浙江西部晚奥陶世五峰期沉积及奥陶系—志留系的分界

浙江西部晚奥陶世五峰期沉积包括三种相:(一)笔石页岩相:由二部分组成,上部堰口组有笔石Diplograptus bohemicus带及三叶虫Dalmanitina sp.,下部于潜组有四个笔石带:(4)Paraorthograptus yuqianensis,(3)Climacograptus venstus,(2)Dicellograptus szechuanensis,(1)Pseudoclimacograptus anhutensis(二)混合相:上部为文昌组,下部为长坞组,(三)壳灰岩相:上部为文昌组，下部为三巨山组，有Toeniolites, Proheliolites等。本区的Dralmdnitina-Hrrnantio层出露清楚，且Da.和H.与Diplograptus bohemicus共生，时代属晚奥陶世晚期。

THE LATE ORDOVICIAN WUFENGIAN SEDIMENTATION AND THE ORDOVICIAN-SILURIAN BOUNDARY IN WESTERN ZHEJIANG PROVINCE

The Late Ordovician Wufengian rocks in western Zhejiang consist of three facies, namely: (1) graptolitic shale facies xomposed of two parts-the upper part is the Yankou Formation, with Diplograptus bohemicus zone, and Dalmanitina sp. (trilobite), and the lower part, the Yuchian Formation, with four graptolitic zones (Paraothograptus yuqiancnsis, Climacograptus venustus, Dicellograptus szechuanensis and Pseudoclimacograptus anhuiensis); (2) mixed facies composed of the Wenchang Formation as its upper part and the Changwu Formation as its lower; and (3) shelly limestone facies whose upper and lower parts are represented by the Wenchang and Sanqushan Formations (with Taeniolites and Proheliolites) respectively.The Dalmanitina-Hirnantia bed is well exposed in western Zhejiang. As it is associated with the Diplograptus bohemicus zone, it is of latest Ordovician age.The Ordovician-Silurjan boundary is drawn as follows:(1) For the graptolitic facies this boundary is drawn between the Diplograptus bohemi-cur zone and the Glyptograpius persculptus zone.(2) For the graptolitic and shelly facies it is placed between the top of the Diplograpius bohemicus zone and the base of the Eospirifer horizon.(3) For the shelly facies it lies between the Dalmamlina-Hirnantra bed and the base of the Eospirifer horizon.