Characteristics and significance of transfer zone in northern Qiongdongnan Basin, South China Sea

Key words:  Qiongdongnan Basin  transfer zone  transfer fault  fault domains  pre-existing structures  fault growth

Abstract:

Based on seismic reflection data and fault characteristics, we firstly analyzed the transfer zone in the northern Qiongdongnan Basin, and then discussed its geological significance by integrating the regional background. The northern Qiongdongnan Basin can be divided into three different types of structural domains, i.e., the Yabei-Songxi half graben, the Songdong half graben and the north slope of Baodao depression, which are separated by two interbasin transfer zones the songxi-songdong transfer zone and the baodao transfer zone. According to the characteristics of boundary faults and internal faults properties within the depression, the area can be further divided into 9 fault domains and 6 fault domain transfer zones. The transfer zones, striking north-south, presents widths varying from 2 to 14.8 km in T⁰₁₀ reflector, forming low uplifts in sections. The basement pre-existing structure, fault segment growth and extension factors were main factors influencing the formation and evolution of the transfer zones in the study area. By integrating the geological background, characteristics of faults and transfer zones, we speculate that the basin is generally formed under the north-south tensional stress in the South China Sea in the late Oligocene. The transfer zones tend to converge with the main extension direction of the basin. The transfer zones are always in the high position which is close to the oil kitchen sags, and usually have high quality reservoir properties. These conditions make transfer zones into hydrocarbon enrichment area.