地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
88 巻 , 1 号
選択された号の論文の10件中1~10を表示しています
  • 米倉 伸之, 松田 時彦, 野上 道男, 貝塚 爽平
    1979 年 88 巻 1 号 p. 1-19
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    The Cordillera Blanca of the Peruvian Andes is a glaciated mountain range, the highest peak of which is Nevados Huascaran, 6768 meters high above sea level. The Cordillera Blanca is composed mainly of a batholith dating from 3 to 12 million years ago. The southwest slopes of the Cordillera are steep fault scarps developed in the Quaternary (WILSON et al., 1967 DALMAYRAC, 1974). These fault scarps are developed along what is here termed the Cordillera Blanca Fault. To the southwest, the Cordillera Blanca is bounded by the fault and the valley of Rio Santa, while to the northeast of the Cordillera, no notable active fault appears in the Mesozoic fold belt (Figs. 1 and 2).
    The Cordillera Blanca Fault is easily recognized even on the LANDSAT images (Photo. 1). The total length of the fault is about 180-200 km and the relative height of fault scarps is over 4000 meters in muximum near Nevados Huascaran. The topographic features of the fault change from north to south. In the northern part, the fault scarp is high and steep and the fault line is simple. In the central part, the fault line waves and a cusp is formed to the northeast of Huaraz city. In the southern part, the relative heights of fault scarps become smaller and many fault scarplets run discontinuously in échelon (Figs. 3 and 5).
    Two regions in the southern part of the Cordillera Blanca Fault were investigated in November, 1970. The amount of fault displacements at the Queroccocha Valley and the Tuco Valley were measured using correlative moraine ridges in the valley sides and surfaces of fluvial terraces in the valley floors (Figs. 5-12). Unfortunately, data on the absolute ages of these landforms was unobtainable. They were estimated by comparing the succession of moraines with the age-known moraines formed from the last glacial expansion to the present in the Chilean Andes (for example, MERCER, 1976).
    Our investigation demonstrates that the Cordillera Blanca Fault is an active normal fault and that faulting has occurred progressively in the late Quaternary. The main results obtained follow :
    1) Faulting has occurred progressively at least during the last 20, 000 years. The outermost morain ridge estimated about 20, 000 years ago (M1) has a vertical offset of 57 meters at the Tuco Valley. The second ridge estimated about 13, 000 years ago (M2) has a vertical offset of 25 meters at the Queroccocha Valley.
    2) The average rate of vertical displacement along the fault is estimated to be 2 meters at the Queroccocha Valley and 3 meters at the Tuco Valley per one thousand years.
    3) The values of vertical offsets which occurred during the different ages suggest that the amount of vertical displacements at one event of the faulting may be 2 and 3 meters at the Queroccocha and Tuco Valleys, respectively.
    4) These results imply that the Cordillera Blanca Fault has a recurrence interval of about one thousand years.
    5) If the faulting has continued at the same rate as in the late Quaternary, the amount of vertical displacement ranges from 2, 000 or 3, 000 meters for one million years. These values are of the same order as the relative heights of fault scarps at the western slope of the Cordillera Blanca. This means that the Cordillera Blanca Fault has been playing an important role in relief forming of the Cordillera Blanca and the Santa Valley.
  • 前田 四郎, 沢野 弘, 川辺 鉄哉
    1979 年 88 巻 1 号 p. 20-28
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    In the Boso Peninsula, the Cenozoic marine strata, especially of younger Cenozoic age, are well exposed successively, and full of fossils along the Yoro, Obitsu and Minato Rivers. Although calcareous nannoplanktons are abundant in these strata, the study on them has rarely been done except by TAKAYAMA (1967), NISHIDA (1976, 77) and MAEDA and SAWANO (1978).
    This study was planned in order to find out the stratigraphic distribution of the assemblages of calcareous nannoplankton from the Anno Formation along the Inokawa River, which is the uppermost tributary of the Obitsu River in the Central Boso.
