GRAPTOLITE SEQUENCE OF THE LLANDOVERY-WENLOCK BOUNDARY INTERVAL AT THE XIANZHONGGOUKOU SECTION,ZIYANG,SHAANXI,CHINA

摘要

1 INTRODUCTIONSince the Liandovery-Wenlock boundary was defined at the base of the Cyrtograptus centrifugus biozone (Martinsson et al., 1981;Loydell and Cave,1993),there had been controversies. In the 2003 Field Meeting of the International Subcommission on Silurian Stratigraphy in Argentina, the Titular Member of the Subcommission were of the opinion that the boundary be retained at the hase of the Cyrtograptus centrifugus Biozone for the sake of stratigraphical stability, but a new GSSP may be sought.