鄂西地区三叠纪嘉陵江组二段与三段局部平行不整合识别及沉积古地理研究

Identification of the Accord Unconformity between the Middle and the Upper Jialingjiang Formation and Palaeogeography

研究区位于上扬子地块的中北缘,南秦岭造山带的南侧,西侧为米仓山断裂带与大巴山弧形断裂带,是北东向构造区与近东西向构造区的叠合位置,在构造分区上具有重要的意义,构造运动在本区具有敏感的响应。前人在对本区的研究中认为晚二叠世–早三叠世的地层中均为整合接触。但在本次调查过程中,通过沉积地层、构造资料的研究对比分析,识别出了嘉陵江组二段与三段(T1-2j2/T1-2j3)之间的局部平行不整合接触关系,代表区域内又一次差异升降运动。同时将印支运动在本区活动的时限由中晚三叠世向前推至早–中三叠世。

The study area is located on the northern edge of the Yangtze Block and the south side of the Southern Qinling orogenic belt, and on the west side of this area there are Micang mountain fault belt area and Dabashan arc fault belt area. This area is an overlaying zone between NE and EW trending structure, and it shows great influences on the structure partition, with sensitive response to tectonic movement in this area. The early study believes that the formations from the Late Permian to the Early Triassic are conformities. However, this study, from the analysis of sediment formations and structure, identifies the accord unconformity between the middle and the upper Jialingjiang formation (T1-2j2/T1-2j3), which stands for another differential subsidence. The latest effect time of Indosinian movement in this area is early-middle Triassic.