The Seismic Geomorphology, Distribution and Origin of the Quaternary Mass Transport Complexes in the Pearl River Canyon, South China Sea

Abstract

Utilizing 3D seismic datasets from the middle reach of Pearl River Canyon, South China Sea, this study has recognized two phases of Quaternary mass transport complexes (MTCs). MTCs1 (older) and MTCs2 (younger), are slope-attached MTCs which developed on low gradient (<2.5°) slope in water depths larger than 900 m. The older MTCs1 has a large coverage area of ca.1490 km2, which could be divided into three parts (MTC1.1, MTC1.2 and MTC1.3) based on their source areas. MTC1.1 was sourced from the upper reach of the canyon in the west and developed on gentle slope with an average gradient of 0.85°. MTC1.2, fed from northern slope with a series of canyons, could be further divided into two parts based on whether it is connected to the canyons mouth or not. The MTC with direct linkage to the canyon mouths commonly develop on relatively higher gradient (l.5°- 2.5°) slope. MTC1.3, fed from the contourites failures of Yunkai Swell in the south, also developed on the shallower slope with an average gradient of 1°and it was associated with some local faults. Comparing with MTCs1, MTCs2 significantly reduced its coverage area to 400 km2 and it was almost completely sourced from the northern slope. High overpressure is necessary for these MTCs on low gradient slope, which resulted mainly from high accumulation of fine grained sediments from paleo-Pearl River and Intermediate water. Most local faults associated with MTCs penetrate the older MTCs1 but barely into the younger MTCs2, suggesting that tectonisms were more active during the period when MTCs1 developed and weakened subsequently. The sediments supply gradually decreased as the sea level rose in the late Quaternary. Therefore, the weakened tectonic activities and lower accumulation rates of fine grained sediments jointly reduced the coverage area of MTCs2, which are manifested by the lack of contourites failures from Yunkai Swell. Our results imply that fine grained sediments, including contourites, could be prone to collapse on low gradient slope under the control of strong tectonisms and high sediment accumulation. The fine grained sediments failures would produce widespread mud-rich MTCs, overlying the sandy turbidites reservoirs and increase the potential of hydrocarbon accumulation. Our understanding about the origin of submarine landslides on low gradient slope is significantly helpful in the submarine hazards prediction.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017