黔北西部及邻区晚三叠世末期-中侏罗世沉积与层序地层特征

黔北西部及邻区晚三叠世末期-中侏罗世,为印支运动导致的海相沉积历史结束后开始的一段陆相沉积时期。其沉积特点是湖泊沉积占主导,河流沉积次之。在纵向上表现为河流沉积出现在该时期地层序列的下部二桥组和上部下沙溪庙组和上沙溪庙组中;湖泊沉积则贯穿整个研究时期的地层中,特别是地层序列中部自流井组中发育良好。河流沉积具二元结构,下部为边滩沉积,上部为堤岸沉积。湖泊沉积分为滨湖、浅湖和深湖三个亚相沉积,在地层序列上显示出两个由浅至深的旋回变化特点。研究时期的地层具有旋回性特点,以不整合面及相应的整合面作为层序界面,可分为5个沉积层序,每个层序由水进体系域和水退体系域组成,粗略地反映了湖平面的5次进退变化。

Sediment and Atratum Succession Characteristic of the Last Stage of Late Triassic and Middle Jurassic in Northwest Guizhou and the Nearby Area

The last stage of late Triassic and middle Jurassic in northwest Guizhou and the nearby area is a land facies sedimentary period after the sea facies sediment caused by indosinian movement.Its sedimentary characteristic is the lake sediment is predominant,and the nest is the river sediment.In the vertical dimension,it shows that the river sediment appears in the lower Er＇qiao formation and upper Xiashaximiao formation and Shangshaximiao formation of the stratum succession in this period,the lake sediment crosses the stratum in the whole study period,especially develops well in the Bailiujing formation.The river sediment is dualistic structure,the lower part is flat sediment and the upper part is embankment sediment.The lake sediment is divided into three sub-fasies sediments： lakeside,low lake and deep lake,it shows two procession features from shallow to deep in the stratum succession.The stratum of the studying period has the feature of procession,the unconformable plane and relevant conformable plane as the succession plane,it can be divided into five sedimentary sequences,and each sequence is made of transgressive systems tract and regressive system tract,reflects 5 times advance and retreat translations on the lake plane.