Structural Characteristics of Tan-Lu Fault Zone in South Area of Bohai Sea and Its Control on Basin Structure

Tan-Lu fault zone in the south area of Bohai Sea has a good prospect for oil and gas exploration. However, due to its complicated structural features, the understanding of hydrocarbon accumulation conditions, main controlling factors and enrichment regularity is not clear at present. On the basis of the previous studies, 3D seismic data and geological information, the structural characteristics and spatiotemporal differences of Tan-Lu fault zone in the south area of Bohai Sea and the control of the development and evolution of Tan-Lu fault zone on the basin structure are studied in this paper. The results show that Tan-Lu fault zone in the south area of Bohai Sea has three branches, each of which is composed of 2-4 faults presenting strike-slip characteristics. The strike-slip strength gradually weakens westward. From Paleogene to Early Eocene, Tan-Lu fault zone in the south area of Bohai Sea presented sinistral strike-slip characteristics. The eastern branch experienced intense strike-slip movement, whereas the middle and western branches moved slightly, and the NWW-trending extensional faults which developed in Mesozoic renewed. Basin in the south area of Bohai Sea shows as a half-graben with northern-faulted and southern-overlapped structural setting or a graben with both northern and southern faulted settings. From the Middle Eocene, Tan-Lu fault zone turned into dextral strike-slip movement. The three branches started to activate and showed both strike-slip and extensional properties. The intensity of fault activity gradually weakened from east to west. The middle branch divided the Huanghekou sag into two subsags. A series of secondary faults formed the broom-like structure combined with the main fault. From Neogene to Quaternary, Tan-Lu fault zone presented dextral strike-slip as well as extrusion movement in the study area and a large number of small-scale secondary faults have developed. The change of subduction direction and rate of Pacific plate and the variation of deep geodynamics mechanism induce the differences of the evolution process of three branches and their controlling effect on the basin structure. Since the strength of dextral strike-slip movement is less than that of sinistral strike-slip, the distribution of the structural units in the south area of Bohai Sea are still showing the sinistral strike-slip characteristic now. © 2017, Editorial Department of Earth Science. All right reserved.