Morphology and seismic-stratigraphic charateristics of the Yitong Submarine Cayons in the northern continental slope of the South China Sea
High-resolution multibeam bathymetric data and multichannel seismic data were used to investigate the morphology and the seismic-stratigraphic characteristics of the Yitong submarine canyon group in the lower part of the northern continental slope, South China Sea.
Multibeam bathymetric data indicate that the submarine canyon group contains 12 submarine canyons, with strikes varying eastward from NWW-SEE, NNW-SSE to N-S directions. In the intercanyon areas, many gullies can be identified. These submarine canyons are 6.1 to 53.3 km long and up to 2.3-11.4 km wide. Maximum incision depth of the canyon valleys ranges from 108 to 652 m, and average slope of the canyon thalwegs varies between 1.4 and 5.4°.
Six seismic sequences were identified, with basal boundaries of the sequences being respectively identified as the base of Quaternary (~2.59 Ma), the base of Pliocene (~5.33 Ma) , the base of upper Miocene (~10 Ma ), the base of middle Miocene (~15.97 Ma), the base of lower Miocene (~23.03 Ma),and the base of Paleogene (~66 Ma) by tying to well controls from ODP Leg 184 and IODP Expedition 349 in the nearby area. Based on seismic parameters like reflection configuration, amplitude and continuity, etc., five types of seismic facies were defined, which are progradational, wavy, chaotic, fill-type and stratified facies, respectively. The progradational seismic facies is developed in all sequences and spatially distributed in the upper slope upstream of the Yitong submarine cayons, and is interpreted as the shelf-edge to upper slope delta deposits. The wavy seismic facies consists of irregular wavy reflections of low amplitude and low continuity, and has been developed at the upper part of the intercanyon areas since the late Miocene. The facies is interpreted as sediment waves formed by sediment creeping or slumping. The chaotic facies occurs in the upper and middle portions of the intercanyon areas, and is interpreted as slides or slumps. The fill-type facies, distributed in the lower part of the canyons, is typified with a concave-upward surface and fill-typed reflections of variable amplitude, and is interpreted as canyon or channel filling. The stratified facies is featured by layered reflections of variable amplitude and moderate continuity. It is distributed in the lower part of the intercanyon areas since the early Miocene or occurs in the Paleogene sequence, and is interpreted as gravity flow deposits.
The Yitong submarine canyons are slope-confined. We speculate that the canyons were initiated from submarine landslides. Retrogressive landsliding might make the canyons extending headward.
This research was funded by the National Natural Science Foundation of China (grant numbers 41676029, 91528304, and 41876049).
Special Session: Canyons and trenches in the South China Sea and West Pacific
morphology, seismic stratigraphy, slope-confined, Yitong Submarine Cayons, South China Sea