ALGAL LIMESTONES AND THEIR SEDIMENTARY FACIES IN THE ZHANGXIA FORMATION (MIDDLE CAMBRIAN),NORTH JIANGSU-WEST SHANDONG REGION

The upper part of the Zhangxia Formation (Middle Cambrian) in the North Jiangsu West Shandong region consist dominantly of the intercalations of algal limestones and oolitic limestones.Macroscopically the algae may be divided into reef,stromatolite mound and biscuit,and microscopically are mostly composed of Epiphyton.Three distinct facies have been distinguished in the upper part of the formation on the basis of sedimentary facies analysis:the algal reef facies,oolitic shoal facies and algal-flat facies.The environmental factors such as sea-level changes,depositional rates,sediment supply and hydrodynamical conditions are all responsible for the formation of the algal limestones in the study area.