The Discovery of the Middle Proterozoic Bingmagou Formation in Lushan County, Henan Province, and its significance

Geological characteristics of Lushan area and features of Bingmagou Formation as well as the crustal evolution process are discussed in this paper. On such a basis, the authors consider that Bingmagou Formation was formed in a river delta sedimentary environment and tended to become transitional to littoral facies. In the late Yanshanian period the northward obduction and napping of the Sanmenxia-Lushan fracture belt led the Bingmagou Formation to form overturn structure. Based on the correlation of Bingmagou Formation strata distributed in Jiyuan, Yichuan, Lushan and Wugang areas, the authors hold that there existed the paleogeographic framework that the land lay in the north and the sea lay in the south during the deposition of Bingmagou Formation. Bingmagou Formation is in angular unconformity contact with the overlying Yunmengshan Formation of Ruyang Group or in parallel unconformity contact with Maanshan Formation of Wufoshan Group, with a crustal uplift taking place between them. It is therefore not suitable to assign Bingmagou Formation to Ruyang or Wufoshan Group. Bingmashan Formation is an independent stratigraphic unit, thus it has important significance in perfecting the stratigraphic time scale of North China and even whole China.