The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 61, Issue 713
Displaying 1-4 of 4 articles from this issue
  • Yosiziro KATO
    1955 Volume 61 Issue 713 Pages 51-61
    Published: February 25, 1955
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    (1) Considering the stratigraphic sequence and geologic structure of the Middle Miocene formations, the Sidara structural basin is divided into four units: the central, the northern, the southern and the eastern Parts., (2) The basement complex is the Ryoke Metamorphic Rocks and unconformably overlain by the Miocene formations., (3) The Tertiary is classified into two groups, the Hokusetu and the Nansetu., The Hokusetu group, composed mainly of clastic sediments, is further divided into four formations, the Taguti, the Kawakado, the Simoda and the Tubogawa in ascending order., The Nansetu group overlies unconformably on the Hokusetu group and comprises pyroclastic and lava flows., (4) The sequence of the volcanic activities in the area is as follows: (a) the eruption of rhyolite and dacite contained in the Nansetu group, (b) the intrusion of andesite sills which have been silicified after the intrusion, and (c) the eruption of andesite and basalt after the formation of the basin structure of Sidara., (5) In the eastern part of the basin the Nansetu group is absent and the Hokusetu group shows a small and rather flat basin structure separated from the major basin of the central part., This minor basin is formed by three fault systems, contemporaneous with each other: N 30°W, N 30°∼50°E and N 10°E in directions., The minor basin, moreover, is abundant in silicified andesite sills., (6) In contrast with the major basin, which has relation with the accumulation of the Nansetu group, the minor basin is caused by the faults which occurred in the Tobe Phase of the Median Line.,
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  • Toru SAKAMOT0
    1955 Volume 61 Issue 713 Pages 62-72
    Published: February 25, 1955
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The stratigraphic succession of the rocks developed in the eastern margin of the Nara basin is as follows; Rokuyaon gravel bed unconformity Kokuzoyama gravel bed unconformity Shirakawaike formation unconformity Tawara formation unconformity Toyoda formation Fujiwara group Iwabuchi formation unconformity Basement rocks The basement rocks consists mainly of injection gneiss in the northern part and of gneissose granite in the southern part and locally of diorite., Fujiwara group; The Iwabuchi formation, the lower part of the Fujiwara group, is composed chiefly of conglomerate, and is subdivided into three parts by the sedimentary facies., The Toyoda formation, the upper part, consists mainly of tuffaceous fine grained sandstone or mudstone., This group is middle Miocene in age according to the molluscan fossils., Shirakawaike formation; The lower part of this formation is chiefly conglomeratic, but upperwards it becomes muddy or sandy., Among the abundant plant remains derived from the lower part, Metasequoia disticha, Cunninghamia Konishii, Menyanthes trifoliata and others, point to an uppermost Pliocene (I1) in age., The main geological structure in this area is controlled by two faults with N-S trend (the Takai and the Sanbyaku faults) and by a flexure (the Tenri flexure).,
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  • Jun TESHIMA
    1955 Volume 61 Issue 713 Pages 73-86
    Published: February 25, 1955
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The Poronai formation, predominantly a mudstone more than 1, 000 meters thick, is the thickest and most extensively distributed formation in the southern half of the Ishikari coal-field, which is known as the Yubari coal-field., The formation contains abundant fossils of molluscs, crustaceaus, simple corals, and rarely plant leaves., From the mode of occurrence of the mentioned fossils, the writer concludes that they were preserved in situ, in other words, they comprise a thanatocoenosis, which represents an original biotope., Qualitatively considered, the fauna is similar throughout the entire thickness of the formation, but quantitatively, such uniformity is not recognized and the fauna differs in composition from horizon., Each horizon or phase shows wide distribution throughout the entire Yubari coal-field., Hitherto subdivision of the Poronai formation has been considered to be extremely difficult by the megafossils., However, the writer is inclined to believe in its possiblity by a quantitative treatment of the megafossils, since he has been successfull in subdividing the Poronai formation into 9 (A-I) sequential parts.,
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  • Satoru OHYA, Shinobu HADA
    1955 Volume 61 Issue 713 Pages 87
    Published: February 25, 1955
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
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