Radiocarbon dating of small snail shells in a loess-palaeosol sequence at Mangshan, central China

In late Quaternary Chinese loess-palaeosol deposits, snail shells are often the only radiocarbon dating material available for building a chronology. However, the reliability of radiocarbon dating different small snail shells remains an open question. Here, we collected different small snail shells from a loess-palaeosol sequence located in central China to test the radiocarbon ages of snail shells. Both solid graphite target AMS (accelerator mass spectrometry) and gas AMS measurements were performed to evaluate the reliability and possible contamination of small shells of different sizes for radiocarbon dating. The 14C ages of the graphitized samples were generally consistent with the corresponding OSL ages, indicating the reliability of small-snail-shell 14C dating in Chinese loess deposits. The ages of the surface fractions of the small snail shells were close to the ages of the interior parts, and contamination after chemical treatment was limited, revealing that the fossil snail shells behaved as a closed system during burial. In addition, the gas measurement results further demonstrated the different degrees of reliability among various snail species. For minute taxa, such as Vallonia and Pupilla, their shells can mainly reveal reliable 14C ages. For larger taxa, such as Cathaica and Metodontia, much attention should be given to selecting appropriate shells. Large individuals and snail hatchlings may contain considerable amounts of old carbon, and only small shells larger than newly incubated snails (<10 mm and > 2 mg) can provide reliable 14C ages. Our study shows that the limestone effect on the radiocarbon ages obtained from most small snail shells is negligible, thus providing a great potential method to constrain the accurate ages of late Quaternary loess deposits.