Abstract: The Upper Sinian Fengtai Formation distributed in Huainan and Huoqiu, western Anhui is represented by a clastic rock series dominated by diamictite with abundant carbonate rocks. It is a clastic rock series dominated by diamictite with abundant carbonate rocks. It is stratigraphically rougbly equivalent to the Luoquan Formation in western Henan. Divergent views have long existed as to the origin of the diamictite of the Fengtai Formation, but most researchers consider that it is glacial mcraine and glaciolacustrine deposits. According to the study of the sedimentary structure, petrology and geochemistry of the diamictite, the authors hold that its origin is rather complex. It has not only some features of tillite but also some features of gravity flow and slump deposits. Therefore the Fengtai Formation might be formed in a preglacial bay （glaciomarine） environment. In a word, the diamictite displays many redeposited features.