The deficiency of organic matter 14C dating in Chinese Loess-paleosol sample

In the absence of reliable charcoal, wood or plant macrofossils, organic matter in loess-paleosols is often used for C-14 dating. However, organic matter can be contaminated by a variety of carbon sources within the sediments, and this may affect the radiocarbon dating results. Specific chemical pretreatments can be applied to minimize such effects, and comparisons with optically stimulated luminescence (OSL) dates from the same sediments allows us to assess potential open system effects on organic matter. Here we present comparisons of the two geochronometers from loess-paleosol deposits in the Chinese Loess Plateau. Our results show that loess -paleosol samples from the past 25 cal kyr BP generally yield reliable C-14 dates, however, beyond this range, specifically similar to 25-59 cal kyr BP, we observe a steady increase in OSL ages with depth, but no consistent increase in corresponding AMS C-14 ages. We suggest that relatively old samples from loess-paleosols should be studied using techniques such as compound-specific radiocarbon dating, ramped pyrolysis or stepped-temperature combustion.