地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
92 巻 , 3 号
選択された号の論文の6件中1~6を表示しています
  • 坂上 澄夫, 柳田 寿一, 川辺 鉄哉, 加瀬 友喜, César RANGEL Z., Manuel ALDANA A., ...
    1983 年 92 巻 3 号 p. 141-151
    発行日: 1983/06/25
    公開日: 2009/11/12
    ジャーナル フリー
    In succession to the field work in 1980, we engaged in the biostratigraphic field survey in the Andean region. The journeys in Peru and Bolivia are shown in Fig. 1.
    In Peru, we had the field surveys to the Tarma and Cajamarca areas. In the Tarma area, two routes along slopes at Umancacha and Tucuhuajanan were selected for measuring the “Upper Triassic” Chambara Formation (lower part of the Pucara Group). Rock samples for conodont analysis were collected at intervals of about 10 m. The Pennsylvanian Tarma Group developed in the vicinity of Tarma City, which consists mainly of limestone, was also measured and many fusulines (Fusulinella etc.), corals, bryozoans, brachiopods and so on were collected. In the Cajamarca area, a large Cretaceous fauna comprising molluscs and echinoids were collected in the valley of Hd. Otuzco, northeastern part of Cajamarca.
    In Bolivia, the Copacabana Group (Lower Permian) developed on a small hill, Cerro Jacha Khatawi near Yaurichambi was studied in detail. We made the geological map of the hill at an original scale of 1 : 5, 000 (Fig. 2) and also made the columnar sections along three routes. Abundant fossils such as fusulines, bryozoans, brachiopods and molluscs were collected there. The fossils of the Copacabana Group in Yampupata and Chirapaca in the Copacabana area (Fig. 3) were also collected. Paleontological studies of them will be made by Japanese partakers.
    Some problems are discussed for our future field work; 1) method of field work, 2) co-operation with the Geological Surveys : INGEMMET in Peru and GEOBOL in Bolivia, and 3) the political situations.
  • 柳町 治
    1983 年 92 巻 3 号 p. 152-172
    発行日: 1983/06/25
    公開日: 2009/11/12
    ジャーナル フリー
    The glacial landforms, consisting of cirques, troughs, moraines, etc., are widely distributed in the vicinity of Mt. Kisokomagatake (2, 956 m) in the northern part of the Kiso Mountain Range. They are obviously classified into the younger and fresh landforms and the older and dissected ones. The older ones are much more extensive than the younger ones. The author discussed the glacial fluctuations and chronology in the drainage basin of Nakagosho-gawa east of Mt. Kisokomagatake, where glacial landforms are well preserved, in order to clarify the developmental period of these two types of glacial landforms (Fig. 1). Geomorphological data (Figs. 2, 11 and 12), geological data (Figs. 3 and 5), sedimentological data (Figs. 710, and Tab. 1) as well as tephrochronological data (Fig. 4 and Tab. 2) were examined to this purpose.
    Since about 80, 000 years B. P., three stages of glacial advance were revealed in the drainage basin of Nakagosho-gawa. Consequently, they are included in the Last Glacial Age and are named, from older to younger, Nakagoshodani Stadial I, II and III, respectively. Glacial landform development during each stadial were quite different, as described below (Figs. 2 and 13) :
    1. Nakagoshodani Stadial I (80, 000-45, 000 years B.P.)
    This stadial is characterized by the largest extension of glacier. Glacier, attained 100 m or more in maximal thickness, extended from the Senjojiki- and Gokurakudaira- Cirque to the east of Shirabidaira (1, 790-1, 600 m a.s.l.) over a horizontal distance of 2.5 to 3.0 km. Glacial snout was located approximately at 1, 550 m a.s.l.. This glacial advance resulted in the formation of large trough (HG) below the above-mentioned cirques as well as the deposition of till (S-1 gravel bed) at Shirabidaira. The total thickness of till composed of ablation and lodgement till amounted to 50 to 60 m. Besides, lateral moraines were formed at Shirabidaira.
    2. Nakagoshodani Stadial II (45, 000-30, 000 years B.P.)
    Though glacier extended to Shirabidaira again, glaciation was limited in extension and magnitude rather than that of the Nakagoshodani Stadial I. Glacier is inferred to have been a maximum thickness of 50 to 70 m. Only the upper part of the trough was further denudated resulting in the formation of relatively small trough (MG) through this glacial advance. Ablation till (S-2 gravel bed), 20 to 30 m in maximum thick, was deposited and formed lateral moraines at Shirabidaira. End and lateral moraines (a, b) were also formed on the thresholds of both the Senjojiki- and Gokurakudaira- Cirque, preceded and accompanied by the retreat of glacier from Shirabidaira.
