塔中Ⅰ号坡折带上奥陶统方解石胶结作用研究

Cementation of Upper Ordovician calcite in Tazhong Ⅰ Offset Structural Belt

碳酸盐岩孔隙演化受各种成岩作用的控制。其中方解石胶结作用是破坏孔隙和降低孔隙度的主要因素之一。塔中Ⅰ号坡折带上奥陶统良里塔格组灰岩成岩类型和威岩期次繁多，关系较为复杂。根据岩心、薄片、阴极发光和地球化学分析等资料，通过对各种成岩产物和成岩组构特征的综合研究，共识别出3期12种方解石胶结类型。第一期胶结作用发生于海底成岩环境，产物主要有微晶、纤状、放射纤维状、束状、放射轴状方解石和似球文石。充填孔隙为0-30％；第二期胶结作用发生于大气淡水环境中，主要胶结物类型有新月型或悬垂状、渗流粉砂、共轴增生等，充填孔隙为5％～100％；第三期胶结作用发生于埋藏环境中，晶体明亮粗大，以粗粒亮晶、嵌晶方解石为主，充填孔隙为5％～100％。文中系统总结了各期胶结作用对孔隙演化的影响，并建立了孔隙演化史。

The pore evolution of carbonate is controlled by all kinds of diageneses, in which the calcite cementation is one of the most important reasons for pore damage and porosity decline. Diagenetic types and stages in limestone of Lianglitage Formation of Upper Ordovician in Tazhong Ⅰ Offset Structural Belt are various and the relationships between them are complex. Based on the analysis and research results of all diagenetic products and structural fabric characteristics by core, thin section, cathodelu-minescence and geochemistry, three phases and ten kinds of calcite cementations have been identified. The first phase cementation occurred in submarine diagenetie environment and the products are mierocrystalline calcite, fibrous calcite, divergent fibrous calcite, fasciculate calcite, radial-axial calcite and subspherical iglite with a pore filling of 0 to 30%. The second phase cementation occurred in atmospheric diagenetic environment and the main products are crescent or pendent calcite, vadose silt, syntaxial cement with a pore filling of 5% to 100%. The third phase cementation occurred in burial diagenetic environment. The crystals of cement are bright and massive and the main types are calcsparite and poikilotopic calcite with a pore filling of 5% to 100%. This paper systematically summarized the influence of cementation on pore evolution and established the history of porosity evolution.