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(super 14) C AMS dating of Icelandic lake sediments.

Arny E Sveinbjornsdottir, Jan Heinemeier, Peter Kristensen, Niels Rud, Aslaug Geirsdottir, Jorunn Hardardottir

Abstract


We report an age-depth profile for the sediments of the Lake Hestvatn, southern Iceland, based on (super 14) C analyses of the organic fraction of bulk sediment samples, molluscs and foraminifera. Our age-depth curve is supported by the occurrence of the well-dated Vedde ash in the lowermost part of the sediments. Comparison of foraminifera dates with the age of the Vedde ash indicates a reservoir age of ca. 400 yr. The results suggest that the sediments at Hestvatn accumulated in a marine environment until ca. 8700 BP and thereafter in freshwater. Owing to the lack of terrestrial macrofossils and the low concentration of molluscs and foraminifera, we were forced to attempt to date most of the core with the organic fraction of the bulk sediment samples. We found, however, that this fraction is not homogeneous in density or (super 14) C age. We believe that during sample pretreatment we managed to isolate a light organic fraction, which closely represents the true age of the sediment, whereas the denser fraction yields ages that are too high. This age diversity may to some extent be explained by the large drainage area of the lake, from which plant remains of different ages may have been washed into the lake.

Keywords


Lake Hestvatn;Vedde Ash;fresh water environment;Iceland;lake sediments;lacustrine environment;accelerator mass spectra;cores;marine environment;Foraminifera;Protista;mass spectra;spectra;isotope ratios;Holocene;microfossils;paleoclimatology;organic compounds;Europe;Western Europe;sediments;Cenozoic;Quaternary;C 14;carbon;dates;isotopes;radioactive isotopes;Invertebrata;Mollusca;C 13 C 12;stable isotopes;absolute age

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