Discussion on Changes of Brachiopod Diversity and Morphologic Features and Their Implications for the Environmental and Biological Crisis of the Great Dying

As concluded in Chap. 6, the decline of brachiopod diversity in deep-water facies took place earlier than in shallow-water facies during the Permian–Triassic transition. This phenomenon lets us recall the scenario that the upward migration of anoxic deep waters in a stratified ocean caused the radiolarian extinction in a Japanese pelagic environment (Isozaki 2009; Takahashi et al. 2013). Therefore, elsewhere we have proposed that the formation of a stratified ocean and, particularly, upward migration of the chemocline (or Oxygen Minimum Zone) in the stratified ocean was possibly responsible for this bathymetry-dependent differential temporal pattern of brachiopod disappearance across the PTB in South China (Fig. 8.1; He et al. 2015). Furthermore, the ocean stratification and upward migration of the chemocline was most likely linked to contemporaneous sustained volcanism. This was evidenced by the frequent occurrences of volcanic ash beds around the horizons where the diversity declined (Fig. 6.2).