Soft‐sediment Deformation Structures Related to Earthquake from the Devonian of the Eastern North Qilian Mts. and Its Tectonic Significance

Abstract: Devonian in the North Qilian orogenic belt and Hexi Corridor developed terrestrial molasse of later stage of foreland basin caused by collision between the North China plate and Qaidam microplate. The foreland basin triggered a intense earthquake, and formed seismites and earthquake‐related soft‐sediment deformation. The soft‐sediment deformation structures of Devonian in the eastern North Qilian Mts. consist of seismo‐cracks, sandstone dykes, syn‐depositional faults, microfolds (micro‐corrugated lamination), fluidized veins, load casts, flame structures, pillow structures and brecciation. The seismo‐cracks, syn‐depositional faults and microfolds are cracks, faults and folds formed directly by oscillation of earthquake. The seismic dykes formed by sediment instilling into seismic cracks. Fluidized veins were made by instilling into the seismo‐fissures of the fluidized sands. The load casts, flame structures and pillow structures were formed by sinking and instilling caused from oscillation of earthquake along the face between sandy and muddy beds. The brecciation resulted from the oscillation of earthquake and cracking of sedimentary layers. The seismites and soft‐sediment deformations in Devonian triggered the earthquake related to tectonic activities during the orogeny and uplift of North Qilian Mts.