Variation in Radiocarbon Ages of Soil Organic Matter Fractions from Late Quaternary Buried Soils

Radiocarbon dating of three organic matter fractions (total, humic acid, and residue) isolated from late Quaternary buried soils of the central Great Plains reveals that there often are considerable differences among, but no consistent order to, the ages of fractions. For late Holocene soils, the residue fraction or the total fraction generally produces the oldest age; for late Pleistocene soils, however, no fraction was consistently the oldest. The absence of a consistent sequence of fraction ages is attributed to postburial contamination of soils. When bulk samples from the same soil were split and sent to two laboratories, different radiocarbon ages were usually obtained. The variability in radiocarbon ages of soil organic matter confirms that caution should be taken when using radiocarbon ages obtained from different laboratories to make regional stratigraphic correlations.