Pedogenic significance of eolian dust in Japanese soils

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The results obtained in this study are as follows:1. The parent material and pedogenesis of Red-Yellow soils in Ryukyu Islands: (1) On the basis of their chemical properties, clay mineral composition and oxygen isotopic ratio of fine quartz, Red-Yellow soils on the Kunigami terrace in Okinawa were formed on eolian dust deposits derived from China. (2) Red soils and Yellow soils were, respectively, formed on the eolian dust deposits at the interglacial ages and the glacial ages. (3) The dithionite soluble iron ( <Fe_d> ), acid oxalate soluble iron ( <Fe_o> ) and total iron ( <Fe_t> ) of Red-Yellow soils in Ryukyu Islands were determined. By using a relationship between the <Fe_o> / <Fe_d> ratio and the ( <Fe_d> - <Fe_o> )/ <Fe_t> ratio, Red soils were clearly distinguished from Yellow soils.2. Tephra and eolian dust deposits in Tanegashima: (1) The stratigraphy of the Jyusanban profile in Tanegashima was identified. Tephra and eolian dust layers in the profile were isolated by determining the phosphate retention, pH(NaF) value, amounts of acid oxalate soluble Al and predominant clay minerals. (2) By using the marker-tephra layers (Ah and AT ashes), which their ages of eruption were already known, the rate of dust deposition in the last glacial age is estimated to be about 7-8.7 g/ <cm^2> /1,000 years in Tanegashima. 3. From <^(14)C> ages and chemical and clay mineralogical properties of eolianites in Kikai, it is estimated that the eolian dust deposition was marked at the last glacial age.