第四紀研究
Online ISSN : 1881-8129
Print ISSN : 0418-2642
ISSN-L : 0418-2642
19 巻 , 2 号
選択された号の論文の6件中1~6を表示しています
  • 岡口 雅子, 大塚 裕之
    1980 年 19 巻 2 号 p. 75-85
    発行日: 1980/08/01
    公開日: 2009/08/21
    ジャーナル フリー
    Fission track ages of zircon crystals separated from the tuff layers in the Kuchinotsu Group and those from the andesite of the Tatsuishi Formation in the Shimabara Peninsula, northwest Kyushu have been determined in order to bring some light on the history of the Hôhi and the Sanin volcanic activities (MATSUMOTO, 1963) in the Early to Middle Pleistocene age in Kyushu and to clarify the absolute ages of the mammalian and floral zones discriminated in the Kuchinotsu Group.
    As the diameter of the fission track has been considerably shortened by annealing, correction was made on each given age in the present study, based on the results of the annealing examination.
    The fission track ages of the Kuchinotsu Group and the Tatsuishi Formation are as follows:
    Fission track ages (m.y.)
    Tatsuishi Formation 0.24±0.06
    Kuchinotsu Group {Kitaarima Formation (Saishoji tuff breccia) 1.43±0.27 Oya Formation {Oya tuff (Tuff VIII) 1.76±0.22 Mukaigoya tuff breccia 1.89±0.16
    The fission track age of the Mukaigoya tuff breccia (1.89±0.16 F.T.m.y) indicates the beginning of the Early Pleistocene Hôhi volcanic activities widely recognized as lavas or pyroclastics in the Early Pleistocene formations in north Kyushu. Furthermore, all the fission track ages of the Kuchinotsu Group seem to be consistent with the results of magnetostratigraphy and biostratigraphy based on the mammalian and plant fossils of this group.
    The Tatsuishi Formation is mainly composed of mud flow of hornblende andesite which belongs to the early volcanic products of the Unzen volcano representing one of the Middle Pleistocene Sanin volcanic activities of west Japan (MATSUMOTO, 1963). The fission track age of the Tatsuishi Formation (0.24±0.06 F.T.m.y) almost corresponds to those of the hornblende andesite of the Tara-dake (MATSUMOTO et al., 1977) of the Nagasaki Prefecture, northwest Kyushu.
  • 西田 史朗
    1980 年 19 巻 2 号 p. 87-96
    発行日: 1980/08/01
    公開日: 2009/08/21
    ジャーナル フリー
    Calcareous nannoplankton biostratigraphy extending from the Naarai Formation up to the Toyosato Formation in the Choshi district, Chiba Prefecture, was carried out with a scanning electron microscopic technique. In the present stratigraphic sequence, lithostratigraphy and magnetostratigraphy are well established by MATOBA (1967) and NIITSUMA (1970) respectively and interpreted micropaleontologically by KOIZUMI and KANAYA (1976).
    In the section studied, eleven calcareous nannoplankton events were recognized, that is, the appearance of Gephyrocapsa caribbeanica and the first occurrence of Gephyrocapsa oceanica in the Naarai Formation, the first occurrence of Gephyrocapsa protohuxleyi, the extinction of Cyclococcolithus macintyrei and the first occurrence of Helicopontosphaera hyalina in the lower part of the Obama Formation, the extinctions of Gephyrocapsa protohuxleyi and Reticulofenestra pacifica and the disappearance of Coccolithus pelagicus in the uppermost part of the Yokone Formation, the extinction of Pseudoemiliania lacunosa in the middle part of the Kurahashi Formation and the disappearance of Gephyrocapsa caribbeanica and the extinction of Reticulofenestra japonica in the lower part of the Toyosato Formation in ascending order. Any specimen of Emiliania huxleyi cannot be detected in the section.
    In this district the first occurrence of Gephyrocapsa oceanica is recongized prior to the appearance of Plio-Pleistocene marker species of planktonic formainifer Globorotalia truncatulinoides which first appeared at ca. 1.8m.y. ago (HAQ et al., 1977). On the other hand the extinction level of Pseudoemiliania lacunosa is estimated at ca. 0.45m.y. ago (THIERSTEIN et al., 1977).
    Based on the both micropaleontological frame work, normal magnetic zone in the Kasuga Formation is correlated to the Orduvai Event, normal magnetic zone in the lower part of the Yokone Formation is correlated to the Jaramillo Event and magnetic reversal in the upper part of the Yokone Formation is supposed to be the boundary of Matuyama-Brunhes magnetic Epochs.
    Accordingly the Kasuga, Obama, Yokone, Kurahashi and Toyosato Formations spread from uppermost Pliocene to middle Pleistocene and their age is estimated at ca. 2.0m.y. to 0.4m.y.
