Transgressive sedimentation and stratigraphic evolution of a wave-dominated macrotidal coast, western Korea

The entire west coast of Korea is macrotidal. However, unlike the embayed tide-dominated coasts to the north and south, the central west coast is relatively straight and wave-dominated. It has developed a retrogradational, coarsening-upward succession as a result of barrier-island retreat during the later stages of the Holocene transgression; within embayments, the transgressive succession is overlain by a fining-upward progradational succession indicating the onset of highstand conditions. A tide-dominated environment may have existed during the early stages of the transgression as the shoreline traversed the flat-floored Yellow Sea, but the coastal zone of central western Korea became wave-dominated as sea level neared the current highstand level and encountered a steeper portion of the pre-transgression surface. The resultant small, coast-normal tidal prism produced relatively weak tidal currents, which allowed for the development of barrier islands, except at the mouths of large embayments. With continued transgression, the former barriers have retreated landward over their back-barrier tidal flats, producing thick transgressive deposits (> 8 m) that were preserved because the vector of coastal retreat had a significant vertical component. Remnants of barrier islands are present only in isolated small embayments; elsewhere back-barrier areas were over-ridden and the barrier became attached to the pre-existing cliffs. The sand then dispersed to form the modern, wave-dominated, open-coast tidal flats. Conditions in the study area lie at the transition between wave- and tide-dominated sedimentation, and slight spatial or temporal changes in the relative important of waves and tidal currents cause significant changes in the morphology and facies. This study confirms earlier work that showed that a tidal range of 4 m is not the upper limit of wave-dominated conditions. Tidal prism has a more direct control on coastal dynamics than tidal range.