Heterogeneous Carbonate Lithium Isotope Records Across the end-Permian Mass Extinction Indicate a Highly Perturbed Lithium Cycle in the Early Triassic

Following the end-Permian mass extinction, temperatures remained elevated for ~5 Myr, suggesting a fundamental restructuring of the Earth’s climate system. Both a weak silicate weathering feedback and CO$^2$ release from enhanced marine authigenic clay precipitation are proposed to have sustained elevated temperatures during the Early Triassic. The lithium isotope (δ$^7$Li) proxy can reveal the roles of terrestrial and marine reverse weathering in maintaining elevated Early Triassic temperatures. We present the first δ$^7$Li values from Upper Permian to Middle Triassic carbonate strata from the Panthalassa Ocean and the western Tethys Ocean. At the Permian/Triassic boundary, carbonate δ$^7$Li values in these records, along with previously published data from the eastern Tethys, are consistently below 0‰, and remain low in the Early Triassic. Differences in carbonate δ$^7$Li values among sections are interpreted as the combined influence of diagenetic alteration and carbonate mineralogy on the isotopic fractionation from co-eval seawater. In the Early Triassic, we observe a large difference between carbonate δ$^7$Li values and published siliciclastic records following the extinction. ... mehrEven after accounting for carbonate diagenesis, these paired records imply Li isotope fractionation between carbonate minerals, authigenic marine clay, and seawater that are distinct from modern marine environments. Inferred minimum and maximum constraints on seawater δ$^7$Li values from these Early Triassic records are also incompatible. We hypothesize that a reduced oceanic Li reservoir—and thus, short residence time—may account for the anomalous Early Triassic δ$^7$Li records, implying a simultaneous increase in continental weathering and marine clay authigenesis. Heterogeneous seawater δ$^7$Li records in the Early Triassic could be, therefore, a potential symptom of perturbed carbon-silica cycling that permitted elevated temperatures to persist far longer than the typical timescale for the silicate weathering feedback on Earth’s climate.