Our analysis shows that the TOC content is markedly higher in the Induan black claystone than the Changhsingian chert. TOC values rapidly increase across the PTB. The onset of the increase in TOC values corresponds to MEE. The rapid and profound increase in TOC values implies the sudden onset of oceanic anoxia as well as the rapid increase in primary production at the PTB.
¦Ä13Corg values are generally higher in the Changhsingian chert than the Induan claystone and chert. The stepwise drop of ¦Ä13Corg values characterizes their excursion of the study section. The largest-scale drop occurs prior to MEE. The minimum ¦Ä13Corg value is recorded at the base of the Induan claystone. The flux of ¦Ä13C-depleted gasses related to the Siberian Traps could have significantly contributed to the marked drop of ¦Ä13Corg values.
Due to the weakened ocean circulation under the predominant condition of global warming, oceanic anoxia suddenly took place at the end of the Permian. The anoxic condition in the surface layer was the most likely kill-mechanism for Permian radiolarians. The anoxic condition persisted into the Induan, but was intermittently weakened. The episodic relaxation of the anoxic condition in the Induan resulted in intermittent and transient blooming of radiolarians and deposition of radiolarian chert with lowered TOC values. These biotic and depositional records of the study section imply the mid-Panthalassic Ocean was under the more hospitable conditions favored by the earlier recovery of radiolarians, relative to the Tethys Ocean and Pangean marginal seas.