南西諸島における赤黄色土壌群母材の広域風成塵起源--土壌,基岩および海底堆積物中の石英,雲母,方解石の酸素および炭素同位体比

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The insoluble residues of Quaternary and Paleozoic limestones have been regarded as the most important parent material of the Dark Red soils developed on these limestones in the Nansei Syoto islands. Oxygen and carbon isotopic studies of the Red and Yellow Soil Group, Quaternary and Paleozoic limestones, Tertiary sandstone, and Paleozoic phyllite in the Nansei Syoto and piston cores in the Okinawa Trough, the Nansei Syoto Trench, and the Amami Plateau, which were located between 24°N and 31°N, were carried out. The oxygen isotopic ratios (δ18O) of quartz (1-10μm) isolated from 43 soils were +17.2±0.6‰. These ratios were similar to those of quartz from the 10 piston cores (+18.1±1.2‰) but slightly higher than those of quartz from loess and loess-derived soils in China, Japan, and Korea, which were located between 31°N and 45°N. The soils belonging to the Red and Yellow Soil Group in the Nansei Syoto were strongly influenced by the East China Sea sediments predominantly transported from the Yangtze River in China and dried during the marine regression in the glacial ages, in which quartz yielded approximately 1 to 2‰ higher δ18O ratios than those in loess and loess-derived soils and the Yellow Sea sediments dominantly transported from the Yellow River. Oxygen and carbon isotopic ratios of quartz, muscovite and calcite isolated from Quaternary limestones and sparites indicated that quartz and muscovite were not authigenic minerals, but eolian deposits transported on coral reefs. Based on these data, the authors conclude that most of the soils belonging to the Red and Yellow Soil Group and developed on limestones and other base rocks in the Nansei Syoto were not residual soils from these rocks, but eolian deposits transported long distances from the arid and semi-arid regions of interior China and East China Sea sediments dried during the marine regression in the glacial ages.
日本第四紀学会の論文

南西諸島における赤黄色土壌群母材の広域風成塵起源--土壌,基岩および海底堆積物中の石英,雲母,方解石の酸素および炭素同位体比

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