Japan Geoscience Union Meeting 2015

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

[S-GL38] Lower-Middle Pleistocene Boundary GSSP in the Kazusa Group

Mon. May 25, 2015 11:00 AM - 12:45 PM 102B (1F)

Convener:*Makoto Okada(Department of Earth Sciences, Faculty of Science, Ibaraki University), Yusuke Suganuma(National institute of Polar Research), Osamu Kazaoka(Research Institute of Environmental Geology, Chiba), Chair:Yusuke Suganuma(National institute of Polar Research), Osamu Kazaoka(Research Institute of Environmental Geology, Chiba)

11:45 AM - 12:00 PM

[SGL38-07] Revised Matuyama-Brunhes polarity transition record from a marine succession at the Chiba composite section

*Makoto OKADA1, Yusuke SUGANUMA2, Toru MARUOKA1, Yuki HANEDA1, Osamu KAZAOKA3 (1.Dept. Earth Sci., Ibaraki Univ., 2.National Inst. Polar Res., 3.Res. Inst. Env. Geol., Chiba Pref.)

Keywords:Chiba section, M-L Pleistocene boundary GSSP, Paleomagnetism, Matuyama-Brunhes boundary

We report revised paleomagnetic records of the Matuyama-Brunhes (M-B) polarity transition from a continuous marine succession at the Chiba section of the Kokumoto Formation, Kazusa Group. The Chi-ba section is the one of the candidate sites for the Lower-Middle Pleistocene Boundary GSSP. An age model for the section, provided by newly obtained oxygen isotopes of benthic foraminifera from a 100 meters succession across the M-B boundary, indicates that the boundary is situated in the interglacial per-iod of MIS19. We have taken 130 oriented mini-cores from a 13 meters succession across the Byk-E tephra bed at the Chiba section and the Yanagawa section. Thermal magnetic experiments suggest that the samples include iron sulfides, magnetites but no hematite. Measurements of magnetic hysteresis indicate that the magnetic domain state is PSD. Progressive alternating field (AF) demagnetization indicate a re-versed to normal polarity transition boundary is at around 1.5 meter below the Byk-E bed as well as pre-vious studies, however the transition boundary is observed at around 1 meter above the Byk-E bed in thermal demagnetization results. Therefore, the reversed to normal polarity transition boundary seen be-low the Byk-E bed is thought to be overprint. This overprints, which might be carried by iron sulfide, are particularly observed in a transitional interval. The virtual geomagnetic pole (VGP) latitudes and prelimi-nary derived paleointensities using thermal demagnetizations from the Chiba section quite match well with the U1308 records. We will show globally comparable VGP and paleointensity records during the M-B polarity transition at the Chiba section.