The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
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Volume 119, Issue 1
Displaying 1-8 of 8 articles from this issue
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Articles
  • A tsunami depositional model in coastal lowland over sand dune: An example from the 17th century tsunami deposit in the eastern Iburi coast, central Hokkaido, northern Japan
    Yasuhiro Takashimizu, Jun Nagai, Satoshi Okamura, Yuichi Nishimura
    2013 Volume 119 Issue 1 Pages 1-16
    Published: January 15, 2013
    Released on J-STAGE: May 08, 2013
    DOIhttps://doi.org/10.5575/geosoc.2012.0067
    JOURNAL FREE ACCESS
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    A reconstruction of a paleo-tsunami flow recorded on the eastern Iburi coast of Hokkaido, northern Japan, has been undertaken using sedimentological analysis. Here, distance from the coastline positively correlates with average sediment grain sizes (mean and median grain sizes expressed in phi scale) but inversely correlates with the standard deviation of grain-size and thickness of the tsunami deposit layer. Grain-fabric and grain-size data in this area indicate at least three tsunami inundation events, with grain-fabric data for tsunami deposits at survey site 1 indicating that these deposits were formed by inflows with ENE paleo-flow directions. This evidence has enabled a depositional model of a tsunami flowing over coastal sand dunes to be formulated, with the first tsunami flow eroding surficial sediments and ripping up and carrying peat clasts. The majority of the tsunami-related water did not return to the sea; this return flow was prevented by a seaside beach ridge, leading to the formation of wide water bodies along the coast. In addition, repeated tsunami inflows did not cause intensive erosional effects at the bottom of these water bodies, with these bodies eventually disappearing due to underground seepage or evaporation.
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  • The depositional environment of the singular Middle Miocene strata from southwestern Tomioka City, Gunma Prefecture, central Japan, from the view point of fossil ostracod assemblage
    Gengo Tanaka, Miho Itami, Sachie Kurosawa, Ayumi Yoshioka, Mari Yokota ...
    2013 Volume 119 Issue 1 Pages 17-24
    Published: January 15, 2013
    Released on J-STAGE: May 08, 2013
    DOIhttps://doi.org/10.5575/geosoc.2012.0074
    JOURNAL FREE ACCESS
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    We present a micropaleontological re-examination of the depositional environment of the ‘Kojyakui-sho’ sediments of the Middle Miocene Obata Formation, part of the Tomioka Group, located along the Kabura-gawa River near Tajima, Tomioka City, western Gunma Prefecture, central Japan. These sediments contain sublittoral and bathyal ostracods, and were deposited in the bathyal zone on a quartz-porphyry bedrock seafloor during the late Early to early Middle Miocene. Planktonic foraminifera and ostracods within these samples indicate that the ‘Kojyakui-sho’ sediments formed during the Miocene Climatic Optimum; this is the second reported occurrence of these Miocene Climatic Optimum bathyal ostracod species in Japan.
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  • Latest Jurassic to earlier Early Cretaceous foraminifers from the Torinosu-type limestone blocks in Southwest Japan: Constraints on chrolonogic calibration of the Torinosu-type limestones
    Fumio Kobayashi, Roland Wernli
    2013 Volume 119 Issue 1 Pages 25-38
    Published: January 15, 2013
    Released on J-STAGE: May 08, 2013
    DOIhttps://doi.org/10.5575/geosoc.2012.0072
    JOURNAL FREE ACCESS
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    Thirty-six taxa of foraminifers were recognized from 31 samples of the Torinosu-type limestone blocks in South of Yatsushiro, Azamui (Kyushu), Nomura (Shikoku), and Yura (Kii) areas, Southwest Japan. Those identified in species level are confined to five: Nautiloculina broennimanni, Freixialina planispiralis, Charentia cuvillieri, Melathrokerion spirialis, and Pseudocyclammina lituus. Such genera as Kurnubia and Alveosepta showing the pre-Kimmeridgian, and orbitolinids characteristic in the post-late Hauterivian are completely absent in them. The Torinosu-type limestones studied are assigned to the latest Jurassic to earlier Early Cretaceous based on the biostratigraphic distribution of the identified five species in the western Tethyan region and chronologic constraints on the studied material excluding the pre-Kimmeridgian and post-late Hauterivian faunal elements.
