Speleothem dating in Norway: an interglacial chronology |
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| Abstract: | Since 1980, speleothems, mollusc shells and vertebrate teeth have been dated at the Uranium Series Radiometric Laboratory at Oslo University: To date, 44 samples have been dated with 230Th/232Th ratios ≥20. As found with other speleothem dates, they tend to cluster into discreet groups, roughly corresponding to ice-free periods of the Late Pleistocene. The direct connection between speleothem depositon and ice-free surface conditions is not always exactly correct, and it is preferable to operate with ‘speleothem chronozones’ when discussing these phenomena. Speleothem chronozones have been found in Norway for 0 to 12 ka BP (Holocenc), 90 to 130 ka BP (Rana-Fauske Chronozone), 170 to 200 ka BP (Gildeskål Chronozone), and greater than 350 ka BP. The latter samples (>350 ka BP) were all younger than 1.5 ma BP, and they most likely fall within the range of 0.3 to 0.8 ma BP, based on regional means of initial 234Usol;238U. Some samples which were contaminated with detrital Thorium gave ‘corrected’ ages (assuming initial 230Th/232Th = 1.5) of 36, 40, 50 and 60 ka BP, respectively. These dates may correlate with the Weichselian Interstadial complex (Ålesund/Sandnes, 30 to 39 ka BP; Jæren/Nygaard, 40 to 50 ka BP; and Brørup/Jämtland, 58 to 68 ka BP) chronozones. More work is required to clarify the problems and increase the statistical significance of the findings. |
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