Responses of the biogeochemical sulfur cycle to Early Permian tectonic and climatic events

Abstract

The late Paleozoic was characterized by a series of continental collisions and ice ages. Despite the drastic environmental changes, sparse sulfur isotope data hinder our understanding of the late Paleozoic biogeochemical sulfur cycle, especially during the Early Permian. To overcome this potential bias, we present a high-resolution sulfur isotope record of carbonate-associated sulfate (CAS) and pyrite from the Carboniferous-Permian successions of the Svalbard archipelago. Throughout the Carboniferous, our results are largely consistent with the global trend, although the development of restricted environments resulted in a regionally observed δ34SCAS peak of +20‰ during the Gzhelian. The Early Permian δ34SCAS data in Svalbard bridge the gap in the existing record, showing a steady increase contemporaneous with the closure of the Ural Seaway and Gondwana glaciation, albeit superimposed by short-term oscillations. The enhanced incorporation of diagenetic sulfate into authigenic carbonates may have caused small-scale oscillations during the regional regression in the Artinskian, but the long-term increasing trend of δ34SCAS and its relation to known geological events can be best explained by the enhanced pyrite burial flux driven by a major shift in the locus of organic carbon burial from the continent to the ocean, with a lesser contribution from the dissolution of epicontinental seaway evaporites. Since the onset of the Middle Carboniferous Bashkirian δ34SCAS excursion also corresponds in timing to the major glaciation event and the closure of the Rheic Seaway, the sulfur isotope record in the course of the consolidation of Pangea is apparently punctuated by the episodes of increased pyrite burial and evaporite sulfate weathering, delineating the links between paleogeography, paleoclimate, and biogeochemical cycles.