020, Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/. Reuse This article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) licence. This licence only allows you to download this work and share it with others as long as you credit the authors, but you can’t change the article in any way or use it commercially. 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Hohl2*, Bi Zhu3, Tianchen He4,5, Wenqing Pan6, 4 Yongquan Chen6, Xizhu Yao1, Shaoyong Jiang1,7 5 6 1State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing, PR 7 China; 8 2State Key Laboratory of Marine Geology, School of Ocean and Earth Science, Tongji 9 University, Shanghai, PR China; 10 3School of Earth Sciences and Engineering, Hohai University, Nanjing, PR China; 11 4School of Earth and Environment, University of Leeds, Leeds, UK; 12 5State Key Laboratory of Palaeobiology and Stratigraphy & Center for Excellence in Life 13 and Paleoenvironment, Nanjing Institute of Geology and Palaeontology, Chinese Academy of 14 Sciences, Nanjing, PR China; 15 6Research Institute of Exploration and Development, Tarim Oil Field Company, PetroChina, 16 Korla, PR China; 17 7State Key Laboratory of Geological Processes and Mineral Resources, School of Earth 18 Resources, China University of Geosciences, Wuhan, PR China; 19 20 * Corresponding authors: Tao Yang and Simon V. Hohl 21 Emails: [email protected] and [email protected] 22 Postal address: Nanjing University Xianlin Campus, No.163 Xianlin Avenue, Qixia District, 23 Nanjing, 210046, PR China. 24 25 26 2nd Revised version for submission to Precambrian Research April 2020 27 Abstract 28 The radiation of early animals during the Cambrian explosion was accompanied by 29 widespread perturbations in oceanic and atmospheric conditions. However, the cause-effect 30 relationships between evolutionary innovations, carbon (C) cycling, and continental 31 weathering are still a matter of debate. Further paleoenvironmental reconstructions of poorly 32 studied paleo-continents covering the Precambrian/Cambrian (PC/C) transition may improve 33 the correlation of the events and their impact on the Earth system on a global scale. The Tarim 34 Basin was presumably located proximal to the well-studied South China craton during the 35 Ediacaran-Cambrian boundary and is expected to contribute equally to our 36 paleoenvironmental reconstructions. Here we apply carbon and strontium (Sr) isotope records 37 (δ13C and 87Sr/86Sr) obtained from well-preserved marine carbonates spanning the late 38 Ediacaran to the late Cambrian from the Keping region in the northwestern Tarim Basin, NW 39 China. By comparison to other carbonate successions from various paleo-continents, our 40 obtained seawater 87Sr/86Sr curve in this study shows a stepwise first-order increase to more 41 radiogenic values superimposed by second-order presumably regional variations. Our 42 obtained δ13C variations exhibit four prominent negative and three positive excursions 43 identical to the global δ13C record. Based on existing paleontological evidence and our new 44 Tarim δ13C and 87Sr/86Sr curves, we propose a stratigraphic correlation from the late Ediacaran 45 to the late Cambrian between the Tarim Basin and other paleo-continents. Besides, our 46 paleoenvironmental reconstruction reveals both regional and global sea-level changes that 47 may have controlled the influx of radiogenic Sr and presumably the influx of nutrients 48 controlling primary production and the rate of organic carbon burial in the Tarim Basin at the 49 time of deposition. These feedbacks may have ultimately influenced the rapid diversification 50 of metazoans and the oxygenation of the Cambrian ocean and atmosphere approaching- 51 present pO2 levels. 52 Keywords: Carbon isotopes, Strontium isotopes, Ediacaran-Cambrian, Tarim Basin, 53 Paleoenvironment 54 55 1. Introduction 56 57 The transitional interval between the terminal Proterozoic and the early Paleozoic is 58 marked by the sudden appearance of abundant and diverse metazoans (Valentine et al., 1999; 59 Conway-Morris, 2003; Maloof et al., 2010; Kouchinsky et al., 2011). This early animal evolution 60 was accompanied by extensive perturbations to climate, carbon (C) cycling, continental 61 weathering and changes to the composition of the oceans (Shields-Zhou and Zhu, 2013). 