REDEFINITION OF THE SEQUENCES AND AGES OF THE QINLING AND BIKOU GROUP COMPLEXES

For many years,views about the sequences and ages of the Qinling and Bikou Group Com-plexes have been very divergent owing to complex structures and scanty fossils therein. Through clarification of the strata coupled with new data obtained by predecessors,the authorshave redefined the sequences and ages of the two group complexes. The Qinling Group Complexincludes three rock associations,1.e。 mica-quartz schist,marble and gneiss. On the basis of theirisotppic ages and regional stratigraphic correlation,the age of the group complex was deter-mined to be Early Proterozoic.The Xiahe Group Complex divorced from the original QinlingGroup Complex is of Middle-Late Proterozoic age according to its isotopic age. The BikouGroup Complex comprises two rock associations,metavolcanic rocks and metasedimentary clas-tic rocks. According to the isotdpic ages and fossils of microfloras,its age is Middle-Late Pro-terozoic. The Yudongzi Group Complex divorced from the originaI Bikou Group Complex isEarly Proterozoic-Archean in age according to the isotopic ages and cherty iron formations。