CAMBRIAN SEDIMENTARY FORMATION OF THE YANGZI PLATFORM

Yangzi Platform was a relatively active platform- It includes deposits of both the stable areas and the transition areas. Laterally, there are two different sedimentary formation areas in eastern and the western parts. The paragenetic bodies of rocks, which were formed in different type of sedimentary areas of in different stages of same area, can be divided into four major sub-formation; phosphorite-bearing carbonate, phosphorite-bearing elastic rock, salt-gupsum一bearing carbonate (or carbonate) and phosphoritebearing silica-mudstone sub-formation. The distribution of Cambrian sedimentary formation in Yangzi Platform u as closely related to crust movement, tectonic settings and paleogeography. Sedimentary formation consisted of more than two types of rocks has occurred in western part of West Yangzi Platform; sedimentary formation consistd of only two types of rocks has been fo :nd in Zunyi, Meitan, liangkou and Xiushan, without phosphorite- bearing carbonate sub一formation; flysh formation has occurred in Zhixing and Youxian. Different petrological formation may be found in a same formation but、;:reed arcaa Carbonate sub-formatin in East Yangzi Platform, e.g., is apparently diloerent trom the west plan-o: m This was controlled by local geological settings. There is no evident reguilarity for the evlution of sedimentary formation. On the contary, it was varied from time to time. The thickness of Cambrian sediments m Yangzi platform varies in different places.It is thicker in the west platform than in the east which is an uncompensate basin. Lapping sedimentary centres of different stages of the platform together, we can see that they migrated in different ways according to different areas. Sedimentary centre in the West Yangzi Platform jumped from one plac to another through time. While the centre in the east platform lapped together during two sedimentary stages, showing that it is an inhernt depressing basin. In brief, the sdimentary formation types and the different development stage were association with crustal activity of the Cambrian in the Yangzi Platform. The formation and development of the sedimentary formation were influenced by paleoclimate, as well. The phosphorite-bearing carbonate sub-formation with higher economic value are always losated at the eastern and the western coast of paleocontinents, around ancient island and offshore riese with low paleolatitudes 3“一42“.As the ocean current carried the phosphorus-rich cold water to rise from depth, the warm and hot climate was favorable to the Separation and concentration of phosphatic materials. Large phosphorite deposits at home and abroad are mostly associated with very thick dolomite. thus far, it may be concluded that phosphorite-bearing carbonate sub-fromation were mostly formed under the paleoclimate condition of the transition period from cold to hot and from moist to dry, at low latitude (paleolatitude or modern latitude).