川西南乐山地区灯影组二-三段岩石学特征及沉积环境分析

Petrological Characteristics and Sedimentary Environment of the Menber 2 and 3 of Dengying Formation,in Leshan Area,Southwest Sichuan

乐山地区位于上扬子地台西南缘,该区灯影组二-三段发育了一套白云岩沉积岩层。在野外实测剖面、显微薄片鉴定和扫描电镜分析的基础上,通过对先锋剖面岩石学特征的研究,结合前人的研究成果,将该区灯影组二-三段分为四个岩性段:灯二段下部以藻白云岩为主,部分层位发育泥微晶-粉细晶白云岩;灯二段上部以泥微晶-粉细晶白云岩为主,偶见藻白云岩;灯三段下部为藻白云岩,偶见泥微晶-粉细晶白云岩;灯三段上部以泥微晶-粉细晶白云岩为主,部分层位发育藻白云岩。根据室内微相分析的结果,参考Wilson的标准微相和碳酸盐台地沉积模式,可识别出云坪和藻云坪两种沉积微相。两种沉积微相在时空上的有序组合,构成了研究区灯影组二-三段碳酸盐岩局限台地内的潮坪亚相。根据沉积相在纵向和横向上的变化,建立了该区的沉积相模式,相对海平面的海退-海侵-海退-海侵沉积旋回很好的控制了沉积相模式的演化,为该区的地质研究和油气勘探提供了重要的基础地质资料。

Leshan is located in the southwest edge of the upper Yangzi platform, where the member 3 of Dengy- ing Formation is mainly composed of dolomites. Based on the field measured sections, microscopic slice identification and scanning electron microscopy analysis, and through the study of petrological characteristics in Xianfeng section, and combined with the previous studies, the member 2 and 3 of Dengying Formation can be divided into four lithologic sections： In the member 2 of Dengying Formation, the lower part is mainly consisted of algal dolo- mite. The dolomicriteaplitic dolomite also can be seen in some part of the horizon. The upper part is major consisted of dolomicrite and aplitic dolomite, and the algal dolostone can be found here occasionally. In the member 3 of Dengying Formation, the lower part is dominated consisted of algal dolomite, and the dolomicrite- aplitic dolomite can be discovered in the horizon occasionally. The upper part is mainly consisted of dolomicrite and aplitic dolomite, and the algal dolostone can be seen in some part of the horizon. Depending on the microfacies analyzing and according to the standard microfacies and carbonate platform model of Wilson, it can be recognized two microfacies ： Dolomitic flat and algal dolomitic flat. The order combination of two microfacies composed the tidal subface of restricted platform in member 2 and 3 of Dengying Formation in the study region. On the basis of longitudinal and transverse changes of the sedimentary facies, a sedimentary facies model of the study area is built. The evolvement of the sedimentary facies model is well controlled by regressive-transgressive-regressive-transgressive sedimentary cycle with relative sea level changes. The research provides important and basic geological data for geological research and oil and gas exploration in the study area.