四川盆地垫江—万县地区长兴组层序格架内沉积相演化

摘要

After integration analysis of outcrop,core,logging and seismic data,it is recognized that Upper PermianChangxing Formation is carbonate platform deposition in Dianjiang-Wanxian area,Sichuan Basin.Because of E-mei taphrogeny,two platforms and two trenches developed in Dianjiang-Wanxian area.Based on the establishment of third-order sequence framework,the distribution of sedimentary facies is studied.It is considered that there is a carbonate platform system during the Changxing period in Dianjiang-Wanxian area,which is controlled by Kaijiang-Liangping trench and includes open platform,platform edge and ramp facies.Reef,bioclastic shoal and tidal flat facies developed in the platform edge during the high system tract period of the two third-order sequences of Changxing Formation are favorable facies belts.And only a little reef and shoal developed in platform edge during the transgression system tract period of the upper third-order sequence.Being affected by regression,reef and shoal moved to the east-north of the study area.%通过对露头剖面、钻井岩心、测井和地震等资料的综合分析,认为四川盆地垫江—万县地区上二叠统长兴组总体为碳酸盐岩台地沉积。由于峨眉地裂运动的影响,造成垫江—万县地区具有＂两台-两槽＂的特征。在三级层序地层格架建立的基础上,研究沉积相的展布规律,发现受开江—梁平海槽的控制,长兴组时期发育较为对称的碳酸盐岩沉积体系,主要发育开阔台地相、台地边缘相及斜坡相。长兴组2个三级层序高水位体系域沉积时期,台地边缘相带内发育的生物礁、生屑滩及潮坪相为有利相带;海侵体系域沉积时期,只有上部三级层序台地边缘发育了一定规模的礁滩体。因海退的影响,上部三级层序发育的台内礁滩体与下部三级层序发育的台内礁滩体相比,具有向研究区北东方向迁移的特征。