有明海北岸低地第四紀堆積物の粘土鉱物組成と堆積環境及び陸上風化環境との関係

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Core samples of the Quaternary sediments to the depth of 120 m were collected at a site in the north coast of Ariake Bay, Kyushu. Particle-size distribution and clay mineralogical composition in the clay fraction were determined for total 106 samples taken at about 1 m interval and correlated with depositional environment and weathering in the terrestrial condition. Depositional environment was assessed by the determination of total sulfur; the ratio of the acid-oxalate-soluble to the DCB-soluble Fe contents was used for the estimation of weathering intensity. Repetition of marine and fluvial deposition was recognized. Marine sediments were dominated with clay and silt. Fluvial sediments had the high contents of fine and coarse sands, and domination with fine sand was ascribed to the deposition in the floodplain while domination with coarse sand to the deposition in the alluvial fan. Concerning the clay mineralogical composition, fluvial sediments were dominated with mica, vermiculite, kaolin minerals, and 2:1 minerals-chlorite intergrades, derived from granitic rocks in the surrounding mountains. Composition of these minerals varied with the particle-size distribution of the sediments. Marine sediments were dominated with smectite in addition to the minerals originating from granitic rocks. Smectite content generally increased with transgression and decreased with regression, and the formation of smectite was suggested to be due to the chemical alteration of pyroclastic materials. In addition, transformation of mica to smectite was observed in the intensive weathering condition.
日本粘土学会の論文
1999-12-28

有明海北岸低地第四紀堆積物の粘土鉱物組成と堆積環境及び陸上風化環境との関係

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