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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.

After a brief presentation of the experimental protocols, this article discusses the results of the 14C dates obtained from charcoal specimens collected on the walls (drawings and torch-wipes) and on the ground of the Chauvet Cave. The dates, which are coherent, can be divided into two periods a few millennia apart: between 33000 and 29000 14C years BP (33 samples including the five parietal representations) and between 27000 and 24500 14 C years BP (13 samples including the four torch-wipes). RésuméAprès une rapide présentation des protocoles expérimentaux utilisés, cet article discute les résultats des datations carbone 14 effectuées sur des échantillons de charbons de bois prélevés sur les parois (dessins et mou-chages de torches) ou le sol de la grotte Chauvet. Les dates, qui sont cohérentes, se placent dans deux périodes séparées par quelques millénaires : entre 33000 et 29000 ans 14C (33 échantillons, dont les cinq représentations pariétales) et entre 27000 et 24500 ans 14C (13 échantillons dont les quatre mouchages de torche).

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