Japan Geoscience Union Meeting 2019

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[J] Oral

S (Solid Earth Sciences ) » S-GL Geology

[S-GL28] Regional geology and tectonics

Mon. May 27, 2019 9:00 AM - 10:30 AM A09 (TOKYO BAY MAKUHARI HALL)

convener:Makoto Otsubo(Geological Survey of Japan, Research Institute of Earthquake and Volcano Geology), Jun Hosoi(Geological Survey of Japan, Institute of Geology and Geoinformation, AIST), Chairperson:Makoto Otsubo(Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan)

9:30 AM - 9:45 AM

[SGL28-03] New age constraints and tectonic significance of Late Oligocene marine biosiliceous deposits in the Hidaka Belt, northeastern Hokkaido, northern Japan

*Futoshi Nanayama1,6, Hiroshi Kurita2, Toru Yamasaki1, Jun Tajika3, Hideki Iwano4, Tohru Danhara4, Takafumi Hirata5 (1.Geological Survey of Japan, AIST, 2.Niigata Univ., 3.Docon Co. Ltd, 4.Kyoto Fission-Track Co. Ltd, 5.Tokyo Univ., 6.CWMD, Kumamoto Univ.)

Keywords:LA-ICP-MS U-Pb age, late Oligocene to early Miocene, Tatsuushi Formation, Hidaka Belt, Hidaka Supergroup, Dinoflagellate cysts

The Tatsuushi Formation distributed in the Kitami-Monbetsu area consisted of siliceous mudstone, and has been incorporated into the Hidaka Supergroup along associated with the surrounding the Uenkotan and Rurochi Formations (Tajika and Iwata, 1994). In this study, the depositional age of the Tatsuushi Formation was examined by three methods. Detrital zircon grains are separated from turbidite sandstone and a U-Pb age of 27.2 ± 0.1 Ma is obtained by the LA-ICP-MS method. Dinoflagellate cysts indicate late Oligocene and early Miocene, respectively. Therefore, the U-Pb age is shown as the depositional age of this formation. The depositional age of the Hidaka Supergroup has been reported Paleocene to Early Eocene so far. Therefore, it is difficult to include this formation in Hidaka Supergroup. The Tatsuushi Formation can be compared to the Erimo Formation in the soutjern Hidaka Belt (Kurita and Kusunoki, 1997) and the lower part of the Tsubetsu and Kawakami Groups based on their depositional ages and affinity of the lithology (Kurita et al., 1998) distributed along the Abashiri tectonic line as the right-lateral strike-slip fault since late Oligocene. These siliceous mudstones may have been formed by the upwelling flow caused by the bottom deepwater brought from the Sea of Okhotsk by the opening of the Kuril basin.

This work was supported by JSPS KAKENHI Grant Number 16K05585.

(References) Kurita and Kusunoki, 1997, Jour. Geol. Soc. Japan, 103, 1179-1182. Kurita et al., 1998, Research reports of JAPEX Research Center, no. 13, 11-31. Tajika and Iwata, 1994, Chikyu monthly, 16, 495-499.