• Wenhuan Zhan

      Articles written in Journal of Earth System Science

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

      Hongjun Chen Wenhuan Zhan Shiguo Wu

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      We document upper slope sedimentary process and strata on the passive margin of the north-western 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.

    • Occurrence of submarine canyons, sediment waves and mass movements along the northern continental slope of the South China Sea

      Hongjun Chen Wenhuan Zhan Liqing Li Ming-ming Wen

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      In this study, we reveal a series of newly discovered submarine canyons, sediment waves, and mass movements on a flat and smooth seafloor using high-resolution, multi-beam bathymetry and shallow seismic surveys along the northern slope of the South China Sea. We also describe their geomorphology and seismic stratigraphy characteristics in detail. These canyons display U-shaped cross sections and are roughly elongated in the NNW–SSE direction; they are typically 8–25 km long, 1.2–7 km wide, and form incisions up to 175 m into Pliocene–Quaternary slope deposits at water depths of 400–1000 m. Slide complexes and the sediment wave field are oriented in the NE–SW direction and cover areas of approximately 1790 and 926 km2, respectively. Debris/turbidity flows are present within these canyons and along their lower slopes. Detailed analysis of seismic facies indicates the presence of six seismic facies, in which Cenozoic strata located above the acoustic basement in the study area can be roughly subdivided into three sequences (1–3), which are separated by regional unconformities (Tg, T4, and T3). By combining these data with the regional geological setting and the results of previous studies, we are able to determine the genetic mechanisms used to create these canyons, sediment wave field, and mass movements. For example, frontally confined slide complexes could have been influenced by high sedimentation rates and high pore pressures. A series of very large subaqueous sediment waves, which record wavelengths of 1.4–2 km and wave heights of 30–50 m, were likely produced by interactions between internal solitary waves and along-slope bottom (contour) currents. Canyons were likely initially created by landslides and then widened laterally by the processes of downcutting, headward erosion, and active bottom currents and debris/turbidity flows on canyon floors. We therefore propose a three-dimensional model to describe the development of these mass movements, the sediment wave field, and canyons. The four stages of this model include a stable stage, followed by the failure of the slope, and subsequent formations of the sediment wave field and canyons.

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