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Unreliability of 14C Dates from Organic Matter of Soils

Published online by Cambridge University Press:  18 July 2016

Nicole Gilet-Blein ,
Gérard Marien  and
Jacques Evin
Nicole Gilet-Blein
Affiliation:
Centre de Datations et d'Analyses Isotopiques, Université Claude-Bernard, Lyon, France
Gérard Marien
Affiliation:
Centre de Datations et d'Analyses Isotopiques, Université Claude-Bernard, Lyon, France
Jacques Evin
Affiliation:
Centre de Datations et d'Analyses Isotopiques, Université Claude-Bernard, Lyon, France
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Abstract

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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.

Type
Soils and Groundwater
Information
Radiocarbon , Volume 22 , Issue 3: Heidelberg , 1980 , pp. 919 - 929
Copyright
Copyright © The American Journal of Science

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