Unreliability of ¹⁴C Dates from Organic Matter of Soils

Abstract

Contamination by recent carbon and the turnover of organic matter make dating of ancient soils difficult. In order to isolate the oldest organic fraction of sediments, two main extraction methods were previously proposed: 1) alkaline solubilization of humus that separates humins, humic acids, and fulvic acids, and 2) successive hydrolyses that solubilize increasingly resisting products. Both preparation methods were tested on the same actual or fossil soils of different pedologic types from five geologic profiles on which other chronologic data are available.Analytic results show that 14C ages obtained from alkaline extraction products differ according to the duration of treatments and characteristics of soils: while hydrolysis should yield more homogeneous results and isolate oldest fractions. It seems likely that true ages of geologic formations were never obtained from their organic matter and that the oldest organic fraction, contemporaneous with the sediment formation, completely disappears. Thus, most ages from 14C dating of organic matter of soils must be too recent.

Compositions and fluxes of particulate organic material in the Amazon River1

“…The A14C value obtained (+ 194 197~: Hedges et al 1986) is decidedly lower than that of CO, in the contemporaneous atmosphere (+ 234a/o Levin et al 1985), indicating a major component of prebomb carbon. However, surface soil organic matter usually reflects the influence of bomb carbon and A14C values in the range of 0 to +5Oo/oo are not uncommon (Gilet-Blein et al 1980;O'Brien et al 198 1).…”

The sedimentology, stratigraphy and14C dating of a turf-banked solifluction lobe: evidence for Holocene slope instability at Okstindan, northern Norway

“…By adopting this procedure it was felt that the most accurate estimates of the timing of solifluction activity could be attained, because several studies have now highlighted the fact that soil organic fractions extracted from the same sample can differ in age by several hundred to several thousand years (e.g. Scharpenseel and Schiffman, 1977;Gilet-Blein et al, 1980;Scharpenseel and Becker-Heidmann, 1992;Matthews, 1993;Martin and Johnson, 1995). In so far as the mobility of soil organic molecules is a function of age, the pre-treatment procedure adopted was therefore expected to yield age-differentiated fractions.…”

Early Occupations and Cultural Sequence at Moose Creek: A Late Pleistocene Site in Central Alaska

“…The 11 190 14 C yr BP hearth discovered below the paleosol thought to be as old as 11 730 14 C yr BP demonstrates the dangers of using soil organics to date human occupations (Geyh et al, 1971;Polach and Costin, 1971;Gilet-Blein et al, 1980;Head et al, 1989). Statistical tests, using the CALIB 3.0.3 radiocarbon calibration program (Stuiver and Reimer, 1993), demonstrate that Nenana complex radiocarbon dates from the entire valley are contemporaneous and average 11 177 ± 52 14 C yr BP (Table 3, 13 242-12 944 cal yr BP 2σ).…”