Research directed toward high precision obsidian hydration dating

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Geological and archaeological obsidians from Easter Island (Chile), Takayama obsidian-mining source (Nagano), Nojiriko group (Nagano) and Nakamoto (Hokkaido) archaeological sites were analysed for their main and trace element content using the instrumental activation analysis expanded from 7 to 23 elements and the 17-element X-ray fluorescence analysis. As a result, hitherto indiscriminable obsidian outcrops become discriminated by improved INAA and EDXRF.The accelerated obsidian hydration experiments were standardized initially at the elevated temperatures of 104, 126, and 152 degree Celsius for the durations of 4, 8, 16, 32, and 64 weeks, and then subsequently applied to obtain the hydration rates of geological and archaeological obsidians at the respective soil temperatures and soil relative humidities that were directly measured by cell-pairs buried at the sites for 1 year before the measurements.Nearly fifty burnt obsidians from archaeological sites are collected and dated using the fission track dating method, thus allowing the possibility to calibrate the carbon-14 dates older than 10 thousands B.P.that are out of the calibration range of C-14 dating by using the tree-ring chronology.The obsidian hydration dating method is temperature dependent, giving the ages younger or older according to the thermal history of obsidian specimens. Therefore, extrapolation into the past is possible if we combine FT dates or well-calibrated C-14 dates with corresponding obsidian hydration dates, and a reconstruction of the palaeoclimate surroundings of the archaeological sites becomes plausible.