A Study of Errors in 14 C Dates of Peat and Sediment

Abstract

It is a well-established fact that 14 C dates from lake sediments are usually too old because of contamination with allochthonous material and/or due to discrete reservoir effects. The latter can occur in soft water lakes and may be examined by the 14 C measurement of aqueous plants or the carbon dissolved and suspended in the water column. Some plants assimilate CO 2 from the sediment. Their 14 C activity is then dependent on the sediment accumulation rate and nutrients stored in the root system may also contribute misleading results. If water is filtered through ultra-fine membranes and then treated chemically, several fractions can be isolated for dating. The present study shows that the 14 C activity of such fractions varies widely but with the weighted mean indicating an overall deficiency. Even the water from a raised bog evidences a 14 C deficiency relative to contemporary atmospheric CO 2 . Charcoal from an archaeologic site and peat from corresponding layers in a nearby bog have yielded significantly different ages. The fact that the Cladium peat was from a very calcareous area is significant. The risk of contamination by younger root material is also documented.