Pedogenesis of late Quaternary deposits, northern Kyonggi Bay, Korea: Implications for relative sea-level change and regional stratigraphic correlation

Abstract

Late Pleistocene and early Holocene paleosols are described from construction pits and boreholes in the northern Kyonggi Bay, west coast of Korea. Thin-section petrography, chemistry, clay mineralogy and geotechnical properties of the paleosols were examined to infer relative sea-level fluctuations during the late Quaternary. Relict laminae and gradational contacts with underlying tidal rhythmites confirm that the late Pleistocene paleosol is a pedogenically altered tidal deposit. Illuvial clay coatings, rootlets and enrichment of kaolinite and chemically stable oxides indicate that pedogenesis occurred on a well-drained, stable surface during the last glacial period. Redoximorphic features, such as drab-colored root traces and sphaerosiderite, however, suggest that waterlogged conditions developed temporarily due to a rise of the water table at the end of the last glacial period. As sea level rose, an early Holocene paleosol formed in freshwater bog deposits, burying the late Pleistocene paleosol. The early Holocene paleosol has abundant sphaerosiderites and organic material. The presence of weakly developed illuvial clay coatings, oxidized siderites and pellets, however, indicates oxidizing condition associated with water-table fall occurred during the early Holocene. Despite the similarity in the degree of chemical and clay mineralogical weathering, the late Pleistocene paleosol is distinguished from its early Holocene counterpart by thicker and more abundant illuvial clay coatings, more Fe 2O 3 and a greater degree of consolidation. Duration of pedogenesis might be a primary cause for the difference of the pedofeatures with climate playing a secondary role. The widespread presence of similar late Pleistocene paleosols highlights its significance as a key stratigraphic marker for regional correlations along the west coast of Korea.