High-Resolution Magneto–Climatostratigraphy of MIS 19 from the Osaka Group, Japan

Abstract

Marine oxygen isotope stage (MIS) 19 has an abnormal climate where the temperature maximum postdated by about 5 kyr the sea-level peak in mid-latitudes, and includes the Matuyama–Brunhes magnetic polarity transition that persisted for several kyr. The stratigraphy of this stage must be precisely understood as a candidate for the Early–Middle Pleistocene boundary. The marine clay layer correlated with MIS 19 in the Osaka Group is able to provide millennial-scale magneto–climatostratigraphy because of its high accumulation rate of about 60 cm/kyr. A new age model based on a diatom sea-level proxy curve tuned to oxygen isotope stack LR04 reveals that the sedimentation rate is almost uniform. The following dated events provide a useful time scale: (1) Two high sea-level intervals that span 784–778 ka and 768–762 ka, correlated with substages 19.3 and 19.1, respectively. The first interval includes a sea-level peak at 780 ka. (2) The warmest temperature interval spans 777–774 ka. (3) The low-palaeointensity interval (LPI) spans 784–776 ka and includes multiple polarity swings. We confirm that the LPI is a useful time measure, applying to the preliminary palaeomagnetic results from the Chiba section of the Kazusa Group in eastern Japan. The beginning of the warmest temperature interval almost coincides with the end of the LPI at 777–776 ka and may provide an important datum level near the Early–Middle Pleistocene boundary.