The Discovery and Significance of Seismites from Xujiahe Formation in Sichuan Analogous Foreland Basin

The sedimentary processes of the Upper Triassic Xujiahe Formation were controlled by the long-term tectonic activity in the peripheral zones of Sichuan basin,a mult-episodic para-foreland basin of the Yangtze block.Based on the outcrop and the core observations,a series of soft sedimentary deformation structures were recognized for the first time in the Triassic Xujiahe formation in Sichuan Basin;these structures include micro-cracks,micro-folds,micro-faults,liquefied sand structure,ball-and-pillow structures and eautochthnous breccias,and so on.These autochthonous structures are here suggested to having been formed related to seismic activity during Indosinian tectonic episode.The increase in abundance of these soft deformation structures towards the outer peripheral zone of the basin to the west and north respectively suggests a causal connection to the overthrusting of Longmenshan to the west and Micangshan-Dabashan to the north fold-thrust belts,Therefore,to a broader extent,this study is of great significance for us to understand the tectonic history of Sichuan basin and adjacent Longmenshan and Micangshan-Dabashan fold-thrust belts.