Redox variations and organic matter accumulation on the Yangtze carbonate platform during Late Ediacaran–Early Cambrian: Constraints from petrology and geochemistry

Gao, Ping; Liu, Guangdi; Jia, Chengzao; Young, Allison L.; Wang, Zecheng; Wang, Tongshan; Zhang, Pengwei; Wang, Dapeng

doi:10.1016/j.palaeo.2016.02.058

Cited by 79 publications

(34 citation statements)

References 76 publications

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“…Bulk dolostones generally display MREE enrichment or flat patterns, and lack the typical Gd anomaly (Zhang et al ., ; Gao et al ., ; Liu et al ., ). Additionally, these samples have high REE concentrations (ΣREE average = 28·9 ppm; Gao et al ., ) and chondritic Y/Ho ratios (average = 23·3; Zhang et al ., ), likely related to an influx of freshwater (Zhang et al ., ), contamination by siliciclastic minerals or burial diagenesis (Della Porta et al ., ). If the aforementioned arguments are viable, then data presented here stress the importance in sampling discrete carbonate phases rather than analyzing bulk rock (e.g.…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Formation, diagenesis and palaeoenvironmental significance of upper Ediacaran fibrous dolomite cements

Cai

Liu

et al. 2019

Sedimentology

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Neoproterozoic marine dolomite cements represent reliable, albeit complex, archives of their palaeoenvironment. Petrological and high-resolution geochemical data from well-preserved fibrous dolomite and pyrite in the upper Ediacaran (ca 551Á1 to 548Á0 Ma) Dengying Formation in south-west China are presented and discussed here. The aim of this research is to reconstruct the redox state of late Ediacaran shallow seawater and porewater in the Sichuan Basin using early marine diagenetic fabrics. Based on crystalline texture and axis, four basic types of fibrous dolomite cements formed penecontemporaneously in a microbialite reef setting at the platform margin: (i) bladed dolomites (replacement from a high-Mg calcite precursor); (ii) fascicular fast dolomites (replacement from an aragonitic precursor); (iii) fascicular slow dolomites; and (iv) radial slow dolomites. The latter two fabrics are considered direct marine porewater precipitates due to their length-slow character, cathodoluminescent zonation, and enriched copper and cobalt concentrations. Marine cements yield rare earth element and yttrium patterns comparable to modern seawater and represent a refined set of archive data relative to previously published bulk dolostones. Redox-sensitive elements and cathodoluminescence indicate that the fascicular fast dolomites formed in suboxic seawater, while fascicular slow and radial slow dolomites formed in euxinic marine porewaters. Microbial sulphate reduction during the formation of fascicular slow and radial slow dolomites is recognized by nanometre-scale spheroidal ankerite and sulphur-containing dolomite, and intergrown pyrite grains with U-shaped d 34 S transects. Data shown here suggest predominantly suboxic shallow late Ediacaran seawater and euxinic marine porewaters, with microbial activity promoting the direct precipitation of dolomite.

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Section: Interpretation and Discussionmentioning

confidence: 99%

Formation, diagenesis and palaeoenvironmental significance of upper Ediacaran fibrous dolomite cements

Cai

Liu

et al. 2019

Sedimentology

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“…This notable Ni–Mo polymetallic ore bedding is widely distributed in Lower Cambrian sediment in the Yangtze Block, which can form in a slope and basin region and also found in a shallow water setting (Lan et al, ). Newly obtained U–Pb age constrain the deposition time of the Ni–Mo ore bedding to about 532–527 Ma (Lan et al, ), indicating the polymetallic ore was deposited in late Cambrian Stage 2 (Gao et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

“…FIGURE 1 (a) Paleoenvironment map of the Yangtze Block during the Early Cambrian (modified from Jin et al, 2016;Zhu et al, 2003). (b) Location map showing the position of the studied well and structural setting of the Sichuan Basin (modified after Gao et al, 2016) [Colour figure can be viewed at wileyonlinelibrary.com] 3 | SAMPLES AND METHODS…”

Section: Geological Settingmentioning

confidence: 99%

“…During Late Ediacaran to Early Cambrian, the Yangtze Platform sediments were deposited in a failed rift basin setting and three distinctly different facies can be divided: the shallow‐water shelf, transition zone, and deepwater basin environment (Gao et al, ; Jin et al, ; Zhu et al, ; Figure a). A succession of unmetamorphosed marine sediments ranging from Ediacaran to the Lower Triassic were overlaid on the Pre‐Ediacaran Proterozoic basement in the Yangtze Platform (Jin et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

