Major sulfur cycle perturbations in the Panthalassic Ocean across the Pliensbachian-Toarcian boundary and the Toarcian Oceanic Anoxic Event

The early Toarcian Oceanic Anoxic Event (T-OAE, similar to 183 Ma) was characterized by marine deoxygenation and the burial of organic-rich sediments at numerous localities worldwide. However, the extent of marine anoxia and its impact on the sulfur cycle during the T-OAE is currently poorly understood. Here, stable sulfur isotopes of reduced metal-bound sulfur (delta S-34(pyrite)) and pyrite sulfur concentrations (S-PY) have been analyzed across the Pliensbachian-Toarcian boundary (Pl-To) and the T-OAE from the Sakahogi and Sakuraguchi-dani sections (Japan), which were deposited in the deep and shallow Panthalassic Ocean, respectively. Our data reveal marked positive delta S-34(pyrite) excursions of >10 parts per thousand across both the Pl-To and the T-OAE at Sakahogi, coincident with increases in S-PY, and a positive excursion of >20 parts per thousand at the onset of the T-OAE at Sakuraguchi-dani. Whilst the development of deep-water anoxic/euxinic conditions could have resulted in an enhanced burial of pyrite, and also partly contributed to the positive excursion of delta S-34(pyrite,) variations in delta(34)S(pyrite )at Sakahogi were most likely controlled by elevated export production and/or preservation. On the shallow shelf generally low and highly variable S-PY and the positive shift in delta S-34(pyrite) were likely attributable mainly to elevated sedimentation rates, with redox playing only a minor role in controlling pyrite abundance. Our discovery of a positive delta S-34(pyrite) excursion across the Pl-To at Sakahogi indicates a hitherto unrecognized perturbation to the deep-water sulfur cycle, potentially associated with increased seafloor organic matter flux and pyrite burial at this time, consistent with a transient interval of anoxia.