Japan Geoscience Union Meeting 2016

Presentation information


Symbol S (Solid Earth Sciences) » S-GL Geology

[S-GL39] Lower-Middle Pleistocene Boundary GSSP in the Kazusa Group

Tue. May 24, 2016 9:00 AM - 10:30 AM 201B (2F)

Convener:*Makoto Okada(Department of Earth Sciences, Faculty of Science, Ibaraki University), Yusuke Suganuma(National institute of Polar Research), Osamu Kazaoka(Research Institute of Environmental Geology, Chiba), Chair:Makoto Okada(Department of Earth Sciences, Faculty of Science, Ibaraki University)

10:00 AM - 10:15 AM

[SGL39-05] Detailed variations in diatom assemblages across the Matuyama-Brunhes magnetic polarity boundary from a core collected adjacent to the Chiba section, central Japan

*Ikuko Tanaka1,2, Masayuki Hyodo1,3, Yuusuke Ueno1, Ikuko Kitaba4, Hiroshi Sato5 (1.Department of Earth and Planetary Sciences, Kobe University, 2.The Japan Society for the Promotion of Science, Research Fellow, 3.Research Center for Inland Seas, Kobe University, 4.Research Organization of Science and Technology/Research Centre for Palaeoclimatology, Ritsumeikan University, 5.Institute of Natural and Environmental Sciences, Univ. of Hyogo)

Keywords:Paralia sulcata, MIS 19, Kokumoto Formation, Matuyama-Brunhes magnetic polarity boundary

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.