塔里木盆地中央隆起区上寒武统—下奥陶统白云岩储层中两类白云石充填物:特征与成因

Feature and Origin of Dolomite Filling in the Upper Cambrian-Lower Ordovician Dolostone of the Central Uplift,Tarim Basin

在塔里木盆地中央隆起区,下古生界白云岩储层中的白云石充填物从形态上可分为菱形和鞍状两类,它们具有不同的岩石学特征,菱形白云石内部结构简单均一,而鞍状白云石内部结构比较复杂,由内核、环带和外缘三部分组成。地球化学组成分析表明,菱形白云石可能形成于成岩作用的早期,成岩物质可能来源于改造的海水,其沉淀是一个相对稳定的过程,后期仅少量受到富铁流体的改造。而鞍状白云石的形成则可能与断裂诱发的深部热流体活动密切相关,其物质可能来源于深部热液在运移过程中对围岩白云石的溶解,鞍状白云石内部复杂的结构可能反映了断裂的幕式活动。因此,两类白云石充填物反映了不同的成岩流体环境,特别是鞍状白云石很可能是热液溶蚀作用发生的重要标志。在白云岩储层研究中,今后需要进一步深入详细分析充填物的产状、充填作用发生的时间和机制,对于研究分析白云岩储层形成机制和储层预测都有重要意义。

Two genetically distinct dolomite fillings are recognized in Lower Paleozoic dolostone in the Upper Cambrian-Lower Ordovician dolostone of the Central uplift, Tarim basin： rhombus and saddle dolomite fillings, which occur in different diagenetic considerations and have different character. The former crystal exhibits homogeneous, the later crystal is composed of three distinct parts that are rim, clitellum and core. Stratigraphie, petrographic and geochemical date suggest, rhombus dolomite filling deposited steadily and source of Mg^2＋ is from the altered seawater. However, material source of saddle dolomite filling is hydrothermal dissolution of dolomite. The formation of saddle dolomite filling, three parts of which formed in different phase, is associated with faulting. The deposition of dolomite filling is porosity decreasing, but saddle dolomite is a sign of dissolution.