Through the feild sections measurement, sample selection and thin section analysis and the selection of geochemical data and previous research matetials, this paper studies the lithology composition and sedimentary structure in Qishan area and analyzes the evolution of sedimentary environment in Middle Ordovician. The results show that in Middle Ordovician Qishan area was in limited sea platform environment with deposition of dolomite at early stage of Lower Majiagou Formation and was in open sea platform environment with midium thich limestone depositing at the middle-late stage of Lower Majiagou Formation. In Upper Majiagou Formation, the area developed deposits of thick lamellar limestone interbedded with deep-water sedimentary construction like debris flow and turbidity flow which indicated platform foreslop enviroment and then in Fengfeng Formation, Qishan was still in platform foreslop enviroment but closer to deep water basin and developed thick lamellar limestone. With such envelops, it can be concluded that in Middle Ordovician, besides Chunhua-Xunyi depression Qishan region should be in another secondary depression with deeper water and steeper slope on southern depression.
Liu Xi Ren Zhanli Li Wenhou Chen Qiang Jia Desheng . A study on the Middle Ordovician sedimentary characteristics and environment of Qishan region at the southwest margin of Ordos Basin[J]. Chinese Journal of Geology, 2017, 52(3): 931-942.