Chapter Sixteen Late Quaternary stratigraphy of the muddy tidal deposits, west coast of Korea

Abstract

Abstract The coastal deposits developed in the macrotidal basin between Youngjong and Yongyou Islands off the western coast of Korea are interpreted to be formed in response to sea-level fluctuationsduring the late Pleistocene and Holocene. Based on detailed analyses of lithofacies and geotechnical properties, these mixed sandy and muddy deposits can be grouped into five lithostratigraphic units. In acending order these are: Unit V (basal gravelly sandy deposit), Unit IV (organic muddy deposit), Unit III (lower part: tidal sandy and muddy deposit; upper part: weathered silty deposit), Unit II (siderite-containing stiff muddy deposit) and Unit I (tidal sandy and muddy deposit). During the early stage of lithostratigraphic development history, both Unit V and IV are interpreted as being deposited in the fluvial topographic low area in the basin. As the late Pleistocene interglacial sea-level transgressed the basin, Unit III was presumably deposited under a macrotidal regime. Following the interglacial highstand of sea-level, the entire basin of the Yellow Sea was exposed subaerially during the Last Glacial Maximum (LGM) in Stage 2, in which Unit III would also have been exposed to subaerial weathering. Naturally, the upper part of Unit III is interpreted as the exposed and weathered part, whereas the lower part would not have been exposed. After the LGM, a swamp environment occurred in a coastal topographic low area (Unit II). For the final stage of the tidal basin history, onset of the Holocene transgression and the accompanying high sea-level allowed development of Unit I, the modern muddy tidal sedimentation facies.