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(Marinoan) Glaciation I

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(Marinoan) Glaciation I Earth and Planetary Science Letters 483 (2018) 52–63 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Cyclostratigraphic constraints on the duration of the Datangpo Formation and the onset age of the Nantuo (Marinoan) glaciation in South China ∗ Xiujuan Bao a, Shihong Zhang a, , Ganqing Jiang b, Huaichun Wu a, Haiyan Li a, Xinqiang Wang a, Zhengze An c, Tianshui Yang a a State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China b Department of Geoscience, University of Nevada, Las Vegas, NV 89154-4010, USA c 103 Geological Team, Guizhou Bureau of Geology and Mineral Resources, Tongren, Guizhou 554300, China a r t i c l e i n f o a b s t r a c t Article history: Constructing an accurate timeline is critical for reconstructing the Earth systems through critical Received 20 July 2017 transitions in climate, geochemistry, and life. Existing dates constrain synchronous initiation (ca. 717 Ma) Received in revised form 26 November 2017 and termination (ca. 660 Ma) of the Sturtian glaciation from multiple continents. The termination of Accepted 3 December 2017 the younger Marinoan glaciation is also well dated at ca. 635 Ma, but the onset of this glaciation is Available online xxxx only roughly constrained as ≤ ca. 654 Ma (South China) and ≥ ca. 639 Ma (Namibia). To test if the Editor: M. Frank Marinoan glaciation started close to ca. 654 Ma or ca. 639 Ma, we have conducted a cyclostratigraphic Keywords: study on the Cryogenian non-glacial Datangpo Formation that conformably overlies and underlies Sturtian Cryogenian and Marinoan glacial diamictites, respectively, in a deep-water basin section in South China. A total Snowball Earth of 28,765 magnetic susceptibility (MS) measurements from a drillcore of the 292-m-thick, muddy Milankovitch cycles siltstone- and shale-dominated Datangpo Formation are used for cyclostratigraphic analysis. The results Datangpo Formation reveal significant decameter- to meter-scale sedimentary cycles of 16–12 m, 3.6–3.0 m, 1.0–0.8 m, and Nantuo Formation 0.6–0.4 m. The ratios of these cycle wavelengths match well with those of the Milankovitch cycles South China calibrated for the Cryogenian Period. The established astrochronologic time scale suggests that the duration of the Datangpo Formation is about 9.8 million years. Together with the radiometric age of ca. 660 Ma for the termination of the Sturtian glaciation, the cyclostratigraphic data suggest that the Nantuo (Marinoan) glaciation in South China initiated at ca. 650 Ma, which is slightly younger than but consistent with the ca. 654 Ma U–Pb age from the top of the Datangpo Formation in shelf sections. This age, however, is significantly older than the ages obtained from Marinoan-age glacial diamictites in South China (ca. 636 Ma) and Namibia (ca. 639 Ma). Given that most of the shelf sections may have suffered from glacial erosion, obtaining the onset age of the Marinoan glaciation should focus on relatively complete, deep-water successions. © 2017 Published by Elsevier B.V. 1. Introduction the synchronous initiation of the Sturtian glaciation at ca. 717 Ma (Bowring et al., 2007; Macdonald et al., 2010; Lan et al., 2014; The Cryogenian Period (717–635 Ma) witnessed episodes of ex- Rooney et al., 2015), and its termination at ca. 660 Ma (Zhou treme cold known as the Sturtian and Marinoan glaciations, during et al., 2004; Kendall et al., 2006; Rooney et al., 2014, 2015) on which ice sheets may have extended to equatorial latitudes, form- multiple continents (Fig. 1b). The synchronous termination of the ing the “Snowball Earth” (Hoffman et al., 1998). The synchroneity Marinoan glaciation is also well dated by U–Pb ID-TIMS ages of ca. of the Cryogenian glaciations is a key prediction of the Snow- 635 Ma from multiple continents (Fig. 1b; Hoffmann et al., 2004; ball Earth hypothesis (Rooney et al., 2015). Recent U–Pb (both Condon et al., 2005; Calver et al., 2013; Rooney et al., 2015), but ID-TIMS and SIMS) and Re–Os ages provide faithful constraints on the onset of the Marinoan glaciation is only roughly constrained as ≤654 Ma (U–Pb SIMS age) in South China (Zhang et al., 2008b; Liu et al., 2015) and ≥639 Ma (U–Pb ID-TIMS age) in Namibia * Corresponding author. (Prave et al., 2016). Because the ca. 654 Ma age constraining E-mail address: [email protected] (S. Zhang). the onset of the Marinoan glaciation in South China is obtained https://doi.org/10.1016/j.epsl.2017.12.001 0012-821X/© 2017 Published by Elsevier B.V. X. Bao et al. / Earth and Planetary Science Letters 483 (2018) 52–63 53 Fig. 1. Summary of available age data from Cryogenian successions. (a) Paleocontinental reconstruction at ca. 635 Ma (Modified from Zhang et al., 