埋藏环境中硫酸盐岩生物岩溶作用的硫同位素证据

为了揭示油气盆地埋藏环境中碳酸盐岩和硫酸盐岩共生时的岩溶发育机制, 以硫酸盐岩为研究对象, 采用室内模拟实验与野外实测资料相结合的方法, 分析了温度、SO₄2-浓度和时间等因素对水-岩-细菌封闭系统内稳定硫同位素的影响, 并指出硫同位素对地球化学作用的指示意义.结果表明, 细菌硫酸盐还原形成的H₂S中硫同位素分馏明显, 并受系统的温度和开放性等因素影响.结合鄂尔多斯盆地奥陶系风化壳中充填的黄铁矿硫同位素特征, 提出了鄂尔多斯盆地奥陶系岩溶的生物成因模式; 揭示了风化壳顶部的黄铁矿化与风化壳下部压释水岩溶共生的机制, 建立了生物岩溶发育的硫同位素地球化学标志.研究成果拓宽了岩溶的压释水成因机制. 

Sulfur Isotopic Evidence for Biological Karst of Sulfate Rocks in Burial Environment

The purpose of this study is to explore the biological karst developing mechanism at the coexistence condition of the sulfate and carbonate rock. The study focuses on the geochemical processes in water-rock-bacteria system by tracing the stable sulfur isotope (34S) fractionation through laboratory experiment combined with the isotope data of the pyrite filling in Ordovician weathering crust in the Ordos basin. The results suggest that the H₂S produced by bacterial sulfate reduction (BSR) is characterized by a significant isotope fractionation of 34S, which was controlled by temperature and the SO₄2- concentration from the dissolution of sulfate rocks in the system. Bacterial sulfate reduction in the experimental system provides an evidence for biological karst on sulfate rocks, and gives a good interpretation for the feature of karst development below the Ordovician weathering crust, Ordos basin. In addition, the presence of pyrite and compacted released water karst confirms that bacterial sulfate reduction took place within the weathering crust during the burial stage. The results provide a new perspective for the analysis of the formation of oil-gas reservoir and the exploration of petroleum gas geology resources.