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Hokkaido University Collection of Scholarly and Academic Papers (135.521 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy

Mostrando recursos 1 - 13 de 13

  1. On the Nature of Remanence in the 1985 Andesitic Pumice with Self-Reversed Magnetization from Nevado del Ruiz, Colombia

    Fujiwara, Yoshiki; Gautam, Pitambar; Yoshida, Mitsuo; Katsui, Yoshio
    The magnetic remanence of the andesitic pumice of the Nevado del Ruiz 1985 eruption has the multi-component nature. The major normal component behavior is due to the titanomagnetite phase with variable chemistry. The major reverse component has a peak demagnetization and acquisition range between 200°-225℃ but no such mineral phase could be detected. The titanomagentite phase contributes to the major normal component and has probably no relation to the reverse magnetization.

  2. On the Nature of Remanence in the 1985 Andesitic Pumice with Self-Reversed Magnetization from Nevado del Ruiz, Colombia

    Fujiwara, Yoshiki; Gautam, Pitambar; Yoshida, Mitsuo; Katsui, Yoshio
    The magnetic remanence of the andesitic pumice of the Nevado del Ruiz 1985 eruption has the multi-component nature. The major normal component behavior is due to the titanomagnetite phase with variable chemistry. The major reverse component has a peak demagnetization and acquisition range between 200°-225℃ but no such mineral phase could be detected. The titanomagentite phase contributes to the major normal component and has probably no relation to the reverse magnetization.

  3. Paleomagnetism of the Northwestern Part of the Mahabharat Synclinorium, Lesser Himalaya, Nepal

    Gautam, Pitambar
    Remanent magnetization of the low-grade metasediments (272 specimens/131 samples from 26 sites), which constitute the Nawakot and Kathmandu Complexes in the northwestern part of the Mahabharat synclinorium, is described. Alternating field (AF) and thermal (TH) demagnetization experiments reveal stable secondary magnetization resting in hematite and represented by normal and reverse polarities. The secondary remanence is of prefolding origin in the rocks from the Nawakot Complex while it post-dates major folding in those from the Kathmandu Complex. The directions are consistent with near-equatorial shallow paleolatitudes. The secondary remanence is interpreted to indicate the occurrence of a series of events, i.e. reheating...

  4. Paleomagnetism of the Northwestern Part of the Mahabharat Synclinorium, Lesser Himalaya, Nepal

    Gautam, Pitambar
    Remanent magnetization of the low-grade metasediments (272 specimens/131 samples from 26 sites), which constitute the Nawakot and Kathmandu Complexes in the northwestern part of the Mahabharat synclinorium, is described. Alternating field (AF) and thermal (TH) demagnetization experiments reveal stable secondary magnetization resting in hematite and represented by normal and reverse polarities. The secondary remanence is of prefolding origin in the rocks from the Nawakot Complex while it post-dates major folding in those from the Kathmandu Complex. The directions are consistent with near-equatorial shallow paleolatitudes. The secondary remanence is interpreted to indicate the occurrence of a series of events, i.e. reheating...

  5. Two Metamorphic Events of the Nepal Himalayas Prior and Posterior to India-Eurasia Collision

    Arita, Kazunori; Gautam, Pitambar; Ganzawa, Yoshihiro
    K-Ar ages were newly determined on biotite from a pelitic gneiss and on hornblende from a calcareous gneiss both from the Higher Himalayas in Nepal. The corresponding ages, 56.7±2.8 Ma and 61.5±3.1 Ma, respectively, are quite old compared with their fission-track ages. We made a synthesis of the various isotopic ages from the Nepal Himalayas available so far, and attempted an analysis on the age versus closure temperature basis. The findings suggest that the Higher Himalayas have undergone two major reheating episodes, during the Himalayan orogeny, which are reflected in two different cooling trajectories roughly corresponding to late Cretaceous to...

