EARLY TRIASSIC WEATHERING INTENSITY AND CLIMATE RECOVERY AFTER THE END-PERMIAN EXTINCTION
Open Access
- Author:
- Taylor, Kaitlin
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 14, 2022
- Committee Members:
- Mark Patzkowsky, Program Head/Chair
Kimberly Lau, Thesis Advisor/Co-Advisor
Matthew S Fantle, Committee Member
Max Lloyd, Committee Member - Keywords:
- global warming
weathering
permian triassic extinction
lithium
isotopes
modeling
diagenesis
climate
climate stability - Abstract:
- The end-Permian mass extinction is characterized by an extinction of ~80% of marine animal genera, making it the most devastating ecological crisis in the Phanerozoic. An extended recovery interval of over 5 Myr is thought to be caused by a persistent 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 400kyr 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 δ7Li). This proxy relies on the observation that 6Li preferentially adsorbs onto the surface of clays, which ultimately results in higher seawater δ7Li when secondary weathering reactions are prevalent, that can then be captured in marine carbonates. Shallow-marine carbonates from South China, Turkey, and Japan were analyzed for δ7Li and Li concentrations to determine weathering intensity over the extinction and the recovery into the Middle Triassic (ca. 252.2-243.5 Ma). The data show a decrease in δ7Li of ~5‰ coincident with the extinction event, followed by a gradual increase over 7 Myr to values ~5‰ higher than latest Permian values. The initial decline in δ7Li may reflect increased weathering intensity due to the increase in atmospheric pCO2 from the eruption of the Siberian traps. However, this does not explain persistently low δ7Li and a decrease in lithium concentrations through the Early Triassic. While δ7Li is commonly used as a measure of terrestrial processes, we suggest that the decrease in Li concentrations at the extinction interval and across the Early Triassic can be attributed to the formation of marine authigenic clays that occurred in combination with enhanced silicate weathering. An increase in marine authigenic clay formation may 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. Modeling the carbon and lithium cycles indicates that along with reverse weathering, a decrease in land surface reactivity or a decrease in weathering to 20% relative to pre-perturbation values could help to explain elevated temperatures through the Early Triassic. The recovery of both δ7Li values and Li concentrations in the Middle Triassic indicates a return to more moderate terrestrial weathering intensity and a decrease in reverse weathering which would facilitate a reduction in temperatures.