川中地区大安寨段介壳滩沉积特征及控制因素

Sedimentary Characteristics and Factors Controlling the Shell Beach in the Da′anzhai Member of the Central Sichuan Basin

在岩芯及显微镜下观察的基础上,明确了川中地区侏罗系大安寨段发育介壳灰岩、含泥质介壳灰岩与泥质介壳灰岩等3种岩石类型,为浅湖—半深湖环境介壳滩不同微相的沉积产物。测井及地震相综合分析认为,介壳滩中可进一步识别出滩主体、滩翼及滩前斜坡等几种微相,这几种微相在平面上的分布主要受古地貌控制:滩主体分布在水下隆起区;滩翼分布于水下隆起周缘;滩前斜坡主要分布于水下隆起区与沉积中心之间的过渡环境。介壳滩在纵向上的演化和迁移主要受湖平面变化控制,湖平面上升期,介壳滩由湖盆中心的低隆起区向湖盆周缘隆起区迁移;而在湖平面下降期,介壳滩又逐渐由湖盆周缘隆起区向湖盆中心低隆起区迁移。

Core and microscope observations reveal that the three types of rocks in the Jurassic Da′anzhai Member of the Central Sichuan Basin, which include shell limestone, muddy shell limestone, and shaly shell limestone, are the sedimentary products of the shell beach in the shallow–semi-deep lake environment. We determined the following sedimentary microfacies on the shell beach based on logging and seismic facies studies: main beach, beach wing, and slope before beach. The distribution of the microfacies is controlled by the ancient landform. The main beach is distributed on the underwater paleo-uplift, the beach wingsurrounds the uplift, and the slope is distributed in the transitional area between the underwater paleo-uplift and the depocenter.The evolution and migration of the shell beach is controlled by the lake level changes. When the lake level rises, the shell beach migrates from the low uplift of the depocenter to the periphery uplift of the basin. When the lake level declines, the shell beach migrates from the periphery uplift of the basin to the low uplift of the depocenter.