New discovery by the "Deep Sea Warrior": Semi-oceanic sedimentation in submarine canyons

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Reporter Cui Shuang

In the recently concluded "Exploration One" TS12 voyage 2nd segment scientific expedition, the "Deep Sea Warrior" manned deep submersible dives many times, taking scientists to see the deep sea. Among them, dr. Wu Bin and Dr. Shan Xin, assistant researchers from the Laboratory of Marine Geological Processes and Environmental Functions of the National Laboratory of Oceanography and the First Institute of Oceanography of the Ministry of Natural Resources, through the analysis of the short column sediments obtained by diving, found that the surface sediments of the submarine canyon were mainly mottled mud, of which there were a variety of relic fossils developed, which belonged to semi-oceanic sediments.

"Semi-pelagic sedimentation is formed by the vertical settlement of sediment particles in shallow seas in water bodies, and the sedimentary mode of action is completely different from turbidity flow, isometric flow, clastic flow (mud and rock flow), etc. Modern semi-oceanic sediments are often accompanied by a large number of biological remains, such as moving algae traces. "Shan Xin said that because the mud in the short column of sediment is mottled and fossil remains can be seen, and they also saw a large number of biological remains when observing the near bottom of the canyon, it is speculated that the deposits found belong to semi-oceanic sediments." Since there have been no turbid currents in this canyon recently, the discovery of large-scale semi-pelagic sediments in the canyon suggests a variety of sedimentary modalities in the canyon. Shan Xin said that although they found the cyclocarbon structure formed by supercritical turbidity in the submarine canyon, because the surface sediment particle size of these spiral ridges belongs to the silt, clay grade and there are many biological remains of the surface sediments, it is speculated that these cyclophoric structures may have been formed and preserved hundreds or thousands of years ago.

According to Wu Bin, since semi-oceanic sedimentation is formed by vertical sedimentation of sediment particles in water bodies layer by layer, the types, abundances and geochemical indicators of micro-paleontology such as foraminifera deposited in semi-oceanic sediments can be reconstructed by using the types, abundances and some geochemical indicators of paleocean parameters, such as salinity, temperature, oxygen content, etc.

"Submarine canyons are important channels for sediment transport, and frequent turbidity flows on the seabed here can lead to major geological disasters and pose a huge threat to submarine facilities such as oil and gas platforms and submarine communication cables." Wu Bin said, "The evolution of canyons and sediment handling processes have attracted much attention from the academic community, and are the frontier and hot issues in the current marine geology and global change research, so it is very important to carry out canyon diving." ”

In the submarine canyon of the South China Sea where semi-pelagic sedimentation is found in the deep diving operation of the voyage, it has special practical value to study the sediment handling process. According to Shan Xin, because the sediments of the South China Sea Canyon are rich in oil and gas resources, the waterways and natural embankments in the canyon are important oil and gas reservoirs, and the study of canyon evolution and sediment handling process can predict the location, porosity, permeability, etc. of the reservoir, and many locations in the South China Sea Canyon are rich in natural gas hydrate resources.

"Since canyon diving can accurately locate a specific canyon, the accurate sampling of the Deep Sea Warrior is of great significance for reconstructing the hydrodynamic conditions at different locations in the canyon." Wu Bin said. According to him, during the investigation of diving into the submarine canyon by submersible, they observed the spiral ridge sedimentary structure with a wavelength of hundreds of meters, a variety of biological relic fossils, obtained a large number of high-precision topographic and geomorphological data and image data, etc., collected a number of sediment short column samples about 30 cm long, and the short column samples they obtained also contained rich ancient marine information, which can be used to reconstruct paleoenvironmental changes.