Mesoproterozoic oxygenation events in North China Craton: geochemical evidence from the Tieling Formation

The emergence of oxygen (O₂) on the earth facilitated the atmospheric-oceanic redox changes and complex biotic evolution. The surface ocean-atmosphere system has long been considered to be characterized by overall low atmospheric oxygen levels during the mid-Proterozoic, but may have been interrupted by transient oxygenation events at 1.44～1.43 Ga. The Mesoproterozoic Tieling Formation in the North China Craton is one of the best-preserved stratigraphic successions and recorded key information on 1.44～1.43 Ga oceanic-atmospheric redox condition. Multiple geochemical proxies suggest several pulses of oxygen increasing process during the deposition of the Tieling Formation. These oxygenation processes were probably gradually enhanced with the maximum O₂ concentration higher than 4% of present atmospheric level. An intensified terrestrial weathering may have accelerated the burial process of pyrite, and eventually led to the oxygenated events during this period. Such an episode of significant oxygen increase was also discovered in synchronous deposited strata in the southern North China and Siberia, indicating that the recognized 1.44～1.43 Ga oxygen increase may represent a multi-basin or even a global oxygenation event.