Hisao Kumai

High-resolution record of the Matuyama–Brunhes transition constrains the age of Javanese Homo erectus in the Sangiran dome, Indonesia

A detailed paleomagnetic study conducted in the Sangiran area, Java, has provided a reliable age constraint on hominid fossil-bearing formations. A reverse-to-normal polarity transition marks a 7-m thick section across the Upper Tuff in the Bapang Formation. The transition has three short reversal episodes and is overlain by a thick normal polarity magnetozone that was fission-track dated to the Brunhes chron. This pattern closely resembles another high-resolution Matuyama–Brunhes (MB) transition record in an Osaka Bay marine core. In the Sangiran sediments, four successive transitional polarity fields lie just below the presumed main MB boundary. Their virtual geomagnetic poles cluster in the western South Pacific, partly overlapping the transitional virtual geomagnetic poles from Hawaiian and Canary Islands’ lavas, which have a mean 40Ar/39Ar age of 776 ± 2 ka. Thus, the polarity transition is unambiguously the MB boundary. A revised correlation of tuff layers in the Bapang Formation reveals that the hominid last occurrence and the tektite level in the Sangiran area are nearly coincident, just below the Upper Middle Tuff, which underlies the MB transition. The stratigraphic relationship of the tektite level to the MB transition in the Sangiran area is consistent with deep-sea core data that show that the meteorite impact preceded the MB reversal by about 12 ka. The MB boundary currently defines the uppermost horizon yielding Homo erectus fossils in the Sangiran area.

A Potential Lower–Middle Pleistocene GSSP with Excellent Magnetostratigraphy Along the West Pacific Margin: The Chiba Section, Central Japan

The Chiba section in Japan represents a potential global boundary stratotype section and point (GSSP) for the Lower–Middle Pleistocene Subseries/Subepoch. The proposed GSSP is placed at the base of the Byakubi ash bed, a regional marker directly correlated to the Matuyama–Brunhes magnetic reversal, which is the primary guide for the Lower–Middle Pleistocene boundary. The Byakubi ash bed occurs within the 2000-m-thick Kazusa Group, which was deposited in bathyal to shelf palaeoenvironments during the Early and Middle Pleistocene. In addition to the numerous marine stratigraphies already studied, this section offers potential correlation to Chinese loess stratigraphy.