Collapse of Late Permian chert factories in the equatorial Tethys and the nature of the Early Triassic chert gap

The Permian witnessed the extensive development of cherts from the palaeoequator to the northern high latitudes. However, large-scale chert deposition was abruptly terminated in the latest Permian, resulting in the Early Triassic "chert gap". Deepwater sedimentary successions in South China across the Permian-Triassic transition recorded the shift from radiolarian- and spicule-bearing siliceous units to carbonate/siliciclastic facies in the equatorial Tethys. In order to constrain the onset time of the chert production crisis and understand its nature, we carried out sedimentological, palaeontological, and geochemical analyses on two deepwater sections along the northern margin of the South China Block. Our results suggest that chert production in equatorial latitudes was already weakened in the Clarkina changxingensis conodont zone. The final collapse of the chert factory occurred in the Clarkina yini - Hindeodus praeparvus/Clarkina zhangi Zone and was accompanied by a significant decrease in SiO₂ content, which predated the negative carbonate carbon isotope excursion and climate warming but coincided with a sharp decline in primary productivity. Combined with Si box model results, our study suggests that global warming cannot maintain a multi-million-year chert gap. Instead, the loss of siliceous skeleton producers was the primary cause of the Early Triassic chert demise.