    3. Nakagoshodani Stadial III (30, 000-10, 000 years B.P.)
    Glaciation was much more limited in extension and magnitude than that of the Nakagoshodani Stadial II. The glaciers descending from both the Gokurakudaira-Cirque and the northern half of the Senjojiki-Cirque excavated in the Nakagoshodani Stadial I and II, attained only a maximum thickness of about 20 m. The glacial snouts were at about 2, 290 m a.s.l.. The upper part of the trough, modified during the Nakagoshodani Stadial II, was further slightly denudated resulting in the formation of small trough (LG) through this glacial advance. The formation of lateral moraine (c) in the Senjojiki-Cirque was prior to that of the end and lateral moraines (d-o) in the trough. In the northwestern part of the SenjojikiCirque (A, B), glacier remained up to the latest stage.
    Judging from the investigation in the drainage basin of Nakagosho-gawa, it can be regarded that the older and younger glacial landforms obviously classified by the degree of dissection are relevant to the Nakagoshodani Stadial I and to Nakagoshodani Stadial III, respectively. Surface area and equilibrium-line altitude of glaciers, the altitude of glacial snouts, etc., during these two stadials are shown in Tab. 3.
  • 小出 仁
    1983 年 92 巻 3 号 p. 173-192
    発行日: 1983/06/25
    公開日: 2009/11/12
    ジャーナル フリー
    The large earthquake occurs due to the emission of elastic waves during fracture propagation and abrupt displacement along a large fault system, which process is triggered by fracturing of a block of rock in the fault system or at fault edge. Earthquake source process is too much complicated for the precise modeling due to the complexity and variety of fault systems. However, the precise observation of fault development during fracture experiments suggests that a large fault is formed by connection of a set of smaller fractures or faults aligned en echelon. Many fault systems show multiple en echelon arrangement of smaller component fractures. Two mechanically different types of steps or bends are distinguished in the en echelon fault system or zigzag fault which is derived from en echelon fractures. One type is the step-up gap or bend which is compressed by the sliding of the fault. The other type is the step-down gap or bend which is extended by the slip of the fault.
    The rough estimation of resistive strength of en echelon fault gaps against fault sliding shows that the step-up gap is much more resistant to fault displacement than the step-down fault gap is. The strength of gap can be roughly estimated from stepping ratio of en echelon steps. The energy of earthquake is proportional to the product of square of offset of en echelon step and length of fault.
    The doughnut pattern of foreshock activity and migration of earthquake fracturing can be adequately described by the model that the earthquakes are generated by a process of fracturing of gaps or bends in a multiple en echelon fault system. This “multiple en echelon fault model of earthquake source mechanism” has been proposed in this paper in an attempt to make the “asperity model” more concrete with respect to fault geometry and fault development mechanism.
    The gaps or bends of en echelon fault system make loci of stress concentration and are expected to be very sensitive to premonitory stress disturbance before earthquake. The gaps and bends of fault system make promising monitoring sites for earthquake prediction.
  • 小林 貞一
    1983 年 92 巻 3 号 p. 193-214
    発行日: 1983/06/25
    公開日: 2009/11/12
    ジャーナル フリー
    In Eastern Asia Cyrena naumanni NEUMAYR, 1890 was the first non-marine shell described from Shikoku Island, followed by REIS (1910), FRECH (1911), GRABAU (1923) and others. SUZUKI (1949) has presented an extensive summary on the non-marine Molluscan fossils of Eastern Asia. Subsequently the non-marine Mesozoic bivalve faunas of Japan were considerably amplified. Its larger part is, however, composed of Upper Triassic and later brackish shells and fresh water ones are mostly early Cretaceous in age. In Thailand there are the paralic Jurassic formation and limnic Cretaceous formation containing Molluscs which are related to the contemporaneous faunas in Laos, Yunnan and Kwangsi. Among them Trigonioides, Plicatounio and Nippononaia are three leading genera in the early Cretaceous period and Pseudohyria and its allies are those in the late Cretaceous period. Now there are a large number of their genera and subgenera which are here classified in five families tentatively.
    In Eastern Asia some Moscovian and Lower Permian naiads are known from Korea and China, and Upper Permian ones from Northeast China. The Utschamitian naiads occur in North and East China in Upper Triassic rocks. Jurassic ones are also related to the Siberian ones, but the TPN fauna may be originated already during the Jurassic period. As the result of studies on the Mesozoic fossils from Korea and Manchuria four distinct faunal suites were distinguished in 1942 with reference to conchostracans, ostracods, Molluscans and fishes. This classification is now well established. The development of the Upper Triassic and Lower Jurassic Daido and the early Cretaceous Kyöngsang suites is related respectively to the early and late Mesozoic orogenies and the late Jurassic Jehol and the late Cretaceous Sungari suites to the metaorogenic crustal undulations in a grand scale. The latter two faunal suites are distributed in large depressions in the interior of the continent, while the former suites are found in intermontane basins along the folded mountains produced by the Sakawa and Akiyoshi cycles of orogeny.
  • 前田 四郎
    1983 年 92 巻 3 号 p. 215-216
    発行日: 1983/06/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 前田 四郎, 北村 建治
    1983 年 92 巻 3 号 p. Plate1-Plate2
    発行日: 1983/06/25
    公開日: 2009/11/12
    ジャーナル フリー
feedback
Top