Characteristics of the Submarine Topography and its Profile Type of the Coast of China

Based on the latest submarine topography data of the China 908 Project (China offshore marine environmental comprehensive investigation and assessment), we analyzed the general China offshore submarine topographical characteristics and the factors influencing its development. The submarine topography off the coast of China follows the NW‐SE trend of the land topography. The gradient of the submarine topography ranges from 0.2% to 1.6% with an average gradient of about 0.8%. The depth contours run mostly parallel to the coast, and extend out to sea in estuary areas. The submarine topography is dominated by the geological structure, which shows the typical characteristics of two uplifts and two subsidence events from north to south. The geological structure combined with the different sedimentary environments and complex hydrodynamic conditions produced topography that can be characterized by three types: sedimentary basins, compression‐uplift, and transition form. In the sedimentary basin and compression‐uplift regions, the topographical undulation is small, sediments are fine‐grained, and the currents flow in a single direction, leading to bays with sedimentary plains and underwater accumulation slopes, which are of the same tectonic origin. Transition‐type topography is characterized by strong undulations and mixed‐size sediment particles, terraces and scarps inshore and shelf plains and erosion‐deposition landforms offshore. This is a result of incomplete fault block development and repeated transgressions. In the deposition reformation regions (transition form type), the topography has strong undulations, the sediments are coarse, tidal sand ridges are well‐developed at terrigenous‐supplied estuaries and convergence zones, and the Holocene sediments are thick, transformed by tides, river runoff, and currents.