中国中西部盆地海相白云岩主要形成机制与模式  

Major formation mechanisms and models of marine dolomite in middle and western basins of China

作　　者：张静[1] 张宝民[1] 单秀琴[1] ZHANG Jing;ZHANG Baomin;SHAN Xiuqin(Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China)

机构地区：[1]中国石油勘探开发研究院,北京100083

出　　处：《地质通报》2017年第4期664-675,共12页Geological Bulletin of China

基　　金：国家科技重大专项项目<大型油气田及煤层气开发>(编号:2011ZX05004)

摘　　要：塔里木、四川及鄂尔多斯盆地是中国中西部海相白云岩的主要发育地区。三大盆地重点层系海相白云岩新近的成因研究表明,大规模准同生白云岩和埋藏成因白云岩的发育均与蒸发台地密切相关。蒸发台地中由海水浓缩形成的富Mg^(2+)卤水一方面在准同生期,通过蒸发泵和下渗机制交代碳酸钙沉积物而形成与蒸发岩共生的准同生白云岩,另一方面作为富含Mg^(2+)的地层孔隙水,在准同生-浅埋藏期乃至中、深埋藏期,通过侧向渗透、侧向与垂向压实排挤和垂向热对流机制与粗结构的碳酸钙沉积物发生交代反应,在蒸发岩系周边和上下形成广泛分布的埋藏成因白云岩。与热流体作用有关的白云石化主要依靠构造断裂、裂缝、不同级次的层序界面、孔洞层等输导体系发生,分布较局限。热流体云化常表现为对先期白云岩进行叠加改造而形成热水改造白云岩。热流体性质不一,可以是深埋藏混合热水、深部循环水、地幔深部的岩浆热液等。白云石(岩)的生物成因不仅表现为微生物作用导致白云石直接沉淀,还表现为生物的存在与活动为白云石化作用提供Mg^(2+)和云化流体通道。由微生物和宏观藻释放出Mg^(2+),在埋藏期对方解石进行交代是各种富含藻类的灰岩中部分白云石的重要形成机制。生物扰动可明显改善岩石的孔渗性,从而显著促进白云石化作用的发生。Marine dolomite is mainly developed in Tarim,Sichuan and Ordos basins in middle and western China.Recent study of the dolomite origin in key strata shows that the formation of massive marine penecontemporaneous dolomite and burial dolomite was closely related to the carbonate evaporative platform.The brine in the evaporative platform was not only the dolomitizing fluid of the penecontemporaneous dolomite which often coexisted with the evaporite and was formed by evaporation pump and seepage reflux mechanism,but also the pore water with abundant Mg2+which could induce further water-rock reaction with coarse limestone by lateral seepage,lateral and vertical compact mechanism and vertical thermal convection mechanism in penecontemporaneous to shal?low burial and even medium to deep burial environment,resulting in widespread burial dolomitization around,above and below the evaporite.Hydrothermal dolomitization was often the reworking action on previous dolomite which was confined to the fractures,se?quence boundaries,beddings and porous strata,with deep mixed hot water,deep circulation water and magmatic solution as the hy?drothermal dolomitizing fluid.Besides microbial dolomitization by which microbe could induce dolomite precipitation,the organic matter might also provide Mg2+to dolomitization,as reflected by the dolomitization of the algal limestone.The release of Mg2+from the microorganism and macro-algae was an important factor for the formation of part of the dolomite in the algal limestone.Biotur?bation could facilitate dolomitization by enhancing the porosity and permeability of the rock which could provide space and channel for the dolomitizing fluid.

关 键 词：海相白云岩 白云石化 云化机制 云化模式 

分 类 号：P581[天文地球—岩石学]