伊犁盆地南缘郎卡地区中侏罗统西山窑组沉积特征及演化

Sedimentary Characteristics and Evolution of the Middle Jurassic Xishanyao Formation in the Langka area,Southern Margin of the Yili Basin

针对伊犁盆地郎卡地区中侏罗统西山窑组铀矿地质勘查中对沉积相研究存在的问题,以钻孔岩芯精细研究为基础,结合区域地质背景及测井、地震、粒度等分析资料进行沉积相标志、沉积相展布及沉积演化等进行综合研究。研究成果表明研究区西山窑组主要发育辫状河三角洲和湖泊2种沉积相。西山窑组下段沉积时期,研究区发育辫状河三角洲平原沉积,分流河道砂体叠置连片分布;西山窑组中段沉积时期,湖平面上升,全区基本演化为辫状河三角洲前缘和滨浅湖沉积,水下分流河道砂体呈条带状展布;西山窑组上段沉积时期,研究区整体呈现出湖退过程,辫状河三角洲进积,以辫状河三角洲前缘沉积为主,水下分流河道在三角洲前缘亚相占主导地位。

To determine the best approach to the analysis of sedimentary facies during uranium exploration in the Langka area,Yili Basin,a series of studies was carried out involving detailed core observation.The appearance,distribution and evolution of the sedimentary facies were examined in the context of the regional geological background,core logging,seismic information and particle-size data.The studies suggest that braided river delta facies and lacustrine facies were developed in the Xishanyao Formation within the study area.During the deposition of the lower Member of Xishanyao Formation,braided delta plain sediments were deposited during the depositional period of the Lower Member,and overlapping distributary channel sandbodies were widely distributed.For the Middle Member,the lake level rose and shallow lake and mainly braided delta front facies were developed in the study area and ribbon-shaped sandbodies of subaqueous distributary channels were also widely developed.For the Upper Member,a regression process was evident in the study area together with progradation of the braided delta system.A mainly braided delta plain developed and its subaqueous distributary channel began to dominate the distribution of depositions.