Earthquake Sedimentary Event Record In Early Triassic In Southeastern Sichuan Basin, Sw China

Abstract

There are some macroscopic and microscopic sedimentary structures of seismic events in the outcrops in Lower Triassic Feixianguan Fm (T1 f). and Jialingjiang Fm (T1 j). in southeastern parts of Sichuan Basin. The following basic types of sedimentary structures could be observed: Soft-sediment liquefied deformation structures include curled deformation (sliding deformation structure," sausage structure") and microscopic folds (laminated plastic deformation). Seismites emerge in T1 f 1 and T1 f 2 in Baimiaozi section, Beibei, Chongqing, while in T1 j 2 at Longdongwan, Xuyong, Sichuan, as well as the same strata at Xingwen, Sichuan and Xishui, Guizhou. The sedimentary sequences of seismites in outcrops are clear, presenting the whole process of paleoearthquake from strong to weak. The author argues that the Sanjiang tectonic belt represented by the evolution of Yidun arc in the western Sichuan had strong activities at the west margin of the upper Yangtze plate, which may be related to the formation of seismites in the early Triassic. Earthquake activities and volcanic eruption can be triggered in large areas by the plate collision and the subduction of oceanic crust in the Sanjiang tectonic belt.