Lithium isotopes reveal enhanced weathering fluxes in North America during the Paleocene–Eocene Thermal Maximum: Perspectives on clay chronology

Silicate weathering regulates Earth’s surface climate over geological timescales by removing atmospheric CO2. Understanding changes in weathering dynamics and rates is key to predicting climate response time scales. We investigated the reactivity of the North American source-to-sink system and the chemical weathering regime during the Paleocene–Eocene Thermal Maximum (PETM). We measured the detrital lithium isotope composition (δ7Li) in a deep-marine sediment core from the Gulf of Mexico, tracking changes in the formation of clay minerals, alongside neodymium isotopes (εNd), to constrain sediment provenance.We find a buffered negative δ7Li excursion during the PETM body, likely reflecting the mixing of newly formed and reworked clays from continental floodplains, followed by a pronounced negative δ7Li excursion during the recovery phase. This pattern is consistent with the continental Bighorn Basin (Wyoming, USA) δ7Li record (Ramos et al., 2022), indicating a rapid propagation of enhanced weathering and erosion fluxes in response to the PETM, which would have contributed to efficient CO2 drawdown (Jaimes-Gutierrez et al., 2025).To fully understand weathering–climate feedbacks during the PETM, future work will target the radiometric dating of clay minerals exported to the ocean during this climatic perturbation. Constraining the timing of clay formation and residence on continental floodplains will allow us to distinguish between newly formed and reworked clays. Such age constraints would provide critical insights into the response timescales of continental weathering processes and thereby improve our understanding of carbon budgets during the PETM.References:Jaimes-Gutierrez, R., Vimpere, L., Wilson, D.J., Blaser, P., Adatte, T., Sahoo, S., and Castelltort, S., 2025, Lithium isotopes reveal enhanced weathering fluxes in North America during the Paleocene–Eocene Thermal Maximum: Geology, doi:https://doi.org/10.1130/G53708.1.Ramos, E.J. et al., 2022, Swift Weathering Response on Floodplains During the Paleocene‐Eocene Thermal Maximum: Geophysical Research Letters, v. 49, doi:10.1029/2021GL097436.