Cyclic cold climate during the Nantuo Glaciation: Evidence from the Cryogenian Nantuo Formation in the Yangtze Block, South China
Introduction
Geological and paleomagnetic evidence indicates that ice sheets might have extended to the low latitude sea level during the Sturtian (ca. 717–660 Ma) and Marinoan glaciations (ca.650–635 Ma) (Hoffman et al., 1998, Hoffman and Li, 2009, Hoffman and Schrag, 2002, Kirschvink, 1992, Macdonald et al., 2010). The snowball Earth hypothesis proposed that the Earth’s surface was completely frozen during these two global glaciations (Hoffman et al., 1998, Hoffman and Schrag, 2002). Global freezing resulted in the stagnation in hydrological cycle, leading to a weak continental weathering and negligible marine primary productivity. As a result, atmospheric pCO2 level could continuously rise due to volcanic degassing during the global glaciation (Hoffman and Schrag, 2002). The Earth remained completely frozen for tens of million years until atmospheric pCO2 level reached a threshold that caused a catastrophic meltdown of the global glaciation (Bao et al., 2008, Fabre and Berger, 2012, Higgins and Schrag, 2003, Hoffman et al., 1998, Hoffman and Schrag, 2002, Le Hir et al., 2007, Lewis et al., 2007).
The snowball Earth hypothesis provided a reasonable interpretation for the global precipitation of 12C-enriched cap carbonate immediately above glacial deposits (Hoffman et al., 1998). However, this scenario cannot be completely supported by the glacial sedimentary record. Some sedimentary structures observed in glacial marine deposits, such as thin-bedded mudstone intercalated with diamictite (Allen and Etienne, 2008, Allen et al., 2004, Busfield and Le Heron, 2014, Hu et al., 2011), wave ripples, and hummocky cross stratification (Busfield and Le Heron, 2016, Le Heron, 2015, Le Heron et al., 2016), indicate the presence of water current and sediment transportation during the global glaciation. Although wave-induced current would have become negligible when the ocean was completely covered by ice (Allen and Etienne, 2008, Allen et al., 2004), recent study proposed that water motion could also be induced by tidal force and hydrothermal activities, and thus may still exist even in the ice-covered ocean (Hoffman et al., 2017a). Therefore, the presence of certain sedimentary structure alone hardly supports the presence of an open ocean (i.e. not covered by ice) during the global glaciation. Instead, analysis of multiple glaciomarine depositional sequences in a basin-to-platform transect might provide more valuable information about the nature of global glaciations (Hoffman et al., 2017a).
In this study, we conducted systematic sedimentary analyses of 6 sections of the Nantuo Formation (654–635 Ma) in the Yangtze Block of South China. Our study demonstrates that the Nantuo Formation may deposit under a cyclic cold-warm climatic condition rather than a long-lasting global glaciation with the Earth’s surface being entirely frozen.
Section snippets
Neoproterozoic depositional history of the Yangtze Block
The South China Block consists of the Yangtze Block to the northwest (present orientation) and the Cathaysia Block to the southeast (Fig. 1A) (Wang and Li, 2003, Zhao and Cawood, 2012, Zheng et al., 2013). The Yangtze and Cathaysia blocks were considered as having been amalgamated along the Jiangnan Orogenic Belt during the assembly of the supercontinent Rodinia at ~830 Ma, followed by a rifting and thermal-subsidence cycle in late Neoproterozoic (Wang and Li, 2003).
The early rifting stage that
Lithofacies
Ten lithofacies were identified from the Nantuo Formation. The descriptions and interpretations are summarized in Table 3 and discussed below.
Facies associations
Based on the stacking pattern and the lateral relationship between lithofacies, three facies associations are recognized: the proximal glaciomarine, distal glaciomarine and non-glacial marine depositional facies (Eyles et al., 1985).