2013, location changes for Tarim and Siberia are based on Wen et al., 2017). Circled numbers ➀–➅ mark the paleogeographic locations of dated Cryogenian successions. The location of the Zavkohan terrane of Mongolia is roughly restored to near Tarim (Bold et al., 2016). (b) Summary of ages and their relative stratigraphic position in Cryogenian successions marked in (a). Notice that the 643 ± 2.3 Ma age above the Sturtian glacial deposits in Australia has been questioned by Rooney et al. (2014). CA – Chang’an Formation; BX – Banxi Group; DST – Doushantuo Formation; Gp – Group; Fm – Formation; I.B. – Ice Brook Fm; LK – Lake; M.B. – Masirah Bay Fm; Mt. – Mount; NT – Nantuo Fm; Rav. – Ravensthroat Fm; XM – Xiangmeng Fm; References for ages: [1] Condon et al. (2005); [2] Zhang et al. (2008b); [3] Liu et al. (2015); [4] Zhou et al. (2004); [5] Lan et al. (2014); [6] Calver et al. (2013); [7] Kendall et al. (2009); [8] Fanning and Link (2008); [9] Hoffmann et al. (2004); [10] Prave et al. (2016); [11] Rooney et al. (2015); [12] Rooney et al. (2014); [13] Lund et al. (2003); [14] Macdonald et al. (2010); [15] Bowring et al. (2007). (c) Summary of the geological time scale for Cryogenian–middle Ediacaran based on available age data, covering three Neoproterozoic glaciations. The ca. 650 Ma age for the Marinoan glaciation is from this study. The age of the Gaskiers glaciation is from Pu et al. (2016). (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.) 54 X. Bao et al. / Earth and Planetary Science Letters 483 (2018) 52–63 Fig. 2. (a) Generalized late Neoproterozoic paleogeographic reconstruction of South China. (b) Depositional model showing the paleogeographic position of the studied drillcore (modified from Jiang et al., 2011). References for ages: 635.2 ± 0.6 Ma (Condon et al., 2005); 654.2 ± 2.7 Ma (Liu et al., 2015); 654.5 ± 3.8 Ma and 636.3 ± 4.9 Ma (Zhang et al., 2008b); 662.9 ± 4.3 Ma (Zhou et al., 2004); 715.9 ± 2.8 Ma (Lan et al., 2014). (c) Stratigraphy of the Datangpo and Nantuo formations from drillcore ZK1909, DST – Doushantuo Fm; TSA – Tiesi’ao Fm. from shelf sections (Figs. 1 and 2) where glacial diamictites of Minguez and Kodama, 2017). Cyclostratigraphic analysis of the the Nantuo Formation (Fm) disconformably overlie the non-glacial Datangpo Fm reveals that the ratios of sedimentary cycles have Datangpo Fm, apotential concern is whether the upper Datangpo a similar hierarchy as that of orbital parameters predicted for the Fm was eroded and the Nantuo glaciation started much later than Cryogenian period, which is one of the few examples that demon- ca. 654 Ma (Zhang et al., 2008b)or even close to ca. 639 Ma. strate the response of Earth’s climate to orbital forcing in the Answering this question requires age constraints from deep-water distant past. In combination with available radiometric ages, the sections where a relatively conformable transition from non-glacial established astrochronological time scale provides constraints on to glacial deposits is preserved. the duration of the Cryogenian non-glacial Datangpo Fm and the In this paper, we present a cyclostratigraphic study of the Cryo- initiation age of the Nantuo (Marinoan) glaciation. genian non-glacial Datangpo Fm from a drillcore (ZK1909) of a basinal section in Songtao County, Guizhou Province, South China 2. Geological setting and the drillcore records (Fig. 2a), using centimeter-scale magnetic susceptibility (MS) mea- surements. The Datangpo Fm in this section preserves a complete 2.1. Regional stratigraphy non-glacial record and is dominated by thinly laminated muddy siltstone and shale amenable for cyclostratigraphic analysis, which The tectonic setting of the late Neoproterozoic Nanhua Basin has proven to be an efficient tool for calibrating the time series and has been interpreted as a back-arc basin (Zhou et al., 2002; duration of stratigraphic intervals and geological events from Ceno- Zhao et al., 2011)or a rift to passive marginal basin (Wang and zoic (e.g., Hinnov, 2013), Mesozoic (e.g., Wu et al., 2014), Paleozoic Li, 2003; Jiang et al., 2003, 2011). However, the rift to passive (e.g. Wu et al., 2013; Fang et al., 2016), to Precambrian time (e.g. marginal basin better explains the consistent southeast-deepening S.C. Zhang et al., 2015; Minguez et al., 2015; Fairchild et al., 2016; stratigraphic pattern in the Yangtze Block (Fig. 2a) from late X. Bao et al. / Earth and Planetary Science Letters 483 (2018) 52–63 55 Neoproterozoic until the late Ordovician (Zhang et al., 2008a; clude glaciogenic rocks of the uppermost Tiesi’ao Fm (equivalent Jiang et al., 2011). of the Chang’an Fm), the non-glacial Datangpo Fm, the Nantuo Neoproterozoic strata in the Nanhua Basin consist of three Fm, and Ediacaran–early Cambrian strata (Fig.
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