Age model, physical properties and paleoceanographic implications of the middle Pleistocene core sediments in the Choshi area, central Japan |
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| Authors: | Koji Kameo Makoto Okada Moamen El-Masry Toshio Hisamitsu Saneatsu Saito Hiroomi Nakazato Naohiko Ohkouchi Minoru Ikehara Hisato Yasuda Hiroshi Kitazato and Asahiko Taira |
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| Institution: | Marine Biosystems Research Center, Chiba University, c/o Department of Earth Sciences, Chiba University, 1-33 Yayoi, Inage, Chiba, Chiba 263-8522, Japan (email: ),;Department of Environmental Sciences, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan,;Geology Department, Faculty of Science, Suez Canal University, Ismailia, Egypt,;Center for Deep Earth Exploration, Japan Agency for Marine-Earth Science and Technology, 3173-25, Showa, Kanazawa, Yokohama, Kanagawa 236-0001, Japan,;IODP Management International, Inc., Sapporo Office CRIS, Hokkaido University, N21W10 Kita, Sapporo, Hokkaido 001-0021, Japan,;Laboratory of Disaster Prevention, National Institute for Rural Engineering, 2-1-6, Kannondai, Tsukuba, Ibaraki 305-8609, Japan,;Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan,;Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan |
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| Abstract: | Abstract A continuous, well-preserved core was obtained from the Choshi area, on the Pacific side of Japan, to investigate paleoceanographic and paleoclimatic changes around the northwestern Pacific region during the middle Pleistocene. Siliciclastic sequences in the core are divided into five formations – the Obama, Yokone, Kurahashi and Toyosato Formations in the Inubo Group and the Katori Formation, in ascending order. Examination of calcareous nannofossils and magnetic polarities detected four datums in the core sediments of the Inubo Group: the top of Reticulofenestra asanoi , the base of Helicosphaera inversa , the top of Pseudoemiliania lacunosa and the Brunhes–Matuyama boundary. Fourteen marine isotope stages (MIS24–MIS11) were identified in the δ18O and δ13C records based on detected datums and the graphic correlation with the standard stack oxygen isotope curve. Magnetic susceptibility and gamma-ray attenuation porosity evaluator density were also measured and low values characterize the glacial intervals. Biogenic sedimentation by primary production may be larger during the glacial periods because of invasions of nutrient-rich northern surface-waters related to the southward shift of the Kuroshio front in the Choshi area. |
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| Keywords: | age model calcareous nannofossils Choshi area middle Pleistocene magnetostratigraphy northwestern Pacific oxygen isotope record physical property |
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