PRECISELY COMPARTMENTALIZED AND CORRELATED LOWER ORDOVICIAN OEPIKODUS EVAE ZONE OF THE FULUOIAN IN THE HUANGHUACHANG SECTION,YICHANG,HUBEI PROVINCE

After the Global Stratotype Section and Point (GSSP) for the base of the Middle Ordovician and the third stage of Ordovician System was confirmed,we systematically restudied the conodont biostratigraphic sequence in the former Oepikodus evae zone of the upper Fuluoian in the Huanghuachang section,through additional collecting and systematical examining conodont samples of the same pivotal horizon (The first appearance datum of the conodont zonation) from the upper part of Honghuayuan Fm.to the lower part of Dawan Fm.The first appearance dadum (FAD) of some conodont species were revised;the apparatus classification of some important multi-element conodonts,including Stolodus stola,Lundodus gladiatus,Oepikodus communis,O.intermedius,Prioniodus honghuayuanensis,Trapezognathus diprio,Baltoniodus cf.B.triangularis (Lindstrm) etc.,were studied;the ancestor Baltoniodus cf.B.triangularis (Lindstrm) of B.triangularis(Lindstrm) and their difference were identified;some genera and species,such as Baltoniodus triangularis (Lindstrm),were re-described in newly-built fossil zone.The zonal index fossil Oepikodus evae itself has not been discovered from the upper part of the former Oepikodus evae zone in the Huanghuachang section,which is conflict to the definition of interval zone and range zone in International Stratigraphic Guide (2000),so the content of the former Oepikodus evae zone should be revised.The boundaries of these conodont zones are strictly defined by the first appearance of the conodont zonation.The interval zone from the Lower Member of Dawan Fm.should be divided to 3 interval zones:O.evae zone,Trapezognathus diprion zone and Baltoniodus cf.B.triangularis zone.The latter two are newly erected.