A Study of Errors in14C Dates of Peat and Sediment

Abstract

It is a well-established fact that¹⁴C 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 the¹⁴C measurement of aqueous plants or the carbon dissolved and suspended in the water column.Some plants assimilate CO₂from the sediment. Their¹⁴C 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 the¹⁴C activity of such fractions varies widely but with the weighted mean indicating an overall deficiency. Even the water from a raised bog evidences a¹⁴C deficiency relative to contemporary atmospheric CO₂.Charcoal from an archaeologic site and peat from corresponding layers in a nearby bog have yielded significantly different ages. The fact that theCladiumpeat was from a very calcareous area is significant. The risk of contamination by younger root material is also documented.