High-Resolution Reconstruction of Continental Weathering Intensity Across the Tonian–cryogenian Transition in South China

The Sturtian glaciation (ca. 717–661 Ma) was one of the most extreme icehouse events in Earth history and represents a critical interval in the transition from the relatively warm Tonian to the severely glaciated Cryogenian. However, widespread glacial erosion during its onset commonly produced stratigraphic hiatuses, leaving successions across the Tonian–Cryogenian boundary incomplete in many regions and hindering precise correlation of basal Cryogenian strata. In contrast to carbonate–diamictite successions that commonly contain depositional gaps, continuously deposited siliciclastic successions provide a better archive for global stratigraphic correlation. Here we investigate drill cores from the Zhaoxing section in South China and present high-resolution geochemical data at 20 cm sampling intervals across the critical interval from the preglacial Gongdong Formation to the glacial Chang’an Formation. Using the Chemical Index of Alteration (CIA) and magnesium isotopes, we reconstruct a high-resolution record of continental chemical weathering intensity. These weathering proxies track regional variations in continental chemical weathering. They thus provide constraints on the broad trends of atmospheric CO₂ drawdown and climatic cooling associated with the initiation of the Sturtian glaciation. Our results offer new insights into surface-environmental evolution across the Tonian–Cryogenian transition and suggest that weathering-proxy-based correlation may provide a useful approach for identifying and correlating basal Cryogenian strata worldwide.