GEOTECTONICS AND HYDROCARBON RESOURCES IN THE SOUTH CHINA SEA
Liu Zhaoshu (South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301)
The northern margin of the South China Sea (SCS) is a tensional margin and the southern margin is a compressive margin. The Taiwan North Luzon island arc and the Manila trench in the direction of near S N are located in the eastern margin of the SCS and they have compressive feature at present. The western margin has shear feature. Those tectonic features in the SCS reflect the creeping of continental margin from northeast to southwest and its main movement features are tension in rear edge, compression in front edge and shearing in both flanks. The main concept of “Continental Margin Spreading” is that the regional stress field was transformed from compression to relaxation on the background of Cathaysian active continental margin of the SCS, the mantle spread toward oceanic side, the continental margin rifted and broke up, and the poly period and poly axis spreading occurred in the seafloor and the graben system of continental margin was formed during the process of continent rifting. Three spreading movements occurred in the SCS from the L. Cretaceous to the Miogene and they obviously controlled the sedimentation in the Pearl River Mouth Basin and determined the spatial distribution of the complex of source, reservoir and cap rocks. The Dongsha Fault uplift is a positive structural element in the Pearl River Mouth Basin, where three spreading cycles, undoubtedly, are closely related to the formation of fault uplift and the distribution of source, reservoir and cap rocks. The direction of the faults in Nansha Fault Block is mainly NE. The NW faults cut Nansha Fault Block into a several EW blocks and the NE faults formed a series of SN en echelon interval fault sag and fault rise. Therefore, those constructed the tectonic frame which seems as the belts in SN direction and the blocks in EW direction in Nansha Fault Block. The Paleocene sediments in the Liyue (Reed Bank) Basin of Nansha Fault Block appear as metamorphic limestone from neritic to littoral facies and this stratum is unconformable to the underlying Cretaceous strata. The upper Eocence sediments seem to be unconformable to the underlying strata which are interbed of littoral sandstone and sandy shale. The gas was obtained from exploring wells in these two layers of the basin. Therefore, the Liyue Basin is full of prospect for gas and oil and worth for further study. The Zengmu graben province is composed of a series fault uplift and fault rift and the Zengmu Basin in this province has been studied in more detail. The studies of tectonic events relative to hydrocarbon structures indicate that Liyue event (K 2) and Nansha event (E 2 2—E 3 2) appear to be strongly folding, thrusting, faulting and metamorphism in the southern edge of the basin and the land. All these reformed strongly the contemporary and former sediments,led to hydrocarbon escape and damaged accumulation of petroleum. Therefore, metamorphic basement is generally regarded as the low limitation for oil exploration. The folds, faults or rises, sedimentary formations and unconformities formed by Miri event (N 2 2) and Balingian event (N 2 2—N 3 2) are good trap structures.
【CateGory Index】： P542