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High latitude carbon-cycle and weathering changes during the Carnian Pluvial Episode in Junggar Basin, northwestern China

Late Triassic; Carnian Pluvial Episode; C-isotope; Mercury; Chemical weathering

Theme 3: Earth-Life Co-evolution Through Time > Session 3f: Rise of Modern-type Ecosystems in Triassic

The Late Triassic Carnian Pluvial Episode (CPE) represents a significant interval of global environmental changes and biological reorganization, driven by carbon cycle perturbations and global warming. While much of the evidence for this event originates from low-latitude regions, its effects at higher latitudes remain largely unclear. We analysed organic C-isotopes, major elements, and mercury (Hg) concentrations in samples from the Junggar Basin in northwestern China (Xinjiang), which during the Late Triassic was situated at approximately 60° N. This fluvial-lacustrine succession reveals four negative carbon isotope excursions (NCIEs) that can be correlated to global CPE records. Two phases of elevated Hg deposition are identified during the CPE. In Phase I, during the first two NCIEs, increased Hg levels appear to be associated with volcanic activity or substantial oxidation of organic matter, and do not record major changes in chemical weathering. In contrast, Phase II, corresponding to the final two NCIEs, shows Hg enrichments influenced by greater inputs of terrestrial organic matter from higher plants into the lacustrine system, and higher chemical weathering. The onset of the first NCIE coincides with notable changes in lithology and macrofloral composition, signalling a transition to a wetter climate, but higher hydrolysis of silicates and runoff occurred only during later phases of the CPE.