Studies on theJahgarusoils and their parent materials : 8. Physical and chemical properties and clay minerals of soil and sediment profiles at Azama, Chinen-son and Futenma, Ginowan-shi, Okinawa Island (Department of Environmental Sciences and Technology)

沖縄本島南部の安座間(O-35)および中部の普天間(O-38)両地点から,泥灰岩層の上部に琉球石灰岩層と島尻マージが堆積した層序の土壌(層)断面を選定し,土壌や堆積物の理化学性および鉱物組成などの特徴を調べた。最上層の土壌の理化学性の特徴は両断面間でかなり異なったが,いずれも島尻マージの理化学性の特徴には概ね類似した。また,粘土およびシルト部分の鉱物組成の特徴は,普天間では島尻マージの特徴に類似したが,安座間ではイライトやバーミキュライトに加えてスメクタイトが優勢で異なり,島尻層群の泥(灰)岩が混入したことを推察した。安座間の粉状∿粒状の未固結琉球石灰岩層直下では,灰白色土層が認められた。他の類似する土層の特徴に比較して,その土層はpHや有機および無機炭素含量がかなり高く,CECや交換性塩基類の含量がいずれも約半分以下の特徴を示した。また,粘土やシルト部分の鉱物組成は,イライト,スメクタイトおよびバーミキュライトや石英が優勢の類似性が認められ,上部の琉球石灰岩層が泥灰岩の灰白色土層の生成に影響を及ぼす要因であることを推察した。普天間の固結琉球石灰岩層直下では,茶褐色土層とその漸移層の黄褐色土層が認められた。黄褐色土層のシルト部分では石英より方解石が優勢で,両堆積物の理化学性は泥灰岩層の特徴に概ね類似した。粘土部分の鉱物組成も,イライト,スメクタイトおよびバーミキュライが優勢で泥灰岩層の特徴に類似し,島尻マージの土色に類似する泥灰岩層風化物が生成する可能性を推察した。両断面の他の堆積物の理化学性や鉱物組成は,いずれも泥灰岩層積物の特徴にかなり類似した。泥灰岩層堆積物は,海成堆積物としての泥(灰)岩の質的差異やそれらが堆積している環境因子の差異によって,一定の傾向を有しながら種々の性質を有する可能性が高いと考えられる。Physical, chemical and mineralogical properties both soil and sediment were investigated in two sediment profiles. Those two profiles consisted of reddish brown soil, Ryukyu limestone and marl in descending oder. The marl and its weathering materials distribute in Okinawa Island occupying a predominant part of agricultural land. Reddish brown soil showed a good deal of similarity in the physical and chemical properties ofShimajiri mahjiwhich is locally called on dark-red soil derived from limestone. Futenma (O-38) soil showed a great deal of similarity in the mineral constituents ofShimajiri mahji. Azama (O-35) soil included illite, vermiculite and smectite as the major clay minerals which suggested contamination with marl. At Azama profile the unique light gray colored sediment underlay soft Ryukyu limestone of powder to granular materials. The pH and the value for organic and inorganic carbon were considerably higher and the CEC and exchangeable bases were less than half in the sediment than those in the other similar sediment. Illite, smectite, vermiculite and quartz were the major crystalline minerals of the sediment. It was considered that the dark gray colored marl had a tinge of white receiving an effect from Ryukyu limestone. At Futenma profile both the unique dark brown and yellowish brown colored sediments underlay had Ryukyu limestone. The second was observed as a transitional horizon of first. Quantitatively calcite was identified larger than quartz in the silt fraction of the second. In the clay fraction both sediments included illite, smectite and vermiculite as the main crystalline minerals which showed a great deal of similarity in those of the marl. Physical and chemical properties both sediments showed almost same tendency with the marl. It was assumed that the weathering materials dirived from the marl may turn dark reddish color which resemble in soil color ofShimajiri mahji. It is satisfactory to consider that changes of the sediments and sedimentation conditions had caused the difference in the marl which keep the certain mineralogical properties constant