CHARACTERISTICS AND FORMATION MECHANISM OF MESO-CENOZOIC SUPERIMPOSED BASINS IN THE EAST DEPRESSION OF THE NORTH YELLOW SEA BASIN

Based on the latest geological-geophysical data, the faults characteristics and structural styles of the Eastern Depression of the Northern Yellow Sea Basin are studied, and the sedimentary-tectonic evolutionary stages summarized. The results show that faults in the Eastern Depression are well developed. The faults of F₁ and F₂ are the most important controlling ones, then followed by F₉、F₁₀、F₁₁ and F₈. The structural deformation, which is rather complex, includes the extensional, compressed, wrenching and inversed deformation. Seven sedimentary-tectonic evolutionary stages are recognized, namely the initial faulting and depressing stage(J₂), the expanding stage of faults and depression (J₃), the faulting and sag formation stage(K₁), the tectonic inversion stage (late K₁-E₂), the intensive faulting and depression stage(E₃), and the regional subsidence stage(N1-Q). The formation mechanism of the Eastern Depression is also discussed with reference to the regional geological background. In Middle Jurassic, the extension caused by block escape brought about the initial faulting and depression. In Late Jurassic, faulting and depressing continued and the crust became thinning due to plate subduction. In the Early Cretaceous, the Tanlu fault experienced a sinistral slip movement as the result of the change in motion of the Izanagi plate, and the faulting sag was formed in the stress field of sinistral rotation together with thermal subsidence. In Late Cretaceous, face to face subduction of plates led to compression inversion which had lasted up to the Eocene in Eastern Depression. In Oligocene, due to the re-orientation of the Pacific plate movement, the retreatment of the subduction zone and the collision of Indian and Eurasian plates, the Tanlu fault became dextral. Strong faulting and depressing of the study area has made the region a dextral transtensional tectonic setting. At the end of Oligocene, due to the increment in the subduction rate of the Pacific plate, the strengthening of Indian-Eurasian collision, and the slowing down of subduction, the inversion structures dominated again in the study area. Regional subsidence appeared again in the Eastern depression during the Miocene to Quaternary, due to thermal attenuation of lithosphere.