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Stratigraphic Architectures and Evolution of the Central Canyon System in the Qiongdongnan Basin, Northern South China Sea

Wang Zhenfeng; Xie Xinong; Zhang Daojun; Li Xushen; Sun Zhipeng; He Yunlong

The Central Canyon in the Qiongdongnan basin has very important significance in petroleum geology with good gas discovery. By means of sequence stratigraphic interpretation, seismic multi-attribute and well data analysis, applying Mass Transport Deposit(MTD) theoretical model, the authors studied the stratigraphic architectures and evolution of the Central Canyon system, in order to understand the reservoir distribution and guide nature gas exploration. As a result, the canyon shows a S-shaped NE-trending depositional system, which originates from the east margins of the Yinggehai basin, pass by the Central depression and the Xisha trough, and terminates in western part of Northwest Subbasin of South China Sea. It is more than 570 km in length and 6-19 km in width developed form Late Miocene to Early Pliocene. Based on the elaborated interpretation of 2D and 3D seismic data and drillhole data, the canyon can be divided into 4 segments, each shows distinct character in morphology section , depositional architectures, genetic facies and sediment resources. Morphology and infilling features indicates that the canyon shows the deeper downcutting and scours to the older strata eastwards. The canyon can be divided in to 4 types in shape, such as V, U, W and composed of them. Among them, V-typed canyon shows the strongest downcutting, and the most obvious scouring. In this paper, the canyon filling can be divided into four phases from bottom to top. The lowest is composed mainly of turbidity channel deposits, with moderate-good continuity, strong amplitude reflectors in the seismic profile; the second is dominated by mass transport deposits, which exhibit messy reflection characteristics; the third shows a composite feature of mass transport deposits and turbidity deposits; the forth is mass transport deposits with clutter reflectors. Detailed observations suggest that the Central Canyon can be ascribed to different gravity sediments and has varied depositional architectures in different segments. Turbidite channel deposits are dominated in the westernmost segment. Interbeds of turbidite channel and mass transport deposits occur in the eastern segment, but there are different ratios in different places. Turbidite channel deposits originate from the west side, however, mass transport deposits originate from the slope system in the northern side of the basin. Those deposits from different sediment-supplies composed of a multiple-episodic and multiple sediment-supplied complex canyon system.

Keywords: Qiongdongnan Basin, Late Miocene-Early Pliocene, deepwater central canyon, turbidite channel, mass transport deposits


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013