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Note
  • Solid geomorphological model covered with map-printed elastic film for application as study materials
    Takashi Ito, Chiduko Okazaki, Akihiko Shibahara, Hiroshi Sawamura, Nao ...
    2013 Volume 119 Issue 1 Pages 39-44
    Published: January 15, 2013
    Released on J-STAGE: May 08, 2013
    DOIhttps://doi.org/10.5575/geosoc.2012.0059
    JOURNAL FREE ACCESS
    Supplementary material
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    A solid geomorphological model covered with map-printed elastic film (OK film: named from the first two letters of the last name, Okazaki, of the chief developer of printable elastic film) was developed as a study material to enable students to examine the geomorphological characteristics of an area; the first model produced was based on a satellite image of central Ibaraki Prefecture and was printed onto OK film. The application of an OK film covering to a solid geomorphological model and subsequent topographic observations were undertaken as part of a first year laboratory class for students of a university in Ibaraki Prefecture. All students who undertook this exercise were able to overlay their own map-printed OK film on a gypsum-based solid geomorphological model within the duration of the laboratory class. The scale of the geomorphological model and the variety of objects that can be printed means that this study material could be used in both natural science (e.g., earth sciences, natural geography) and/or social studies (e.g., human geography) classes at a range of levels, from elementary school to university, in addition to potential use within teacher training courses.
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  • Radiolarians from the Upper Cretaceous Himenoura Group, Nakakoshiki-jima Island, Kagoshima Prefecture, Japan.
    Miki Aramaki, Toshifumi Komatsu, Yuka Miyake, Osamu Takahashi, Yukiyas ...
    2013 Volume 119 Issue 1 Pages 45-50
    Published: January 15, 2013
    Released on J-STAGE: May 08, 2013
    DOIhttps://doi.org/10.5575/geosoc.2012.0069
    JOURNAL FREE ACCESS
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    Upper Cretaceous radiolarians are commonly found in the E1 lithological unit of the Himenoura Group, Nakakoshiki-jima Island, Kagoshima Prefecture, Kyushu, Japan. This radiolarian assemblage is characterized by Amphipyndax stocki, Dictyomitra koslovae, D. multicostata, Pseudoaulofacus floresensis, and Stichomitra asymbatos, indicative of deposition between the Santonian and middle Campanian. The E1 lithological unit probably formed during the middle Campanian, as the underlying D lithological unit contains abundant middle Campanian inoceramids.
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  • Permian lyttoniid brachiopod Petasmaia from Akasaka, Mino Belt, central Japan
    Jun-ichi Tazawa, Teruo Ono
    2013 Volume 119 Issue 1 Pages 51-55
    Published: January 15, 2013
    Released on J-STAGE: May 08, 2013
    DOIhttps://doi.org/10.5575/geosoc.2012.0076
    JOURNAL FREE ACCESS
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    A lyttoniid brachiopod species, Petasmaia expansa Cooper and Grant, 1969, is described from the middle member (Neoschwagerina margaritae Zone; upper Murgabian) of the Akasaka Limestone within the Mino Belt of central Japan. Petasmaia is a rare brachiopod genus, with the only two known species identified so far obtained from the Lower and Middle Permian of West Texas and from the Middle Permian of Akasaka. The presence of P. expansa in the Akasaka area suggests that reef-seamount complexes of the Mino Belt, including those within the Akasaka area, formed in a mid-Panthalassan equatorial region between the Palaeotethys and the North American continent in the Middle Permian.
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