Plutonium-based radiometric dating of rapidly accumulated sediments in the Sanyuan sinkhole, southern Chinese Loess Plateau

Radionuclides, such as ²¹⁰Pb, ¹³⁷Cs and ^239,240Pu, have been widely used for dating recent sediments in terrestrial and marine environments, while ¹²⁹I, as an important artificial radionuclide in the environment, is also a potential tracer for sediment dating and environmental process studies. However, they were not always successfully applied to sediment dating because of their different sources, half-lives, environmental behaviour and measurement techniques. The dating applicability of these nuclides in a sedimentary environment with rapid accumulation on land was investigated for sinkhole sediment from the southern Chinese Loess Plateau. Our results showed that ²¹⁰Pb and ¹³⁷Cs could not be adequately used for dating the sediments due to the difficulties in accurately measuring ¹³⁷Cs and excess ²¹⁰Pb (²¹⁰Pb_ex) signals caused by the dilution effect of rapid accumulation. ¹²⁹I is not an ideal dating tracer because of its multisource feature causing no remarkable peak value in the sediment cores. The depth distribution of ^239,240Pu in the sediment core showed a single peak corresponding to its maximum fallout in 1963 from the atmospheric nuclear weapons test, suggesting that Pu isotopes have significant advantages in dating recent sediments. The sensitive inductively coupled plasma–mass spectrometry (ICP-MS) measurement technique enables the determination of very low levels of ²³⁹Pu and ²⁴⁰Pu and makes ^239,240Pu a suitable tracer for dating the rapidly accumulated sediment. Based on the ^239,240Pu mass balance equation estimation and field observations, we proposed the water-eroded input from soil surrounding the sinkhole as another vital source of the sediments in addition to the aeolian contribution.