Newly collected high-resolution acoustic data are used to describe the morphologies and sedimentary characteristics along the slopes of isolated carbonate platforms in the Xisha (Paracel) Archipelago. Base on multibeam bathymetric and seismic data, we identified seven types of morphological and depositional features around the platforms, including erosive grooves, mass transport deposits (MTDs), gullies, confined channels, canyons, mounded sediments and marginal contourite depressions. The occurrence of erosive channelized features around the platforms indicate that gravity flow is a major sediment-export mechanism for the transportation of excess neritic carbonates towards the slope. Marginal contourite depressions and mounded sediments are interpreted as bottom-current reworking products, suggesting an important role of bottom current and deep-water circulation of the South China Sea in shaping the slope morphology of the carbonate platforms. Furthermore, the bottom-current products tend to develop along the slopes of the carbonate platforms at the Xisha Uplift margin, in particular, erosional features formed by bottom current frequently occur in the southern side of the carbonate platforms. By comprehensive analysis of morphological and depositional features, we establish a facies model around the carbonate platforms to interpret different sedimentary transport processes, such as off-platform and along-slope sediment transport processes. These findings highlight a notable and complex relay-style channelized transport system consisting of grooves/gullies-channels-canyons, which has implications for linking neritic carbonate platforms into deep-sea basins.
Seismic imaging of a mid-crustal low-velocity layer beneath the northern coast of the South China Sea and its tectonic implications
