STRATIGRAPHY AND SUBAERIAL EXPOSURE OF LATE QUATERNARY TIDAL DEPOSITSIN HAENAM BAY, KOREA (SOUTH-EASTERN YELLOW SEA)

Late Quaternary stratigraphy of the coastal deposits in Haenam Bay, so uth-western coast of Korea (south-eastern Yellow Sea) consists of two depositional units: a Holocene intertidal deposit (Unit I), and an und erlying Late Pleistocene tidal deposit (Unit II), both of which are di stinguished by distinct unconformity. The yellowish colour and more co nsolidated and oxidized nature are characteristics of the sediments in the upper part of Unit II. In spite of the lack of primary sedimentar y structures, a conspicuous cryogenic structure was found in the upper parr of Unit II, reflecting cold and dry conditions. The magnetic sus ceptibility enhancement in the upper part of Unit II added the possibi lity of pedogenesis during subaerial exposure. The upper parr of Unit II is characterized by the deficiency of smectite and chlorite, in con trast 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 alteratio n 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 appear s to have undergone subaerial exposure and weathering during low sea-l evel stands. The supporting evidence of the sediment properties, inclu ding 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 weathe ring of Late Pleistocene sediments in the tidal-dominated Haenam Bay s edimentary basin. (C) 1998 Academic Press.