CHARACTERISTICS OF THE LATE ORDOVICIAN TURBIDITE SERIES IN JIANGSHAN,ZHEJIANG WITH DISCUSSION ON THE WEST ZHEJIANG TURBIDITE FAN MODEL

It is suggested that the late Late Ordovician Changwu Formation in Jiangshan, Zhejiang are composed mainly of the tidal flat deposits and turbidity current deposits in terms of sedimentary sequences and environmental indicators. During the Late Ordovician, there occurred three turbidity current events in western Zhejiang, the second of which had the maximum energy and most important influences. On the basis of the regional geological data from western Zhejiang and southern Anhui, in conjunction with the study of sedimentary systems in the Zhejiang-Anhui marine basin, the sedimentary environments in the study area may be divided into four types, i.e. tidal flat, organic reefs, continental shelf and deep-water basin. Meanwhile, the regional correlations have also been made for the turbidite series there. A model for the development of the West Zhejing turbidite fan is proposed according to the Bouma sequence, grain size, sedimentary structures and palaeocurrent data. The present paper further deals with three tectonic factors controlling the development of the turbidity current deposits, i.e. left-lateral shear-tension movement of three deep faults controlling the Zhejiang-Anhui marine basin, the uplift of the Cathaysia and differential subsidence of the Zhejiang-Anhui marine basin. This has provided a useful tool for interpreting tectonics and palaeogeography of the Cathaysia from Phanerozoic time onwards.