四川盆地中二叠统栖霞组滩相白云岩多重成因机理及叠加效应

本文以四川盆地二叠系栖霞组滩相白云岩为研究对象,充分利用野外剖面资料、钻井资料、测试分析资料,对栖霞组滩相白云岩成因机理及其叠加效应进行了深入研究。结果表明,四川盆地栖霞组白云岩的规模变化较大,从不到1米至几十米不等,区域上主要分布于盆地西部,盆内其它地区零星发育。白云岩的发育与沉积背景关系密切,其中分布于盆地西部的白云岩为台地边缘滩相沉积背景,而盆地内零星分布主要为台内滩沉积背景。栖霞组白云岩成因包括三种类型:(1)高能滩混合水白云岩化形成的白云岩;(2)埋藏白云岩化形成的白云岩;(3)热液白云岩化形成的白云岩。其中,高能滩混合水白云岩化形和热液白云岩化为主要的白云岩化作用。现今无论是在野外剖面还是钻井岩心中所看到的白云岩为多种白云岩化作用的叠加结果,叠加效应体现在白云石晶体形态上、碳氧同位素和包裹体温度上。在白云岩形成过程中,滩相沉积是白云岩化的基础;不同类型的白云岩化作用是关键;裂缝的发育为白云岩化创造了条件。

The genetic mechanism of shoal facies dolomite and its additive effect of Permian Qixia Formation in Sichuan Basin

The genetic mechanism of shoal facies dolomite of the Permian Qixia Formation in the Sichuan Basin and its additive effect are researched in depth using outcrop, drilling, and analysis data. The results show that dolomite developed widely in the Sichuan Basin in depths ranging from one meter to dozens of meters. The dolomite developed mainly in the western part of the basin and sporadically in the interior. The development of dolomite has a close relation with the sedimentary environments. The massive dolomite in the western basin developed in the environment of platform margin banks, while the sporadic dolomite of the interior basin developed in inner platform bank. The three genetic types of shoal facies dolomite of the Qixia Formation form by three main processes: (a) mixed water dolomitization in high energy beaches; (2) burial dolomitization; (3) hydrothermal dolomitization. The main forms of dolomitization are mixed water dolomitization in high-energy beaches and hydrothermal dolomitization. Today, the dolomite we see both in outcrops or drilling cores result from the superposition of multiple layers of dolomitization. The additive effect is reflected in the dolomite crystal morphology, carbon and oxygen isotopes, and fluid inclusions temperature. Different types of dolomitization are the key for this process. The beach facies serves as the foundation for dolomitization and fractured development creates the conditions necessary for dolomitization.