Constraints on the continental weathering intensity through the Permian using lithium isotopes of well-preserved brachiopod shells

•We provide new δ7Li data for the Permian based on well-preserved brachiopod shells and coeval host bulk carbonates.•The δ7Li offsets between brachiopod shells and their host bulk carbonates vary across the studied sections, likely due to diagenetic alteration of the bulk carbonates.•Our new δ7Li data from well-preserved brachiopods indicate that the δ7Li of Permian seawater underwent significant changes.•A simple Li isotope mass balance model suggests that continental weathering regimes changed dramatically during the Permian.•Changes in continental weathering may be linked to major climate shifts that occurred during the Permian. Lithium isotopic compositions (δ7Li) in marine carbonates provide a powerful means to track continental weathering intensity through geological history and promote our understanding of how and why Earth remained habitable. However, δ7Li values in ancient carbonates can be affected by factors such as primary carbonate mineralogy (e.g., aragonite, high-Mg calcite, low-Mg calcite) and post-depositional diagenesis, which may alter their primary signals. Modern articulate brachiopod shells have shown a constant δ7Li offset compared to contemporary seawater, suggesting that fossil brachiopod shells could serve as robust archives for this geochemical proxy due to their diagenetically resistant low-Mg calcite composition. Despite this potential, few studies have explored this topic. In this study, we analyze and compare the geochemical compositions of fossil brachiopod shells and their enclosing carbonate rocks from Permian strata in South China to investigate whether brachiopod shells can reliably preserve the δ7Li values of ancient seawater and, if they do, to obtain new constraints on changes in the continental weathering regimes through the Permian. We used several diagenetic screening methods, including scanning electron microscopy, cathodoluminescence microscopy, and elemental concentrations to detect potential diagenetic alteration. Our results indicate that 32 out of 49 shells preserve primary δ7Li values. Notably, we observed that δ7Li offsets between brachiopod shells and their enclosing carbonate rocks vary across the studied sections, likely due to diagenetic alteration of the bulk carbonates. Using the δ7Li values from well-preserved brachiopod shells, we reconstructed δ7Li variations of Permian seawater. We identified three distinct intervals: (1) extremely low δ7Lisw values (as low as 6.7 ± 2.9‰, n = 12, 1sd) during the A