Plio-Pleisatocene environmental changes in Java and hominind evolution and dispersion

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Javan hominid fossils are important to study hominid dispersion, namely "Out-of-Africa" problem. However, their ages have not been established, and still disputed. In this study, we reconstructed paleoenvironmental changes from the Sangiran hominid fossil-bearing formation, central Java, and discuss the relationship between hominid dispersion and environment changes. In addition, a new paleomagnetic dating technique was studied, and tried to apply to the Javan paleomagnetic stratigraphy data. The following results were obtained:(1) A technique of environmental magnetism was first applied to the black clay of the Pucangan (Sangiran) Formation in Sangiran, central Java. As a result, we found a large environmental change that occurred just above the T11 tuff horizon, coincided with the occurrence of the earliest Homo erectus fossil in Sangiran. We confirmed the method was valid to the sediments with less content of biological fossils like pollen or diatom, often used for paleoenvironmental study.(2) Detailed paleoenvironmental study with pollen and diatom fossils is difficult because of poor content, except some parts of the Pucangan (Sangiran) Formation.(3) The magnetostratrigraphy data in Sangiran show that the Upper Olduvai transition represents a number of geomagnetic fluctuations. The same field behavior was observed in the Chinese loess in Baoji, south-central China. Thus we confirmed that it is a real geomagnetic feature, and that the magnetostratigraphic correlation by Hyodo et al. (1992; 1993; 2002) is reasonable.(4) We revealed millennial to submillennial-scale features for the Matuyama-Brunhes polarity transition using a 1700-m core from Osaka Bay. The features are utilized to confirm the magnetostratigraphic correlation in Sangiran.