New U–Pb zircon ages of the Ediacaran–Cambrian boundary strata in South China

Chen, Daizhao; Zhou, Xiqiang; Fu, Yong; Wang, Jianguo; Yan, Detian

doi:10.1111/ter.12134

Cited by 146 publications

(78 citation statements)

References 37 publications

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“…During the Late Ediacaran, three detached carbonate platforms were built in the upper, middle and lower Yangtze areas of South China, and surrounded by siliceous slopes and basins where bedded chert was intercalated with minor black shale (Fig. A; Liu & Xu, ; Chen et al ., ). The upper Yangtze area was occupied by a rimmed carbonate platform, characterized by the broad tidal flat and lagoon in the platform interior and the narrow microbial reef‐shoal complex along the platform margin (Liu & Xu, ).…”

Section: Geological Settingmentioning

confidence: 97%

“…(A) Palaeogeographic map of the Yangtze Block during the late Ediacaran (modified from Chen et al ., ). Note the representative Dengying Formation sections of similar peritidal environments.…”

Section: Geological Settingmentioning

confidence: 99%

“…() and Chen et al . (). AD , Algal Dolomite Member; BW , Beiwan Member; DST , Doushantuo Formation; G, Gaojiashan Member; GYY , Guanyingya Formation; MDP , Maidiping Formation; NTT , Niutitang Formation.…”

Section: Geological Settingmentioning

confidence: 99%

“…B; Zhu et al ., , ; Hao et al ., ; Li et al ., ). Based on the combination of chemostratigraphic, biostratigraphic and chronological correlations, the Dengying Formation is estimated to span about 9 Myr ( ca 551 to 542 Ma; Condon et al ., ; Chen et al ., ).…”

Section: Geological Settingmentioning

confidence: 99%

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Cavity‐filling dolomite speleothems and submarine cements in the Ediacaran Dengying microbialites, South China: Responses to high‐frequency sea‐level fluctuations in an ‘aragonite–dolomite sea’

et al. 2019

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Speleothems, mostly composed of calcium carbonate, are widely present in modern karst‐originated caves, but have rarely been reported in palaeokarst systems. This study presents a novel type of dolomite speleothem and subsequent submarine dolomite cement, which are widely present in the upper Ediacaran Dengying Formation in the upper Yangtze area. These precipitated materials occur in the cavity system that cuts across several peritidal cycles. The interconnected cavity networks with irregular shapes, embayed walls, internal breccias on cavity floor and their preferential development in the shallower cycle tops (for example, tepee‐deformed beds) suggest that they were initially generated by subaerial dissolution. As the earliest infills, the hemispherical protrusions, icicle‐like pendants and ground‐up columns show similar morphological features and occurrence patterns to the cave popcorn, stalactites and stalagmites, respectively. Thus, these earliest infills are speleothems resulting from associated meteoric precipitation during subaerial exposure. The isopachous growth pattern of subsequent more extensive fibrous dolomite cements points to a submarine diagenetic environment in which they were precipitated. Microscopically, the micritic to micro‐crystalline dolomite, acicular dolomite in speleothems and the subsequent fibrous dolomite share similar crystal fabrics to metastable precursors (for example, Mg‐calcite). Meanwhile, the carbon‐oxygen isotope compositions of the speleothem and fibrous dolomite, although partly altered by burial diagenesis, share a large overlap with host rock and coeval marine carbonates all over the Yangtze Platform. For these reasons, these speleothems and fibrous cements are considered to have been initially precipitated as metastable carbonate precursors in meteoric and submarine environments, respectively, and stabilized during submarine mimetic dolomitization. The cyclic occurrence of cavity systems filled with speleothems and submarine cements reflects periodic subaerial exposure and marine flooding of broad tidal flat in the upper Yangtze area, driven by high‐frequency sea‐level fluctuations. Furthermore, the Neoproterozoic seawater chemistry that favoured early dolomitization of carbonate precursor mineralogies was an advantage for the preservation of fabrics from metastable precursor minerals.

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Section: Geological Settingmentioning

confidence: 97%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

See 2 more Smart Citations

Cavity‐filling dolomite speleothems and submarine cements in the Ediacaran Dengying microbialites, South China: Responses to high‐frequency sea‐level fluctuations in an ‘aragonite–dolomite sea’

et al. 2019

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“…1). Based on the 551 Ma U-Pb zircon depositional age of a volcanic ash at the top of the Miaohe Member, which has historically been correlated with Doushantuo Member IV (Condon et al, 2005), and an estimated 541 Ma age for the Ediacaran-Cambrian boundary (Amthor et al, 2003;Chen et al, 2015), the >650 m thick Dengying Formation represents the last 10 million years of the Ediacaran Period. 1C), which are generally correlated with Hamajing, Shibantan, and Baimatuo members, respectively, in the Yangtze Gorges area (Zhou & Xiao, 2007;Zhu et al, 2007;Duda et al, 2015).…”

