Volcanism-driven synchronous terrestrial and marine anoxia during the Kungurian (early Permian)

Abstract

During the Late Paleozoic Icehouse (LPI) interval from the Late Devonian to the Late Permian, Earth transitioned repeatedly between icehouse to greenhouse conditions and widespread ocean anoxic conditions prevailed in the Kungurian stage of the Permian. Previous studies of Kungurian anoxia have focused on marine strata, and the driving mechanism for these dramatic environmental and climatic changes are poorly understood. We studied Kungurian-aged deltaic deposits from the Yuzhou Coalfield in the southern North China Platform to investigate terrestrial environmental conditions contemporaneous with anoxic marine strata. A significant anoxic interval was recognized by high-resolution mineralogical and geochemical analyses that coincides with the Kungurian negative carbon isotope excursion (KCIE) and peaks in Hg/TOC ratio. Proxy evidence from the Yuzhou Coalfield shows this anoxic interval was accompanied by warmer and more humid climates, high paleo-productivity, and strong continental weathering. We attribute early Kungurian anoxia in the Yuzhou Coalfield to carbon cycle perturbation due to its synchronous occurrence with the KCIE and volcanism in the Tarim and Zaduo large igneous provinces. Based on the relationship between pCO₂ concentration and carbon isotope fractionation, we suggest that volcanic eruptions, magma intrusions into organic-rich storage, and methane hydrate dissolution released large quantities of isotopically depleted carbon into the atmosphere, leading to the KCIE. Massive emissions of volcanic Hg contributed to the mercury anomaly in sedimentary strata. Global climatic warming likely enhanced oceanic evaporation and intensified the hydrological cycle, resulting in increased continental weathering, terrestrial runoff and nutrient inputs, as well as water stratification and widespread bottom water anoxia in marine and terrestrial settings. Our results show that Kungurian anoxia occurred synchronously in both marine and freshwater settings, as it did in the stratigraphically younger Toarcian (T-OAE) and Cretaceous (OAE1a and OAE1b) Ocean Anoxic Events (OAEs).