Response of geomorphic and geological processes to insufficient and ample sediment supply along the upper continental slope in the north-western South China Sea

Abstract

We document upper slope sedimentary process and strata on the passive margin of the northwestern South China Sea (SCS) using multibeam bathymetry and high-resolution seismic data. The upper slope can be divided into two segments based on geomorphology, strata, and sediment supply. (1) The east segment is characterised by deep incised canyons and gullies, and slope failure. Submarine canyons with both U-and V-shaped morphology (13-28 km long × 2-4 km wide) are oriented NNE-SSW or NNW-SSE and are approximately perpendicular to the slope. Erosion is dominant, with escarpments, slumps, and several mass transport deposits (MTDs). Shelf-margin clinoforms show strongly upward vertical aggradation with time and are strongly aggradational in style. Since 5.5 Ma, the shelf break line migrated southwards and then retreated to its present position. The segment is classified as erosion-dominated due to insufficient sediment supply. (2) The west segment has a smooth surface, gentle gradient, and a strongly progradational style, with MTDs triggered by high sedimentation rates. Shelf-margin clinoforms display a combination of progradational and aggradational stacking patterns. The shelf break line migrated southwards with time. The segment is classified as deposition-dominated, resulting from plentiful sediment supply. Depositional models have been constructed for each segment: a constant shelf break model with insufficient sediment supply in the east, and a migration shelf break model with plenty sediment supply in the west. This case study contributes to the understanding of the upper slope sedimentary process and stratigraphic style under different sediment supply conditions.

Along‐strike variability in shelf‐margin morphology and accretion pattern: An example from the northern margin of the South China Sea

“…100-300 m, and they carve the eastern QDN slope into an overall linear shape. Note that the incision depths of these gullies gradually increase to the east (Figure 5c; also see figure 2 in Chen, Zhan, & Wu, 2016).…”

Pliocene seismic stratigraphy and deep‐water sedimentation in the Qiongdongnan Basin, South China Sea: Source‐to‐sink systems and hydrocarbon accumulation significance

“…Seismic facies interpretation results indicate that the western submarine fan is clearly larger and with more sand‐rich material than that of the eastern area. Chen et al () obtained the geomorphology of the slope in QDNB using the detailed multibeam bathymetry data. The few seismic profiles also yielded the shelf‐margin migration and the corresponding sediment supply since 5.5 Ma.…”

“…The few seismic profiles also yielded the shelf‐margin migration and the corresponding sediment supply since 5.5 Ma. The progradational reflection features of our seismic data in the eastern upper slope of QDNB become weak since 5.5 Ma and disappear gradually; this is consistent with the observations delineating the east segment as an erosion‐dominated slope with insufficient sediment supply (Chen et al, ). However, according to our study, the development of many shelf‐edge deltas in the western upper slope of QDNB during 10.5–5.5 Ma, also confirmed by the results of Chen et al (), delineates the west segment as a deposition‐dominated slope with sufficient sediment supply.…”

“…Cao, Jiang, Wang, Zhang, & Sun, ; Chen, Xu, & Shen, ; Clift et al, ; Clift & Sun, ; Shao et al, ; Wang et al, ; Wei et al, ; Yan, Carter, Palk, Brichau, & Hu, ) and petroleum resources exploration in the South China Sea (e.g. Chen, Zhan, & Wu, ; Jiang et al, ; Jiang, Xie, Ren, Zhang, & Su, ; Liu et al, ; Pang et al, ; Sun, Wu, Lü, & Yuan, ; Wang et al, ; Xiao, Wang, Jiang, Lü, & Yue, ; Zhang, Zhu, & Gao, ; Zhu et al, ). As the largest supplying river for the northwestern South China Sea, the Red River is generally thought as the main water source for the Central Canyon filling of the QDNB since the Late Miocene (Chen et al, ; Clift & Sun, ; D. Li, Xu, & Wang, ; Y. F. Wang, Wang, Li, & Xu, ).…”

“…Chen, Zhan, & Wu, ; Jiang et al, ; Jiang, Xie, Ren, Zhang, & Su, ; Liu et al, ; Pang et al, ; Sun, Wu, Lü, & Yuan, ; Wang et al, ; Xiao, Wang, Jiang, Lü, & Yue, ; Zhang, Zhu, & Gao, ; Zhu et al, ). As the largest supplying river for the northwestern South China Sea, the Red River is generally thought as the main water source for the Central Canyon filling of the QDNB since the Late Miocene (Chen et al, ; Clift & Sun, ; D. Li, Xu, & Wang, ; Y. F. Wang, Wang, Li, & Xu, ). However, there is growing evidence that the source area of the QDNB was not solely from the Red River.…”