沖縄本島の低〜中位段丘面を形成する琉球石灰岩層中の埋没土の特徴

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The physical, chemical and mineralogical properties of buried reddish brown colored soils were investigated. Those buried soils were found in three Ryukyu-limestone profiles which were formed in the different ages of the lowest to highest terrace formation of Okinawa island. The buried soils appeared to be approximately similar in the physical and chemical properties to "Shimajiri mahji", the local name for Ryukyu-limestone derived dark-red soil in the Okinawa islands. It occupies a predominant part of agricultural land. But there were few differences in the properties of soil pH and phosphate absorption coefficient. It was suggested that the Makiminato-limestone which form the youngest terrace will effect considerably on the chemical properties of the buried soils in the limestone. The available phosphorus content of the buried soils tended to increase with age in the following order ; Naha-limestone (oldest), Yomitan-limestone (middle) and Makiminato-limestone (Youngest). The content of heavy minarals in the fine sand fraction of the buried soils was less than 1% and the heavy mineral composition varied somewhat among the buried soils in each different limestone. The primary minerals in the silt fraction and the light minerals in the fine sand fraction of the buried soils were mainly guartz, in addition, a moderate amount of calcite and small amount of feldspars were found in the buried soils in Makiminato-limestone. The main crystalline minerals in the clay fraction were kaolinite and illite accompanied by a moderate to small amount of vermiculite and vermiculite-chlorite intergrade mineral. A moderate amount of smectite was found in the clay fraction of the buried soils in Makiminato-limestone. The main crystalline clay minerals of the buried soils in Makiminato-limestone showed a great deal of similarity in composition to those in the marl. From these findings and the present state of knowledge of the "Uruma crust movement", it was assumed that the weathering materials, as a case of the parent material derived from Ryukyu-limestone, might originate in the deposits contaminated with marl or mudstone.
日本ペドロジー学会の論文
1991-12-31

沖縄本島の低〜中位段丘面を形成する琉球石灰岩層中の埋没土の特徴

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