Sedimentary Rocks of Gaoyuzhuang Formation of Mesoproterozoic in Jixian County and Its Geological Significance

The Proterczoic section in Jixian,Tianjin,is highly worthy of an integrated research.The Gaoyuzhuang formation plays a the key role of linking the old and new strata.Gaoyuzhuang formation is rather thick compared with the whole Proterczoic section,and it has multiple types of rocks with special origins.The main kinds of rocks include carbonate rocks,mudstone,silicalite,and quartz sandstone.The carbonate rocks are predominantly composed of pelsparite,nodular limestone,calcarenite,Molar-tooth carbonates,and other fine-grained dolomite.Silicalite includes chert and depositional quartz with textures of oolite and pebble.The quartz sandstone appears at the bottom of Gaoyuzhuang formation.The petrology shows that the depositional environment of the study area is carbonate tide-flat and shallow sea,which is also strongly affected by the volcanic materials and wind brought clastics from Gaoyuzhuang formation.Molar-tooth carbonates are expected to propel the study of the Proterczoic chronology and tectono-sedimentary evolution of North China.