The Late Ordovician Wufengian Sediments and the Ordovician‐Silurian Boundary in Western Zhejiang Province

Abstract

Abstract The Late Ordovician Wufengian sediments in western Zhejiang include three facies: 1) graptolite shale facies, composed of two parts— the upper part the Yankou Formation, with the Diplograptus bohemicus (graptolite) zone and Dalmanitina sp. (trilobite), and the lower part the yuqian Formation with four graptolite zones: (4) the Paraorthograptus yuqianensis zone, (3) the Climacograptus venustus zone, (2) the Dicellograptus szechuanensis zone and (1) the Pseudoclimacograptus anhuiensis zone; 2) mixed facies, consisting of the Wenchang Formation in its upper part and the Changwu Formation in its lower; and 3) shelly limestone facies, whose upper and lower parts are separately the Wenchang Formation and Sanjushan Formation, containing Taeniolites, Proheliolites, etc. In this region the Dalmanitina‐Hirnantia bed is well exposed, and Da. and H. are associated with Diplograptus bohemicus, belonging to the late Late Ordovician.The Ordovician‐Silurian boundary is drawn as follows: (1) for the graptolite facies, it lies between the Diplograptus bohemicus zone and Glyptograptus persculptus zone; (2) for the graptolite‐shelly limestone facies (brachiopod fauna), it is placed between the top of the Diplograptus bohemicus zone and the base of the horizon with the Eospirifer fauna; and 3) for the shelly facies (brachiopod fauna), it is drawn between the top of the horizon with the Dalmanitina‐Hirnantia fauna and the base of the horizon with the Eospirifer fauna.