Thick salt deposits were developed in Paleogene in the northern Dongpu depression. Under sustained stretching stress

extensional forced folds were formed in the overlying formations of salt beds due to their differential subsidence.At the same time

continuous down-tilting of the secondary fault blocks in the underlying formations resulted in increasing of downslide shear stress and even exceeding the shear strength of salt beds

thus listric detached faults were formed in the overlying beds

and rollover anticlines were formed in the upper wall of salt detached faults. The detached deformational salt structures would not only constitute good migration pathway but also provide various traps for hydrocarbon accumulation

such as oil and gas reservoirs in fault block traps

extensional forced fold traps

rollover anticlinal traps

traps in the footwall of the detached faults and reverse drag fault traps in Dongpu depression. The development of detached deformational salt structures led to the formation of hydrocarbon enrichment in the central uplift zone of Dongpu depression