Slope failure and canyon development along the northern south China sea margin

Abstract

The continental margin of the northern South China Sea is a NE-SW trending passive continental margin. Mapping of the continental slope from short offset processed 3D seismic across the offshore Pearl River Mouth Basin shows the margin to be characterised by a canyoned morphology from 600 to 1,500 m water depth. Shallower than these depths the slope is undisturbed while at greater depths there is a return to a smooth base of slope morphology with broad runout channels reflecting mass transport deposition fed from the canyons. The canyons are typically ∼1 km wide and up to 20 km long, steep sided and asymmetric with a higher slope angle along their eastern margins. Comparatively, the western margins show increased evidence of slumping and slope failure. The intercanyon ridges exhibit arcuate slump features. Mapping of the base Pleistocene shows this slumping has resulted in removal of Quaternary sediment along the intercanyon ridges. Mass transport deposits are also identified along the lower slope. The erosion of these canyons is considered to be related to the internal waves generated from the strong Kuroshio Current crossing the shallow bathymetry of the Luzon Strait into the South China Sea resulting in internal waves interacting with the slope below 600 m. Understanding the dynamics of canyon systems such as these is essential for determining risk to deep sea exploration infrastructure. © Springer Science+Business Media B.V. 2012.