Oil & Gas Geology ›› 2016, Vol. 37 ›› Issue (4): 464-472.doi: 10.11743/ogg20160402

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Variation of Sr content and 87Sr/86Sr isotope fractionation during dolomitization and their implications

Wang Lichao1, Hu Wenxuan1,2, Wang Xiaolin1,2, Cao Jian1,2, Wu Haiguang1, Liao Zhiwei1, Wan Ye1   

  1. 1. State Key Laboratory for Mineral Deposit Research, Nanjing University, Nanjing, Jiangsu 210023, China;
    2. Institute of Energy Sciences, Nanjing University, Nanjing, Jiangsu 210023, China
  • Received:2015-03-10 Revised:2016-06-20 Online:2016-08-08 Published:2016-09-06

Abstract: 87Sr/86Sr ratio of dolomite is an important indicator for identifying source and characteristics of fluids related to formation and evolution of dolomite.Meanwhile,the ratio has been widely used in study of seawater 87Sr/86Sr ratio evolution of fossil seawater and strontium isotope stratigraphy.Thus,the existence and degree of influence of dolomitization on the 87Sr/86Sr ratio is crucial to understand the geologic significances of 87Sr/86Sr ratio of dolomite.However,no systematic research of this issue has been published.The Geshan section in Yixing County of Lower Yangtze region has excellent outcrops of carbonates including limestone,dolomitic limestone,calcite dolomite and dolomite,providing a chance to study the geochemical behaviors of strontium during dolomitization.In this study,we systematically analyzed the Sr contents and 87Sr/86Sr ratios of these carbonates.The Sr contents of these carbonates decrease significantly with enhancing dolomitization degree,from 1358μg/g of limestone to 94μg/g of dolomite,while the 87Sr/86Sr ratios increase from 0.708019 to 0.708182.An analysis of the relevant published data shows that the evolution feature of Sr is common to some degree,indicating that it may be attributed to the habitual behaviors of Sr during dolomitization.As Ca is replaced by Mg during dolomitization,the isomorphous Sr is lost simultaneously,leading to the lowering Sr content.In addition,lighter 86Sr emigrates from the process due to the constrint of mass effect,resulting in higher 87Sr/86Sr ratio.Therefore,the influences of dolomitization on 87Sr/86Sr ratio must be considered when identifying the source of dolomitization fluids,establishing the 87Sr/86Sr evolution curve of fossil seawater and analyzing the age of dolomite,so as to obtain correct understandings.

Key words: Sr content, 87Sr/86Sr ratio, dolomitization, strontium isotope stratigraphy, Lower Yangtze region

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