Early Jurassic long-term oceanic sulfur-cycle perturbations in the Tibetan Himalaya

Abstract The Early Jurassic is an important interval characterized by several global carbon-isotope ( δ 13 C) perturbations. Although the δ 13 C records are becoming better documented during this time interval, we have a relatively poor understanding of the associated long-term environmental and climatic changes. In order to decipher these events, we here present new stable sulfur-isotope data of carbonate-associated sulfate ( δ 34 SCAS) for the Sinemurian–Pliensbachian interval from the Wolong section in the Tibetan Himalaya that was located palaeogeographically in the southern hemisphere. An overall positive shift in δ 34 SCAS coincides with the negative δ 13 C excursion around the Sinemurian–Pliensbachian boundary, suggesting an increased 34S-depleted pyrite burial rate. The ensuing overarching negative δ 34 SCAS shift coincides with the upper Pliensbachian positive δ 13 C excursion. The initial falling limb of the δ 34 SCAS shift suggests a transient δ 34 S-depleted sulfate input, but this trend was soon reversed to become positive, likely caused by a persistently enhanced 32S-rich pyrite burial flux in the latest Pliensbachian. Modeling results show that maximum oceanic sulfate concentration likely decreased during the Sinemurian–Toarcian interval, probably due to large-scale evaporite deposition in the western Tethys and proto-Atlantic and enhanced pyrite burial in a number of marine settings. The concentration of seawater sulfate could have been high enough to maintain a homogeneous sulfur-isotope ocean in the late Sinemurian, but its persistent decrease may have initiated a spatially heterogeneous ocean after the Pliensbachian: an oceanic geochemical state that was amplified during the Toarcian Oceanic Anoxic Event.