Discovery and significance on the seismite of Silurian Xiaoheba Formation in Baojing area of Northwestern Hunan

A set of sand-mud deposit was mainly developed in the Silurian Xiaoheba Formation in Baojing area of northwest Hunan Province. There are many typical seismite characteristics in some layers of Xiaoheba Formation, such as step micro-fault, pinch and swell structure, ball and pillow structure, load casts and flamy structure, liquefaction sandy dyke, liquefied fold, seismic fissure bed and autoclastic brecciated structure. Based on the vertical statistics of the seismite characteristics in well Baocan 1, Baocan 2 and Baocan 3, the authors identified 74 ancient seismic strata. According to the concept of seismic episode, the authors summarized the seismic episodes in Xiaoheba Formation. By transverse comparison of the seismic episodes in the wells, the authors found that the seismic episodes are mainly distributed in two members of Xiaoheba Formation. And then two active seismic periods and three seismic quiet periods during the Xiaoheba period have were identified. Through the relationship analysis of seismite characteristics, earthquake intensity and distance, combining with the tectonic setting of the study area, the authors found that the development of the seismites was controlled by the tectonic evolution of Baojing-Cili fault zone. The research results have important significance for the palaeostructure recovery, stratigraphic correlation and reservoir prediction.