The Seismic Induced Soft Sediment Deformation Structures in the Middle Jurassic of Western Qaidamu Basin

Abstract:Intervals of soft‐sediment deformation structures are well‐exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft‐sediment deformation structures can be identified, such as convoluted bedding, liquefied sand veins, load and flame structures, slump structures and sliding‐overlapping structures. Based on their genesis, soft‐sediment deformation structures can be classified as three types: seismic induced structures, vertical loading structures, and horizontal shear structures. Based on their geometry and genesis analysis, they are seismic‐induced structures. According to the characteristics of convoluted bedding structures and liquefied sand veins, it can be inferred that there were earthquakes greater than magnitude 6 in the study area during the middle Jurassic. Furthermore, the study of the slump structures and sliding‐overlapping structures indicates that there was a southeastern slope during the middle Jurassic. Since the distance from the study area to the Altyn Mountain and the Altyn fault is no more than 10km, it can be also inferred that the Altyn Mountain existed then and that the Altyn strike‐slip fault was active during the middle Jurassic.