THE ESTABLISHMENT OF THE YEMAJIE FORMATION IN THE BEISHAN MOUNTAINS,GANSU

There outcrops a sequence of metaclastic rocks on the north slope of Mount Pingtou at Mazongshan Town-ship,Subei county,Gansu province.In 1968 the Second Regional Geological Survey Party assigned it to the UpperRock Formation of the Pingtoushan Group of the Jixian system.In 1981 Miu Changquan,Gao Zhenjia et al. foundstromatolite fossils in this group and then assigned it to the Daholuoxhan Group of the Qingbaikou System.In themonograph“Regional Geology of Gansu Province”published in 1989,it is defined as the Lower Rock Formation ofthe Dahuoluoshan Group and determined to be underlain disconformably by the Pingtoushan Group. It has not beenformally named owing to limited studies, In light of the principles of lithostratigraphic classification and the strati-graphic system of the Beishan Mountains,the author has restudied the stratigraphic classification of this sequence,determined the unit stratotype and boundary-stratotype and named it the Yemajie Formation.This paper describesthe stratotype section of this formation and its extension and change and discusses its time span.