Unveiling a new oceanic anoxic event at the Norian/Rhaetian boundary (Late Triassic)
Manuel Rigo, Xin Jin, Linda Godfrey, Miriam Katz, Honami Sato, Yuki Tomimatsu, Mariachiara Zaffani, Matteo Maron, S. Satolli, Giuseppe Concheri, Alessandra Cardinali, Qiangwang Wu, Yixing Du, Jerry Z. X. Lei, Connor S. van Wieren, Lydia S. Tackett, Hamish J. Campbell, Angela Bertinelli, Tetsuji Onoue
Abstract
Abstract The latest Triassic was characterised by protracted biotic extinctions concluding in the End-Triassic Extinction (~ 200 Ma) and a global carbon cycle perturbation. The onset of declining diversity is closely related to reducing conditions that spread globally from upper Sevatian (uppermost Norian) to across the Norian-Rhaetian boundary, likely triggered by unusually high volcanic activity. We correlate significant organic carbon cycle perturbations to an increase of CO 2 in the ocean–atmosphere system, likely outgassed by the Angayucham igneous province, the onset of which is indicated by the initiation of a rapid decline in 87 Sr/ 86 Sr and 188 Os/ 187 Os seawater values. A possible causal mechanism involves elevated CO 2 levels causing global warming and accelerating chemical weathering, which increased nutrient discharge to the oceans and greatly increased biological productivity. Higher export production and oxidation of organic matter led to a global O 2 decrease in marine water across the Norian/Rhaetian boundary (NRB). Biotic consequences of dysoxia/anoxia include worldwide extinctions in some fossil groups, such as bivalves, ammonoids, conodonts, radiolarians.