洪積層における粒度分布とその応用地質学的意義 : 大津市村付近 (平尾-国分) の例
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From the geological survey and results obtained by the grain size analyses of the sediments of the Pleistocene system distributed between Hirao and Ishiyama, the writer has drawn the following conclusions on a part of the uppermost Kobiwako group.<BR>1) The Pleistocene system in this area is divided into two formations, the Kokubu (upper) formation and the Yakino (lower) formation.<BR>2) On the triangle diagram (pebble + sand, clay and silt), the sedimentary materials of the Pleistocene system of this area are classified into six groups in the Kokubu formation and five groups in the Yakino formation. The distribution mode of grain size is given as the bimodal distribution which consists of the traction and suspension load.<BR>3) In relation to the coefficient of sorting (<I>So</I>) and the medium grain size (<I>Md</I>), the sedimentary material of the Pleistocene system of this area is classified into six types (II, III, V, VI, VIII and IX) in the Kokubu formation and five types (II, III, VI, VIII and IX) in the Yakino formation. The writer proposes to call their grain size rank the “<I>So</I>-<I>Md</I> Rank”.<BR>4) By plotting the medium grain size (<I>Md</I>) on Hjulstroms diagram, it was clarified that Md is proportional to the settling velocity (<I>Sv</I>) and is in inverse proportion to the critical velocity (<I>Cv</I>), and also the coefficient curve of sorting is recognized as the interrelation curve between the critical and settling velocity curves.<BR>5) The transition of the grain size type, depositional movement and index number of sedimentary facies of the Kokubu formation is conspicuous in comparison with the Yakino formation. It may be deduced, therefore, that the former is the disturbed zone nearer to the lake beach than the latter in the sedimentary environment.<BR>6) The difference of the background between the two formations may be suggested by the difference in their sedimentary materials.<BR>7) From the relation of “N value” and index number of plasticity, the upholding strength of each grain size type is divided into <I>A</I>, <I>B</I> and <I>C</I> in grade. The relation between each grade is shown as <I>A</I>><I>B</I>≥<I>C</I>.<BR>8) The rate of increase of the upholding strength of each grain size type is in inverse proportion, thus |<I>K</I>-<I>r</I>| = <I>e</I>.<BR><I>K</I> : rate of contained water, <BR><I>r</I> : index number of plasticity.<BR>9) The strata conspicuous in the transition of the sedimentary environment may be conspicuous in the transition of the grain size type and upholding strength.
- 社団法人 東京地学協会の論文
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