Nine human remains were recovered from Shiraho-Saonetabaru Cave on Ishigaki Island, Okinawa Prefecture, Japan, between 2007 and 2009. Six of the nine samples produced well-preserved biogenic collagen, which was submitted to radiocarbon dating by accelerator mass spectrometry. Three human samples (Nos. 2, 4, and 8) from the fossil chamber were dated to between 16 and 20 ka BP, and can clearly be assigned to the Late Pleistocene. One animal bone from the same chamber which was treated and measured for radiocarbon independently was also of great antiquity (c. 12 ka BP). These dates are the first concrete evidence of human occupation on the Ryukyu Islands during the Pleistocene, based on the direct radiocarbon dates of human remains. It is expected that more human remains and archaeological objects of the Pleistocene will be recovered from Shiraho-Saonetabaru Cave and the surrounding region by future intensive collaborations between anthropologists, archaeologists, and speleologists.
Newly determined remanent magnetization directions of both tephras and fine-grained clastic sediments are used to redefine the Gauss-Matuyama boundary (GMB) in the Tokai Group of central Japan. Samples collected from sites within a ~-m-thick sedimentary sequence were subjected to progressive thermal or alternatingfield demagnetization, and the demagnetization data were statistically analyzed to determine site-mean remanent magnetization directions. Demagnetization results and rock magnetic experiments show that most samples contain magnetite as the dominant magnetic carrier and that most samples also contain hematite. In the northern part of the Kameyama area in Mie Prefecture, the GMB lies about m below the Reiho volcanic ash bed. This finding is clearly different from a previous magnetostratigraphic study that determined the Reiho ash bed to be of normal polarity and that placed the GMB above the bed. A recent tephrostratigraphic study proposed that the Reiho ash bed could be correlated with a tephra bed below the GMB in a sedimentary sequence on the Boso Peninsula, more than km to the east of the present study area, but this idea needs to be reconsidered. The site-mean directions, which include those reported from above the Reiho ash bed, pass a reversals test and yield an overall mean direction that provides a reliable paleomagnetic direction for the latest Pliocene to earliest Pleistocene (around. Ma). The mean direction is marked by a slight easterly deflection of declination from the north, and this raises the possibility that during the Quaternary, a small but significant clockwise rotation (.. °) occurred in the study area with respect to Earth s rotational axis.
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