CLIMATE WARMING, EUXINIA AND CARBON ISOTOPE PERTURBATIONS DURING THE CARNIAN (TRIASSIC) CRISIS

The Carnian Pluvial Event (CPE, Triassic) and associated biotic changes are major enigmas of the Mesozoic record that appear related to a phase of intense humidity in western Tethys. We show that the CPE also occurred in eastern Tethys (South China), suggestive of a global climate perturbation. Oxygen isotope records from conodont apatite show that the CPE coincided precisely with 4°C of sea-surface temperature warming. This was followed by a transient cooling event and then a prolonged ~7°C warming in the later Carnian. Carbon isotope perturbations associated with the CPE in South China are seen to be contemporaneous with those in western Tethys, and mark the start of a prolonged period of carbon cycle instability that persisted until the late Carnian. While carbonate platform shutdown in western Tethys can be attributed to an influx of clastic sediment, the eastern Tethyan carbonate platforms are overlain by deep-water anoxic facies. The transition from oxygenated to euxinic facies was via a condensed, manganiferous carbonate (MnO content up to 15.1 wt%), that records an intense Mn shuttle operating in the basin. Significant clastic influx in South China only occurred after the Carnian climatic changes and was due to foreland basin development at the onset of the Indosinian orogeny. The Carnian biotic crisis thus coincides with many phenomena associated with major extinction events: warming, δ¹³C oscillations, carbonate production crisis, oceanic anoxia, biotic turnover and flood basalt eruptions (of the Wrangellia Province).