川北上寺剖面罗德阶—吴家坪阶牙形石生物地层

ROADIAN-WUCHIAPINGIAN CONODONT BIOSTRATIGRAPHY AT THE SHANGSI SECTION,NORTHERN SICHUAN

在四川北部广元上寺剖面茅口组—吴家坪组首次发现了重要的牙形石属种Clakina postbitteri postbitteri、C.postbitteri hongshuiensis、C.dukouensis和C.asymmetrica,识别出8个牙形石带,自下至上依次为Jinogondolella nankingensis带、J.aserrata带、J.postserrata带、Clarkina postbitteri postbitteri带、C.dukouensis带、C.asymmetrica带、C.guangyuanensis带和C.orientalis带。比较精确地确定该剖面瓜德鲁普统-乐平统界线以Clarkina postbitteri postbitteri的出现为标志,使该剖面成为川北一个发育较为连续的、可与国内外同期地层精确对比的牙形石带序列的重要剖面。根据上寺剖面的岩性与牙形石产出状况分析,认为前乐平统生物灾变事件至少部分受到火山活动影响,灾变事件在本剖面响应的时间应在J.postserrata带晚期直至乐平统-瓜德鲁普统的界线处,持续时间相对较长。

Several important conodont species, Clakina postbitteri postbitteri, C. postbitteri hongshuiensis, C. dukouensis and C. asymmetrica, are identified in the Maokou Wujiangping formations at the Shangsi Section. Eight conodont zones have been recognized, which include the Jinogondolella nankingensis Zone, Y. aserrata Zone, J. postserrata Zone, Clarkina postbitteri postbitteri Zone, C. dukouensis Zone, C. asymmetrica Zone, C. guangyuanensis Zone and C. orientalis Zone. The Guadalupian-Lopingian boundary at this section is marked by the first appearance of Clarkina postbitteri postbitteri. Its relatively continuous conodont sequence can be correlated with the other sections in the world. According to the li- thology and the yield of the conodonts at this section, the Pre-Lopingian Mass Extinction was at least in part influenced by the volcanic activities, and the response time of the Pre-Lopingian Mass Extinction at this section was relatively long, ranging from the late J. postserrata Zone to the Guadalupian-Lopingian boundary.