Abstract

The eastern Yellow Sea is characterized by a number of tidal sand ridges which occur as a series of linear sediment bodies in the shelf (shelf sand ridges) and as a group of individual sand bodies in the nearshore (nearshore sand ridges). The shelf sand ridges are present in water depths of 50–90 m and show large, elongate shapes with a length up to 200 km. In contrast, the nearshore sand ridges are much smaller in size (up to 34 km length) and occur in water depths shallower than about 30 m. Detailed interpretation of seismic and lithologic data, using radiocarbon dating to constrain the ages of the ridges, has shown that the regional sea-level changes played a major role in the existence and development of different morphologic features of these sand ridges. The shelf sand ridges developed mainly during the postglacial transgression (ca. 14,000–9,500 yr B.P.), possibly during episodes of stillstand or very slow rise of sea level. The shape of the shelf sand ridges more or less results from an erosional process dominantly acting during the postglacial transgression. The substratum of the shelf sand ridges consists of the regressive or lowstand deltaic mud deposits, probably formed prior to the last glacial maximum (> ca. 17,000 yr B.P.). In contrast, the nearshore sand ridges have undergone tidal action during the recent highstand of sea level (ca. < 7,000 yr B.P.) and show a typical modern geomorphology of erosional sand ridges. The substratum of the nearshore sand ridges consists of remnants of the last interglacial tidal deposits. Large dunes indicate a strong hydrodynamic influence on the entire ridge surface at present.