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

[SGL39-02] Zircon LA-ICP-MS U-Pb dating on some Quaternary tephras in Boso Peninsula

*Hisatoshi Ito¹, Futoshi Nanayama², Hiroomi Nakazato³ (1.Central Research Institute of Electric Power Industry, 2.National Institute of Advanced Industrial Science and Technology, 3.National Agriculture and Food Research Organization)

Keywords:U-Pb dating, zircon, tephra, Matuyama-Brunhes boundary

Zircon U-Pb dating using LA-ICP-MS was applied to some Quaternary tephras in Boso Peninsula, central Japan. Accurate age determination of these tephras is of critical importance because they are relevant to a candidate site for the Global Boundary Stratotype Section and Point of the early-middle Pleistocene boundary. Recently, a precise zircon SHRIMP U-Pb age of 0.773 ± 0.007 Ma from a tephra just below the Matuyama-Brunhes (MB) boundary was reported (Suganuma et al., 2015). Here, we show other precise zircon LA-ICP-MS U-Pb ages from the Ks11 and Ch2 tephras above the MB boundary. The Ks11 tephra yielded a weighted mean age of 0.52 ± 0.04 Ma and the Ch2 tephra yielded a weighted mean age of 0.61 ± 0.02 Ma, both of which are in agreement with the stratigraphy. The good agreement between zircon U-Pb ages and the stratigraphy validates the reliability of the established stratigraphy and our dating approach. These U-Pb ages should help to further establish Japanese and worldwide Pleistocene chronostratigraphy.