TROPOSPHERIC ORIGIN OF QUARTZ IN ANDO SOILS AND RED-YELLOW SOILS ON BASALTS, JAPAN
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概要
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Fine quartz silt (1-10μm diameter, characteristic size of aerosolic dust) isolated from two Ando soils from volcanic ashes (Fukuoka and Iwate), two Red-Yellow soils on basalts (Saga and Nagasaki) and one loess deposit (Saga) exhibited a very narrow range of oxygen isotopic ratios (expressed as parts per thousand relative to Standard Mean Ocean Water, SMOW, δ^<18>O) varying from 15.8 to 16.2 ‰. These values were almost identical with those reported for a mud-rain deposit (δ^<18>O=16.2‰) and two north Pacific pelagic sediments near the Japanese Islands (δ^<18>O=16.2 and 16.6‰), all derived from continental aerosolic dusts, carried by Westerly Winds. The quartz oxygen isotopic ratios of the selected Ando soils precluded both an indigenous volcanic ash (magmatic) origin and secondary crystallization under the ambient temperature. The oxygen isotopic results together with the covariant relationship between the fine-grained-quartz and 2:1 type clay mineral contents suggest that the great bulk of the 2:1 clay mineral-bearing phase of Ando soils of Japan is also of tropospheric origin, resulting from long distance eolian transport from Asian semi-arid and arid regions.
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