Channel-related sediment waves on the eastern slope offshore Dongsha Islands, northern South China Sea

Abstract

The characteristics and origin of the sediment waves on the eastern slope offshore Dongsha Islands, northern South China Sea (SCS) were analyzed by integrating high-resolution multibeam bathymetric, seismic and piston core data. Four sediment wave fields were identified, which are the West Dongsha Channel (WDSW), West Taiwan Channel (WTSW), South Taiwan Channel (STSW) and West Penghu Channel (WPSW) sediment wave fields, respectively. They are distributed on the right levees (looking downstream) and adjacent overbank areas of related channels (WDSW, WTSW, and STSW), or developed outside the channel mouths (WPSW). Each sediment wave field consists of several to tens of rows of sediment waves. These sediment waves are up to 2.8–7.2km in wavelength and 30–60m in wave height. With wave crests orthogonal to or oblique to the orientation of the channels, the sediment waves gradually decrease in dimension both in downslope direction and with the distance increasing away from the channel. Most sediment waves are asymmetric in cross sections with a thicker upslope flank and a thinner downslope flank, and therefore migrate upslope. Piston cores suggest that sandy turbidites developed with normal size grading dominate the channels, while massive muds with thin sandy or silty turbidite interbeds prevail in the inter-channel regions on which the sediment waves situated. The sediment waves on the channel levees and related overbank areas (WDSW, WTSW, and STWD) were presumably built by the turbidity currents overspilled from the channels; while those in WPSW, located outside the mouth of the West Penghu Channel, are suggested generated by unconfined sheet-like turbidity currents outside the channel mouth.