09:15 〜 09:30
[BCG07-02] The Jurassic-Cretaceous boundary and the Mariana radiolarian fauna
キーワード：マリアナ海溝、放散虫、ジュラ紀/白亜紀境界、化石鉱脈
Despite being one of the most significant geological sequence boundaries in the Mesozoic Era, the Jurassic-Cretaceous boundary (JKB) remains undefined. It is the last “system” boundary in the geological time scale without a designated Global Boundary Stratotype Section and Point (GSSP). In 2020, the former Berriasian Working Group (BWG) proposed a GSSP candidate for the JKB, but it was not supported by the International Subcommission on Cretaceous Stratigraphy. A new BWG was formed in 2021 and has been conducting further considerations. The scope of the study has been expanded both upwards and downwards from the previously proposed JKB, rather than the nearby layers of the boundary so far.
The Mariana Radiolarian Fauna came from the Mariana Trench and is dated around the JKB. The fauna was obtained in 1993 by a Japanese submergible “Shinkai 6500” belonging to the Japan Agency for Marine-Earth Science and Technology. A single rock sample of tuffaceous clayey radiolarite (D-181-R-003) is regarded as one of fossil Largerstätten because it contains extremely-well preserved radiolarian tests with diversified morphotypes. The Mariana Fauna has been utilized not only for scientific research but also for education and outreach activities for more than 30 years since its discovery. Outreach items include calendars (Figure), playing cards, a pictorial book and others. The geological age of the fauna has not been determined precisely because the definition of the JKB itself is still under discussion and the GSSP is not decided yet. Although the fauna has been dated as an early Berriasian age, this age assignment can be changed depending on the definition of the JKB.
The Mariana Radiolarian Fauna came from the Mariana Trench and is dated around the JKB. The fauna was obtained in 1993 by a Japanese submergible “Shinkai 6500” belonging to the Japan Agency for Marine-Earth Science and Technology. A single rock sample of tuffaceous clayey radiolarite (D-181-R-003) is regarded as one of fossil Largerstätten because it contains extremely-well preserved radiolarian tests with diversified morphotypes. The Mariana Fauna has been utilized not only for scientific research but also for education and outreach activities for more than 30 years since its discovery. Outreach items include calendars (Figure), playing cards, a pictorial book and others. The geological age of the fauna has not been determined precisely because the definition of the JKB itself is still under discussion and the GSSP is not decided yet. Although the fauna has been dated as an early Berriasian age, this age assignment can be changed depending on the definition of the JKB.