The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 121, Issue 3
Displaying 1-5 of 5 articles from this issue
SPECIAL ISSUE Ten years' activities of the Topic session “The Jurassic+”: Perspective for research on the Jurassic
Review
  • Hisashi Suzuki, Hans-Jürgen Gawlick, Tetsuji Onoue, Teiji Mikami, Hona ...
    2015 Volume 121 Issue 3 Pages 83-90
    Published: March 15, 2015
    Released on J-STAGE: June 19, 2015
    JOURNAL FREE ACCESS
    This paper summarises the recent progress and current status of research undertaken on the Jurassic strata of the Northern Calcareous Alps. The Jurassic GSSP (Global Boundary Stratotype Section and Point) at the Kuhjoch section of the Northern Calcareous Alps is also explained in detail. The base of the Jurassic strata is defined at this location by the occurrence of the oldest known Jurassic ammonite, Psiloceras spelae tirolicum Hillebrandt & Krystyn. The Upper Triassic to Lower Jurassic successions of the Northern Calcareous Alps were developed along the passive continental margin of the Neotethys Ocean. In Middle Jurassic time, a change in the plate tectonic setting influenced the sedimentary facies, which suggest northwest-verging nappe stacking in association with the partial closure of the Neotethys Ocean. Deep-water radiolarite basins developed in the area in front of the advancing nappes and were the sites of mass flow deposits that produced olistoliths of various sizes. These olistoliths were included in the radiolarite matrices. Therefore, the use of radiolarian fossils as a dating method plays an important role in understanding the formations of the Northern Calcareous Alps.
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  • Tetsuji Onoue, Honami Sato
    2015 Volume 121 Issue 3 Pages 91-108
    Published: March 15, 2015
    Released on J-STAGE: June 19, 2015
    JOURNAL FREE ACCESS
    Triassic and Jurassic bedded chert sequences in Japanese accretionary complexes are recognized as pelagic deep-sea deposits characterized by very low sedimentation rates (less than a few millimeters per thousand years) and the absence of coarse-grained terrigenous clastics. Owing to their low sedimentation rates and long-term continuous deposition, these bedded cherts may record the accretionary history of extraterrestrial material over geologic time. Here, we review studies of extraterrestrial material contained in bedded chert sequences from the Jurassic accretionary complexes, southwest Japan. Cosmic spherules, which are submillimeter-sized extraterrestrial particles that melt during atmospheric entry, have been found in Triassic and Jurassic bedded cherts from the Mino-Tanba and Chichibu belts. Two major spherule types have been identified, based mainly on their mineral and chemical compositions: iron-type and silicate-type. The extraterrestrial origin is indicated by the presence of metallic iron and nickel in the iron-type spherules, and by the chondritic composition and mineral assemblages of the silicate-type spherules, which contain olivine and low-Ca pyroxene. The detection of platinum group elements (PGE) and data on osmium (Os) isotope ratios (187Os/188Os) in the cherts provide evidence for crater-forming meteorite impact events. Anomalously high PGE concentrations and negative Os isotope-ratio excursions reported from Upper Triassic bedded cherts are also interpreted to indicate a large extraterrestrial impact event. Systematic studies of ancient cosmic spherules and extraterrestrial PGE signatures in bedded cherts could provide evidence for long-term changes in the composition and flux of incoming extraterrestrial matter.
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  • Li Gang, Atsushi Matsuoka
    2015 Volume 121 Issue 3 Pages 109-122
    Published: March 15, 2015
    Released on J-STAGE: June 19, 2015
    JOURNAL FREE ACCESS
    The well-developed Jurassic and Cretaceous strata of northeastern China are mostly of non-marine origin. The definition of the non marine Jurassic/Cretaceous (J/K) boundary in northeastern China is based mainly on the age assignment of the well-known non-marine Jehol Biota of eastern Asia. Although the Eosestheria-Ephemeropsis-Lycoptera-bearing strata in China, Mongolia, and Transbaikalia (Russia) were originally assigned to the Early Cretaceous in the 1920s, the age of the entire Jehol Group of western Liaoning, northeastern China, which contains the Jehol Biota in the lower part and the Fuxin Biota in the upper part, was revised to Middle-Late Jurassic during the early 1960s. This age revision was further supported by the recovery of an apparent Bathonian (Middle Jurassic) Arctocephalites ammonite fauna and a Late Jurassic Buchia fauna from eastern Heilongjiang Province in the middle 1980s. During the early 1990s, through revisions of the ages of the above-mentioned marine faunas of eastern Heilongjiang from Jurassic to Early Cretaceous, the Jehol Biota was re-dated as Early Cretaceous by some authors. At the same time, the recovery of feathered dinosaurs, early birds, mammals, and angiosperms from the Yixian and Jiufotang formations encouraged precise radiometric dating of the Jehol Group and its underlying strata in western Liaoning and northern Hebei. The new radiometric dating indicates that the non-marine J/K boundary in northern China falls within the contemporaneous Houcheng Formation (northern Hebei) and Tuchengzi Formation (western Liaoning), which are stratigraphically much lower than the Jehol Group of western Liaoning.
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