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No.27 (1980/11) >

Title :ジャーガルとその母材に関する研究 : (第 6 報)沖縄本島, 具志川市具志川および名護市為又原土壌(層)断面の理化学性と粘土鉱物(農芸化学科)
Title alternative :Studies on theJaagarusoils and their parent materials : VI. Physical and chemical properties and clay minerals of soil profiles at Gushikawa, Gushikawashi and Bimatabaru, Nago-shi, Okinawa Island (Department of Agricultural Chemistry)
Authors :渡嘉敷, 義浩
仲村, 健
Authors alternative :Tokashiki, Yoshihiro
Nakamura, Takeshi
Issue Date :29-Nov-1980
Abstract :泥(灰)岩層の上部に国頭礫層および国頭マージが堆積する, 沖縄本島中部の具志川市具志川(O-30)および本島北部の名護市為又原(O-31)土壌(層)断面について, 理化学性や粘土鉱物および1次鉱物組成などの特徴を調べた。そして, 土層間に堆積する特異的な土層の生成および諸性質の発現を考察し, さらに粘土部分中の鉱物の起源を推察した。両土壌(層)断面の珪岩礫を含有する国頭礫層の上層部は, 赤黄色で強酸性, 粘土含量の少ない軽埴土, 壌土および砂壌土質を示し, 置換性塩基量, CEC, 塩基飽和度およびリン酸吸収係数のいずれもかなり低い特徴を示した。また主要粘土鉱物はカオリン鉱物, イライトやバーミキユライト-クロライト中間種が含有され, 他にバーミキユライトーイライトあるいはクロライトーバーミキユライトの不規則混層鉱物がそれぞれ随伴し, 1次鉱物のほとんどが石英からなり, 他に長石あるいはクリストバライトが付随した。他方, 両断面の泥灰岩層は少量の炭酸カルシウムを含有し, 灰色で弱アルカリ性を示し希塩酸溶液で発泡した。この土層は粘土含量の比較的少ない埴壌土やシルト質壌土質を示し, 置換性塩基は特にCa量が著しく多く, 次にMg量が続き, CECやリン酸吸収係数もかなり大きな値を示した。また粘土鉱物組成はイライト, モンモリロナイトが主体を占め, 他にバーミキユライト, バーミキユライト-クロライト中間種, クロライトおよびカオリン鉱物が随伴した。シルト部分の1次鉱物は主に石英で, 他に少量の長石およびクリストバライトが含まれた。具志川(O-30)では国頭礫層と泥灰岩層との層間には, 薄い赤色土層が上層から運搬集積され, 強酸性の重埴土質で置換性塩基のCa量よりMg量に富む, CECおよびリン酸吸収係数のいずれもかなり大きな性質の特異な土層が生成された。この土層には2 : 1型や2 : 2型鉱物からなる中間種や不規則混層鉱物は含まれず, イライトやバーミキユライトが主要粘土鉱物で, これらにカオリン鉱物が附随し, シルト部分には石英だけが含有された。また, 同断面の薄い赤色土層直下の泥岩層は, 酸性硫酸塩土壌への可能性を有する強酸性の軽埴土質, および置換性塩基のMg量がCa量より多い特徴を除けば, 泥灰岩層の特徴によく類似した。これらのことから, 泥岩層と泥灰岩層との差異は, 土層中の炭酸カルシウム含有量の多少にあることを推察し, さらに堆積物の質とその周辺の堆積環境条件の影響によることを推察した。一方, 為又原(O-31)では, 国頭礫層と泥灰岩層との層間に珪岩礫を含有する, かなり厚い赤黄色の酸性∿弱アルカリ性を示す埴壌土および壌土質の土層が生成された。粘土鉱物はイライトやモンモリロナイトが主体で, 他にバーミキユライト, バーミキユライト-クロライト中間種, カオリン鉱物が随伴し, 1次鉱物は石英が主でその他に長石やクリストバライトが含有された。この土層の諸性質は, 国頭礫層と泥灰岩層との中間的な性質を示し, 堆積時期における両堆積物の混合撹拌を推測させ, 主要粘土鉱物のモンモリロナイトはもともと生成されていた泥灰岩層のものであることを推察した。
Two soil profiles were selected in the middle and the northern parts of Okinawa Island in order to characterize physical, chemical and mineralogical properties of the soil in relation to the underlying deposit materials. And special attentions were payed to peculiar layers interlain for genesis and mineralogy. These two profiles consisted of acidic red and yellow soils which were locally calledKunigami maaji, Kunigami gravel and marl (or mudstone) in descending order. One soil profile (no. O-30) was located at Gushikawa, Gushikawa-shi of the middle part of Okinawa Island and the other profile (no. O-31) was at Bimatabaru, Nago-shi of the northern part. In the both profiles the layers ofKunigami maajisoil and Kunigami gravels which contained quartzite were red to yellowish, strongly acidic, and of light clay to sandy loam. The upper layers were considerably low in exchangeable bases, CEC, base saturation and phosphorus absorption coefficient. The major crystalline materials in the clay fraction were kaolin minerals, illite and vermiculite-chlorite intergrade, and the minor ones were vermiculite, and illite or chlorite and vermiculite irregular mixed-layer mineral. In the silt fraction the primary mineral quartz was the major constituent, and also found were feldspars and/or cristobalite in a minor quantity. On the other hand, the lower layers consisting of marl deposite at the both profiles showed grayish color, slightly deposit at the both profiles showed grayish color, slightly alkaline reaction, and clay loam to silty loam texture. They contained a small quantity of free calcium carbonate and effervesced with dilute hydrochloric acid solution. The CEC and phosphorus absorption coefficient were comparatively high and exchangeable calcium was much higher than magnesium. The major crystalline materials in the clay fraction were illite and montmorillonite accompanied by a minor amount of vermiculite, vermiculite-chlorite intergrade, chlorite and kaolin minerals. The primary mineral in the silt fraction was mainly consisted of quartz accompanied by a small amount of feldspars and cristobalite. At Gushikawa profile (no. O-30) a peculiar red colored thin layer was found between Kunigami gravel and marl deposit. It was assumed that the red layer was formed by a translocation-accumulation process of the materials from overlying Kunigami gravel to the present position. The red layer was strongly acidic and of heavy clay. Exchangeable magnesium was higher than calcium, and the CEC and phosphorus absorption coefficient were much higher in this layer than those in the overlying layer of Kunigami gravel. Neither the intergrade nore the mixed-layer minerals were identified in the clay fraction, and quartz alone was identified in the silt fraction of the red layer. The mudstone deposit overlain by the red layer was quite similar to the color of previously mentioned marl deposit. But it carried some properties of acid sulfate soil, namely it was strongly acid and contained more exchangeable magnesium than calcium and showed texture of light clay. Accordingly a remarkable difference was recongnized between the mustone and marl deposits by the contents of calcium carbonate. It was assumed that changes of substances and sedimentation condition had caused the difference in the deposits of mudstone and marl. At the Bimatabaru profile (no. O-31) thick layers containing quartzite gravels were found between Kunigami gravel and marl deposit. These layers were red and yellow in color, clay loam to loam in texture and acid to slightly alkaline in reaction. The major crystalline minerals in the clay fraction from these layers were illite and montmorillonite accompanied by a small amount of vermiculite, vermiculite-chlorite intergrade and kaolin minerals. In the silt fraction identified were quartz in a large quantity and feldspars and cristobalite in a small quantity. Any of physical, chemical and mineralogical properties of the layers were inter
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/4084
Citation :琉球大学農学部学術報告 = The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus no.27 p.27 -41
Appears in Collections:No.27 (1980/11)

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