AMS radiocarbon dating of organic fractions from varved lake sediments: an empirical test of reliability |
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| Authors: | Frank Oldfield Peter R J Crooks Douglas D Harkness Gunilla Petterson |
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| Institution: | (1) Department of Geography, University of Liverpool, Liverpool, L69 3BX, UK;(2) Department of Geography, St Martin's College of Higher Education, Lancaster, LA1 3JD, UK;(3) NERC Radiocarbon Dating Laboratory, East Kilbride, Glasgow, G75 0QU, UK;(4) Department of Environmental Health, UmeÅ University, S-901 87 UmeÅ, Sweden |
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| Abstract: | Replicate cores of annually laminated (varved) sediments have been used to test the accuracy and precision of chronologies of lake sediment accumulation over the last 1000 years, based on AMS 14C measurements. The internally consistent results show that in the case of the soft-water lake sediments studied (Kassjön, northern Sweden), all the organic fractions that include aquatic components give significantly older dates than expected. Only the single terrestrial macrofossil and the fine, unidentified residual particulate fraction provide dates close to the true age of the sediments. The results also show that age discrepancies for some fractions are not constant over time. The age discrepancies may arise from some carbon reservoir effect within the aquatic ecosystem, from resuspension and focusing of older marginal organic material into the deepest part of the lake or from some combination of these processes. More work is needed on the 14C  age of organic fractions in varve-dated sediments from a range of lake types. |
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| Keywords: | radiocarbon AMS organic fractions late Holocene varves chronology |
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