地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
78 巻 , 1 号
選択された号の論文の6件中1~6を表示しています
  • 中村 拓
    1969 年 78 巻 1 号 p. 1-18
    発行日: 1969/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 岡田 篤正, 高橋 健一
    1969 年 78 巻 1 号 p. 19-37
    発行日: 1969/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    The Tamba Mountainland is bordered by fault scarps at its southeastern margin and gently descends nouthwestwards (Fig. 1). Along the western margin of this tilted block, the Takeda, a tributary of the Yura pouring into the Sea of Japan, flows northward and is divided by the lowest watershed in the main divide of Honshu Island from the Saji, the upper part of the Kako flowing southward into the Seto Inland Sea. This wide (about 700 meters) and low (about 100 meters high above sea level) watershed (Fig. 5) suggests that the Takeda and the Yura must have formerly been flowing southward into the Inland Sea. The assumed former river system flowing southward is named Palaeo-Yura-Kako River.
    River terraces along the Yura and the Takeda are classified into five : namely, HitO terraces, Osadano terraces (Oe terraces), Nanryo terraces, Hori terraces and Izaki terraces in the descending order. The deposits of the highest Hit terraces and high Oe terraces along the lower reach of the Yura in the vicinity of Oe Town, are composed of ill-sorted, angular, and coarse-grained gravel beds, not including chert gravels derived from the Tamba Palaeozoic zone in the upper drainage basin of the Yura. The facies of these gravel beds are remarkably different from those of lower terrace deposits and the present river deposits. On the other hand, the high Osadano terraces along the Takeda (Fig. 3-C) consist of well-sorted, round, and fine-grained materials. Hit5 terraces are only distributed in the lower reach of the Yura (Fig. 3-A -B) and disappear upstream. Osadano terraces are widely distributed forming the depositional terraces along the whole stream course and lie buried to upstream of the Takeda. At some places, these higher terrace deposits show characteristic imbrication of gravels transported by streams flowing southward. Other terraces lower than Osadano terraces are approximately parallel to the profile of the present Yura (Fig. 6-B).
    From the facts mentioned above, the writers concluded that the geomorphic development of the Drainage basin of the Yura was as follows :
    (1) The Palaeo-Yura-Kako had flowed southward, consequently to the Tamba Mountainland, through the present courses of the Takeda and the Kako into the Inland Sea.
    (2) Tributaries of the upper part of the Palaeo-Yura-Kako were captured by a river flowing northward into the Sea of Japan after the deposition of Hit5 terrace gravels. Consequently, the divide of the Palaeo-Yura-Kako migrated to the northwestern margin of the Fukuchiyama Basin.
    (3) As a result of successive subsidence toward northwest of the upper drainage basin of the Palaeo-Yura-Kako, lakes and swamps were formed and the Osadano formation was thickly deposited in the Fukuchiyama-Ayabe Basin and in the valley of the Takeda, probably in the last Interglacial age. Finally, the lakes in the Basin spilled over its northwestern margin and rivers flowing northward extended to grow up into the drainage basin. of the present Yura.
    (4) Since then, the lower terraces (Nanryi terraces, Hori terraces, and Izaki terraces) had been formed along the present course of the Yura, caused by the rejuvenations due to the shifting of divide and the lowering sea level in the Wtirm Glacial age.
  • 須田 皖次
    1969 年 78 巻 1 号 p. 38-44
    発行日: 1969/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • トムリンソン R. F.
    1969 年 78 巻 1 号 p. 45-48
    発行日: 1969/02/25
    公開日: 2010/04/23
    ジャーナル フリー
  • 若生 達夫
    1969 年 78 巻 1 号 p. 49
    発行日: 1969/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 川上 喜代四
    1969 年 78 巻 1 号 p. Plate1-Plate2
    発行日: 1969/02/25
    公開日: 2009/11/12
    ジャーナル フリー
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