Seismic sequence of Triassic Yanchang Formation in Ordos Basin

According to Cross theory on high resolution sequence stratigraphy,Triassic Yanchang Formation is divided into one second-order sequence and five third-order sequences.The top boundary of the second-order sequence is the unconformity between Jurassic and Triassic,the bottom boundary is the bottom of Yanchang Formation,and the maximum flooding surface is Zhangjiatan shale which distributes broadly in the basin.The third-order sequences can be identified by the surface of interrupted deposition,flooding surface,scour surface,sedimentary transformation surface and lithology transformation surface.The characteristics of sequence boundary surface in seismic profile are concluded.According to these characteristics,the seismic profile is interpreted and the evolution of Yanchang Formation in vertical direction is analyzed.