The establishment of Late Paleozoic stratigraphic framework in the northern belt of Beishan orogenic belt of Inner Mongolia

The Beishan orogenic belt of Inner Mongolia is an important area for studying the spatial-temporal evolution of the central Asian orogenic belt and the key to the connection between the Tianshan orogenic belt and the Xingmeng orogenic belt.The restriction of poor working conditions for a long time has led to its relatively weak research, so people's understanding of the late Paleozoic stratigraphic framework is in a state of confusion and contradiction.On the basis of completing the 1: 50000 regional survey in recent years, through the study of regional distribution of the Late Paleozoic formation as well as the combing of composition and age ascription system comb, and in combination with the tectono-magmatic configuration and structure of the orogenic belt, the authors reestablished the Late Paleozoic stratigraphic framework of Heying Mountain stratigraphic division in Beishan region of Inner Mongolia.The authors made reclassification and identification of Hongjianshan Formation, Suishishan Formation, Qinghegou Formation and Yuanzhuishan Formation of Quershan Group in the Late Silurian-Middle Devonian period as well as Lütiaoshan Formation, Baishan Formation of the Carboniferous period, Shuangbaotang Formation and Jinta Formation of the Permian period.It is shown that the Quershan Group is a volcano-sedimentary assemblage of the island arc on the continental margin, including island arc volcanic rocks of Hongjianshan Formation and intracarc basin clastic rock assemblages of Suishishan Formation and Qinghegou Formation in Late Silurian-Middle Devonian period, and island arc volcanic assemblage of Yuanzhui Mountain in the late Devonian period.The Lütiaoshan Formation and Baishan Formation of Carboniferous were formed in the trench-arc-basin system with Hongshishan-Baiheshan junction as the boundary, and there exists obvious difference in the north and in the south.The northern area of the Lütiaoshan Formation is a low maturity littoral neritic clastic rock deposit on the northern margin of the inter-arc basin; the southern region is a relatively high maturity littoral shallow sea-semi-deep sea clastic rock deposit on the southern margin of the inter-arc basin.The northern part of Baishan Formation is the Late Carboniferous inherited island arc volcanic assemblage and the southern part is the Carboniferous continental margin mountain arc volcanic assemblage.Shuangbaotang Formation and Jinta Formation are post-collision and post-collision rift basin sediments.They have the dual structure of lower clastic rock and upper volcanic rock.According to the fossil assemblage, they were formed in the Early-Middle Permian period.