Age model, physical properties and paleoceanographic implications of the middle Pleistocene core sediments in the Choshi area, central Japan

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 δ 18 O and δ 13 C 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.

MIS11–19 pollen stratigraphy from the 250‐m Choshi core, northeast Boso Peninsula, central Japan: Implications for the early/mid‐Brunhes (400–780 ka) climate signals

“…1999). Our pollen signals are primarily consistent with δ 18 O from the Choshi core (initially presented by El‐Masry 2002; refined by Kameo et al . 2006), correlating pollen zones CH9 (19–33 m), CH8 (33–48 m), CH7‐5 (48–119 m), CH4 (119–128 m), CH3 (128–140 m) and CH2‐1 (140–167 m) with MIS11, MIS12, MIS13–15, MIS16, MIS17 and MIS18–19, respectively.…”

“…2006), correlating pollen zones CH9 (19–33 m), CH8 (33–48 m), CH7‐5 (48–119 m), CH4 (119–128 m), CH3 (128–140 m) and CH2‐1 (140–167 m) with MIS11, MIS12, MIS13–15, MIS16, MIS17 and MIS18–19, respectively. This primary age model is supported by other multiproxy records (El‐Masry 2002; Kameo et al . 2006).…”

“…2006). The cool signal was initially visualized at 100–108 m by El‐Masry (2002), and afterwards in revised δ 18 O and δ 13 C records by Kameo et al . (2006).…”

“…The Choshi core covers the time ranges of the Umegase, Kokumoto, Kakinokidai, Chonan, Kasamori, Kongochi and Jizodo Formations of the Kazusa–Shimosa Groups, spanning 395–925 ka (MIS11–25). The B–M paleomagnetic boundary (780 ka) is recognizable at a depth of 162–169 m, with the best estimate being 168 m (El‐Masry 2002; Kameo et al . 2006).…”

Early Pleistocene evolution of the Japan Sea Intermediate Water

“…Igarashi, 1994;Pickering et al, 1999; Kameo et al, 2006;Kitamura et al, 2008). In addition, anoxic conditions within intermediate water have not been identified from sediments deposited in the Japan Sea during interglacial periods (Kido et al, 2007).…”