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Late Neoproterozoic to early Cambrian sulphur cycle—An isotopic investigation of sedimentary rocks from the Yangtze Platform

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Progress in Natural Science:Materials International 2003年第12期 66-70页

作者： tatiana goldberg 1*, {{2.strauss 1, guo qingjun 2.and liu congqiang 2.1. Geologisch Palontologisches Institut, Westflische Wilhelms Universitt, Corrensstr. 2., 48149 Münster, Germany {2.institute of geochemistry, Chinese academy of {12., guiyang 550002. china) Geologisch-Palaontologisches Institut Westfalische Wilhelms-Universitat Corrensstr. 24 48149 Münster Germany institute of geochemistry Chinese Academy of Sciences Guiyang 550002 China

The sulphur cycle responds to changes in seawater chemistry, biological evolution and tectonic activity. We follow an isotopic approach in order to constrain the state of the ocean/atmosphere system during late Neoproterozoic and early Cambrian. For this purpose, a sedimentary succession deposited on the Yangtze Platform, South china, was analysed for its sulphur isotopic composition in different S bearing phases. Redox changes were defined by the degree of pyritization (DOP) values in order to show variations in the oxygenation of the depositional environment. The sulphur isotopic composition of late Neoproterozoic to early Cambrian seawater sulphate ranges from +30‰ to +35‰ as evident from trace sulphate in unaltered carbonates and phosphorites. The isotopic composition for pyrite and organic sulphur varies between -16‰ and +2.‰. The apparent sulphur isotopic fractionation between seawater sulphate and pyrite as well as organically bound sulphur varies between 7‰ and 50‰. This large fractionation, as well as its variability suggests a biological origin for pyrite and organically bound sulphur. The temporal evolution of different geochemical proxy signals is comparable for different successions across the Yangtze Platform.

关键词： sulphur cycle Yangtze Platform stable isotopes.

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Organic Carbon Isotope geochemistry of the Neoproterozoic Doushantuo Formation,South china

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Acta Geologica Sinica(English Edition) 2006年第5期80卷 670-683页

作者： guo qingjun {2. congqiang {2. *strauss tatiana goldberg ZHU Maoyan PI Daohui WANG Jian State Key Laboratory of Environmental geochemistry Institute of Geochemistry Chinese Academy of Sciences Guiyang Guizhou 550002 China Geologisch-Palaontologisches Institut Universitat Miinster Corrensstrasse 24 48149 Miinster Germany School of Earth sciences James Cook University Townsville QLD 4811 Australia Nanjing institute of Geology and Palaeontology Chinese Academy of Sciences Nanjing Jiangsu 210008 China Guizhou Phosphorite Ore Company Weng＇an Guizhou

The Neoproterozoic Doushantuo Formation on the Yangtze Platform, South china, documents a sedimentary succession with different sedimentary facies from carbonate platform to slope and to deep sea basin, and hosts one of the world-class phosphorite deposits. In these strata, exquisitely preserved fossils have been discovered： the Weng＇an biota. This study presents carbon isotope geochemistry which is associated paired carbonate and organic matter from the Weng＇an section of a carbonate platform （shelf of the Yangtze Platform, Guizhou Province） from the Songtao section and Nanming section of a transition belt （slope of the Yangtze Platform, Guizhou Province） and from the Yanwutan section （basin area of the Yangtze Platform, Hunan Province）. Environmental variations and bio-events on the Yangtze Platform during the Late Neoproterozoic and their causal relationship are discussed. Negative carbon isotope values for carbonate and organic carbon （mean δ^13Corg = -35.0‰） from the uppermost Nantuo Formation are followed by an overall increase in δ^13C up-section. Carbon isotope values vary between -9.9‰ and 3.6‰ for carbonate and between -35.6‰ and -2..5‰ for organic carbon, respectively. Heavier δ^13Ccarb values suggest an increase in organic carbon burial, possibly related to increasing productivity （such as the Weng＇an biota）. The δ^13C values of the sediments from the Doushantuo Formation decreased from the platform via the slope to basin, reflecting a reduced environment with minor dissolved inorganic carbon possibly due to a lower primary productivity. It is deduced that the classical upwelling process, the stratification structure and the hydrothermal eruption are principally important mechanisms to interpret the carbon isotopic compositions of the sediments from the Doushantuo Formation.

关键词： Late Neoproterozoic Doushantuo Formation organic carbon isotopic composition the Yangtze Platform

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Isotopic evolution of the terminal Neoproterozoic and early Cambrian carbon cycle on the northern Yangtze Platform, South china

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Progress in Natural Science:Materials International 2003年第12期 62-65页

作者： guo qingjun 1,2. **,{2., harald strauss 3.and tatiana goldberg 3.1. institute of geochemistry, Chinese academy of sciences, guiyang 550002. china 2. *Graduate School, Chinese academy of Science, Beijing 100018, china 3. Geologisch Palontologisches Institut, Westflische Wilhelms Universitt Münster, 48148 Münster, Germany) institute of geochemistry，Chinese {{2.of sciences，guiyang 550002.china Graduate School，Chinese academy of Science，Beijing 100018，china institute of geochemistry，Chinese {{2.of sciences，guiyang 550002.china Geologisch-Palaontologisches Institut，Westfalische Wilhelms-Universitat Münster，48148 Münster，Germany

Profound geotectonic, climatic and biological changes occur during the terminal Neoproterozoic and its transition into the early Cambrian. These are reflected in temporal variations of the chemical and isotopic composition of seawater. We are studying a sequence of sedimentary rocks at the Shatan section, northern Yangtze Platform, Sichuan Province of china. This succession comprises, in ascending stratigraphic order, predominantly calcareous sediments of the Sinian upper Dengying Formation and black shales of the lower Cambrian guojiaba Formation (time equivalent of Niutitang Fm.). Paleoenvironmental setting represents shallow water shelf deposits. The objective of our study is to provide temporal records for the isotopic compositions of organic and carbonate carbon throughout this time interval. Organic carbon isotope values display a range between -35.8‰ and -30.1‰ with clear stratigraphic variations. Carbonate carbon isotope data vary between -3.5‰ and +0.5‰. These secular variations are interpreted to reflect perturbations of the global carbon cycle, specifically changes in the fractional burial of organic carbon. However, local conditions have further affected the isotopic signals.

关键词： terminal Neoproterozoic Early Cambrian carbonate and organic carbon isotopic composition Yangtze Platform Shatan section.

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