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.
This list includes most of the measurements made since the beginning of the compilation of our previous list (R, 1983, v 25, p 59–126), in 1982 and 1983, as well as some earlier measurements of extended geologic or archaeologic studies.
This list includes most of the samples measured during 1974 and most of those measured previously but not published in the preceding date list (R, 1975, v 17, p 4–34.)
This list includes most of the measurements made in 1975 and 1976. Results lower than Ly-1000 are old measurements obtained with counters previously described, especially in R, 1973, v 15, p 134, when the laboratory was in the basement of the Nuclear Physics Institute. At the end of 1974 all the apparatus was transferred to a specially designed building with an isolated counting room overlain by 4m non-radioactive earth.
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