A summary of the Chiba Section, Japan

千葉セクション

Yuki Haneda , Hiroki Hayashi , Misato Hongo , Kenji Horie , Masayuki Hyodo , Atsuo Igarashi , Osamu Ishizuka , Toshiaki Irizuki , Takuya Itaki , Kentaro Izumi , Koji Kameo , Moto Kawamata , Kenji Kawamura , Jun-Ichi Kimura , Takahiro Kojima , Yoshimi Kubota , Hiroomi Nakazato , Naohisa Nishida , Itaru Ogitsu , Makoto Okada , Masaaki Okuda , Jun’ichi Okuno , Yasufumi Satoguchi , Ryoko Senda , Quentin Simon (1) , Testuo Sueyoshi , Kizuku Shikoku , Yusuke Suganuma , Manami Sugaya , Yoshihiro Takeshita , Mami Takehara , Masami Watanabe , Hisashi Yabusaki , Takeshi Yoshida

1 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

We propose the extensively studied Chiba section of the Chiba composite section (CbCS) as the Global Boundary Stratotype Section and Point (GSSP) to define the base of the Middle Pleistocene Subseries and Chibanian Stage. The CbCS is a continuous and expanded marine sedimentary succession within the middle of the Ko-kumoto Formation, Boso Peninsula, Chiba Prefecture. It contains well-preserved pollen, marine micro-and macrofossils, a tightly-defined Matuyama-Brunhes (M-B) paleomagnetic polarity boundary, and numerous tephra beds, allowing the establishment of a robust and precise chronostratigraphic framework across the Lower-Middle Pleistocene boundary. Its deep-marine, open-ocean continental slope setting, coupled with high sedimentation rates with no evidence of abrupt deposition, has resulted in preserving both terrestrial and marine environmental changes in and around Marine Isotope Stage (MIS). We have performed high-resolution oxygen isotope analysis , as well as detailed sedimentological, geochemical, and biostrati-graphic studies of the CbCS, confirming the completeness of the stratigraphic interval spanning the Lower-Middle Pleistocene boundary. The M-B polarity boundary serves as the agreed primary guide for the Lower-Middle Pleistocene boundary, and the CbCS represents one of the most detailed marine sedimentary records yet obtained for this reversal, yielding an astronomical age of. ka with a duration of ca.. kyr. This section therefore offers an exceptional opportunity to calibrate the geological time scale as well as understand the dynamics of the geodynamo. The widespread Byk-E tephra lies close to the reversal, allowing precise regional lithostrati-graphic correlation. The CbCS is easy to access from international airports. The section will be permanently preserved and maintained by the local government as a natural monument. Based on these attributes , the base of the Byk-E tephra bed in the Chiba section is the best horizon for establishing the GSSP that will define the Lower-Middle Pleistocene boundary.

Mots clés: Matuyama-Brunhes boundary; Chiba composite section; Lower-Middle Pleistocene boundary; Marine Isotope Stage (MIS) 19; Global Boundary Stratotype Section and Point (GSSP)

Domaines: Planète et Univers [physics]; Sciences de la Terre

Yuki Haneda, Hiroki Hayashi, Misato Hongo, Kenji Horie, Masayuki Hyodo, et al.. A summary of the Chiba Section, Japan. Journal of the Geological Society of Japan, 2019, 125 (1), pp.5-22. ⟨10.5575/geosoc.2018.0056⟩. ⟨hal-02340017⟩