Formation， evolution， and distribution law of Mesozoic-Paleozoic buried hills in Jiyang Depression

Buried hill is an essential field of oil-gas exploration in Jiyang Depression. Deepening the formation mechanisms and establishing a predictable classification scheme of buried hills are the key to the exploration of hidden buried hills. Based on 3D seismic data and drilling data， this paper analyzed the structural characteristics of buried hills， fault activity rates and equilibrium cross-section， recovered the superposed evolution processes of buried hills at key stages， established the genesis-structure classification system of buried hills， and clarified the spatial distribution law of buried hill types. The results show that the buried hills in Jiyang Depression have experienced three stages of evolution since the Mesozoic， namely， Indosinian compression and thrust， Yanshanian sinistral transtension， and Himalayan dextral transtension. The former two form the prototype and initial pattern of NW-trending buried hills， respectively， while the latter results in the formation of the NEE-trending buried hills， forming the current “seven-longitude and four-latitude” distribution pattern of buried hills. According to the difference in the structural location and the movement of buried hills during the Yanshanian and Himalayan periods， buried hills in Jiyang Depression are divided into four types： Meso-Cenozoic uplift type residual hills， Mesozoic uplift-Cenozoic sink type fault-block hills， Mesozoic sink-Cenozoic uplift type detached hills， and strike-slip reformed type fault-block hills. Their orderly distribution fits the structures of the faulted basin. From the bulge zone， slope zone， and depression zone to the steep slope zone， the Mesozoic-Cenozoic uplift type residual hills， the Mesozoic sink-Cenozoic uplift type fault-block hills， and the Mesozoic uplift-Cenozoic sink type detached hills are successively developed.