Precise age for the Permian-Triassic boundary in South China from high precision U-Pb geochronology and Bayesian age-depth modelling

This study is based on zircon U-Pb ages of 12 volcanic ash layers and volcanogenic sandstones from two marine sections with conformable formational Permian-Triassic boundaries (PTB) in the Nanpanjiang Basin (South China). Our dates of single, thermally annealed and chemically abraded zircons bracket the PTB in Dongpan and Penglaitan and provide the basis for a first proof-of-concept study utilizing a Bayesian chronology model comparing the three sections of Dongpan, Penglaitan and the Global Stratotype Section and Point (GSSP) Meishan. Our Bayesian modeling demonstrates that the formational boundaries in Dongpan (251.938 ± 0.029 Ma), Penglaitan (251.982 ± 0.031 Ma) and Meishan (251.956 ± 0.033 Ma) are synchronous within analytical uncertainty of ca. 30 ka. It also provides quantitative evidence that the ages of the paleontologically defined boundaries, based on conodont Unitary Associations zones in Meishan and on macrofaunas in Dongpan, are identical and coincide with the age of the formational boundaries. The age model also confirms the extreme condensation around the PTB in Meishan, which distorts the projection of any stratigraphic points or intervals onto other more expanded sections by means of Bayesian age-depth models. Dongpan and Penglaitan possess significantly higher sedimentation rates and thus offer a greater potential for high resolution studies of environmental proxies and correlations around the PTB than Meishan. This study highlights the power of high-resolution radio-isotopic ages that allow a robust intercalibration of patterns of biotic changes and fluctuating environmental proxies and will help recognizing their global, regional or local significance.