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Variations of sulfur and carbon isotopes in seawater during the Doushantuo stage in late Neoproterozoic

chinese Science Bulletin 2003年第13期48卷 1375-1380页

作者： zhang tonggang, chu xuelei, zhang qirui, feng lianjun & huo weiguo key lab of mineral resources exploration and research, institute of geology and geophysics, chinese academy of sciences, beijing 100029, china key lab. of mineral resources exploration and research Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China

Successive analyses of sulfur and carbon isotopic compositions of carbonates strata in the Doushantuo Formation in the Yangtze area were accomplished through a method of extracting trace sulfate from carbonates. Sulfur and carbon isotopic compositions of coeval seawater were estimated from the samples that show the least diagenetic alteration. A high-resolution age curve of sulfur isotopes in seawater sulfates was obtained in the Doushantuo stage, which reflects the trend of variation in seawater sulfur isotopes after the Neoproterozoic snowball Earth event. Similar characteristics of variation in carbon isotopes were observed in the coeval carbonates. A large positive d 34S excursion over +20?occurs in ancient seawater sulfates in the early Doushantuo stage. Simultaneously, the d 13C values in ancient seawater carbonates exhibit a positive excursion up to 10. The maximum d 34S and d 13C values are +46.4 and +6.9? respectively. In the middle Doushantuo stage, the range of variation in d 34S values of seawater is relatively narrow, but d 13C values are quite high. Then, d 34S values of seawater become oscillating, and the same occurs in d 13C values. Negative excursions in d 34S and d 13C values occur simultaneously at the end of the Doushantuo stage, and the minimum d 34S and d 13C values dropped down to -10.1 and -5.7? respectively. The characteristics of variations in the sulfur and carbon isotopes of ancient seawater imply strong changes in oceanic environment that became beneficial to inhabitation and propagation of organism. The organic productivity and burial rate of organic carbon once reached a quite high level during the Doushantuo stage. However, the state of environment became unstable after the global glaciation. The global climate and environment possibly were fluctuating and reiterating. The negative excursions in d 34S and d 13C values occurring at the end of the Doushantuo stage may represent a global event, which might be related to oxidation of dee

关键词：硫碳同位素分馏新元古代成岩作用

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Variations of sulfur and carbon isotopes in seawater during the Doushantuo stage in late Neoproterozoic

Variations of sulfur and carbon isotopes in seawater during ...

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中国科学院地质与地球物理研究所2003学术年会

Successive analyses of sulfur and carbon isotopic compositions of carbonates strata in the Doushantuo Formation in the Yangtze area were accomplished through a method of extracting trace sulfate from *** and carbon isotopic compositions of coeval seawater were estimated from the samples that show the least diagenetic alteration.A high-resolution age curve of sulfur isotopes in seawater sulfates was obtained in the Doushantuo stage, which reflects the trend of variation in seawater sulfur isotopes after the Neoproterozoic snowball Earth *** characteristics of variation in carbon isotopes were observed in the coeval carbonates.A large positiveδS excursion over +20‰occurs in ancient seawater sulfates in the early Doushantuo ***,theδC values in ancient seawater carbonates exhibit a positive excursion up to 10‰. The maximumδS andδC values are +46.4‰and +6.9‰, *** the middle Doushantuo stage,the range of variation inδS values of seawater is relatively narrow,butδC values are quite ***,δS values of seawater become oscillating,and the same occurs inδC values. Negative excursions inδS andδC values occur simultaneously at the end of the Doushantuo stage,and the minimumδS andδC values dropped down to-10.1‰and -5.7‰,*** characteristics of variations in the sulfur and carbon isotopes of ancient seawater imply strong changes in oceanic environment that became beneficial to inhabitation and propagation of *** organic productivity and burial rate of organic carbon once reached a quite high level during the Doushantuo ***,the state of environment became unstable after the global glacistion. The global climate and environment possibly were fluctuating and *** negative excursions inδS andδC values occurring at the end of the Doushantuo stage may represent a global event,which might be related to oxidation of deep seawater.

关键词： Doushantuo stage sulfur isotope carbon isotope snowball Earth bacterial sulfate reduction isotopic fractionation

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