Sedimentary records of seismic events in a lacustrine basin of continental depression: A case study of the Triassic Yanchang Formation in the Ordos Basin, Northern China

Being a continental lake basin, the Ordos Basin was filled with a Triassic sedimentary succession including the Yanchang Formation in which there are widespread seismites formed via sudden seismic events. Our study focuses on types and characteristics of these seismites and concerns their sequence of the formation, genetic mechanism, and significance. The results show that the identification marks denoting the seismic sedimentary event of the Yanchang Formation include ten different types. The sedimentary sequence consists of the five units: A or F (Liquefaction homogeneous stratum), B (Micro synsedimentary fault stratum), C (Crimped deformation stratum), D (Liquefied sandstone vein), and E (Sand ball-pillow stratum) that can be further divided into five subtypes: ABCD, BCD or CD, AB, BCE or BE, and BEBE. The strong episodic activity of the boundary faults controlling the basin is the direct cause of the seismic sedimentary events. The study of seismites is helpful to understand the structural geology of Ordos Basin, the relationship between the dynamic mechanisms of the sedimentation in different reservoir sand bodies, and provide a new perspective for oil and gas exploration.