Fe–S system was studied in a deepwater P–Tr boundary section (Xiakou, central China).
Redox conditions changed from stably euxinic to fluctuating during the end-Permian.
The onset of Fe–S system perturbations preceded the mass extinction by ∼10 kyr.
Two euxinic pulses coincided with mass extinction episodes and volcanic eruptions.
These relationships favor volcanism as the trigger for the end-Permian crisis.