鄂尔多斯盆地延长组下组合沉积期湖盆迁移演化及沉积响应

Migration evolution of lake basin and sedimentary response in deposition period of lower assemblage in Yanchang Formation,Ordos Basin,China

依据野外露头、岩心观察及实验室测试资料,对鄂尔多斯盆地延长组下组合长9、长10段沉积微相、岩矿特征、粒度特征及地层结构等进行了系统研究,结果表明:(1)延长组下组合沉积时期,湖盆沉积中心并不固定,从早期的"泄水区"逐步转变为"汇水区",湖盆沉积中心向西作大规模迁移。(2)沉积中心迁移导致盆地东南与西北沉积体系先后呈现出不对称发育的沉积格局,早期(长10期)西部(西北)与北部河流沉积体系强盛,基本无南部物源体系;晚期(长9期)开始发育南部(西南)物源体系。(3)盆地南部昆仑-秦岭洋由东向西呈"剪刀式"碰撞闭合是湖盆沉积中心迁移演化,以及沉积体系不对称发育的根源。(4)受湖盆沉积中心迁移演化的控制,长9与长10的有利勘探方向不同,长9期西部体系勘探前景最好;长10期河道砂体与上覆长9油页岩匹配,在纵向上可以形成"上生下储"式成藏组合,值得关注。

According to a large number of data on field outcrops,core observation and laboratory test,this paper makes a systematic study on the sedimentary microfacies,mineral and lithological features,grain-size characteristics and stratal configuration of Member Chang 9 and Member Chang 10 of the lower assemblage in Triassic Yanchang Formation.The results show as follows.（1） During the sedimentary period of the lower assemblage in Yanchang Formation,the depocenter of the lake basin was not fixed,transforming from an early ＂discharge area＂ to a ＂collection area＂ gradually and made a large-scale migration westward.（2）Because of the depocenter migration,the southeast and northwest sedimentary system of the basin showed the sedimentary pattern with asymmetric development successively.In the early stage （Chang 10）,western （northwest） and northern fluvial sedimentary system was strong,southern provenance system was not developed basically and in the late stage （Chang 9）,the southern （southwestern） provenance system began to develop.（3） The KunlunQinling Ocean in the south of the basin appeared the collision and closure as a form of ＂scissors＂ from east to west.It was the depocenter migration evolution and the source of that the sedimentary system developed asymmetrically.（4） Controlled by depocenter migration evolution,the favorable exploration direction of Member Chang 9 and Member Chang 10,will be different.In the sedimentary period of Member Chang 9,the exploration prospect of the west system is the best and in the sedimentary period of Member Chang 10,the channel sand body matches the oil shale of Member Chang 9.Member Chang 10 can form reservoir-forming combinations of ＂upper generation and lower storage＂ in the longitudinal direction and should be attended to.