Sulfur isotopic evidence for global marine anoxia and low seawater sulfate concentration during the Late Triassic

Marine anoxia during the Late Triassic has mostly been reported from the western Tethys and Panthalassa, which were near the Central Atlantic Magmatic Province (CAMP), but whether it developed in global open oceans (e.g., the eastern Tethys) is unknown. Whether the marine anoxia was global or regional requires more research. Here, we present carbonate-associated sulfate (CAS) and pyrite delta S-34(py) data for the Late Triassic-Early Jurassic interval from the Wenquan Section in Qiantang Basin, Tibet. We found an 8 parts per thousand magnitude of Rhaetian positive sulfur isotope excursion (RPSE) of delta S-34(CAS) values, followed by a decrease in the isotopic offset between delta S-34(CAS) and delta S-34(PY) (i.e., Delta S-34(CAS-PY)). The decline in the isotopic offset between delta S-34(CAS) and delta S-34(py) may be due to low oceanic sulfate concentrations (similar to 0.1-0.3 mM) during the Late Triassic-Early Jurassic, according to our modeling. The RPSE found in this study was also found in western Tethys and eastern Panthalassa. Our sulfur cycle model shows that the RPSE is related to a 3.3-4.3-fold increase in the pyrite burial flux over a short time interval (70-106 kyr) and that a low sulfate concentration of 0.5 mM is needed to reproduce the magnitude of the positive delta S-34(CAS) shift. The similarities in the delta S-34(CAS) trends suggest that the RPSE may be a global oceanographic phenomenon. Thus, our delta S-34(CAS) data from the eastern Tethys support the global nature of the Late Triassic oceanic deoxygenation event, which regulated the sulfur cycle.