Pedogenic significance of eolian dust in Japanese soils

本研究得到的结果如下：1。琉球群岛红黄土的母质及成土机理：(1)根据其化学性质、黏土矿物组成及细石英氧同位素比值分析，冲绳国神阶地红黄土是由源自中国的风沙沉积形成的。(2)在间冰期和冰期风沙沉积上分别形成红壤和黄壤。(3)测定了琉球群岛红黄壤中二硫代可溶性铁（<Fe_d>）、酸草酸可溶性铁（<Fe_o>）和总铁（<Fe_t>）。利用<Fe_o> / <Fe_d>比值与(<Fe_d> - <Fe_o>)/ <Fe_t>比值的关系，可以明显区分红壤与黄壤。(1)确定了种子岛菊三坂剖面的地层特征。通过测定磷潴留、pH（NaF）值、酸草酸溶铝量和主要粘土矿物的含量，对剖面中的尘螨和风积尘层进行了分离。(2)利用已知喷发年龄的标志火山灰层（Ah和AT灰烬），估计种子岛末冰期的尘埃沉积速率约为7 ~ 8.7 g/ <cm^2> / 1000年。根据Kikai地区风成岩<^(14)C>年龄及化学和粘土矿物学特征，推测其风成尘沉积标志于末次冰期。

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.