Gravity Flow on Slope and Abyssal Systems in the Qiongdongnan Basin,Northern South China Sea

The study of new seismic data permits the identification of sediment gravity flows in terms of internal architecture and the distribution on shelf and abyssal setting in the Qiongdongnan Basin (QDNB).Six gravity flow types are recognized:(1) turbidite channels with a truncational basal and concordant overburden relationship along the shelf edge and slope,comprising laterally-shifting and vertically-aggrading channel complexes;(2) slides with a spoon-shaped morphology slip steps on the shelf-break and generated from the deformation of poorly-consolidated and high water content sediments;(3) slumps are limited on the shelf slope,triggered either by an anomalous slope gradient or by fault activity;(4) turbidite sheet complexes(TSC) were ascribed to the basin-floor fan and slope fan origin,occasionally feeding the deep marine deposits by turbidity currents;(5) sediment waves occurring in the lower slope-basin floor,and covering an area of approximately 400 km~2,were generated beneath currents flowing across the sea bed;and(6) the central canyon in the deep water area represents an exceptive type of gravity flow composed of an association of debris flow,turbidite channels,and TSC.It presents planar multisegment and vertical multiphase characteristics.Turbidite associated with good petrophysical property in the canyon could be treated as a potential exploration target in the QDNB.