Forming mechanism of the submarine canyon on the north slope of the South China Sea
DING Wei-wei1, LI Jia-biao1, Li Jun2(1.Second Institute of Oceanography, SOA, Laboratory of Submarine Geosciences, SOA, Hangzhou 310012, China; 2. China Institute for Marine Affairs, SOA, Beijing 100860, China)
Submarine canyons are common features on continental margins wordwide, either active or passive. Most of them are located entirely on the upper slope, while there are also some large canyons with head that deeply indent the shelfbreak. They are generally in "V" shape (erosional situation) or "U" shape (depositional situation). What makes investigation of a submarine canyon interesting is that submarine canyons are prominent topographic features on the sea floors of continental margins. They not only shape the present morphology of continental margins, but also acted as the main conduits for transferring terrestrial sediments toward the deep sea and fed the fan system. Apart from constituting an important archive for documenting the sedimentation process history of an area, submarine canyons are also studied as modern analogues for deepwater hydrocarbon reservoirs because of their association with sand-rich turbidites.The geological and morphological characteristics of the submarine canyons on the north slope of the South China Sea were studied and the forming mechanism were discussed based on the interpretation of the multi-channel seismic profiles obtained during a "973" survey and other seismic data, including the off Zhujiang River Mouth submarine canyon, the south Taiwan Bank submarine canyon and the Penghu submarine canyon. It shows that these submarine canyons have the similar orientation, the character of direction-turning, but with different forming mechanism: The off Zhujiang River Mouth submarine canyon is related with the terrestrial downslope sediment flows carried by the paleo-Zhujiang River and has the horn shape. The south Taiwan Bank submarine canyon is controlled by the faults in NW direction. These faults weaken the surface strata, and the sediments flows will develop along them. The uplift of the sea mountain in the downslope blocks the flows' way and makes them turn into EW direction. The downward erosion, excavation, and sliding by down slope sediment flows are the major forming processes in the upper part of the Penghu submarine canyon, while the lower part mainly develop along the extending of the Manila Trench where the South China Sea is subducting under the Philippine Plate.