川西北地区中二叠统层序地层研究

Study on the Middle Permian Sequence Stratigraphy of Northwest Sichuan Basin

以野外露头剖面为主,结合钻测井资料,将四川盆地西北部中二叠统划分为5个三级层序(SQ1—SQ5),平均延续时间约为3.4 Ma。三级层序界面主要为Ⅱ型层序界面,表现为岩性岩相转换界面,也可表现为暴露溶蚀面,以界面下溶蚀缝洞及其方解石斑块发育为特征;顶部为Ⅰ型层序界面,与东吴运动形成的不整合面叠合到一起,可表现为非均质、强烈的岩溶。受陆表海台地背景控制,在区内广大地区三级层序仅见海侵体系域和高水位体系域发育,海侵体系域多表现为低能的台内洼地沉积,高水位体系域多表现为相对高能的生屑滩沉积。三级层序往往具有海侵体系域的厚度大于高水位体系域的厚度的特征,反映了三级层序海平面变化是一个缓慢海进—快速海退的过程。

Through considerable outcrop, combined with drilling and logging data, we carry on research on middle Permian sequence stratigraphy of northwest Sichuan Basin. Believe middle Permian which is divided into five third - order sequences （SQ1--SQ5） is appropriate in the Sichuan Basin, and the average delay time is about 3.4 Ma. Three sequence boundaries mainly type is II sequence boundaries, manifested as lithology- lithofacies conversion interface. It can also perform exposed corroded surface, corrode fissure cave and calcite plaque development under interface. The top is type I sequence boundaries, superimposed together with unconformity which is formed by Soo- chow movement. It can perform non -homogeneous, strong karst. Epicontinental sea platform background control the development of TST and HST which only appears in the 3 order sequence around the research area. Transgress- ive systems tract expression as the relatively low -energy depressions deposition. Highstand systems tract more per- formance for the relatively high - energy bioclastic beach sediment. The sequence is mainly of TST 〉 HST, reflects the process of a low transgression - rapid regression in this period.