Discovery of Eemian marine deposits along the Baeksu tidal shore, southwest coast of Korea

This is the first report of an OSL (optically stimulated luminescence) -dated Eemian marine deposit along the southwest coast of Korea. It was discovered on the Baeksu intertidal shoreface/tidal flat system. Based on the analysis of (up to 46-m-long) drilled cores, the Baeksu tidal deposits can be divided into four sedimentary units. In ascending order these are: 1) basal fluvial gravels, 2) Eemian tidal mud, 3) gravel lag/paleosol, and 4) Holocene tidal deposits. The Eemian tidal sequences were encountered at a core interval of −20 to −38 m below mean sea level, the OSL ages ranging from 138 to 110 ka. Pollen analyses reveal a higher AP (arboreal pollen) to NAP (nonarboreal pollen) ratio, suggesting warm climate conditions similar to that of the Holocene. In addition, marine dinoflagellates and salt marsh pollen were found, these palynofloral records thus also attesting to marine influence in the deposits. In expectation that the Eemian tidal mud succession occurs on a wider geographic scale, the deposit is allocated the stratigraphic name Baeksu Formation (Eemian), the stratotype locality being situated at −20 m below the surface at the Baeksu borehole site. The presence of Eemian tidal muds along the west coast of Korea, which correlate with marine strata in the western Yellow Sea and Bohai Sea, explicitly reveals the occurrence of marine incursions into the eastern margin of the paleo(?)-Yellow Sea land during the last interglacial.