鄂西地区上二叠统的牙形石及其分带意义

湖北恩施天桥剖面发育有完好的二叠系大隆组下段硅质岩层。对其下伏吴家坪组灰岩及上覆大隆组上段灰岩中牙形石的研究表明，吴家坪组灰岩自下而上可分为Clarkina postbitteri postbitteri带、Clarkina dukouensis带、Clarkina asymmetrica带以及Clarkina guangyuanensis—Clarkina transcaucasica带，属吴家坪阶中下部牙形石带；大隆组上段灰岩可划分出两个牙形石带，即Clarkina subcarinata—Clarkina wangi带和Clarkina changxingensis changxingensis—Clarkina deflecta带，为长兴阶底部牙形石带。认为鄂西地区大隆组下段硅质岩的时代应归属于二叠纪吴家坪中期至长兴早期。

UPPER PERMIAN CONODONTS ZONATION AND ITS IMPLICATION IN WESTERN HUBEI PROVINCE

Tianqiao section in Enshi area,Western Hubei Province yields perfect chert of Permian Dalong Formation.Five conodont zones are recognized in the underlain limestone of Wuchiaping Formation, namely Clarkina postbitteri postbitteri zone, Clarkina dukouensis zone, Clarkina asymmetrica zone, Clarkina guangyuanensis zone and Clarkina transcaucasica zone in ascending order,which are typical early and middle Wuchiapingian conodont zones. In the overlain limestone of upper Dalong Formation,there are Clarkina subcarinata-Clarkina wangi zone and Clarkina changxingensis changxingensis-Clarkina deflecta zone in ascending order, which are typical early Changhsingian conodont zones.These conodont zones suggest that the chert in Dalong Formation was accumulated from the middle Wuchiapingian to the early Changhsingian.