A synthetic study of the Paleocene molluscan faunas in Japan

2022 Fiscal Year Final Research Report

• Project/Area Number: 18K03817
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17050:Biogeosciences-related
• Research Institution: Hokkaido University of Education
• Principal Investigator: Matsubara Takashi 北海道教育大学, 教育学部, 教授 (30311484)
• Project Period (FY): 2018-04-01 – 2023-03-31
• Keywords: 暁新世 / 貝類化石群 / 分類学 / 古生物地理学

Outline of Final Research Achievements

To clarify the characteristics of Paleocene molluscan faunas in Japan, I investigated the following areas: the Hamatonbetsu area in northern Hokkaido, the Kon-Sen district in eastern Hokkaido, the Sukumo area in eastern Shikoku, and the Amakusa-Shimojima area in western Kyushu. As a result, some new species can be discriminated. It became clear that the molluscan fauna of the Okuutsunai Member of the Hakobuchi Formation in the Hamatonbetsu area, characterized by the abundant occurrence of glycymeridid bivalves, is a sole Paleocene shallow marine molluscan fauna in Japan. In addition, it became obvious that Paleocene deep sea molluscan assemblages between South Sakhalin and western Shikoku are characterized by protobranch bivalves as Acila (Truncacila) hokkaidoensis and apporhaid gastropods. It is suggested that the Paleocene molluscan faunal turnover had occurred before the Paleocene-Eocene Thermal Maximum (PETM) in the Northwestern Pacific.

Free Research Field

古生物

Academic Significance and Societal Importance of the Research Achievements

本研究の結果，これまで明らかではなかった北海道浜頓別地域の函淵層奥宇津内部層や根釧地区霧多布層・汐見層，高知県宿毛地域の百笑層の貝類化石群の群集組成が明らかとなったほか，いくつかの新種が確認できた。また，暁新世の深海性貝類化石群は南サハリンから四国西部まで同一の古生物地理区に属していたことが明らかとなった．さらに，汐見層の貝類化石群の研究を通じて，日本の暁新世の貝類化石群の組成の転換は暁新世-始新世境界の最温暖期（PETM）よりも前に起こっていたことが示唆された。