Lateral and vertical distributions of facies associations
In the shallow water environments (inner shelf), the Nantuo Formation is mainly composed of coarse-grained glacial deposits. At the Jiulongwan section (inner shelf), a thick sequence of massive diamictite and pebbly sandstone (∼15 m) that represents the proximal glaciomarine deposit unconformably overlies the sandstones of the Tonian Liantuo Formation. These proximal glaciomarine deposits are directly succeeded by a 2-m thick shale layer in the lower part of the Nantuo Formation, indicating a
Dynamic evolution of the Nantuo Glaciation
It is proposed that excessive topography relief would result in complex facies associations during the Neoproterozoic global glaciation (Hoffman et al., 2017b). Particularly, deposition of diamictite during ice sheet melting might create topographic variations even within short distance. Oversteepening of diamictite could generate reworked sediments, such as crudely stratified diamictite, pebbly sandstone and stratified sandstone (Hoffman et al., 2017b). This scenario seems to be a good
Conclusions
Detailed facies analysis of six successions of the Nantuo Formation in the Yangtze Block was conducted in this study. The main conclusions are listed as below:
- (1)
The Nantuo Formation includes ten lithofacies and three facies associations. These facies and facies associations display pronounced lateral and vertical changes among different sections. The change of well-correlated facies associations may suggest dynamic ice sheets in certain period of the Nantuo Glaciation.
- (2)
Four depositional stages of
Acknowledgements
We thank Gewei Shuai, Fangbing Li, Yixin Cui, Fan Yang and Haoran Ma for their assistance in the field. This study is supported by the Natural Science Foundation of China (41322021 and 41772359), the Strategic Priority Research Program (B) of Chinese Academy of Sciences (grant number XDB18000000) and the Natural Science Foundation of China (41602343). We are grateful to two anonymous reviewers for their constructive comments and suggestions.
References (59)
- et al.
Sedimentation in glacial environments and the identification of tills and tillites in ancient sedimentary sequences
Precambr. Res.
(1981) - et al.
Models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(1985) - et al.
Are basal Ediacaran (635 Ma) post-glacial “cap dolostones” diachronous?
Earth Planet. Sci. Lett.
(2007) - et al.
A palaeogeographic context for Neoproterozoic glaciation
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2009) - et al.
Stratigraphy and paleogeography of the Ediacaran Doushantuo Formation (ca. 635–551Ma) in South China
Gondwana Res.
(2011) - et al.
Hydrothermal dolomitization in Dengying Formation, Gaoshiti-Moxi area, Sichuan Basin, SW China
Pet. Explor. Dev.
(2016) - et al.
Global synchronous initiation of the 2nd episode of Sturtian glaciation: SIMS zircon U-Pb and O isotope evidence from the Jiangkou Group, South China
Precambr. Res.
(2015) - et al.
A rapid and synchronous initiation of the wide spread Cryogenian glaciations
Precambr. Res.
(2014) - et al.
Ocean oxidation during the deposition of basal Ediacaran Doushantuo cap carbonates in the Yangtze Platform, South China
Precambr. Res.
(2016) The significance of ice-rafted debris in Sturtian glacial successions
Sed. Geol.
(2015)
Investigating plausible mechanisms to trigger a deglaciation from a hard snowball Earth
Comptes Rendus Geoscience
Evidence for a redox stratified Cryogenian marine basin, Datangpo Formation, South China
Earth Planet. Sci. Lett.
Neoproterozoic glaciations in a revised global palaeogeography from the breakup of Rodinia to the assembly of Gondwanaland
Sed. Geol.
New U-Pb age constraints on the upper Banxi Group and synchrony of the Sturtian glaciation in South China
Geosci. Front.
History of Neoproterozoic rift basins in South China: implications for Rodinia break-up
Precambr. Res.
Newly discovered Sturtian cap carbonate in the Nanhua Basin, South China
Precambr. Res.
Precambrian geology of China
Precambr. Res.
Introduction to tectonics of China
Gondwana Res.
Sedimentary challenge to Snowball Earth
Nature geocience
The Neoproterozoic Fiq glaciation and its aftermath, Huqf supergroup of Oman
Basin Res.
Triple oxygen isotope evidence for elevated CO2 levels after a Neoproterozoic glaciation
Nature
Sedimentary and sea level changes during glacial cycles and their control on glacimarine facies architecture
Geol. Soc. Lond. Spec. Publ.
Geochronologic constraints on the chronostratigraphic framework of the Neoproterozoic Huqf Supergroup, Sultanate of Oman
Am. J. Sci.
Sequencing the Sturtian icehouse: dynamic ice behaviour in South Australia
J. Geol. Soc.
A Neoproterozoic ice advance sequence, Sperry Wash, California
Sedimentology
U-Pb ages from the Neoproterozoic Doushantuo Formation, China
Science
Neoproterozoic glacial-rainout intervals: observations and implications
Geology
How tillite weathering during the snowball Earth aftermath induced cap carbonate deposition
Geology
Aftermath of a snowball Earth
Geochem. Geophys. Geosyst.
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