川东北南江地区灯影组三段岩石特征及沉积环境分析

南江地区位于上扬子地台东北缘,该区灯影组三段发育了一套以白云岩为主的沉积岩层。通过对杨坝剖面岩石学特征及沉积相的研究,结合前人的研究成果,认为该区灯影组三段可分为三个岩性段:下部以粉-微晶、泥微晶白云岩为主;中部以砂屑白云岩为主,局部可见角砾状泥微晶白云岩;上部以硅化细-粉晶白云岩、硅化叠层藻白云岩为主,部分层位发育角砾状粉微晶白云岩、中-细晶白云岩。岩层中主要发育纹层状、条带状、藻叠层及缝合线构造;并且认为研究区灯影组三段地层发育在碳酸盐台地-陆表海环境中,从底到顶可识别出泻湖、浅水碳酸盐砂滩、潮坪三种亚相的沉积。总体上为一海侵-海退的沉积旋回。

Lithology characteristic and sedimentary environment of the Member 3 of Dengying Formation, in Yangba area, northeast Sichuan

Nanjiang Yangba, is located in the northeast edge of upper Yangzi platform where the member 3 of Dengying Formation is mainly composed of dolomites. Based on studies in rock characteristics and sedimentary facies of Yangba Profile, and also combined with results of previous studies, indicate that the member 3 of Dengying Formation, in this district, can be divided into three lithologic sections: the lower part is mainly consisted of the silt-micritic and mud dolomicrites; the middle part is mostly composed of dolarenites with local brecciated mud dolomicrites; the major composition of the upper part is the silicified fine-microcrystalline dolomites, silicified stromatolithic dolomites with local brecciated silt-micriticdolomites and finely crystalline dolomite; most of the rocks have laminated, banded, stromatolithic and stylolitic structure; and considered that the member 3 of Dengying Formation in this area is deposited in the environment of carbonate platform-the epicontinental ocean, and there are three sedimentary subfacies: lagoon, shallow-water carbonate sand beach, tidal flat. The entire profile is a transgressive - regressive sedimentary cycle.