Earthquake-induced soft-sediment deformation structures from the Upper Triassic of the Jiyuan district, southern North China Craton: Implications for the Qinling Orogeny

Soft-sediment deformation structures are abundant in the upper part of the Upper Triassic Tanzhuang Formation in the Jiyuan district, southern North China Craton. These deformation structures include large load casts, flame structures, ball-and-pillow structures, lenticular sand bodies, synsedimentary faults, and slump structures. The lenticular sand bodies, synsedimentary faults, and slump structures developed in the deep lake environment, while large load casts, flame structures, ball-and-pillow structures occurred in the deltaic environment. Based on the geometrical characteristics of the soft-sediment deformation structures and criteria for recognizing the effects of seismic events, we exclude two major autogenic triggers (including slumping and sediment overloading) and infer that a seismic event was responsible for triggering deformation. Seismic activity was likely associated with activity on the Luanchuan Fault in the Qinling Orogen. The large size and complexity of the soft-sediment deformation structures, together with their long distance from the inferred epicentre, indicate a high-magnitude earthquake that is associated with the intensive uplift in the orogenic setting. Comparison of our data with soft-sediment deformation structures from the Ordos Basin and the Yima district suggests that the Qinling Orogen was subjected to at least two phases of uplift during Late Triassic orogenesis.