Geomorphology and Subsurface Ceology of the Alluvial Plain of the lower Yahagi River, Central Japan
Geomorphology and Subsurface Ceology of the Alluvial Plain of the lower Yahagi River, Central Japan
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日本中部矢萩川下游冲积平原的地貌和地下地质
DOI：
10.4116/jaqua.11.193
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发表时间：
1972
期刊：
影响因子：
--
通讯作者：
Megumi Ozawa
中科院分区：
文献类型：
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作者：
A. Moriyama;Megumi Ozawa
关于Yahagi河下游的冲积平原和冲积物的形态，没有全面的报告。作者通过航空摄影测量和对许多钻孔数据的分析对它们进行了调查。这种冲积平原的形态特征是遍布平原的许多小的微丘地（图1）。虽然该区与一般河流的天然堤后沼泽类型相对应，但目前的河道形态仍表现为辫状河的河床形态。作者认为这与流域地质有关。Yahagi流域的大部分由花岗岩组成，因此，尽管是天然堤后沼泽类型，但河流输送砾石的辫状格局特征在河口附近占主导地位（图14）。辫状河道中的微高地是形成“岛滩”的原因，而这些微高地又是形成“岛滩”的原因（微丘状高地），而在沿海地区，这种冲积充填物的沉积结构表现为层状板状沉积结构（图5、6、7），而新东海道线以北内陆地区的构造则是一种混乱无序的构造（图8、9、10）。作者的结论是，这取决于外海潮流或离岸流所搬运的推移质的扩展，以及冲积高地或封闭海的通道带中粗物质的透镜状沉积。P.的人，中泥层（MM）约在B前7，000年左右。P.和上层砂层（美国）大约在公元前B 4500年。（图15）。最大“绳文”海侵的海岸可能位于新东海道线以北一点。通过快速的冲淤作用，“弥生”晚期的海岸可能位于连接伊敷和吉良的线附近。冈崎地区下方存在较宽的埋藏阶地（图7、8、9、11），作者将其命名为冈崎埋藏阶地（图4）。这对应于上八木川的越户阶地。但它们在投影纵剖面上是不连续的（图13）。作者解释说，冈崎和丰田之间的阴谋峡谷的存在，因为冲积平原和埋藏山谷的纵向剖面显示了峡谷和Koshido-Okazaki埋藏阶地的两个梯度剖面。
No all-inclusive reports have been made on the morphology of the alluvial plain and the alluvial fills of the lower Yahagi River. The authors investigated them through aerial photographic surveys and analysis of many boring data.This alluvial plain morphology is characterized by the presence of numerous small microuplands all over the plain (Fig. 1). Although the area corresponds with the natural levee-back swamp type of the ordinary rivers, the channel pattern at present shows the braided one of bed morphology. The authors recognized it has a connection with the geology of the drainage area. A larger part of the drainage basin of the Yahagi consists of granitic rocks, so in spite of the natural levee-back swamp type, the braided pattern characteristic of the river transporting gravels is predominant near as far as the mouth of the River (Fig. 14). Numberless small micro-uplands are due to the micro-uplands in the braided channels, moreover they are supposed to have been made into “shima-batake” (micro butte-like uplands) by artificial changes of prolonged paddy field cultivation.Whereas the sedimentary structure of this alluvial fills at the coastal area represents a well stratified slaty one (Fig. 5, 6, 7), the structure at the inland area north of the New Tokaido Line has a disordered and confusive one (Fig. 8, 9, 10). The authors concluded that these depend upon the expanse of the transported bed loads by tidal or off-shore currents in the open sea and the lens-like deposition of coarse materials in the channel belts on the alluvial upland or in the closed sea.Using measured 14C age of these layers at the coastal area, the lower sands (LS) accumulated from about 10, 000 years B. P., and the middle muds (MM) about 7, 000 years B. P. and the upper sands (US) about 4, 500 years B. P. (Fig. 15). The coast of the maximum “Jomon” transgression may have lain a little north of the New Tokaido Line. By rapid and succesive alluviations, the coast at the age of late “Yayoi” may have lain near at the line which links Isshiki with Kira.Wider buried terrace exists beneeth the Okazaki district (Fig. 7, 8, 9, 11), and the authors named it the Okazaki buried terrace (Fig. 4). This corresponds with the Koshido terrace on the upper Yahagi River. But they are discontinuous on the projected longitudinal profile (Fig. 13). The authors explained it by the presence of the conspicious gorge between Okazaki and Toyota, as the longitudinal profiles on the alluvial plain and buried valley reveal two graided profiles at the gorge as well as those of the Koshido-Okazaki buried terraces.