Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

H (Human Geosciences) » H-QR Quaternary research

[H-QR04] Quaternary, Diachronic dynamics of human-environment interactions

Sun. May 20, 2018 1:45 PM - 3:15 PM A08 (Tokyo Bay Makuhari Hall)

convener:Mamoru Koarai(Earth Science course, College of Science, Ibaraki University), Toshihiko Sugai(Department of Natural Environmental Studies, Institute of Environmental Studies, Graduate School of Frontier Science, The University of Tokyo), Kiyohide Mizuno(国立研究開発法人産業技術総合研究所地質情報研究部門, 共同), Minoru YONEDA(The University Museum, The University of Tokyo), Chairperson:Mizuno Kiyohide, Aoki Kaori

2:45 PM - 3:00 PM

[HQR04-10] Integrated stratigraphy of the early Pleistocene Sakishima Formation in the Shima Peninsula, Mie Prefecture

*Rei Nakashima1, Masayuki Utsunomiya1, Takeyuki Ueki2, Kiyohide Mizuno1, Hirokuni Oda1 (1.Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology, 2.Chiba Institute of Science)

Keywords:Early Pleistocene, Volcanic ash, Paleomagnetism, Calcareous nano fossil, Sakishima Formation

The Early Pleistocene Sakishima Formation is distributed in Isobe-cho, Shima City, Mie Prefecture. The formation is a valley-fill deposits covering the Shimanto belt rocks which forms the basement of the southern part of the Shima peninsula. And it is covered by the middle/lower terrace deposits. The Sakishima Formation intercalates the Isobe volcanic ash, and this volcanic ash was compared with Shishimuta Azuki Volcanic Ash (Ss-Az) in the Ma3 marine clay layer (MIS 21: reverse polarity in the Matuyama chron) of the Osaka Group (Machida and Arai, 2003). On the other hand, Tanioka et al. (2004) showed the paleomagnetism of the Sakishima Formation is the normal polarity. As mentioned above, the depositional age of the Sakishima Formation is not clear yet. Therefore, we reexamined the petrological features of Isobe volcanic ash and palaeomagnetism, and conducted to analyze calcareous nannofossils at the type section of the Sakishima Formation.

As a result of the analyze of the shape of the volcanic glass shards, refractive index and chemical composition of the glass shards and orthopyroxene, we could compare the Isobe volcanic ash with the Shishimuta Azuki volcanic ash. As for paleomagnetic analysis, we found that the upper and lower layers including Isobe volcanic ash are all inverse magnetized. About calcareous nannofossils, mudstone 1-2 m below the Isobe volcanic ash contains Reticulofenestra asanoi, Gephyrocapsa parallela and Pseudoemiliania lacunosa. Co-occurrence of these species imply the geologic age of the mudstone is MIS 30-21 in the Matuyama chron. To summarize the above results, we reconfirmed that the Sakishima Formation is included in the Matuyama chron, and the Isobe volcanic ash is compared with Shishimuta Azuki volcanic ash in the Osaka Group.