ASSIGNMENTS OF THE MAIN STRATA IN THE EASTERN QINLING MOUNTAINS AREA ALONG THE HENAN-SHAANXI BORDER AND RELATED STRUCTURAL FEATURES

Progress has been made in recent geological surveys.According the results obtained in the surveys,the authors put forwards some new views on the following problems.（1）Paleozoic animal fossils have been for the first time collected from the strata assigned to the lower Proterozoic " Taowan Formation" by predecessors in the vicinity of Guanpo and Lancao, Lushi.So the age of the strata is tentatively assigned to Silurian and the strata are named the"Yunjiashan Group".（2）It has been found that the lower Proterozoic “Lower Kuanping Formation（i.e. Erlangping Group）”originally determined by predecessors does not represent the same strata as the Kuanping Group.It shows conformable gradational relationships with the Silurian Yunjiashan Group,so it should belong to the early Paleozoic products and is renamed the" Danfanyao Group".（3）A part of the "Upper Kuanping Formation" （i.e. the Xiaozhai and Baoshuping Formations）in northern Xixia origihally defined by predecessors is by no means of Proterozoic age.It is preliminarily considered that it belongs to the metamorphosed Upper Triassic,but the possibility that it might belong to the Silurian "Yunjiashan" Group cannot be ruled out.（4）The original Upper Sinian "Zitiangou Fomation" , "Houshangou Formation" and "Ganjiaogou Formation" should be assigned to the Kuanping Group.The authors consider" that the gravelly marble in the so-called Zitiangou Formation is not till and shows no stratigraphic implications.It should belong to a sequence of mélange accumulation of tectonic origin.（5）The major basement fractures in the Eastern Qinling Mountains occupy an important position in geological surveys.They exerted an important controlling effect on the rock formations of various ages.（6）The Anping-Dafanyao down-faulted belt is a very peculiar tectonic unit that has long not drawn people’s attention.It was an ancient volcanic island arc during early Paleozoic time.（7） Through a study of the geological history of this area,it may be found that the Heigou fracture was the demarcation line between the Eastern Qinling geosyncline and the Western Henan platform in Protexozoic and Paleozoic times.From the Xiao Qinling Mountains sourhwards up to the Qinling Mountain Range,with the evolution of the geological history,the crust subsided step by step,the subsidence centre also shifted southwards gradually and the age of the strata became younger.