Lithium and Strontium Isotopes Evidence for Continental Weathering Changes During the Carnian Pluvial Episode (late Triassic)

The Carnian Pluvial Episode (CPE, ~233 Ma) was a major climatic event during the Late Triassic, characterized by an accelerated hydrological cycle, global warming, a massive influx of terrigenous siliciclastic input, marine anoxia, and profound biotic turnovers across marine and terrestrial realms. Although a causal connection between the CPE and emplacement of the Wrangellia Large Igneous Province (LIP) is widely recognized, whether Wrangellia volcanism triggered global-scale changes in continental chemical weathering remains debated. Because silicate weathering is a key long-term sink for atmospheric CO2, reconstructing shifts in weathering regime and intensity is essential for understanding climate feedbacks during this interval. Here, we present lithium (Li) and strontium (Sr) isotope records from two marine successions spanning the CPE: a pelagic chert section (N-O, Inuyama, Japan) and a semi-deep-water carbonate section (LC, Nanpanjiang Basin, South China). The N-O cherts record a negative δ⁷Li excursion of ~5‰, whereas the LC carbonates show a positive δ⁷Li excursion of ~5-6‰. Despite the opposite trends in the two sections, both records consistently indicate enhanced physical erosion and reduced chemical weathering intensity during the CPE. This interpretation is further supported by a negative excursion of 87Sr/86Sr in the LC section over the same interval. We attribute the contrasting δ⁷Li responses to different pre-CPE weathering states: the Nanpanjiang Basin was likely affected by the contemporaneous Indosinian Orogeny and thus characterized by relatively intense weathering before the event, as reflected by lower δ⁷Li and higher 87Sr/86Sr values. Overall, our results point to a broadly synchronous global shift toward erosion-dominated continental weathering during the CPE, driven by greenhouse-gas emissions from Wrangellia LIP volcanism. Resulting warming and hydrological intensification increased erosion rates while reducing chemical weathering intensity.