OSL年代およびAMS^<14>C年代に基づく北海道北部における化石周氷河現象の形成年代の推定

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In northern Hokkaido, only a few absolute ages have been obtained from periglacial phenomena, which characterize the landscape of the area. The present lack of age constraints has prevented studies on precise geomorphic development and terrestrial palaeoenvironmental reconstruction in this area during the last glacial period. The aim of this study is to apply optically stimulated luminescence (OSL) dating and AMS14C dating methods to establish the chronology of fossil frost cracks, periglacial slope deposits, and involutions from a region in northern Hokkaido including Rishiri Island. The samples for OSL dating were taken from five localities. To compare OSL and AMS14C aging, a loess sample for OSL dating and a charcoal sample for AMS14C were collected at Loc. 3 from the same homogeneous silt layer. Besides, at Loc. 4, an OSL and a charcoal sample were collected from a channel deposit. These charcoal samples were subjected to AMS14C dating as independent age controls. OSL ages and calibrated 14C ages from the charcoal were in close agreement in each locality. These results suggest that OSL ages of loess and channel deposit in this study are reliable. From Horonobe (Loc. 1) in the southern Soya hills and from Rishiri Island (Loc. 2), two OSL ages from periglacial slope deposits indicate 21 and 22 ka. Their OSL ages, showing involution from east of Wakkanai (Loc. 3), suggest that the sand was deposited between 54 and 42 ka and that the involution was formed afterwards before 13 ka. At Loc. 4, the fossil frost crack southeast of Cape Soya was formed between 120 and 13 ka, and at Loc. 5, the fossil frost crack was formed between 24 and 15 ka. These results indicate that many periglacial phenomena were possibly formed at about 20 ka in northern Hokkaido.
2011-06-25

OSL年代およびAMS^<14>C年代に基づく北海道北部における化石周氷河現象の形成年代の推定

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