川中地区上三叠统须二段和须四段储集砂体成因类型及其发育的主控因素

Genetic types and main controlling factors of sandbodies in second and fourth members of Xujiahe Formation,upper Triassic,Central Sichuan Basin

利用野外露头、钻井岩心和测井等地质资料,研究了川中地区上三叠统须家河组二段和四段砂体成因类型及特征,分析了砂体形成及分布的受控因素。研究区砂体主要由浅水三角洲前缘和滨浅湖滩坝砂体组成。古地貌形态对砂体的形成起重要的控制作用。当基准面下降时,来自盆地周边山系的碎屑物质沿高可容纳空间的沟谷带进入湖盆,在河流、波浪和沿岸流的冲刷作用下,形成不同程度席状化的三角洲前缘砂体。随着基准面的上升,波浪和湖流的改造作用占主导地位,沉积物将发生再分配,在缺少物源的滨岸区或雷口坡组顶部古残丘附近沉积下来,形成新的滩坝砂体。随着湖岸线的频繁迁移,砂体既可向湖方向推进,也可向平行岸线方向迁移,最终形成分布面积广、厚度稳定的若干砂岩体叠加层。

Based on the geological data of outcrop,drill core and logging and so on,the genetic types and characters of sandbodies in the second and fourth members of Xujiahe Formation in Central Si-chuan Basin were researched,and the controlling factors of sedi-mentation and distribution of the sandbodies were analyzed. The sandbodies in the research area mainly are composed of shallow-water delta front sandstone and the beach bar sandstone of shore -shallow lacustrine facies. Ancient landform was important on controlling the sandbodies deposition. When base level dropped,clastic deposit came from the cordillera of peripheral basin en-tered lake basin along the ravines with high accommodation space. By the washing action of rivers,wave and littoral current,the blanket delta-front sandbodies were formed. When the base level raised,the action of wave and lake current was dominant with the redistribution of sediments. The sediments deposited in the lakeshore lacks of source or near paleo-hammock on the top of Leikoupo Formation to form new sandbodies of the beach bar. With frequent migration of lake strandline,the sandbodies may advance not only to the direction of lake but in the parallel direc-tion of lake strandline. Several superimposed layers of sandbodies with broad area and stable thickness would be formed finally.