期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 108, 期 49, 页码 19563-19568出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1113106108
关键词
paleomagnetism; marine isotope stage 19; magnetostratigraphy; geochronology
资金
- Japan Society for the Promotion of Science [13440255, 1540315, 18200053, 22320154]
- Center for Advance Marine Core Research, Kochi University (CMCR) [05B020, 09A006]
- Center for Geological Survey, Geological Agency, Indonesia
- Grants-in-Aid for Scientific Research [22320154, 10J00341, 22340154, 13440255, 18200053] Funding Source: KAKEN
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.
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