Transgressive sand ridges on the mid-shelf of the southern sea of Korea (Korea Strait): formation and development in high-energy environments

The mid-shelf of the southern sea of Korea (Korea Strait) is covered by a series of shore-parallel sand ridges up to 63 km long, 3–9 km wide, and 22 m thick. The ridges are a moribund type but show well-organized, dipping strata, indicating appreciable progradation. The submerged paleo-channel system (the paleo-Seomjin River) associated with the sand ridge field suggests that the ridges primarily originated from river-mouth sandy shoals, which subsequently developed into shore-parallel, linear sand bodies in high-energy environments. The combined effect of coastal (tidal and longshore) and offshore ocean currents was possibly responsible for shore-parallel sediment transport and growth of the ridges. 14C dates, core lithology, and sea-level data suggest that the sand ridges mainly formed and developed during the middle period of the postglacial transgression. They are postulated to have developed sequentially from offshore to onshore in response to sea-level rise during that time. Very slow sea-level rise and high sediment supply through the paleo-channel system probably provided favorable conditions for forming the sand ridges. The ridges became inactive during the late transgression period as a result of a substantial reduction of wave and current strength and remained on the mid-shelf.