Radiolarian biostratigraphy of the Miocene Masuporo and Wakkanai Formations of the Uruyagawa section, Wakkanai, Hokkaido, Japan, with special reference to unconformity

• Motoyama Isao

• Nakamura Sachiko

Bibliographic Information

Other Title

• 北海道稚内市宇流谷川における中新統増幌層と稚内層の放散虫化石層序と不整合境界の再認定
• ホッカイドウ ワッカナイシ ウルヤガワ ニ オケル チュウシントウ マスポロソウ ト ワッカナイソウ ノ ホウサンチュウ カセキソウ ジョ ト フセイゴウ キョウカイ ノ サイニンテイ

Abstract

Radiolarian biostratigraphy was studied for the Miocene Masuporo and Wakkanai Formations in the type section of the Masuporo Formation to understand Miocene radiolarian faunal characters in the northernmost part of Japan and to reassess the unconformable relationship between the two formations. The upper Masuporo Formation yielded radiolarian assemblages that are indicative of Subzone a of the Eucyrtidium inflatum Zone. The Wakkanai Formation is characterized by radiolarian assemblages of the Lychnocanoma magnacornuta Zone. The radiolarian assemblages of Subzone a of the E. inflatum Zone of the studied section contain cosmopolitan or mid-latitude species such as Axoprunum angelinum, Cycladophora cosma cosma, Cyrtocapsella japonica, Cyrtocapsella tetrapera, Eucyrtidium asanoi and Lipmanella redondoensis, and lack such low-latitude species as Didymocyrtis laticonus, Lithopera neotera, Lithopera thornburgi and Calocycletta caepa. These characters resemble to those of radiolarian assemblages reported from the Middle Miocene samples of North Pacific ODP Sites 883, 884 and 887. This indicates that the northern Hokkaido region was under boreal cool water conditions during that time. Based on the radiolarian biostratigraphy, this work newly places the boundary between the Masuporo and Wakkanai Formations of the studied section on the bottom of a gravelly sand-stone bed that is better correlated with the basal bed of the Wakkanai Formation in other areas. This boundary horizon is lying 80 m above the previously indicated one in the same section and characterized by the absence of Subzone b of the Eucyrtidium inflatum Zone. This biostratigraphic result supports previous microfossil studies that indicate a time gap of 1.5 million years between the two formations.

Journal

• The Journal of the Geological Society of Japan

  The Journal of the Geological Society of Japan 108 (4), 219-232_2, 2002

  The Geological Society of Japan

Keywords

• Hokkaido

Details

• CRID: 1390001206238823424
• NII Article ID: 110003013236
• NII Article ID: 10012469859
• NII Book ID: AN00141768
• DOI: 10.5575/geosoc.108.219
• ISSN: 13499963
• ISSN: 00167630
• NDL BIB ID: 6148051
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I6148051
• Data Source:
  • JaLC
  • NDL
  • Crossref
  • CiNii Articles
• Abstract License Flag: Disallowed