Stratigraphy and subaerial exposure of late Quaternary tidal deposits in Haenam Bay, Korea (south-eastern Yellow Sea)

Late Quaternary stratigraphy of the coastal deposits in Haenam Bay, south-western coast of Korea (south-eastern Yellow Sea) consists of two depositional units: a Holocene intertidal deposit (Unit I), and an underlying Late Pleistocene tidal deposit (Unit II), both of which are distinguished by distinct unconformity. The yellowish colour and more consolidated and oxidized nature are characteristics of the sediments in the upper part of Unit II. In spite of the lack of primary sedimentary structures, a conspicuous cryogenic structure was found in the upper parr of Unit II, reflecting cold and dry conditions. The magnetic susceptibility enhancement in the upper part of Unit II added the possibility of pedogenesis during subaerial exposure. The upper parr of Unit II is characterized by the deficiency of smectite and chlorite, in contrast to the clay mineral suites of Unit I and lower part of Unit II, which may be attributed to post-depositional and diagenetic alteration. The degree of weathering measured by the chemical index of alteration shows that the removal of labile minerals by leaching also occurred in the upper part of Unit II. Thus, the upper part of this unit appears to have undergone subaerial exposure and weathering during low sea-level stands. The supporting evidence of the sediment properties, including sediment colour and structure, water contents and shear strength, geochemical and clay mineralogical data, and magnetic susceptibility, provides the potential signature of the subaerial exposure and weathering of Late Pleistocene sediments in the tidal-dominated Haenam Bay sedimentary basin. (C) 1998 Academic Press.