塔里木盆地中央隆起区寒武-奥陶系白云岩结构特征及成因探讨

白云岩研究的关键在于对白云石化作用的理解,而岩石结构作为白云石化作用分析的基础,不仅对白云岩的成因具有指示意义还深刻地影响着白云岩储层的质量。通过岩芯、薄片、扫描电镜、阴极发光以及碳、氧、锶同位素等测试手段,结合国际上常用的分类术语,对塔里木盆地中央隆起区寒武-奥陶系白云岩按结构进行了分类,并探讨了不同结构类型与其成因之间的关系。研究表明,白云岩结构与其形成环境和形成过程密切相关,其中保留原始结构的白云岩（包括泥-粉晶白云岩和颗粒白云岩）属于同生或准同生阶段、与蒸发海水有关的拟晶白云石化作用的产物,大量过饱和白云石化流体的通过有利于原始结构的保存;晶粒白云岩中,具有平直晶面结构的细晶、自形白云岩和细晶、半自形白云岩与浅埋藏成岩阶段的低温白云石化作用有关,云化流体以轻微蒸发的海源流体为主,浅埋藏晚期的过度白云石化作用导致晶体由平面-自形向平面-半自形转化;中-粗晶、他形白云岩是中或深埋藏成岩阶段的高温/热液白云石化或重结晶作用的结果,较高的形成温度导致晶体发生曲面化。

Textural Types and Origin of the Cambrian-Ordovician Dolomite in the Central Tarim Basin

The study of the dolomite texture, as the foundation of dolomitization analysis, not only indicates the origin of the dolomites but also controls the dolomite reservoir quality significantly. The main objectives of this paper are to investigate the dolomite texture types and origin of the Cambrian-Ordovician dolomite in the central Tarim Basin, based on the analysis of the core, thin-section, SEM, cathodoluminescence and C-O-Sr isotope, as well as the widely used terminology for dolomite texture in international academic circles. The results show that there are two types of replacement dolomite: one is the dolomite with well-preserved precursor lithologic fabric that can be subdivided to micritic dolomite and (relict) dolo-grainstone, the other type is the crystalline dolomite, including fine crystalline, planar-e(euhedral) dolomite, fine crystalline, planar-s(subhedral) dolomite and medium to coarse crystalline, nonplanar-a(anhedral) dolomite. Additionaly, two types of void-filling dolomite cement have been observed that are very fine to fine crystalline, planar-e(s) dolomite void-filling and medium to coarse crystalline, saddle dolomite void-filling, respectively. Different texture types of the dolomite indicate that the diagenetic environments and formation processes of the dolomite are various. For the study area, the dolomite with well-preserved precursor fabrics is associated with the mimetic dolomitization during the penecontemporaneous period. Abundance of high-supersaturation dolomitizing fluid is beneficial to  the perservation  of precursor fabrics. The planar-e and planar-s dolomite  are  probably formed from reflux of penesaline seawater during early diagenetic stage by the low-temperature dolomitization. Overdolomitization may play a vital role in planar-e crystals transferring to planar-s crystals with decreasing of pore space. The nonplanar-a dolomite is interpreted as the product of high-temperature/hydrothermal dolomitization and recrystallization during the medium or deep burial, the high temperature is the key to cause dolomite crystal boundary transferring to nonplanar-anhedral.