[H-QR05] Quaternary, Diachronic dynamics of human-environment interactions

[HQR05-P09] Discovery of Aso-3 Tephra in the Omaezaki Area (Preliminary Report)

*Toshinori Sasaki¹, Takuya Morimoto², Shohei Oonaka³, Hisanori Oominami², Komei Nishimura², Tatsuyuki Ueno⁴, Norihisa Goto⁴ (1.Central Research Institute of Electric Power Industry, 2.Chubu Electric Power Company, Incorporated, 3.Dia Nippon Engineering Consultants Co., Ltd., 4.Hanshin Consultants Co., Ltd.)

Keywords:Aso-3 tephra, Furuya Layer, Omaezaki Area

It reports the identification of vitric tephra within the Lower Furuya Layer (Ikeya and Horie, 1982; Hisamatsu et al., 2024) distributed in the Omaezaki region of Shizuoka Prefecture, Japan. This tephra, temporarily named SKR Tephra, was observed through trenching and boring core samples as part of a fault investigation, showing a consistent layer thickness of about 3 cm across all trench faces. Microscopic examination revealed fine volcanic glass as the primary component, with the presence of heavy minerals, orthopyroxene. The volcanic glass, mostly of very fine sand size, includes bubble-wall type particles in clear and brownish varieties, with a ratio of approximately 7:3 between them. Refractive index measurements and principal component analysis of the volcanic glass indicate distinct characteristics, suggesting a strong correlation with Aso-3ii tephra (Matsu’ura et al., 2021). The Aso-3ii tephra is associated with Marine Isotope Stage 6 based on stratigraphy in the MD012422 core off Shikoku and U1437B core off the Izu Islands (Matsu’ura et al. 2021, 2023). However, due to similarities in refractive indices and major components with Aso-3 tephra and the several widespread tephra with similar characteristics between Aso-2 and Aso-4 (Nagahashi et al., 2007), a correlation study with the Aso-3 pyroclastic flow deposits near the source is being undertaken.
References:
Ikeya and Horie (1982) Quat. Res. (Jpn), 21(2), 75-93.
Hisamatsu et al. (2024) Bul. of the Mus. of Nat. and Env. Hist., Shizuoka, in press.
Matsu’ura et al. (2021) Quat. Sci. Rev. 257, 106808.
Matsu’ura et al. (2023) Quat. Sci. Rev. 319, 108305.
Nagahashi et al. (2007) Quat. Res. (Jpn), 46(4), 305-325.