NITROGEN ISOTOPE STRATIGRAPHY OF THE PERMIAN-TRIASSIC TRANSITION AT PENGLAITAN, SOUTH CHINA

The Permian-Triassic boundary (PTB) mass extinction, at 251.939 ± 0.031 Ma, was the most devastating biotic crisis in Earth’s history, resulting in the extinction of approximately 90% of marine species. The stratotype section for the PTB at Meishan, in South China, is condensed, and contains depositional hiatuses and unconformities. These factors make studying the timing and tempo of extinction at Meishan challenging. However, another PTB section in South China, Penglaitan, is orders of magnitude thicker than Meishan, and contains a continuous record of the latest Permian and earliest Triassic. During the Permian, Penglaitan was positioned on the southern margin of the South China block within the Nanpanjing Basin, a deep marine embayment within the Yangtze Platform. Tuffaceous intervals prior to and following the PTB reflect regional volcanic input from a magmatic arc on the margin of the South China block. Today, Penglaitan is exposed along the north bank of the Hongshui River, southeast of Laibin, Guangxi Province, China. Prior studies at Meishan have shown positive d¹⁵N values throughout the Late Permian, which rapidly decrease to values near zero at the PTB, and then to negative values in the Early Triassic. This reflects a transition from normal, complex trophic structuring before and during the Changhsingian, followed by a shift towards ecologic destabilization and disturbance characterized by enhanced N fixation from the atmosphere. Paleontological studies of the Penglaitan section have revealed that the PTB was a single, geologically rapid extinction, but the expanded and continuous record allows us to explore the development of ecological stresses prior to the final extinction. By generating a sub-meter scale record of d¹⁵N from a core spanning the PTB at Penglaitan, we can constrain the timing of the onset of nitrogen cycle instability, as well as characterize how local events such as regional volcanism affected ecosystems and decreased resilience in response to extinction events. These data will then be compared to other d¹⁵N records from the PTB, in order to better understand the global spatiotemporal extent of the extinction event.