[S-GL38] 上総層群における下部ー中部更新統境界GSSP

[SGL38-07] 千葉複合セクションにおける松山ーブルネ極性反転記録

*岡田 誠¹、菅沼 悠介²、丸岡 亨¹、羽田 裕貴¹、風岡 修³ (1.茨城大理、2.国立極地研、3.千葉県地質環境研)

キーワード：千葉セクション, 中部ー下部更新統境界GSSP, 古地磁気学, 松山ーブルン境界

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.