BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 69 , Issue 4
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Article
  • Minoru Kaneko, Hiroyuki Ishikawa, Masahiro Nomura, Tsutomu Nakazawa
    2018 Volume 69 Issue 4 Pages 211-232
    Published: October 19, 2018
    Released: November 12, 2018
    JOURNALS FREE ACCESS

    Foraminiferal assemblages from the Pleistocene Shimosa Group in core GS-UR-1, Urawa, Saitama City, central Japan are examined. From 51 samples among 98 analyzed samples obtained from the core material, 72 species in 38 genera of benthic foraminifers and 32 species in 8 genera of planktonic foraminifers were identified. Based on the foraminiferal assemblages, 13 foraminiferal zones such as Zones I–IV of the Jizodo Formation, Zones I–III of the Yabu Formation, Zone I of the Kamiizumi Formation, and Zones I–V of the Kioroshi Formation are established in the Shimosa Group, in ascending order. The succession of the foraminiferal assemblages reveals that each formation generally represents an environmental change from an inner bay or a central bay, via a bay mouth, to a central bay, controlled by sea-level change accompanying topographic change. Peaks of the abundance of planktonic foraminifers are observed in Zone I of the Jizodo Formation and Zone II of the Yabu Formation, which indicates that the open ocean water flowed into the Paleo-Tokyo Bay at the timing, and these stratigraphic levels are potential key beds for stratal correlation.

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