ACCURATE DATING OF ORGANIC DEPOSITS BY AMS C-14 MEASUREMENT OF MACROFOSSILS

We made a comparative study of AMS C-14 ages of organic deposits (minerotrophic peats and gyttjas) and macrofossils in order to evaluate the magnitude of a number of sources of error that may be present in bulk sediment samples. The consistency of C-14 ages found for coexisting macrofossils suggests that they are unlikely to record disturbances. Some of our gyttja samples yielded an age 0.2-0.6 ka C-14 years too old due to hardwater effect. We also found an aging effect in several bulk samples with a high admixture of siliciclastic material; this is attributed to fluvial input of reworked, older organic debris. Rejuvenation of bulk material as a result of root contamination occurs mainly in samples overlain by slowly accumulated deposits, and particularly in samples affected by (sub)recent roots.