    Calcareous nannoplankton floras were obtained from 32 horizons as shown in Fig. 2. A total of 16 species of calcareous nannoplankton belonging to 10 genera were identified. Among calcareous nannoplankton floras, Reticulofenestra japonica was very abundant through the lower horizon to upper one of the formation. The lower horizon was characterized by the abundance of R. pseudoumbilica, Cyclococcolithina leptopora and Cy. macintyrei, and the middle horizon by existence of R. pacifica and Coccolithus productus. On the contrary, in the upper horizon, Pseudoemiliania lacunosa and Gephyrocapsa caribbeanica increased in number, while the genus of Discoaster decreased distinctly.
    It is worthy of note that R. pseudoumbilica could not be seen in the uppermost horizon of the formation. Based on the remarkable facts of the first appearance of R. pacifica, Ps. lacunosa and G. caribbeanica, and the extinction of Sphenolithus abies and R. pseudoumbilica, the calcareous nannoplankton floras of the Anno Formation were divided into 6 assemblage zones.
    Judging from the characteristics of the assemblages, it is thought that the Anno Formation was deposited from the late stage of early pliocene to middle pliocene in geologic age.
  • 山際 延夫, 鳴橋 憲一, 辻井 安喜, 藤田 孝子, 和田 朋子
    1979 年 88 巻 1 号 p. 29-39
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    Recently, many corals were collected by the writers from the Imaura Group in the eastern part of the Shima Peninsula. This Group geotectonically belongs to the southern subbelt of the Chichibu belt. It is bounded on the north by the Middle to Upper Permian Aonomine Group and on the south by the Tsuiji Group probably correlated with the Konose Group in Kyushu. These Groups are in contact with each other by faults.
    The Imaura Group (10220 m+thick) trends ENE-WSW and dips northward of about 5060 degrees ; mainly composed of sandstone, mudstone and alternations of sandstone & mudstone, occasionally intercalating grey limestone lenses.
    The limestone lenses in the Imaura Group yield 46 coral species including 9 new species as shown in Table 2. The coral assemblage listed in Table 2 is very similar to those of the Upper Jurassic in the outer zone of Southwest Japan, Kwanto massif and Soma area. This datum does not conflict with the evidence from the Torinosu type pelecypod assemblage in this Group.
  • 奥村 清, 吉田 晴彦, 加藤 邦宜
    1979 年 88 巻 1 号 p. 40-52
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
    上で述べたことを次に要約する。
    (1) 宮田累層産軟体動物化石群は一般に親潮系冷水種を高い割合で含み, 相模湾沿岸に分布する中部洪積統の中では特異な存在である。古生物学的特徴からは宮田累層を二宮層, 長沼層と対比することは困難である。
    (2) 宮田累層の堆積環境は, 堆積期の中期にはかなり潮通しが良く, 主として砂底に生息する軟体動物の生息に適していたが, 末期にはやや内湾的で泥底に生息する軟体動物に適した環境に移行した。
    (3) 宮田累層の軟体動物化石群には上浅海帯で形成されたものと, 亜浅海帯や下浅海帯で形成されたものとがある。後者に属するものは上部浅海帯からの落ちこみによって生じたいわゆる混合群集である。
    (4) 宮田累層産の親潮系冷水種は主として上浅海帯のような浅海底の生息種である。亜浅海帯や下浅海帯に生息できるものは黒潮系暖水種である。しかし, 浅海底に生息していた黒潮型暖水種も少なくない。このことから富田累層堆積の場は主として暖流の支配下にあったが, 浅海帯はかなり長期に亘って寒流の影響を強く受ける環境であった.
  • 小林 貞一
    1979 年 88 巻 1 号 p. 53-55
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 井上 英二
    1979 年 88 巻 1 号 p. 56
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 前田 四郎
    1979 年 88 巻 1 号 p. 56a-57
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 石原 丈実
    1979 年 88 巻 1 号 p. 57
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 1979 年 88 巻 1 号 p. e1
    発行日: 1979年
    公開日: 2010/02/25
    ジャーナル フリー
  • 米倉 伸之, 松田 時彦, 野上 道男, 貝塚 爽平
    1979 年 88 巻 1 号 p. Plate1-Plate2
    発行日: 1979/02/25
    公開日: 2009/11/12
    ジャーナル フリー
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