Depositional feature of the Chang 1 of Yanchang Formation in Jingbian-Ansai Area,Ordos Basin,China

Aim To discuss the characteristic and distribution of sedimentary facies of the Member 1 of Yanchang Formation,Upper Triassic in Jingbian-Ansai Area in Ordos Basin.Methods The main methods used in the study include the fieldwork of geological survey,stratigraphic classification,and electrofacise analyses.Facies maps have been drawn according as the rate of sand.Results Research results indicated that the sediment environment in Hengshan,Zichang,Ansai and Jingbian Area in Ordos basin was lacustrine-delta in the end of Late Triassic.The depression center was located in Zichang Area.The lacustrine-delta sequence in the Chang 1 of Yanchang Formation is featured with a fining upward: the delta-plain in the bottom,delta-front located in the lower part and the pre-delta in the middle and the deep lacustrine facies in the upper part.Conclusion The transmeridional structure belt of the middle of the Ordos Base controlled the evolution of the lake.The shale of the deep lake may be the other important source rock in Zichang Area.