14 C Dating of Soil Organic Carbon (SOC) in Loess-Paleosol Using Sequential Pyrolysis and Accelerator Mass Spectrometry (AMS)

The chemical extraction of soil organic carbon (SOC) fractions from soils often does not produce satisfactory results for radiocarbon dating. In this study, a sequential pyrolysis technique was investigated. The soil was pyrolyzed at temperatures of 200, 400, 600, and 800 °C to partition organic carbon into pyrolytic volatile (Py-V) and pyrolytic residue (Py-R) fractions. The preliminary results show that the 14 C dates of both fractions become progressively older as the pyrolysis temperature is increased. In addition, the ages of the Py-V fractions are consistently younger than the corresponding Py-R fractions extracted at the same temperature. Experimental results of known-age paleosol samples indicate that the Py-V fractions obtained between 600 and 800 °C yield the most reliable ages. This technique provides a new approach to improve the accuracy of 14 C dating of loess-paleosol sequences.