Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 52 , Issue 6-7
Bulletin of the Geological Survey of Japan
Showing 1-7 articles out of 7 articles from the selected issue
  • Satoshi NAKAE
    2001 Volume 52 Issue 6-7 Pages 245-252
    Published: July 31, 2001
    Released: March 13, 2015
    Permian radiolarians are detected from cherts of the Tamba Terrane in the Nishizu district, southwestern Fukui Prefecture. The Tamba Terrane exposed in the district is mainly composed of basalt, limestone, chert, mudstone and sandstone. It is characterized by a chaotic mixture of these rocks; i.e., slabs of basalt, limestone, chert, mudstone and sandstone are embedded in pelitic mixed rocks. Only a few biostratigraphical studies in the district have previously been appeared and some of them described the occurrence of Permian, Triassic and Jurassic radiolarians,but the ages of the rocks constituting the Tamba Terrane in the district are still uncertained. Newly recovered radiolarians treated herein can give the chert sequence in the Nishizu district additional ages of late Early, middle Middle and middle Late Permian. Moreover, cherts generally occur as slabs, which are classified into small-scale lenticular and large-scale sheet-like types, both of which are assigned to Permian in age.
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  • Akinobu MIYAKOSHI, Youhei UCHIDA
    2001 Volume 52 Issue 6-7 Pages 253-290
    Published: July 31, 2001
    Released: March 13, 2015
    Temperature-depth profiles and groundwater levels were measured on 88 observation wells in the Kanto Plain. From observation results, subsurface temperature distribution in the Kanto Plain is assumed to be strongly affected by thermal advection due to groundwater flow, which has regional difference between high temperature area and low temperature area. The high temperature area is located in a low land around the Kinu, Tone Rivers and central part of the Kanto Plain. The low temperature area, on the other hand, is located in a high land and/or a mountain area around the Kanto Plain. Considering from observed distribution of subsurface temperatures and hydraulic heads, two local groundwater flow systems which discharge to the Tone River in Gunma Prefecture and to the Kinu River in Tochigi Prefecture, and one regional groundwater自owsystem which recharged in the peripheral area in the plain and discharges to central part of the plain are estimated. Moreover, there are subsurface temperature inversions in shallow layer due to the effect of surface warming. The distribution of inversion in the Kanto Plain has tendency that the depth of inversion in the recharge area is deeper than that in the discharge area, and this tendency suggests the existence of the regional groundwater flow system in the Kanto Plain.
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  • Masaki TAKAHASHl, Hideki IWANO, Yukio YANAGISAWA, Hiroki HAYASHI
    2001 Volume 52 Issue 6-7 Pages 291-301
    Published: July 31, 2001
    Released: March 13, 2015
    The fission track dating was applied for the Kt-7 Tuff, interbedded in the uppermost part of the Miocene Kubota Formation in the eastern Tanagura area, Northeast Japan. The fission track age of the Kt-7 Tuff (10.6±0.3Ma; 1σ error) is almost equal to the K-Ar and fission track ages of the Kt -1 Tuff, interbedded in the lowest part of the Kubota Formation. These radiometric ages show good agreement with the previously established calcareous and siliceous microfossil biostratigraphy. The integrated stratigraphy based on microfossils as well as K-Ar and fission track ages indicate a high sedimentation rate of the Kubota Formation.
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