T02_P05

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

Gu Y^1,2,  Lu H¹, Hajdas I², Haghipour N², Zhang H¹, Wu J¹, Shao K¹

¹Laboratory of AMS Dating and the Environment, School of Geography and Ocean Science, Nanjing University, Nanjing, China, ²Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland

Radiocarbon age obtained on small snail shells show that the limestone effect is smaller than for the large shells, providing great potential to constrain accurate ages of late Quaternary loess deposits. In the Chinese Loess Plateau (CLP), snail shells are often the only radiocarbon dating material available for building chronology. However, the reliability of different small snail shells for radiocarbon dating remains an open question. Here, we collected different small snail shells from a loess-paleosol sequence located at south-east CLP to test their availability. Both solid graphite target AMS measurement and gas AMS measurement were performed to evaluate the reliability and possible contamination of different sizes of small shells for radiocarbon dating. ¹⁴C ages of graphitized samples are generally consistent with corresponding OSL ages, indicating the reliability of small snails ¹⁴C dating at CLP. Ages of the surface fraction of small snails are close to the ages of the interior part and the contamination after chemical treatment is limited, indicating fossil snail shells behave as a close system during burial. In addition, gas measurement results further demonstrate 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. While for larger taxa, such as Cathaica and Metodontia, much attention should be paid to selecting the appropriate shells. Large individuals and snail hatchlings may contain considerable old carbon and only small shells larger than newly incubation (<10 mm and > 2 mg) can provide reliable ¹⁴C ages.