四川宣汉盘龙洞上二叠统长兴组白云岩组构定向与统计特征及其成因意义

Origin Evidenced by Statistic Feature and Orientation Fabric in the Upper Permian Changxing Formation Dolostone of Panlongdong,Northeastern Sichuan

四川盆地东北部发育的长兴组礁滩相白云岩层是油气勘探的重点对象,盘龙洞剖面是四川盆地发育最好的长兴组露头,其成岩作用研究对于认识川东北长兴组储层的形成演化控制因素具有很强的借鉴作用。白云岩的组构和产状包含了成因信息,笔者根据薄片观察发现白云石交代结构可分为"均一"与"不等晶"交代两种类型,过渡关系与阴极发光观察结果均表明细中晶是由粉晶发育而来的,且细中晶白云石具"组构定向"现象。首次对该地区白云岩的组构进行了定量统计。统计结果表明,细中晶白云石粒径大小和含量在纵向上有明显的变化规律,含量自上而下减少、粒径变小。结合成岩作用、流体包裹体、阴极发光研究结果综合分析后认为:白云石化作用开始于成岩早期,白云化流体具有低温、高盐度的特点,白云化流体自上而下运移。

The dolostone of the Changxing Formation in Sichuan Basin is an important target of the exploration of petroleum. The Panlongdong profile is the best outcrop in northeast Sichuan, and the research of diagenesis of this profile is of vital importance for understanding the formation and evolution of Changxing reservoirs. The fabric and occurrence of dolostone contains genetic information. With the help of CL, we found that fabrics of dolostone can be divided into two types： uniform and heterogeneous, and the coarse dolomites are developed from the fine dolomites. The growth of powder dolomites is directional. Based on the research of diagenesis, statistics analysis of contents and sizes of dolomites are performed for the first time. The statistic result shows that the content and size of dolomite gradually reduced downward, which indicates that the dolomitizing fluid migrated downward, and the prevailing mimetic dolomites proves evidence of penecontemporaneous dolomitization.