    Biostratigraphical range of Gephyrocapsa protohuxleyi extended from ca. 1.5m.y. to ca. 0.5my. ago. Extinctions of Reticulofenestra pacifica and Reticulofenestra japonica are conservatively estimated at ca. 0.5m.y. ago because of their abundant occurrences and high possibilities of secondary fossils.
    Present stratigraphic sequence will offer an important land-based micropaleontological control for the marine Pleistocene in mid-latitude area.
  • 吉田 澪
    1980 年 19 巻 2 号 p. 99-106
    発行日: 1980/08/01
    公開日: 2009/08/21
    ジャーナル フリー
    前報において, 強磁性鉱物の磁気的性質のちがいによってテフラの同定を行なう試みの第一段階として, 分級作用の影響は認められないこと, 異種テフラ間の差異は明確であることなどを確認した.
    本報では, 桜島の噴出時期の異なる軽石中の強磁性鉱物の性質を比較するとともに, 起源・噴出時期の明らかなものについて, 地理的広がりを以って基本的データを集積するため, 桜島の大正 (5地点, 5試料), 安永 (5地点, 8試料), 文明 (3地点, 3点), 時代末詳 (1地点, 3試料) の各軽石と, 霧島火山群・御池噴出の御池軽石 (7地点, 7試料), 指宿火山群・池田湖噴出の開聞C軽石 (4地点, 6試料) を供試して, X線回折による格子定数 (aÅ) の測定, 化学分析, 熱磁気分析によるキュリー温度 (Tc℃) の測定などを行なって検討した.
    その結果, 大正, 安永, 文明の各軽石試料の性質は異なっているが (Table 2), 特に, キュリー温度のちがいは明確で, 化学組成のちがいと良く対応しており, これによって, 各軽石を容易に識別することができる. 大正・時代末詳両軽石の性質は良く似ているが, これについては, 桜島熔岩のSiO2含量が循環的に変動していることが知られており, この両者の類似性は, マグマの組成変動のサイクルを反映しているものと考えられる. しかしこれらの軽石は, 断面内での出現位置, 風化の程度が顕著に異なっているため, この方面からの識別が容易であろう. 同じ安永・時代末詳の軽石間では, 降下単層が異なっても強磁性鉱物の性質はちがわなかった. 御池軽石は文明軽石と多少似た性質を示したが, 開聞C軽石は, 今回の試料の中では特にTi含量が少なく, そのためキュリー温度が高く, 特異的であった.
  • 辻 誠一郎
    1980 年 19 巻 2 号 p. 107-115
    発行日: 1980/08/01
    公開日: 2009/08/21
    ジャーナル フリー
    The Kissawa Formation deposited during the Shimosueyoshi Transgression, ca 150, 000-ca 130, 000 FT y.B.P., is subdivided into six local pollen assemblage zones at Saigato, namely from the lower Ka-I, II, III, IV, V and VI, based on the occurrence of the tree pollen with a high value. Macro-plant remains which are mostly seeds and fruits occur commonly from the upper Ka-I to the Ka-V. Specific compositions of the plant fossil assemblages change conspicuously in two horizons, i.e. the upper Ka-I and the boundary between the Ka-V and the Ka-VI. During the zones of the upper Ka-I to the Ka-V, such warm temperate to sub-tropic elements as Lagerstroemia, Sapium sebiferum, Melia azedarach, Aleurites cordata, Ehretia dicksonii and Buxus, and the temperate elements commonly distributed in Japan coexist constantly. The temperate trees of Ulmus and/or Zelkova predominate in the lower Ka-I of the initial layer, and those of Cryptomeria, Alnus and Picea in the Ka-VI are predominant. Because of this, it is assumed that the climatic condition during the Shimosueyoshi Transgression is similar to that of the present at least.
  • 佐瀬 隆
    1980 年 19 巻 2 号 p. 117-124
    発行日: 1980/08/01
    公開日: 2009/08/21
    ジャーナル フリー
    Plant opals in buried soils right below the Nanbu pumice layer (about 8, 600 years old, Oike and Takahashi, 1970) in the Nanbu area, Tohoku district, were separated and examined under the microscope. The constituents of plant opals in the buried soils gave the following informations on the vegetations of the Nanbu area in the early Holocene.
    1) Plant opals were mostly originated from Gramineae, among which the Panicoid type (mostly produced by Paniceae) and the Sasaoid type (produced by so-called Sasa) dominate over the Festucoid type (produced by Poaceae). This means that the grass vegetation were constituted mostly of Paniceae and Sasa in the Nanbu area in the early Holocene.
    2) Plant opals originated from trees, possibly Fagaceae and Magnoliaceae, were also found. However, their amount was far smaller than those from Gramineae.
  • 1980 年 19 巻 2 号 p. 129
    発行日: 1980年
    公開日: 2009/08/21
    ジャーナル フリー
feedback
Top