HIGH PRECISION U-PB DATING OF THE PERMIAN-TRIASSIC BOUNDARY IN MARINE DEEP WATER SETTINGS

We present new zircon U-Pb ages of ten volcanic ash layers and volcaniclastic sandstones from two basinal sections with conformable formational Permian-Triassic boundaries (PTB) in the Nanpanjiang Basin (South China). Our new dates obtained from single, thermally annealed and chemically abraded zircons closely bracket the PTB in Dongpan and Penglaitan and are included into a Bayesian chronology model comparing three sections (Dongpan, Penglaitan and Meishan¹). Our Bayesian modeling demonstrates that the formational boundaries in Dongpan, Penglaitan and Meishan are all synchronous within analytical uncertainty of ≈ 30 ka. It also highlights that the ages of the paleontologically defined boundary based on conodont Unitary Associations zones in Meishan²and on macrofaunas in Dongpan, are identical and match with the age of the formational boundary in both sections. 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 much higher sedimentation rates than Meishan and thus offer a greater potential for high resolution studies of environmental proxies and correlations around the PTB. As the youngest preserved Permian bed in Penglaitan is a volcanogenic sandstone, Dongpan offers the probably most complete section with no indication of a potential hiatus at the boundary between the Dalong and the Ziyun formations. This study highlights the power of high-resolution radio-isotopic ages that allow a robust intercalibration of quantitative biochronology and environmental changes across multiple sections.

1 Burgess, S.D., Bowring, S.A. & Shen, S.Z., 2014. High-precision timeline for Earth’s most severe extinction. PNAS 111, 3316-3321.

2 Brosse, M., Bucher, H. & Goudemand, N. 2016. Quantitative biochronology of the Permian-Triassic boundary in South China based on conodont Unitary Associations. Earth Science Reviews. 155:153-171.