野尻湖周辺の火山灰およびその他の堆積物中の粘土鉱物学的特徴
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In a previous paper, we have reported the assemblage of clay minerals in the Nojiri Loam Formation distributed near Kannoki. Here, we describe the clay minerals in the Nojiri-ko Formation and Nojiri Loam Formation distributed at Lake Nojiri and its outskirts. For analysis of the clay mineral assmblages, identification was made by X-ray diffraction and by electron microscopy. The results obtained may be summarized as follows. (1) The Nojiri Loam Formation near Kannoki, which consists of aeolian sediments, contains mainly allophane. This indicates that the rocks have not been weathered so much. However, in Sections I and II of the Upper Nojiri Loam Formation and in the uppermost part of Section III of the Lower Nojiri Loam Formation, clay minerals such as chlorite (or vermiculite), halloysite, kaolinite, etc. are recognized. The weathering of these loams thus appears to be fairly well progressed, so that the above-mentioned parts of the Nojiri Loam Formation may have cropped out at the ground surface for a relatively long period. (2) The Nojiri-ko Formation, which consists of lacustrine deposits, contains abundant allophane and some halloysite. This may not represent weathering, but may indicate washing out of clay minerals after their deposition. On the other hand, the presence of abundant montmorillonite in some parts of the Nojiri-ko Formation suggests the possible in flow of material from the area surrounding the lake deposits. It is difficult to decide the precise weathering course and sedimentary environments from the clay minerals contained in the lake deposits. (3) The Nojiri-ko Formation near Muko-Shinden, which has been considered to represent marsh deposits, is rich in clay minerals such as chlorite (or vermiculite), illite, halloysite, kaolinite, ete. This indicates that the weathering of the Nojiri-ko Formation was well progressed. The clay minerals in the Scoria Member of the Middle Nojiri-ko Formation consist mainly of halloysite, revealing a well progressed stage of weathering, although the weathering of the lake deposits and aeolian sediments in the same formation is of lesser degree.
- 日本地質学会の論文
- 1980-03-29
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