湖北宜昌真金和陈家河奥陶系牯牛潭组至宝塔组的牙形刺及其地层意义

ORDOVICIAN CONODONTS FROM THE KUNIUTAN TO PAGODA FORMATIONS AT CHENJIAHE AND ZHENJIN OF YICHANG,HUBEI PROVINCE,CHINA AND THEIR STRATIGRAPHIC SIGNIFICANCE

根据采自湖北宜昌分乡陈家河和远安真金两剖面奥陶系牯牛潭组至宝塔组的牙形刺,将该段地层的牙形刺生物带自上而下综合划分为Hamarodus brevirameus,Amorphognathus superbus,Baltoniodus alobatus,Pygodus anserinus-Yangtzeplacognathus jianyeensis,Yangtzeplacognathus protoramosus,Yangtzeplacognathus foliaceus,Histiodella kristinae-Eoplacognathus suecicus,Dzikodus tablepointensis,Lenodus variabilis和Lenodus antivariabilis等牙形刺生物带。其中宝塔组之Hamarodus brevirameus,Amorphognathus superbus生物带及Baltoniodus alobatus生物带顶部归为凯迪阶(Katian),庙坡组Baltoniodus alobatus生物带大部和Pygodus anserinus-Yangtzeplacognathus jianyeensis生物带中上部归为桑比阶(Sandbian),而牯牛潭组的Yangtzeplacognathus protoramosus至Lenodus antivariabilis等牙形刺生物带和庙坡组Pygodus anserinus-Yangtzeplacognathus jianyeensis生物带下部则归入达瑞威尔阶(Darriwillian)。这一牙形刺带序列与宜昌黄花场和分乡剖面的牙形刺生物带相一致。

This paper describes the conodont faunas from the Pagoda Formation（Katian）to the Kuniutan Formation（Darriwilian）at the Chenjiahe and Zhenjin sections in Yichang,Hubei Province,with ten conodont biozones recognized.They include,in descending order,the Hamarodus brevirameus,Amorphognathus superbus,Baltoniodus alobatus,Pygodus anserinus-Yangtzeplacognathus jianyeensis,Yangtzeplacognathus protoramosus,Yangtzeplacognathus foliaceus,Histiodella kristinae-Eoplacognathus suecicus,Dzikodus tablepointensis,Lenodus variabilis,and L.antivariabilis biozones.The Katian/Sandbian boundary is within the Baltoniodus alobatus Biozone,while the Sandbian/Darriwilian boundary within the lower part of the Pygodus anserinus-Yangtzeplacognathus jianyeensis Biozone.The conodont biostratigraphic succession documented herein can be consistently correlated to that of the Huanghuachang and Fenxiang sections described by An（1987）and Zhang（1998）.The conodont succession provides important data not only for supporting the regional biostratigraphic framework,but also for better understanding of the spacial and temporal distribution of the conodont biofacies in this classical region on the Yangtze Platform,where two Ordovician GSSPs（for the base of Dapingian and Hirnantian respectively）are located.