C-14 AMS DATING OF ICELANDIC LAKE-SEDIMENTS

We report an age-depth profile for the sediments of the Lake Hestvatn, southern Iceland, based on C-14 analyses of the organic fraction of b ulk sediment samples, molluscs and foraminifera, Our age-depth curve i s supported by the occurrence of the well-dated Vedde ash in the lower most part of the sediments. Comparison of foraminifera dates with the age of the Vedde ash indicates a reservoir age of ca. 400 yr. The resu lts suggest that the sediments at Hestvatn accumulated in a marine env ironment until ca. 8700 BP and thereafter in freshwater.Owing to the l ack of terrestrial macrofossils and the low concentration of molluscs and foraminifera, we were forced to attempt to date most of the core w ith the organic fraction of the bulk sediment samples. We found, howev er, that this fraction is not homogeneous in density or C-14 age, we b elieve that during sample pretreatment we managed to isolate a light o rganic 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 o f the lake, from which plant remains of different ages may have been w ashed into the lake.