GEOGRAPHY

This study reveals the formation mechanism of isolated submarine canyon system in the northwest continental margin of the South China Sea


Recently, the team of Li Wei, a researcher at the South China Sea Institute of Oceanology, Chinese Academy of Sciences, together with Professor Chen Hongjun of Guangzhou Marine Geological Survey and other researchers, systematically studied an isolated submarine canyon group in the gentle land slope area (< 0.5°) in the northwest of the South China Sea, and revealed its formation mechanism and evolution process. The study was published in Geomorphology. Li Wei is the first author of the paper, and Li Wei and Chen Hongjun are the corresponding authors.

Seabed canyons are narrow geomorphological units widely distributed on active and passive continental margins and island periphery, and their importance lies in their ability to serve as the main passage for land-based detritus, organic matter and pollutants into the deep sea, and also have important impacts on oil and gas enrichment, marine carbon sinks and ecological environment. The formation mechanism of submarine canyons often reflects deep-water sedimentation processes on long-term scales, and also records important information such as regional sediment supply, tectonic activities and sea level changes. However, how landslides control the formation of submarine canyons is still unclear.

Location map of submarine canyon group in the northwest continental margin of the South China Sea and map of multi-beam topography of the seabed. Photo courtesy of the research team

Taking the northwest continental margin of the South China Sea as the research area, the researchers studied in detail the geomorphology and internal geological structure of the submarine canyon group in the study area through seabed multibeam bathymetry and two-dimensional multi-channel seismic data. The results show that there are seafloor landslide sediments (also known as block sedimentary transport system: MTC) at the bottom of the submarine canyon group that develops on the relatively gentle land slope (<0.5°), while no other submarine canyons, waterways and gullies are observed around the canyon group.

The researchers believe that the negative terrain formed by submarine landslides provides space for sediment transported to the lower slopes and is able to capture sediment gravity flows, thereby contributing to the formation of submarine canyons at the top of the MTC. In addition, lateral sediments were found on the southwest side walls of the three submarine canyons, indicating that they migrated northeast due to bathymetric flows; Small-scale MTCs inside canyons suggest that they have undergone multiple erosion-filling processes controlled by sea level changes, with high sea levels now eventually leading to submarine canyons isolated on gentle slopes.

The results not only reveal the key role of submarine landslides in the initial formation of submarine canyons, but also clarify the important influence of relative sea level changes on the evolution of submarine canyons in gentle land slope areas. (Source: China Science News, Zhu Hanbin, Li Shu)

Related paper information:https://doi.org/10.1016/j.geomorph.2023.108746



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