Hydrological cycles perturbation of continental weathering during the Triassic-Jurassic transition and Toarcian Oceanic Anoxic Event

The Early Jurassic represents a critical interval in Earth’s history, characterized by significant ecosystem perturbations both on land and in oceans. Huge releases of greenhouse gas (e.g., CO₂, CH₄) by large scale of volcanic eruptions are generally assumed to cause significant increases in temperature during the Triassic-Jurassic transition (TJT) and Toarcian Oceanic Anoxic Event (T-OAE). However, terrestrial environmental responses to the climate perturbations on land, e.g., type and intensity of continental weathering, during these two hyperthermal events are still unclear. Here, we present a continuous lacustrine succession from the Chuxiong Basin in Yunnan Province, China, through the analysis of an approximately 1800 meter core. By integration of sedimentological, paleontological, geochemical, and astronomical data, we have established a chronology spanning about 21 million years from the Rhaetian (Late Triassic) to the Aalenian (late Early Jurassic), calibrated by the long eccentricity cycles. Distinct negative carbon isotope excursions and peaks in sedimentary Hg abundance, confirm significant volcanism during both the TJT and T-OAE. However, the Chemical Index of Alteration (CIA) and clay mineral data show opposing responses for the two events, indicating increasing and decreasing (or constant) chemical weathering intensity during TJT and T-OAE, respectively. Therefore, we proposed that these event-specific chemical weathering variations imply responses of volcanism-induced hydrological changes at different latitudes during these events.