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The Paleo-Morphology of Passive Margins and Its Controls on Deepwater Systems: A Case Study From the Pearl River Month Basin, Northern South China Sea

Wang, Yingmin; Zhu, Weilin; Xu, Qiang; Wang, Yongfeng; Gong, Chenglin; Zhuo, Haiteng; Li, Weiguo

The paleo-morphology of continental margins in different tectonic stages has key controls on deep-water systems and yet is an area that still poorly understood. Three tectonic stages are recognized in the northern continental margin of the South China Sea (SCS) which are separated by breakup unconformity (32 Ma), shelf-break shift unconformity (23 Ma) and slope gradient jump unconformity (13.8 Ma), and are characterized by the wide shelf and faulted slope (stage 1), the narrow shelf and gentle slope (stage 2), and the wide shelf and steep slope (stage 3) respectively.

During stage 1 (32-23 Ma), the margin of Pearl River Mouth Basin (PRMB) were composed of a wide shelf and a faulted narrow slope. A series of depression were well developed on the shelf, and were filled with terrigenous sediment, resulting in extensive deltaic and coastal systems. The associated sandy facies formed excellent petroleum reservoirs. The slope was restricted close to deep ocean basins, and coarse-grained proximal basin-floor fans were developed within residual marine rift basins induced by local faulting.

During stage 2 (23-13.8 Ma), sea-floor spreaded to a critical width and intense regional tilting took place. The faulted slope stage ceased, and flexural slope formed on the landward side, leading to a drastically migrating of the shelf edge landward. This resulted in a continental margin characterized by a narrow shelf and a wide and gentle slope. Under a narrower shelf, terrestrial sediments were readily delivered to the shelf edge, forming shelf-margin deltas and associated extensive, sand-rich, submarine fan systems and their associated excellent deep-water reservoirs.

During stage 3 (13.8-Quaternary), slope gradient increased to a critical value due to increased basin subsidence, sufficient sediment input and subsequent isostatic adjustments, forming a continental margin with a wide shelf and a steep slope. More sediment were store on the shelf, and the mounts of sediments carried to the slope and beyond were therefore decreased, leading to the development of MTDs, submarine canyons, and their associated mud-rich fan systems.

The proposed three different tectonic stages are common in both the Atlantic and other passive margins. Coastal to deltaic systems deposited during stage 1, together with the submarine fans developed during stage 2, are excellent reservoirs on passive margins.


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