51 / 2025-03-29 16:33:55

Limited change in silicate weathering intensity during the Permian–Triassic transition indicates ineffective climate regulation by weathering feedbacks

Chemical Index of Alteration; Clay mineralogy; Weathering condition; Permian-Triassic; Climate regulation

Theme 3: Earth-Life Co-evolution Through Time > Session 3g: Impact of Volcanism on the Habitability of the Earth

The Permian-Triassic transition marked a profoundly dramatic climate warming event that not only contributed greatly in the largest biotic crisis on the surface of the Earth during the Phanerozoic, but also led to a lethally hot world persisting for millions of years into the Early Triassic, delaying the recovery of life. How the climate remained exceptionally hot for such a long time was enigmatic. Silicate weathering, considered a major geological thermostat, has long been postulated to have increased dramatically during that time. However, evidences of such remains inconclusive.

Understanding how the silicate weathering conditions have evolved during the Permian-Triassic transition holds immense importance in unravelling this enigma. In this study, we have compiled the Chemical Index of Alteration (CIA) data from 37 terrestrial and marine Permian-Triassic sections that are relatively well-studied with well-defined time framework and constrained provenances. After careful screening and evaluation of the suitability of the data as a weathering index, a prevailing pattern has emerged showing no discernable increase in CIA across the Permian-Triassic transition. In fact, most of the sections examined exhibit a decreasing trend in CIA, indicating decreased chemical weathering intensity. In addition, our investigation of clay mineral assemblages from several sections reveals the increase of illite and chlorite at the expense of kaolinite, further supporting the notion of decreased chemical weathering intensity.

These results stand in stark contrast to previous expectations. Considering the results from the most recent modeling studies on seawater Li and Sr isotope evolution showing limited increase in the chemical weathering influxes, our results highlight the possibility of the inefficacy of silicate weathering as a climate regulator at that critical time. Our finding provides an ancient reference for understanding the role of continental silicate weathering in the regulation of climate, especially amid rapid global warming conditions that modern humanity is currently experiencing.