NEW ADVANCES ON THE STUDY OF MIDDLE-LATE ORDOVICIAN CONODONTS IN BACHU, XINJIANG

Abstract

Diverse conodonts including 47 species of 24 genera are discovered from the Middle and Upper Ordovician in the Yijianfang section of Bachu, Southern Xinjiang, and 8 conodont zones or assemblage zones have been recognized based on the first occurrence of zonal species, in descending order they are as follows: The Qiaerbake Formation (O 3q) 8) Baltoniodus alobatus zone; 7) Prioniodus variabilis zone; 6) Pygodus anserinus zone The Yijianfang Formation(O 2yj) 5) Eoplacognathus crassus zone; 4) Lenodus(Amorphognathus) variabilis zone; 3) Microzarkodina parva zone The Yingshan Formation(O 1-2y) 2) Paroistodus cf.originalis zone; 1) Pteracontiodus exilis-Scolopodus bicostatus assemblage zone On the basis of a detailed comparison and discussion, we concluded that this zone sequence could be well correlated with those zones established in the golden spike section at Huangnitang, Changshan of Zhejiang and around the Darriwillian in other areas of China (Chen et al., 1998; Wang and Bergstrm, 1999; Wang et al., 1993; Zhao et al., 2000) (Table Ⅱ), and confirmed the Yijianfang Formation to be essentially equivalent to the Darriwilian Stage, while the Qiaerbake Formation in Xinjiang is a correlative of the Miaopo Formation of the Yangtze Region.