The sand ridge field of the South Yellow Sea: Origin by river–sea interaction

The origin of a large field of sand ridges offshore from the north Jiangsu coast in the South Yellow Sea has been investigated on the basis of bathymetry, seabed samples, high-resolution seismic profiles and 31 to 71 m deep boreholes. Sediment composition including heavy minerals and clay minerals sampled from surface sediments shows that most of the sand was derived from the Changjiang (Yangtze) River, but in the northern part of the field particularly the clay came from the Huanghe (Yellow) River. Seismic profiles show late Pleistocene distributary channels of the ancient Changjiang River underlying much of the southern part of the sand ridge field. The Holocene transgression cut a widespread ravinement surface reworking abundant late Pleistocene sandy sediment. The available sand was reworked by tidal currents into large ridges. The location of the ridges is strongly influenced by relict channels in the southern part of the field and by tidal currents in the northern, and especially the northeastern part of the field, resulting in a radiating ridge pattern. These ridges provide an example of the evolution of a large scale geomorphic feature resulting from river–sea interaction, in which climatic and sea level changes played an important role.