鄂尔多斯盆地西缘上三叠统延长组沉积相特征研究

Study on Sedimentary Faciess Features of the Upper Triassic Yanchang Formation,in the Western Margin,Ordos Basin

通过对鄂尔多斯盆地西缘北部汝箕沟剖面、南部阎家庄剖面和中部环78、环52、演40井岩芯的详细观察,并结合前人的研究资料及岩性和岩相组合、沉积相分析,探讨了研究区延长组沉积相特征与演化过程。研究结果表明:鄂尔多斯盆地西缘延长组发育12种岩相类型,7种岩相组合。延长组时期为扇三角洲—湖泊、辫状河三角洲、冲积扇沉积体系,其中也充分发育筛状沉积、水上分流河道、分流河道间、水下分流河道、河口坝、远砂坝、等沉积微相和亚相类型。北部汝箕沟地区在延长组沉积早期主要为扇三角洲相,进入中期由湖泊相过渡为扇三角洲相,晚期则发育深湖相;中部环县—演武地区在延长组早期为辫状河三角洲相,中期发育辫状河三角洲相和湖泊相,晚期过渡为三角洲相并受到抬升剥蚀作用;南部阎家庄在延长组则发育冲积扇相,随后便受到抬升剥蚀作用。

The study was based on detailed observations of the outcrop profiles in Rujigou and Yanjiazhuang,and drill cores from Huan52,Huan78 and Yan40 wells in the study area,and combined with previous research results.Analysis of the lithology and rock associations is discussed,as well as the sedimentary facies and their characteristics and the evolutionary process of the Yanchang Formation in the study area.The research suggests that 12 lithological types and seven rock association types are recognized in the Yanchang Formation at the western margin of the Ordos Basin.Within the study area,fan delta-lake,a braided river delta and an alluvial fan sedimentary system were the main developments in the Yanchang period.Cribriform deposition,water distributary channels,interdistributary channels,underwater distributary channels,mouth bar and distal bar were also substantially developed,together with other sedimentary microfacies and subfacies types.In the northern part of the study area in Rujigou,fan delta facies were mainly developed in the early Yanchang Formation,with lacustrine facies transitioning into fan delta facies in the middle stage.Deep-lake facies developed in the late stage.In the central area of the Yanchang Formation,in Huanxian-Yanwu,early braided river facies developed,and delta front subfacies and lacustrine facies were formed in the middle stage,with transition to delta facies subjected to uplift-denudation.In southern Yan Jia Zhuang,in the early Yanchang Formation the main developments were alluvial fan facies,then fan delta front facies in the middle stage,and uplifting and denudation in the late stage.