Japan Geoscience Union Meeting 2014

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

[S-GL44_2PM2] The Lower-Middle Pleistocene boundary of the Kazusa Group

Fri. May 2, 2014 4:15 PM - 5:45 PM 421 (4F)

Convener:*Makoto Okada(Department of Earth Sciences, Faculty of Science, Ibaraki University), Chair:Makoto Okada(Department of Earth Sciences, Faculty of Science, Ibaraki University)

5:15 PM - 5:30 PM

[SGL44-12] Tephras of the Kokumoto Formation in the Mobara area

*Hiroomi NAKAZATO1, Futoshi NANAYAMA2 (1.NARO, 2.AIST)

Keywords:tephra, stratigraphy, TNTT

Authors are examining the tephra stratigraphy of the Kazusa Group as part of the geologic map investigation in 1/50,000 Mobara district. The tephras of Ku0.6-Ku6E were confirmed from the Kokumoto Formation. The TNTT tephra (Niitsuma, 1971) which is just above the B/M boundary is pursued to Obota, Chonan town by Okada and Niitsuma (1989). The TNTT is a fine vitric volcanic ash with abundant hornblende (n2=1.680-1.703) and the pumice type volcanic glass (n=1.505-1.510). This tephra was correlated with the tephras from the Older Ontake Volcano (Takeshita et al., 2005). The distribution of the TNTT was confirmed to Baba, Mutsuzawa town in the authors' investigations. Tephras of Ku0.6, Ku0.9 and Ku2.5 were confirmed in Terasaki, Mobara city where is the northeast limit of distribution of the Kokumoto Formation. The TNTT and the B/M boundary horizon are able to trace to this region.