Research On Depositional Record On Initial Fracture Stage In North Part Of The South China Sea

Northern South China Sea continental margin located in the convergence zone among the Eurasian plate, the Pacific plate, Australian plate, its rich structural information was inestimable for discussing geological evolution and structural properties of South China Sea. The region distributed a number of Cenozoic sedimentary basins. The paper selected the Pearl River Mouth Basin, the Qiongdongnan Basin and the Zhongjiannan Basin as the three representative research areas compared with core from ODP Leg 184 Site 1148, the integrated use of sedimentology, sequence stratigraphy, structural geology, geochemistry and other methods on the Cenozoic evolution of northern South China Sea was to carry out a study about tectonic evolution regularity among the respective regions, and to try to answer tectonic migration, differences of regional evolution and similar important issues on the northern margin of the South China Sea.In the paper, the three basins were researched in the construction of the basin tectonic evolution, and divided several major tectonic unconformities under the background of the South China Sea regional evolution. According to rift basin development history, we outlined the“rift– rift to sag– sag”three structural features. The boundaries of the rift to sag stage varied from basin to basin, the Pearl River Mouth Basin were T70 interface (early Oligocene/late Oligocene boundary) and T60 interface (Oligocene/Miocene boundary); the Qiongdongnan Basin were T60 interface (Oligocene/Miocene boundary) and T40 interface (mid-Miocene/late Miocene boundary); the Zhongjiannan Basin were T5 interface (mid-Eocene/late Eocene boundary) and T3 interface (mid-Miocene/late Miocene boundary). The ODP site 1148 and the Pearl River Mouth Basin were conformable in the regional structural position, and the site 1148 sedimentary record showed several times interval slump deposits and 3Ma depositional break in the period of early to late Oligocene.In northern continental margin of South China Sea the time of tectonic movement displayed the gradual migration characteristics between eastern and western region. By analyzing episodic rifting events, depositional environment and depositional facies, seismic profile characteristics to determine the migration of structure, the result embodied in northern South China Sea from east to west direction, "the Pearl River Mouth Basin�'Qiongdongnan Basin", "the Pearl River Mouth Basin�'Zhongjiannan Basin" whose tectonic events tendency gradually became later.Evolution differences of regional structures mainly reflected all below:rift period:In the Qiongdongnan Basin, early formation tended to lift before stable deposition. In the Zhongjiannan Basin, intension of tectonic movement gradually became weaker from SW to NE. In the Pearl River Mouth Basin early formation tended to deposit before lifting, the intension of rift movement became more and more weak from E to W. sag period:Both the Qiongdongnan Basin and the Pearl River Mouth Basin represented the thicker deposit in the western part compared to the eastern part.As above mentioned, the initial fracture of the South China Sea started from the ease, gradually extended according to the“tore”model. Neglecting the reflect of the Red River fault zone, the intension of rift movement became more and more weak from east to west for the northern South China Sea. After that the migration about tectonic subsidence or depositional center showed a more complicated way.