Episodes 2021; 44(3): 317-347
Published online September 1, 2021
Copyright © International Union of Geological Sciences.
Yusuke Suganuma1,2*, Makoto Okada3, Martin J. Head4, Koji Kameo5, Yuki Haneda1,3,6, Hiroki Hayashi7, Toshiaki Irizuki7, Takuya Itaki6, Kentaro Izumi8, Yoshimi Kubota9, Hiroomi Nakazato10, Naohisa Nishida11, Masaaki Okuda12, Yasufumi Satoguchi13, Quentin Simon14, Yoshihiro Takeshita15
†This paper is dedicated to the memory of the late Prof. Hisao Kumai in appreciation of his crucial work in promoting the Chiba section as a candidate for the Middle Pleistocene GSSP
1National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan
2Department of Polar Science, The Graduate University for Advanced Studies (SOKENDAI), Midori-cho 10-3, Tachikawa, Tokyo 190-8518, Japan
3Department of Earth Sciences, Ibaraki University, 2-2-1 Bunkyo, Mito, Ibaraki 310-8512, Japan
4Department of Earth Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
5Department of Earth Sciences, Chiba University, 1-33 Yayoi, Inage, Chiba, Chiba 263-8522, Japan
6Geological Survey of Japan, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan
7Interdisciplinary Graduate School of Science and Engineering, Shimane University, Nishikawatsucho 1060, Matsue, Shimane 690-8504, Japan
8Faculty and Graduate School of Education, Chiba University, 1-33 Yayoi-cho, Inage, Chiba, Chiba 263-8522, Japan
9Department of Geology and Paleontology, National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan
10Institute for Rural Engineering, NARO, 2-1-6 Kannondai, Tsukuba, Ibaraki 305-8609, Japan
11Department of Environmental Sciences, Tokyo Gakugei University, 4-1-1 Nukuikita, Koganei, Tokyo 184-8501, Japan
12Natural History Museum and Institute, Chiba, 955-2 Aoba-cho, Chuo, Chiba 260-8682, Japan
13Lake Biwa Museum, 1019 Oroshimo-cho, Kusatsu 525-0001, Japan
14CEREGE UM34, Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, 13545 Aix en Provence, France
15Institute of Education, Shinshu University, 6-ro Nishinagano, Nagano 380-8544, Japan
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The Executive Committee of the International Union of Geological Sciences on January 17, 2020 ratified the Global Boundary Stratotype Section and Point (GSSP) defining the base of the Chibanian Stage/Age and Middle Pleistocene Subseries/Subepoch at the Chiba section of the Chiba composite section, Japan. The Chiba composite section is a continuous and expanded marine sedimentary succession in the east-central Japanese archipelago facing the Pacific Ocean. It contains well-preserved pollen, marine micro- and macrofossils, a tightly-defined Matuyama–Brunhes (M–B) paleomagnetic polarity boundary, two geomagnetic field paleointensity proxies, and numerous tephra beds, allowing the establishment of a robust and precise chronostratigraphic framework. Its open-ocean continental slope setting has captured both terrestrial and marine environmental signals from upper Marine Isotope Stage (MIS) 20 to lower MIS 18. The M–B reversal serves as the primary guide for the Lower–Middle Pleistocene boundary, yielding an astronomical age of 772.9 ka. The GSSP is positioned 1.1 m below the directional midpoint of the reversal, at the base of a regional lithostratigraphic marker, the Ontake- Byakubi-E (Byk-E) tephra bed, in the Chiba section. The GSSP has an astronomical age of 774.1 ka and occurs immediately below the top of Marine Isotope Substage 19c.