Abstract: The vertical distribution and geometry of evaporates in Tongnanba area are generally steady and continuous.However,when the overlying and underlying competent dolomite are deformed by folds and faults,they occur in special shapes like moundy,wedge and spindle set.The evaporates are characterized by multilayers (57-110),a large gross thickness (273-415m),and close relationship with the shapes and structures of competent beds.The initial dominant wavelengths of the dolomite layers are larger than the thickness of evaporates,the evaporates and the surrounding multiple competent beds interact with each other,and the contact strain zones have relatively large influences on the evaporates,therefore,the evaporates are apt to form disharmonious folds.The evaporates are easy to form creep fractures due to the influences of stress,temperature,fluid and other factors,and abnormally-shaped evaporate bodies are developed due to faulting of the competent beds.It was proved that sealing capability of multilayer evaporates was weaker than that of single evaporates with large thickness.The thickness of evaporate body enlarges significantly when they get abnormally-shaped,thus the surrounding areas are favorable targets for hydrocarbon exploration.

Key words: creep fracture, contact strain zone, rheology, evaporate, Tongnanba area