Seismic characteristics and processes of the Plio-Quaternary unidirectionally migrating channels and contourites in the northern slope of the South China Sea

The Plio-Quaternary unidirectionally migrating channels (UMCs) and contourites in the northern slope of the South China Sea were investigated in this paper using seismic data. The UMCs include thalweg deposits (TDs) and laterally migrating deposits (LMDs), which result from the interaction between gravity flow and contour current. The LMDs migrating directions are northeast (NE) and west-southwest (WSW) and also display weak seismic reflection and obvious multi-stages. By contrast, the TDs show high seismic reflection and lateral aggradation. Giant elongated, confined, and slope sheeted drifts, as well as sediment waves are widespread in the northern slope of the South China Sea. Helicoidal contour currents can generate giant elongated and confined drifts associated with moats. By contrast, tabular contour currents can develop slope sheeted drifts with rare moats. NE-migrating channels, giant elongated drifts, and a number of sediment waves are exclusively formed at water depths of 200 m–1200 m. Drifts, sediment waves, and few WSW-migrating channels are developed at water depths of 1200 m–3000 m. The intermediate water contour current circulates clockwise, moving from Xisha Islands to Dongsha Islands and extending into the eastern part of Dongsha Islands because of the bathymetry. Deep water contour current may circulate counterclockwise and be transported northeastward through Dongsha Islands to Xisha Islands, bifurcating in the Xisha Islands because of topographical prominences. ► Distributions of unidirectionally migrating channels and contourites had been studied. ► Circulations of intermediate and deep water contour current had been improved. ► Process of migrating channels and drifts had been worked.