Tectonic and oceanographic controls on the slope-confined dendritic canyon system in the Dongsha Slope, South China Sea

Abstract

Dendritic canyon system is the most widespread type of submarine canyons along continental margins and plays important roles in sediment delivery and deep-water ecosystem. Based on high-resolution multibeam bathymetric and seismic reflection data, this study investigates a slope-confined dendritic canyon system in the Dongsha Slope, South China Sea. The dendritic canyon system between water depths of 550–2200 m consists of one main canyon (C2) and three V-shaped tributaries (C1, C3, and C4), in association with clearly visible tectonic deformation (uplifting and faulting) at the upper segment. The main canyon is characterized by a concave-up longitudinal profile, while the tributaries show convex-up and/or linear profiles, probably indicating that they are affected by tectonic deformation to variable degrees. The alignments and locations of tributaries C3 and C4 are determined by the NE-SW trending faults, while the distribution of the tributary C1 and the upper segment of C2 is less affected by faults, which also indicates that tectonic controls on the dendritic canyon system vary spatially among tributaries. Widespread NE-SW oriented sediment waves and southeast-facing scarps and isolated scour depressions at canyon banks highlight the significant influence of northwestward-propagating internal tide/wave on the morpho-sedimentary processes. The internal tides/waves within canyons not only flushed canyon floor, but also contributed to the asymmetric distribution of sidewall gullies and failures. The obliquely shoaling internal waves, combined with other hydrodynamics (e.g., Kuroshio Current and mesoscale eddies), could significantly intensify along-slope bottom currents and erode the NE-SW-oriented trough and tributaries. Under the significant erosion of ocean currents, some of the sidewall gullies, troughs and sub-tributaries may finally evolve into new tributaries. This study reveals the coupling relationship between slope-confined dendritic canyon system and tectonic/oceanographic processes, which can shed light on the slope/canyon evolution of similar settings worldwide.