Abstract: The types and characteristics of the sedimentary facies developed in Pukou formation of Upper Cretaceous in Huaiyin sag of Yanfu depression are analyzed. It is considered that the sedimentary structures of Pukou formation in Huaiyin sag are different from those in Yanfu depression, and the new characteristics of salt rocks of over 1000 m thickness appear in this area. From studies of these characteristcs of structures, palaeontology, drilling, well logging, seismic profile, salt chemistry and lacustrine sedimentary system, it is recognized that the new characteristics occur in structures of section Pukou II and III in Huaiyin sag, and the huge thickness of salt rocks is formed by the crust salt materials upwelling along deep fracture in the form of hot bittern and entering lacustrine basin in this area.

Key words: Huaiyin sag, Pukou formation, salt rock, deep brine, discordogenic fault