Early Triassic Weathering Intensity and Climate Recovery After the end-Permian Extinction

The eruption of the Siberian Traps large igneous province in the late Permian caused environmental changes that resulted in the extinction of ~80% of marine animal genera making it the most devastating ecological crisis in the Phanerozoic. The intensity of this extinction event was compounded by an extended recovery interval of 5 Myr characterized by a greenhouse climate and extensive marine anoxia. The negative feedback between atmospheric CO2 and the weathering of continental rocks is expected to remove excess atmospheric CO2 within 0.5 to 1 Myr under typical conditions, leaving the cause of persistent warm temperatures poorly understood. The intensity of silicate weathering reactions, defined as the formation of secondary minerals relative to release of cations from the dissolution of primary minerals, can be assessed using lithium isotope ratios (7Li/6Li, commonly denoted as 7Li). This proxy relies on the observation that 6Li preferentially adsorbs onto the surface of clays, which ultimately results in higher seawater 7Li that can then be captured in marine carbonates. Shallow-marine carbonates from south China, Turkey, and Japan were analyzed for 7Li to determine weathering intensity over the extinction and the recovery (ca. 252.2-243.5 Ma). The data show a decrease in 7Li of ~10 coincident with the extinction event, followed by a gradual increase over 7 Myr to values ~7 higher than latest Permian values. The initial decline in 7Li may reflect increased weathering due to the decimation of terrestrial ecosystems, which has also been supported by a switch from meandering to braided streams and the occurrence of pedoliths in the Early Triassic. While 7Li is commonly used as a measure of terrestrial processes, we suggest that the slow increase in 7Li to pre-extinction levels can alternatively be attributed to the formation of marine authigenic clays. Marine authigenic clay formation may also explain the slow environmental recovery in the Early Triassic as the CO2 released in these reactions would buffer the carbon cycle from returning to pre-extinction conditions. Thus, the 7Li record provides a window into how the potentially competing effects of terrestrial and marine weathering affect global climate recovery after massive CO2 injections from large igneous provinces.