Coupled volcanic activity and marine anoxia in the Upper Yangtze region prior to the Capitanian mass extinction

Abstract

The Capitanian mass extinction was a severe biotic crisis in geological history. To present more evidence for this event, this study acquired geochemical data from shelf-margin facies deposits in the Upper Yangtze region, China (i.e., the Shangsi section; the third member of the Maokou Formation [Mao III Member] prior to the Capitanian mass extinction). A significant Hg anomaly is associated with the negative δ13Ccarb excursion in the Mao III Member, suggesting a link to the volcanic activity of the Emeishan large igneous province (ELIP). With increasing water depth, enhanced marine anoxia and stronger water column stratification existed, as evidenced by both organic and inorganic geochemical proxy data. This suggests a possible oceanographic change in response to ELIP volcanism. We propose a three-stage model for the coupled volcanic–climatic–oceanic variations in the Upper Yangtze region during the early Capitanian and the volcanism associated with the ELIP was a potential driving mechanism of the environmental changes and biotic crisis. The ELIP volcanism could have caused the widespread marine anoxia along the continental margin, due to climate warming and the release of nutrient elements. The significant water column stratification and basin restriction were enhanced by climate warming, which would have resulted in expansion of oxygen minimum zones into shelf habitats. This coincided with a decrease in the fusulinacean foraminiferal assemblages and calcareous algae in the Shangsi section. The enhanced marine anoxia and intensified water column stratification may have had a direct role in the death of these organisms. Therefore, widespread marine anoxia/euxinia driven by volcanic activity and climate warming resulted from the ELIP eruption could finally led to the Capitanian biotic crisis.