気候の乾燥化の証拠としての東アジアの開析 pediment

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The term “pediment” used in this paper is limited to the piedmont gentle slope that truncates hard bedrocks and is formed by the process other than a periglacial action. Longitudinal profiles of pediments in Japan, Korea and the Liaotung Peninsula are concave in shape and more inclined closer to the knickpoint. the inclination of pediment decreases downslope gradually. In Japan the upper part of pediments is 13°-12°in gradient and the lower part is 8°, and the longitudinal length is about 1000-1500 meters in almost all pediments. In Korea and the Liaotung Peninsula the inclination of pediments is 10°-6° in the upper part and about 3°-1° in lower and the length is about 4000-5000 meters in most pediments, where the pediments continue to the plains which are supposed to be pediplains. All the pediments already stopped to grow and they have been dissected by stream-lets. The development of these pediments belongs to the Riss-Würm Interglacial and they stopped to grow a period before the Würm Glacial. It is concluded that the pediments had been formed under the arid climate with the following facts : 1) Most part of granitic bedrocks of the pediments are weathered more than 30-40 meters in thickness, but partially not weathered and solid. Quarries are located on these solid bedrocks. But differences between weathered and solid bedrocks cannot be seen in the shapes of pediments. So pediment surfaces are smooth from weathered to solid bedrocks. There is no soil (or A and B horizon of pedology) on the bedrocks covered with The deposits, and upper parts of the hedrcoks are like Zone 1 of weathering zones being divided by B. RUXTON and L. BERRY (1957). These facts indicate that chemical weathering of the granitic bedrocks started after pedimentation truncating solid bedrocks had stopped. According to N. M. STRAKHOV (1967), chemical weathering are not active in the regions of desert, semi-desert, steppe and tundra. 2) The facies of the deposits on these pediments are similar to those on pediments which are developing in arid and semi-arid regions nowadays. 3) Under the humid climate in East Asia at present, landslide and mudflow are the most active erosional process on the escarpments behind these pediments. These landslides and mudflows often occur on weathered shallow valley bottoms, so the escarpments behind these pediments are eroded linearly.
社団法人東京地学協会の論文

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赤木祥彦
福岡教育大学

気候の乾燥化の証拠としての東アジアの開析 pediment

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