渝东北巫溪地区奥陶纪-志留纪转换期白云质条带形成机理及地质意义  

Formation Mechanism and Geological Significances of the Ferrodolomite Layers in Strata of the Ordovician-Silurian Transition Zone in the Wuxi Area of the NE Chongqing

作　　者：冯明友[1] 尚俊鑫 刘田 刘小洪[1] 王兴志[1] 朱逸青 王珏博[1] FENG Ming-you;SHANG Jun-xin;LIU Tian;LIU Xiao-hong;WANG Xing-zhi;ZHU Yi-qing;WANG Jue-bo(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;Gas Production Plant of PetroChina Changqing Oilfield Company,Yulin,Shanxi 719000,China;PetroChina Southwest Oil&Gasfield Company,Chengdu 610051,China)

机构地区：[1]西南石油大学地球科学与技术学院,成都610500 [2]中国石油长庆油田分公司第二采气厂,山西榆林719000 [3]中国石油西南油气田分公司,成都610051

出　　处：《矿物岩石地球化学通报》2022年第3期599-611,共13页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家“十三五”科技重大专项课题(2017ZX05001001-002);四川省教育厅科研项目(16ZB0089)。

摘　　要：为厘清渝东北巫溪地区O/S界线附近白云质条带的形成环境及条件,对其开展了岩石学、矿物学及地球化学系统研究。结果表明,该条带多呈薄层状与泥页岩互层产出,以(含)铁白云石为典型特征。铁白云石晶体多为粉-细晶,具球状、似“雾心亮边”结构,呈飘浮状分散于硅质中或围绕基性火山岩岩屑生长。铁白云石属产甲烷菌和硫酸盐还原菌共同作用的微生物成因。火山活动产生的大量火山物质以及海平面快速下降引发的沉积环境突变导致的生物大灭绝为其形成提供了物质基础,相对封闭的贫氧环境有利于有机质在甲烷菌和硫酸盐还原作用下形成HCO_(3)^(-),早期沉积的基性火山物质大量脱水析出的Fe^(2+)、Mg^(2+)、Ca^(2+)等离子与HCO_(3)^(-)结合形成铁白云石。白云质条带的发育程度可作为奥陶纪-志留纪转换期火山作用及环境改变控制下细菌介导的成岩早期岩石-流体作用证据。In order to clarify the formation environments and conditions of ferrodolomite layers in the strata of the Ordovician-Silurian transition zone in the Wuxi area of the Northeastern Chongqing, a systematic study on petrography, mineralogy and geochemistry of the ferrodolomite layers has been performed in this paper. The results show that the dolomite layers occurred as several thinly bedded layers interbedded with muddy shale layers in strata, and they are mainly composed of ferrodolomite/ankerite in form of powder crystalline-microcrystalline with spherical and cloudy center bright rim textures. Ankerites are floatingly dispersed in siliceous parts or occurred around mafic volcanic debris in those ferrodolomite layers. It is beloved that ankerite belongs to the microbial genesis under the interaction of methanogens(AOM) and sulfate-reducing bacteria(BSR). A large amount of volcanic materials produced by volcanic activity and biological mass extinction caused by the abrupt change of sedimentary environment resulted from the rapid drop of sea-level in the area had laid the material foundation for the formation of ankerite layers. The relatively anoxic environment was conducive to the formation of HCO_(3)^(-) by the methanogens and sulfate reduction of organic matters. The ferrodolomite or ankerite was formed by the combination of Fe^(2+), Mg^(2+), Ca^(2+) and other ions, which were sourced from the dehydration of early deposited volcanic materials, with the above HCO_(3)^(-). The development degrees of the ferrodolomite layers can be used as evidences for the rock-fluid interaction at the early diagenetic stage resulted from the bacterially-mediated effect under the controlling of volcanism and environmental change during the Ordovician-Silurian transition period.

关 键 词：O/S转换期 铁白云石 火山作用 细菌介导 早期成岩作用 

分 类 号：P588.245[天文地球—岩石学] P595[天文地球—地质学]