  6. Two Metamorphic Events of the Nepal Himalayas Prior and Posterior to India-Eurasia Collision

    Arita, Kazunori; Gautam, Pitambar; Ganzawa, Yoshihiro
    K-Ar ages were newly determined on biotite from a pelitic gneiss and on hornblende from a calcareous gneiss both from the Higher Himalayas in Nepal. The corresponding ages, 56.7±2.8 Ma and 61.5±3.1 Ma, respectively, are quite old compared with their fission-track ages. We made a synthesis of the various isotopic ages from the Nepal Himalayas available so far, and attempted an analysis on the age versus closure temperature basis. The findings suggest that the Higher Himalayas have undergone two major reheating episodes, during the Himalayan orogeny, which are reflected in two different cooling trajectories roughly corresponding to late Cretaceous to...

  7. Magnetic Properties of some late Paleozoic to Tertiary Sedimentary Rocks of Tansen Area, Lesser Himalaya, Nepal

    Gautam, Pitambar
    Magnetic properties of a total number of 117 samples collected with an aim of preliminary paleomagnetic study from 26 sites in the Tansen area were investigated. Measurements of natural remanent magnetization (NRM) showed that only 11 sites (61 samples), which are represented by olive green sandstones and siltstones and redbeds (red-colored shale, sandstone and iron-rich rocks) possess magnetizations strong enough to be analyzed for stability of the remanence by alternating field (AF) and thermal (TH) demagnetization techniques. Demagnetization behavior, isothermal remanent magnetization (IRM) characteristics, X-ray diffraction patterns and variation of saturation magnetization with temperature have been studied. Chemical changes of...

  8. Magnetic Properties of some late Paleozoic to Tertiary Sedimentary Rocks of Tansen Area, Lesser Himalaya, Nepal

    Gautam, Pitambar
    Magnetic properties of a total number of 117 samples collected with an aim of preliminary paleomagnetic study from 26 sites in the Tansen area were investigated. Measurements of natural remanent magnetization (NRM) showed that only 11 sites (61 samples), which are represented by olive green sandstones and siltstones and redbeds (red-colored shale, sandstone and iron-rich rocks) possess magnetizations strong enough to be analyzed for stability of the remanence by alternating field (AF) and thermal (TH) demagnetization techniques. Demagnetization behavior, isothermal remanent magnetization (IRM) characteristics, X-ray diffraction patterns and variation of saturation magnetization with temperature have been studied. Chemical changes of...

  9. A Paleomagnetic Reconnaissance of some late Precambrian to Early Paleozoic Rocks of Tansen Area, Lesser Himalaya, Nepal

    Gautam, Pitambar
    For a preliminary paleomagnetic research on Late Precambrian to Early Paleozoic rocks in the Tansen area (West Central Nepal) carbonate, sandstone, quartzite and slate were collected from 30 sites at 4 localities. Detailed analyses of magnetic remanence were made using alternating field and thermal demagnetization techniques. Most of the specimens were found to be weakly magnetized (intensities of 10^-7 emu/cc, in order). Three magnetic components have been distinguished: (1) a predominant secondary component of recent origin, which represents a larger portion of the magnetization intensity in weakly magnetized specimens and thus hinders the separation of primary components. (2) another component...

  10. A Paleomagnetic Reconnaissance of some late Precambrian to Early Paleozoic Rocks of Tansen Area, Lesser Himalaya, Nepal

    Gautam, Pitambar
    For a preliminary paleomagnetic research on Late Precambrian to Early Paleozoic rocks in the Tansen area (West Central Nepal) carbonate, sandstone, quartzite and slate were collected from 30 sites at 4 localities. Detailed analyses of magnetic remanence were made using alternating field and thermal demagnetization techniques. Most of the specimens were found to be weakly magnetized (intensities of 10^-7 emu/cc, in order). Three magnetic components have been distinguished: (1) a predominant secondary component of recent origin, which represents a larger portion of the magnetization intensity in weakly magnetized specimens and thus hinders the separation of primary components. (2) another component...

  11. Scanning Electron Microscopy of Planktonic Foraminifera : A Preparation Technique

    Honjo, Susumu; Okada, Hisatake

  12. Study of Nannofossils by the Scanning Electron Microscope

    Honjo, Susumu; Minoura, Nachio; Okada, Hisatake

  13. Neogene Molluscan Fauna in Hokkaido : Part III. Description of the Ainonai Fauna Associated with Desmostylus cf. minor Nagao, from Kitami District, East Hokkaido

    Uozumi, Satoru; Fujie, Tsutomu; Matsui, Masaru

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