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Along-Strike Variability of Morphology and Sedimentation of the Northern Continental Margin of the South China Sea

Zhuo, Haiteng; Wang, Yingmin; Xu, Qiang; Li, Dong; Wang, Yongfeng; Wang, Ying

Analyses of a large amount of 2-D and 3-D seismic data permit a systematical investigation of the along-strike variations in the morphology and sedimentation of the northern margin of the South China Sea (SCS). Results show that the studied margin can be divided into three sectors along depositional strike, including the Yinggehai and western Qiongdongnan margin (Sector 1), eastern Qiongdongnan margin (Sector 2) and Pearl River Mouth margin (Sector 3). Each displays distinct characteristics in the scale, slope morphology, canyon development, sequence stacking pattern as well as the resulting deposits.

Sector 1 has a moderate margin relief and the modern slope morphology can be fitted with an exponential equation, showing a concave-upward geometry. Due to sufficient sediment supply, the margin is featured by rapid slope progradation and obvious shelf aggradation, leading to a long-term rising shelf edge trajectory. Deep-water deposits are dominated by small scale slumps and turbidites with short run-out distances. Submarine canyons are rare in both ancient and recent sequences.

Sector 2 is featured by the steep slope and prominent shelf edges. The upper slope shows a planar geometry and can be well fitted using a linear equation. This sector is largely sediment-starved because of the large amounts of accommodation created by the activity of underlying faults since 10.5 Ma. Pre-existing fault caused the shelf edge trajectory to be fixed or slightly propagating. The sedimentation on this margin is characterized by densely distributed small-scale gullies in the upper slope and large-scale detached slump deposits in the lower slope.

Sector 3 has the highest margin relief and gentlest upper continental slope. A Gaussian distribution function can be applied to fit most of the slope profiles. Truncations around the modern shelf edge reveal modifications of external forces to the morphology, such as internal waves and ocean currents. Due to a longer duration, the shelf margin evolution of Sector 3 is much more complicated, revealing combined structural and sedimentary influences. Submarine channel-fan systems have developed since 23.8 Ma, as is proved by offshore drilling. Since 13.8 Ma, mature and tremendous submarine canyons have prevailed in central Pearl River Mouth basin.

The along-strike variability of the morphology and sedimentation of the northern SCS margin can be attributed to the local structural style, sediment supply and extrinsic processes.


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