[S-GL39] 上総層群における下部ー中部更新統境界GSSP

[SGL39-05] 房総半島マツヤマ－ブリュンヌ地磁気逆転境界における高解像度珪藻化石群集解析

*田中 郁子^1,2、兵頭 政幸^1,3、上野 友輔¹、北場 育子⁴、佐藤 裕司⁵ (1.神戸大学大学院理学研究科、2.日本学術振興会特別研究員、3.神戸大学内海域教育研究センター、4.立命館大学古気候学研究センター、5.兵庫県立大学　自然・環境科学研究所)

キーワード：パラリア・サルカータ、MIS 19、国本層、マツヤマ－ブリュンヌ地磁気逆転境界

We conducted diatom analysis of a core named TB2 of the Kokumoto Formation of the Kazusa Group drilled near the Chiba section, a candidate for the Early to Middle Pleistocene boundary. 71 taxa of diatoms were identified. The number of total valves is controlled by coastal species such as Paralia sulcata, Cyclotella striata + C. stylorum, and Actinoptychus senarius. The coastal species show variations well correlated with the ratio of Ca/Ti, a biological production proxy, and planktonic δ¹⁸O, representing the highest peak at 44.5-33.9m and the second one at 19.9-14.8m. The former is correlated with highstand MIS 19.3 and the latter with highstand MIS 19.1. This result suggests not only the biogenic production rate but the production of coastal diatom species increases as the sea-level rise. Cold diatom species of the Oyashio Current are dominant below a depth of 25 m, and warm species of the Kuroshio Current become dominant above it. This suggests occurrence of a large current system change during MIS 19.