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Main factors controlling the organic matter enrichment in the Lower Cambrian sediments of the Sichuan Basin, SW China

Wang

Tian

et al. 2019

Geological Journal

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The Lower Cambrian Qiongzhusi Formation contains more than 200 m of marine sediments mainly consisting of mudstone and black shales, which are widely accepted as the most important hydrocarbon source rocks of the Ediacaran–Cambrian giant gas field in the Sichuan Basin. The geochemical compositions of biomarkers and trace elements obtained from black shales at the bottom of the Qiongzhusi Formation were used to reconstruct the palaeoproductivity and palaeoenvironment and to determine the main factors controlling the deposition and preservation of this organic‐rich shales. Based on varieties of steroids and hopanoids compositions, multifarious palaeobios such as pelagophyceae, dinoflagellate, diatom (or its ancestor), sponges, and aerobic/anaerobic bacteria have been proved to evolve in the Early Cambrian in the Sichuan Basin. In addition, a relative high concentration of Cubio compared with modern oceanic palaeoproductivity proxies indicate a moderate to relatively high palaeoproductivity, which is favourable for the organic matter accumulation of this source rocks. Moreover, the evidence from biomarkers and trace element ratios suggest that the Lower Cambrian sediments were deposited under a non‐sulphurized anoxic condition, which provided a favourable preservation condition. The covariation among Porg, Cubio, and TOC shows that the palaeoproductivity is the main controlling factor for the high organic content of the black shales of the Qiongzhusi Formation.

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“…Uranium, vanadium, and molybdenum are widely applied to determine the redox conditions due to their redox‐sensitive property (Gao et al, ; Liu, Feng, Shen, Khan, & Planavsky, ). U and V can be enriched in suboxic and anoxic conditions (Lewan & Maynard, ; Morford & Emerson, ), and Mo accumulates under euxinic conditions that contain free of H 2 S (Crusius, Calvert, Pedersen, & Sage, ; Dahl, Chappaz, Fitts, & Lyons, ).…”

Section: Discussionmentioning

confidence: 99%

Mineralogy and geochemical investigation of Cambrian and Ordovician–Silurian shales in South China: Implication for potential environment pollutions

et al. 2019

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Rapid expansion of shale gas development in China raises environmental and human health concerns. Several studies present related information on these concerns in the United States and Canada, yet they are few in China at present. This paper presents a series of original and published mineralogical and trace elements data from two gas shales (Niutitang shale and Longmaxi shale) considered as producing gas shale in China. Mineralogical and geochemical data surveyed can be applied to evaluate the potential environment pollutions during shale weathering and hydraulic fracturing. After compilations of the mineralogical and trace elements data, we can conclude that (a) there is generally more pyrite compared with carbonate for Niutitang shales, indicating that Niutitang shales are more prone to generate the hydrogen ions than Longmaxi shales; (b) many of the environmental hazardous trace elements considered here show an association with organic matter and/or pyrite, indicating that these trace elements are prone to mobilize and release during shale weathering and hydraulic fracturing; (c) some environmental hazardous elements like As, Ni, and Ba that have extremely high concentrations in some regions as compared with the screening limits for soil and drinking water should attract more attention; and (d) clay-rich shale with abundant organic matter may be the most favourable shale gas reservoir for the Niutitang shale, especially for those shales in Lower Yangtze region. Moreover, more mineralogical and geochemical data will be required for a comprehensive environmental impacts assessment. KEYWORDS environmental and human impacts, mineralogy, pyrite oxidization, shale, South China, trace elements

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Redox variations and organic matter accumulation on the Yangtze carbonate platform during Late Ediacaran–Early Cambrian: Constraints from petrology and geochemistry

Cited by 79 publications

References 76 publications

Formation, diagenesis and palaeoenvironmental significance of upper Ediacaran fibrous dolomite cements

Formation, diagenesis and palaeoenvironmental significance of upper Ediacaran fibrous dolomite cements

Main factors controlling the organic matter enrichment in the Lower Cambrian sediments of the Sichuan Basin, SW China

Mineralogy and geochemical investigation of Cambrian and Ordovician–Silurian shales in South China: Implication for potential environment pollutions

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