62 However, the cause-effect relationships between this evolutionary innovation and these 63 environmental perturbations are still a matter of broad scientific debate and 64 paleoenvironmental reconstructions of less studied paleo-continents covering the 65 Precambrian/Cambrian (PC/C) transition can help this situation. Most studies from China 66 covering this interval focus on sedimentary successions in South China. For instance, Li et al. 67 (2013) suggested that muted continental weathering during the early Cambrian was indicated 68 by decreasing seawater strontium isotope ratios (87Sr/86Sr). Ediacaran-Cambrian marine 69 carbonate successions outcropping in the Tarim Basin were deposited on a shallow-water 70 continental shelf, which was presumably situated close to the South China craton and at a 71 similar low-middle latitude position (Fig. 1A) (McKerrow et al., 1992; Merdith et al., 2017; 72 Huang et al., 2000; Zhan et al., 2007). In the past, Ediacaran-Cambrian Tarim Basin sediment 73 successions have only received minor attention (Zhou et al., 2018; Zhu et al., 2019) but a few 74 recent chemo-stratigraphic studies provided some preliminary results on their stratigraphic 75 subdivision and paleoenvironmental conditions. He et al. (2007) and Guo et al. (2017) provided 76 the first C isotope stratigraphic correlations for the late-Ediacaran Cambrian strata in the Tarim 77 Basin between the Sugetbrak, the Penglaiba, the Wushi phosphorite and the Dongergou 78 sections, while Wang et al. (2011b) presented paired C and Sr isotope trends from the 79 Cambrian Series 2 to Series 3 at the Penglaiba section. However, there is still a chemo- 80 stratigraphic gap (especially in regard of the Sr isotope stratigraphy) spanning the late- 81 Ediacaran to the late-Cambrian time interval, which limits the stratigraphic correlation of the 82 Tarim Basin with other parts of the world. 83 C and Sr isotope compositions obtained from well-preserved (i.e. low diagenetic fluid flow 84 overprinted) ancient carbonate rocks may retain primary compositions of the 85 contemporaneous seawater and provide constraints on the isotope-based chemo- 86 stratigraphic correlation (DePaolo and Ingram, 1985; Montañez et al., 1996; Montañez and 87 Banner, 2000; Zhu et al., 2007; Wang et al., 2011b; McArthur et al., 2012; Li et al., 2013; Zhou 88 et al., 2018; Zhu et al., 2019). For instance, the first appearance datum of small shelly fossils 89 (SSFs) is globally accompanied by a negative δ13C excursion and a declining trend in seawater 90 87Sr/86Sr ratios (Cowie and Glaessner, 1975; Landing, 1989; Zhu et al., 2006; Li et al., 2013; Zhu 91 et al., 2019), although there are still debates about the exact boundary definition between the 92 Ediacaran and the Cambrian (Geyer and Landing, 2017). 93 Secular variations in seawater 87Sr/86Sr ratios have been widely applied to reflect 94 continental uplift, silicate weathering and variations in atmospheric carbon dioxide 95 concentration (Burke et al., 1982; Keto and Jacobsen, 1987; Kaufman et al., 1993; Derry et al., 96 1994; Montañez et al., 1996; Denison et al., 1998; Montañez and Banner, 2000; Ebneth et al., 97 2001; Thomas et al., 2001; Melezhik et al., 2009; Sawaki et al., 2010). The 87Sr/86Sr ratio of 98 seawater is controlled by a balance between continental weathering-derived Sr, hydrothermal 99 Sr input and seafloor weathering (Palmer and Edmond, 1989). Continental source generally 100 yields more radiogenic 87Sr/86Sr ratios due to the more radiogenic 87Sr resulting from the excess 101 decay of incompatible 87Rb (rubidium) in evolved differentiated crustal rocks, while 102 hydrothermal and seafloor weathering origin Sr deplete in radiogenic 87Sr and therefore low 103 87Sr/86Sr ratios. Neglectable isotopic fractionation of the Rb/Sr system occurs during marine 104 authigenic carbonate formation (Banner and Kaufman, 1994), together with its long residence 105 time in the modern oceans, Sr is homogeneously distributed in the oceans and the seawater 106 87Sr/86Sr ratio ideally represents a global signature