Seismic geomorphology, classification and genesis of unidirectionally migrating deep-water channels in the northern slope of the Baiyun Sag, South China Sea

Unidirectionally migrating deep-water channel is a kind of newly recognized deep-water channel, which is mainly formed by the interplay between along slope bottom current and downslope erosional turbidity current. Using newly... [ view full abstract ]

Unidirectionally migrating deep-water channel is a kind of newly recognized deep-water channel, which is mainly formed by the interplay between along slope bottom current and downslope erosional turbidity current. Using newly available high-quality 3D seismic surveys covering an area of 6550 km2 in the north slope of the Baiyun Sag, South China Sea, this study identified 18 slope-confined, unidirectionally migrating deep-water channels (numbered as C1 to C18 herein from west to east) and systematically investigated these channels and classified them into four types based on their seismic geomorphology and initial mechanisms.
Type I channels (represented by C1，C2，C7，C9，C10) start at a point ca.10km from the shelf-break, they are characterized by smooth channel heads without headscarps and deformations. Their topographic profiles along the thalweg show overall concave-upwards geometry with slope declining downslope from ca.3°to ca.1.5°gradually. These morphology characters reveal that the initial mechanism of type I channel is the shelf-sourced, oceanographic processes-induced turbidity current.
Type II channels (represented by C3-C5), whose heads are much closer to the shelf-edge delta, develop headscarps and a striking knickpoint, showing a sharp slope gradient change from ca.5°at the upper reaches to ca.1.2°at the middle-lower reaches. Their morphology characteristics show that the turbidity currents forming these channels are initiated by the delta-lip failures.
Type III channels (represented by C11-C18), located closely to Dongsha Rise to the east, have larger distances (>25km) from channel head to the shelf break than other channels. Their heads regions are characterized by remarkable wrinkle-like deformations associated with slumps and small faults, suggesting that type III channels are initiated by the slumps generated by tectonic activities (earthquakes) of Dongsha Rise.
Type IV channel (only C8) is located between C7 and C9. However, C8 starts from a much deeper water depth of approximately 962m at a point 27.7km from shelf break. In addition, the channel head of C8 could extend upslope to C7’s head, indicating that its corresponding erosional turbidity current should be the overflow turbidity current from C7.
This classification would help us understand the sedimentary processes of the interplays between bottom currents and turbidity currents initiated by different mechanisms, which are significant to establish sedimentary models for different types of unidirectionally migrating channels.