Sedimentary evolution and control factors of the Rizhao Canyons in the Zhongjiannan Basin, western South China Sea
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Abstract: Submarine canyon is an important channel for long-distance sediment transport, and an important part of deep-water sedimentary system. The large-scale Rizhao Canyons have been discovered for the first time in 2015 in the continental slope area of the western South China Sea. Based on the interpretation and analysis of multi-beam bathymetry and two-dimensional multi-channel seismic data, the geology of the canyons has however not been studied yet. In this paper, the morphology and distribution characteristics of the canyon are carefully described, the sedimentary filling structure and its evolution process of the canyon are analyzed, and then its controlling factors are discussed. The results show that Rizhao Canyons group is a large slope restricted canyon group composed of one east−west west main and nine branch canyons extending to the south. The canyon was formed from the late Miocene to the Quaternary. The east−west main canyon is located in the transition zone between the northern terrace and the southern Zhongjiannan Slope, and it is mainly formed by the scouring and erosion of the material source from the west, approximately along the slope direction. Its development and evolution is mainly controlled by sediment supply and topographic conditions, the development of 9 branch canyons is mainly controlled by gravity flow and collapse from the east−west main canyon. This understanding result is a supplement to the study of “source-channel–sink” sedimentary system in the west of the South China Sea, and has important guiding significance for the study of marine geological hazards.
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Key words:
- canyon /
- geomorphology /
- sedimentary evolution /
- control factors /
- Zhongjiannan Basin /
- western South China Sea
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Figure 1. Geographical location of Zhongjiannan Basin study area (a) and bathymetric contour map of the study area and its periphery (b) (Yang et al., 2015).
Figure 2. Sequence stratigraphic division in the seismic line L5 passing through drilling 121-CM-1X Well, according to Fyhn et al. (2009) (a) and sequence stratigraphic division in the seismic survey line L1 in the study area (b). According to the calibration of 121-CM-1X drilling data, Sequence A is Quaternary, Sequence B is Pliocene, and Sequence C is Pliocene. The locations of the seismic line L5 and L1 are marked on Fig. 1b.
Figure 3. Topographic slope map of Rizhao submarine canyon (a) and sketch of canyon shape (b) (the location is shown in Fig. 1b).
Figure 5. Seismic profile and interpretation of the canyons C5, C6, and main canyon, middle part of C5 on seismic profile L1 (a), middle part of C5 on seismic profile L′3 (b), upper part of C6 on seismic profile L′3 (c) and the main canyon on seismic profile L′3 (d) (profile location is shown in Figs 1b and 2).
Figure 6. Seismic line L1 across the lower section of canyons C6–C8 (a), local topographic map of canyons area (b), seismic survey line L2 across the downstream of canyons C1–C3 and the mouth (c) and seismic line L′4 across the downstream of the canyons and the mouth (d) (see Fig. 1b for profile location).
Figure 7. The interpretation of seismic profile L6 across the continental shelf and the upper slope in the west of the study areas (modified from Fyhn et al. (2009); location of lines is shown in Fig. 1b).
Table 1. Genetic classification of main canyons in the South China Sea
Classification basis Major characteristics Typical example Geomorphic morphological characteristics Large-scale canyon dominated by a main canyon with less developed branch canyons Taitung Canyon, Taiwan Canyon, Dongsha Canyon, Zhujiang River Estuary Canyon, Penxi Canyos Composed of several small and short canyons Penghu Canyons, Yitong Canyons, Xishabei Canyons It is composed of the main canyon and multiple branch canyons Rizhao Canyons Development location, genesis The continental erosion canyon is generally related to onshore rivers or deltas Taiwan Shoal submarine canyon, Zhujiang River Estuary Canyon, Dongsha Canyon The head is developed only in the continental slope area, usually related to the turbidity current events, gravity-flow transport, traceable slump, and bottom current Shenhu Canyons,
Rizhao CanyonsTable 2. Typical seismic facies analysis and corresponding sedimentary facies interpretation of canyon system
Serial No. Line No. Seismic profile Seismic reflection characteristics Sedimentary facies Origin a L1 low continuous reflection and chaotic reflection gravity flow deposit gravity flow b L1 parallel reflection channel-fill facies turbidity current c L1 medium-high continuous and two-way onlap reflection d L' 3 medium continuous and two-way onlap reflection e L' 3 medium-low continuous reflection f L' 3 medium-high continuous onlap reflection channel migration gravity flow g L1 medium continuous reflection slump mass gravity flow h L1 medium continuous reflection in the upper part,
chaotic reflection in the lower partslump mass, sliding mass chaotic reflection filling in the channel channel-fill facies turbidity current i L' 4 local strong amplitude continuous-low
continuous reflectiondeep water fan -
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