U-Pb Ages from the Neoproterozoic Doushantuo Formation, China

Condon, Daniel J.; Zhu, Maoyan; Bowring, Samuel A.; Wang, Wei; Yang, Anshu; Yugan, Jin

doi:10.1126/science.1107765

Cited by 1,171 publications

(730 citation statements)

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“…The smooth and consistent variation in  13 C values throughout the sampled sections parallels  13 C variations of contemporaneous terminal Neoproterozoic sections (Ries et al, 2010) from China (Condon et al, 2005;Jiang et al, 2003), Australia (Calver, 2000; Page 30 of 74…”

Section: Carbon Isotopesmentioning

confidence: 99%

Dynamic redox conditions control late Ediacaran metazoan ecosystems in the Nama Group, Namibia

Wood

Poulton

Prave

et al. 2015

Precambrian Research

172

194

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A c c e p t e d M a n u s c r i p t 3 ABSTRACTThe first appearance of skeletal metazoans in the late Ediacaran (~550 million years ago; Ma) has been linked to the widespread development of oxygenated oceanic conditions, but a precise spatial and temporal reconstruction of their evolution has not been resolved. Here we consider the evolution of ocean chemistry from ~550 to ~541 Ma across shelf-to-basin transects in the Zaris and Witputs Sub-Basins of the Nama Group, Namibia. New carbon isotope data capture the final stages of the Shuram/Wonoka deep negative C-isotope excursion, and these are complemented with a reconstruction of water column redox dynamics utilizing Fe-S-C systematics and the distribution of skeletal and soft-bodied metazoans. Combined, these inter-basinal datasets provide insight into the potential role of ocean redox chemistry during this pivotal interval of major biological innovation.The strongly negative  13 C values in the lower parts of the sections reflect both a secular, global change in the C-isotopic composition of Ediacaran seawater, as well as the influence of 'local' basinal effects as shown by the most negative  13 C values occurring in the transition from distal to proximal ramp settings. Critical, though, is that the transition to positive  13 C values postdates the appearance of calcified metazoans, indicating that the onset of biomineralization did not occur under post-excursion conditions. Significantly, we find that anoxic and ferruginous deeper water column conditions were prevalent during and after the transition to positive  13 C that marks the end of the Shuram/Wonoka excursion. Thus, if the C isotope trend reflects the transition to global-scale oxygenation in the aftermath of the oxidation of a large-scale, isotopically light organic carbon pool, it was not sufficient to fully oxygenate the deep ocean. Page 4 of 74A c c e p t e d M a n u s c r i p t 4 Both sub-basins reveal highly dynamic redox structures, where shallow, inner ramp settings experienced transient oxygenation. Anoxic conditions were caused either by episodic upwelling of deeper anoxic waters or higher rates of productivity. These settings supported short-lived and monospecific skeletal metazoan communities. By contrast, microbial (thrombolite) reefs, found in deeper inner-and mid-ramp settings, supported more biodiverse communities with complex ecologies and large skeletal metazoans. These long-lived reef communities, as well as Ediacaran soft-bodied biotas, are found particularly within transgressive systems, where oxygenation was persistent. We suggest that a mid-ramp position enabled physical ventilation mechanisms for shallow water column oxygenation to operate during flooding and transgressive sea-level rise. Our data support a prominent role for oxygen, and for stable oxygenated conditions in particular, in controlling both the distribution and ecology of Ediacaran skeletal metazoan communities.Keywords: Oxygenation; Neoproterozoic; Biomineralisation; Metazoans; Ediacaran; Ecosystems Introductio...

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Section: Carbon Isotopesmentioning

confidence: 99%

Dynamic redox conditions control late Ediacaran metazoan ecosystems in the Nama Group, Namibia

Wood

Poulton

Prave

et al. 2015

Precambrian Research

172

194

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“…Likewise, the basal, globally correlated cap carbonate to the Marinoan glaciation, which defines the Cryogenian-Ediacaran boundary, is well-constrained to ca. 635 Ma based on radiometric ages in China (Condon et al, 2005;Zhang et al, 2008), Namibia (Hoffmann et al, 2004), Tasmania (Calver et al, 2013) and NW Canada (Re-Os date; Rooney et al, 2015). Both early and late Cryogenian glaciations, referred to as the Sturtian and Marinoan (based on locations in South Australia), respectively, appear to be globally distributed (Li et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

The Late Cryogenian Warm Interval, NE Svalbard: Chemostratigraphy and genesis

Fairchild

Bonnand²,

Davies

et al. 2016

Precambrian Research

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms At the base of E3, interstratification of cap carbonate with ice-rafted and redeposited glacial sediments occurs. Early diagenetic stabilization of carbonate mineralogy from a precursor, possibly ikaite, to calcite or dolomite is inferred. E3 is predominantly dolomitic silt-shale, with sub-millimetre lamination, lacking sand or current-related sedimentary structures. Thin fine laminae are partly pyritized and interpreted as microbial mats. Dolomite content is 25-50%, with δ 13 C values consistently around +4‰, a value attributed to buffering by dissolution of a precursor metastable carbonate phase. Local calcite cement associates with low δ 13 C values. The carbonates form silt-sized, chemically zoned rhombic crystals from an environment with dynamically changing Fe and Mn. Three-dimensional reconstructions of cm-scale disturbance structures indicate that they represent horizontally directed sock-like folds, developed by release of overpressure into thin surficial sediment overlying an early-cemented layer.A shoaling upwards unit near the top of E3 displays calcium sulphate pseudomorphs in dolomite in the north, but storm-dominated limestones in the south, both being overlain by peritidal oolitic dolomites, exposed under the succeeding Wilsonbreen glacial deposits. There is no Trezona δ 13 C anomaly, possibly implying top-truncation of the succession.Regular 0.5 m-scale sedimentary rhythms, reflecting subtle variations in sediment texture or composition occur throughout E3 and are interpreted as allocyclic. They are thought to be mainly primary in origin, locally modified slightly during early diagenetic cementation. Rhythms are proposed to represent ca. 18 kyr precession cycles, implying 6-8 Myr deposition between glaciations.

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“…The Doushantuo cap carbonate succession displays a distinct suite of sedimentary structures and textures including cemented breccias, sheet cracks, tepee-shaped structures, stromatactis-like cavities, peloids, and local barite fans, and negative carbon isotope excursion of about −5‰ (Jiang et al, 2003a(Jiang et al, , 2006Lin et al, 2011;Peng et al, 2011), similar to those observed in equivalent cap carbonates worldwide (Kennedy, 1996;Hoffman et al, 1998;James et al, 2001;Frimmel and Folling, 2004;Shields et al, 2007b;Shen et al, 2008). Additionally, U-Pb Zircon dates indicate that the cap carbonates were deposited at 635 Ma (Condon et al, 2005).…”

Section: Geological Settingmentioning

confidence: 66%

“…B: A conceptual transect (a-a′ in A; not to scale) across the Yangtze block showing the stratigraphic occurrence of the Doushantuo cap carbonates (Jiang et al, 2003a, b). Age data are from Condon et al (2005) and Zhang et al (2008). C: Simplified geological map of the Yangtze Gorges area (Zhao et al, 1985).…”

Section: Geological Settingmentioning

confidence: 99%