The Ordovician sedimentary facies and palaeogeography and their tectonic controls in Jiangshan,Zhejiang

In the light of petrographic,palaeoecological and geochemical characteristics and sedi-mentary sequences,in reference to regional geological data,the present paper deals with the evolution of the Ordovician sedimentary facies and environments in Jiangshan,Zhe-jiang.The Ordovician sedimentary facies sequences here are classified,from base upwards, into restricted platform facies,shelf facies,deep-water basin facies,shallow marine shelf fa-cies and turbidite facies.The crustal movements operating in the middle Caledonian are characteristic of differential elevation and subsidence.The crust was stable during the Ear-ly Ordovician.From the middle Early Ordovician onwards,the increasing basin activities resulted in the development of wide-spread deep-water anoxic sediments and turbidity cur-rent sediments.Till the Wufengian(Late Ordovician),the marine basin became a graben basin controlled by deep faults.There was indeed the "Cathaysia" on the eastern part of the study area,which was believed to be a principal source area for the Zhejiang-Anhui ma-rine basin during Ordovician Time.