Section: Stratigraphic and Geochronological Constraintsmentioning

confidence: 99%

Environmental context for the terminal Ediacaran biomineralization of animals

et al. 2016

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In terminal Ediacaran strata of South China, the onset of calcareous biomineralization is preserved in the paleontological transition from Conotubus to Cloudina in repetitious limestone facies of the Dengying Formation. Both fossils have similar size, funnel-in-funnel construction, and epibenthic lifestyle, but Cloudina is biomineralized, whereas Conotubus is not. To provide environmental context for this evolutionary milestone, we conducted a high-resolution elemental and stable isotope study of the richly fossiliferous Gaojiashan Member. Coincident with the first appearance of Cloudina is a significant positive carbonate carbon isotope excursion (up to +6‰) and an increase in the abundance and (34) S composition of pyrite. In contrast, δ(34) S values of carbonate-associated sulfate remain steady throughout the succession, resulting in anomalously large (>70‰) sulfur isotope fractionations in the lower half of the member. The fractionation trend likely relates to changes in microbial communities, with sulfur disproportionation involved in the lower interval, whereas microbial sulfate reduction was the principal metabolic pathway in the upper. We speculate that the coupled paleontological and biogeochemical anomalies may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin, which stimulated primary productivity, the spread of an oxygen minimum zone, and the development of euxinic conditions in subtidal and basinal environments. Enhanced production and burial of organic matter is thus directly connected to the carbon isotope anomaly, and likely promoted pyritization as the main taphonomic pathway for Conotubus and other soft-bodied Ediacara biotas. Our studies suggest that the Ediacaran confluence of ecological pressures from predation and environmental pressures from an increase in seawater alkalinity set the stage for an unprecedented geobiological response: the evolutionary novelty of animal biomineralization.

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Germanium/silicon of the Ediacaran-Cambrian Laobao cherts: Implications for the bedded chert formation and paleoenvironment interpretations

Dong

Shen

Lee

et al. 2015

Geochem. Geophys. Geosyst.

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Sedimentary strata of the terminal Ediacaran (635-542 Ma) to early Laobao-Liuchapo bedded cherts in the South China Block include the Ediacaran Oxidation Event and the Cambrian explosion. Understanding the origin and depositional environment of the bedded cherts may provide insight into how the Earth's surface environment changed between the Proterozoic and Phanerozoic. We measured major and trace element compositions and Ge/Si ratios of the Laobao cherts from northern Guangxi province. The Laobao cherts were deposited in the deep basinal environment of the South China Block. We show that the composition of the Laobao cherts is determined by a mixture of four components: quartz, clay, carbonate, and pyrite/iron-oxide. The quartz component is the dominant component of the Laobao cherts. The maximum estimated Ge/Si of the quartz component is between 0.4 and 0.5 lmol/ mol, which is close to the Ge/Si of modern seawater and biogenic silica but 1 order of magnitude lower than that of hydrothermal fluids. These Ge/Si systematics suggest that normal seawater rather than midocean ridge hydrothermal fluids is the primary Si source for the Laobao cherts. The Ge/Si of the clay component varies between 1 and 10 lmol/mol, which is comparable to the Ge/Si of typical marine clays, but 10-100 times lower than that of chert nodules from early Ediacaran beds (the Doushantuo Formation) predating the terminal Ediacaran Laobao cherts studied here. Our observations indicate that the clay component Ge/Si ratio decreased from the early Ediacaran to the late Ediacaran. We speculate that high Ge/Si ratios in clays reflect the preferential chelation of Ge by dissolved organic compounds adsorbed onto clays. If so, this suggests that the decrease in Ge/Si ratio of the clay component in the Ediacaran signifies a decrease in the total dissolved organic carbon content of seawater toward the Ediacaran-Cambrian transition, consistent with oxidation of the oceans during the late Ediacaran. Finally, the seawater origin of the Laobao cherts also suggests that replacement of carbonate may not be the primary cause for bedded chert formation. Instead, direct precipitation from seawater or early diagenetic silicification of calcareous sediments, perhaps due to the emergence of Si-accumulation bacteria, may have been responsible for the bedded Laobao-Liuchapo chert formation in South China Block.

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New U–Pb zircon ages of the Ediacaran–Cambrian boundary strata in South China

Abstract: The Ediacaran-Cambrian transition is a critical interval marking drastic biological, oceanic and geochemical co-evolutions in geological history, but it is poorly constrained geochronologically in South China. We present two new sets of SIMS U-Pb zircon ages from

Cited by 146 publications

References 37 publications

Cavity‐filling dolomite speleothems and submarine cements in the Ediacaran Dengying microbialites, South China: Responses to high‐frequency sea‐level fluctuations in an ‘aragonite–dolomite sea’

Cavity‐filling dolomite speleothems and submarine cements in the Ediacaran Dengying microbialites, South China: Responses to high‐frequency sea‐level fluctuations in an ‘aragonite–dolomite sea’

Environmental context for the terminal Ediacaran biomineralization of animals

Germanium/silicon of the Ediacaran-Cambrian Laobao cherts: Implications for the bedded chert formation and paleoenvironment interpretations

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