Molluscan fauna of the “Miocene" Namigata Formation in the Namigata area, Okayama Prefecture, southwest Japan

• Matsubara Takashi

  Division of Natural History, Museum of Nature and Human Activities Hyogo

Bibliographic Information

Other Title

• 岡山県浪形地域の“中新統”浪形層の貝類化石群

Abstract

The molluscan fauna of the Namigata Formation, traditionally accepted to be of Miocene age, are reexamined taxonomically, and the geologic age of the formation and its paleogeographic implications are discussed. The formation is subdivided into the main part and two new members (the Senjuin Shell-Sandstone and Ônishi Conglomerate members). The Namigata Formation yielded 13 species of Gastropoda, 16 species of Bivalvia and 1 species of Scaphopoda. The occurrences of Molopophorus watanabei Otuka, Acila (Truncacila) nagaoi Oyama and Mizuno, Chlamys (Nomurachlamys?) namigataensis (Ozaki), and Isognomon (Hippochaeta) hataii Noda and Furuichi indicate that the molluscan age should be revised to the late Late Eocene-Early Oligocene. Taking account of the latest elasmobranch data and preliminary strontium isotope ratio, the age of the formation is confined to the late Late Eocene. The present and recent results show that the First Seto Inland Sea was actually composed of two sea areas that existed at different times: the Paleogene sea area is estimated to have been an open sea facing south to the Pacific Ocean, whereas that in the Miocene is thought to have been an embayment connected to the northwest to the Sea of Japan. Therefore, the concept of the so-called Miocene First Seto Inland Sea should be reassessed in the Cenozoic geohistory of the Japanese Islands.<br>Selected molluscan species including Felaniella (Felaniella) namigataensis n. sp. are taxonomically described and/or discussed.

Journal

• The Journal of the Geological Society of Japan

  The Journal of the Geological Society of Japan 119 (4), 249-266, 2013-04-15

  The Geological Society of Japan

Keywords

• First Seto Inland Sea
• geologic age
• Mollusca
• Namigata Formation
• taxonomy
• paleogeography

Details

• CRID: 1390282681218849280
• NII Article ID: 130003363931
• NII Book ID: AN00141768
• DOI: 10.5575/geosoc.2012.0048
• COI: 1:CAS:528:DC%2BC3sXos1ymsL4%3D
• ISSN: 13499963
• ISSN: 00167630
• NDL BIB ID: 024638583
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I024638583
• Web Site: https://www.jstage.jst.go.jp/article/geosoc/119/4/119_2012.0048/_pdf
• Text Lang: ja
• Data Source:
  • JaLC
  • NDL
  • Crossref
  • CiNii Articles
  • KAKEN
• Abstract License Flag: Disallowed