11:00 〜 11:15
[MIS20-02] ジュラ系・白亜系境界と放散虫のバイオイベント
キーワード：ジュラ系・白亜系境界、GSSP、放散虫、進化系列、太平洋
The Global Boundary Stratotype Section and Point (GSSP) of the Jurassic/ Cretaceous (J/K) boundary is the last among the GSSPs in the Phanerozoic. It will be defined the base of the Berriasian Stage. The definition was decided as the evolutionary first appearance biohorizon of Calpionella alpina by the Berriasian Working Group in the International Subcommission on Cretaceous Stratigraphy. Unfortunately, the primary marker cannot be found in the Pacific and circum-Pacific areas since the distribution of Calpionella is limited to the western Tethys regions. To determine the base of the Berriasian outside of the western Tethys, alternative proxies are needed. Radiolarians are good candidates for determining the J/K boundary. Evolutionary series of several radiolarian lineages across the J/K boundary are reviewed and suitable bioevents, which are approximate to the J/K boundary, are proposed. These lineages include the genera Eucyrtidiellum, Cinguloturris, Ristola, Hemicryptocapsa, and Pseudodictyomitra.