Abstract: The Xingning-Jinghai sag is a Mesozoic-Cenozoic superimposed sag lying at the ultra-deep water transitional crust, and a new Mesozoic oil and gas exploration target in northern South China sea. Based on fine interpretation of 2D and 3D seismic data, the structural characteristics, structural evolution history and source rocks feature of the Mesozoic-Cenozoic sag are analyzed comprehensively. The study results show that the Xingning-Jinghai sag has gone through three tectonic evolution stages:the Mesozoic compression and denudation, the stretching rift and thermal subsidence since the Cenozoic. Under the control of the structural evolution, three sets of Mesozoic source rocks, the Triassic, Jurassic and Cretaceous, are developed, of which the Mesozoic marine mudstone is dominant; two sets of favorable reservoir-caprock assemblages are formed:one is the Jurassic and Cretaceous shallow marine and lacustrine sandstone-mudstone interlayers, and the other is the Cenozoic Enping Formation shallow marine and delta sandstone and the Zhuhai Formation marine mudstone; and several types of traps are developed, of which the traps near the sag are favorable exploration targets.

Key words: ultra-deep water area in northern South China Sea, Xingning-Jinghai sag, structural evolution, sag structure, Mesozoic