Distribution, formation and evolution of sand ridges on the East China Sea shelf

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Based on the integrated results of multiple data types including MBES (Multi-Beam Echo Sounding) and historical topography maps, the LSR (Linear Sand Ridges) on the ECS (East China Sea) shelf are identified, divided into subareas, and classified. The distribution of sand ridge crests is also established. The strikes of the LSR on the ECS shelf fall in a normal distribution with the center point being 155° azimuth with additional peak points at 125°, 130°, 140°, and 180° azimuth. The distribution of the ECS shelf sand ridges is congested in the central area, sparse in the south and north ends, divergent and bifurcated in the eastern area, and densely convergent in the western area. The LSR are divided into seven subzones according to the strikes and distribution of the sand ridges; estuary mouth ridges and open shelf sand ridges are identified and marked out. The high amplitude change of sea level resulting from the glacial-interglacial cycle is the main cause of the vast development of sand ridges on the ECS shelf. Abundant sediments on the shelf carried by the PYR (Paleo-Yangtze River) are the material source for the LSR formation, and the negative seafloor topography influences the strikes of LSR. Based on the effects of LSR distribution, change of sea level, and the simulation of ancient tidal currents, the evolution of the LSR on the ECS shelf is divided into four main stages: Stage I before 14.5 ka BP, Stage II between 12 and 14 ka BP, Stage III from 1.5 to 9.5 ka BP, and Stage IV after 9 ka BP.