柴西北缘跃进二号地区晚新生代沉积特征及沉积相演化

Late Cenozoic Sedimentary Characteristics and Sedimentary Facies Evolution in Yuejin 2 Area of Northwest Qaidam

柴西北缘跃进二号地区沉积相特征精细研究对油气及铀矿勘查意义重大。笔者通过收集柴西北缘典型油气矿区200余孔典型钻孔资料,结合区域古地理及构造特征,分析砂体等厚度图,绘制柴西北缘晚新生代上油砂山组、狮子沟组及七个泉组沉积相平面图,揭示柴西北缘在晚新生代主要发育辫状河三角洲前缘、扇三角洲平原、辫状河三角洲平原、滩坝、扇三角洲前缘、洪泛泛滥平原及滨浅湖等沉积亚相及沉积相。通过对跃进二号地区ZK8-20、跃Ⅱ5-21、ZKⅡ1-10、跃Ⅱ4-11下、跃Ⅱ2-6等钻孔不同地层岩性、颜色、沉积序列、测井曲线、沉积结构构造等的综合分析,根据沉积学原理,认为该区在上油砂山组及狮子沟组主要发育辫状河三角洲平原,表现为水上分流河道及分流河道间沉积特征;第四系七个泉组主要发育辫状河三角洲前缘沉积相,表现为河口坝沉积微相、分流间湾微相及水下分流河道微相等。识别出研究区在晚新生代沉积相主要表现为退积式分布特征,湖水平面在狮子沟组有轻微下降,在七个泉组上升;研究区垂向上从下向上发育辫状河三角洲前缘亚相、辫状河三角洲平原亚相、滨浅湖亚相,形成了上部湖相,下部辫状河三角洲相的沉积模式。

The detailed study of the sedimentary facies in Yuejin 2 area of northwest Qaidam is of great significance to the exploration of oil,gas and uranium deposits.On the basis of the data from more than 200 typical boreholes in northwest Qaidam,the regional palaeogeography and tectonic features,and the iso thickness map of the sand body,the authors have drawn the plane maps of sedimentary facies for upper Youshashan Formation,Shizigou Formation and Qigequan Formation in this area,revealing that braided river delta front,fan delta plain,braided river delta plain,beach bar,fan delta front,flood-flood plain,and shore shallow lake developed in the late Cenozoic in northwest Qaidam.Through comprehensive analysis of lithology,color,sedimentary sequence,logging curve,and the sedimentary structure of ZK8-20,ZKII5-21,ZKII1-10,Yuejin II4-11,Yuejin II2-6 and other boreholes in Yuejin 2 area,it is considered that braided river delta plain mainly developed in upper Youshashan Formation and Shizigou Formation of this area,showing the sedimentary characteristics of distributary channel above water and among distributary channels.The Qigequan Formation is mainly developed the differentiation river delta front,characterized by underwater distributary channel,distributary bay and mouth bar.The late Cenozoic sedimentary facies are mainly characterized by regressive distribution in the study area.The lake level slightly decreased in Shizigou Formation and rose in Qigequan Formation.Littoral-shallow lake subfacies,discerned river delta plain subfacies and discerned river delta front subfacies developed vertically from top to bottom,forming the sedimentary model of upper lacustrine facies and lower discerned river delta facies.