THE EXPANSION OF REDUCED ENVIRONMENTS DURING THE IREVIKEN BIOGEOCHEMICAL EVENT: NEW Δ34S DATA ACROSS THE LLANDOVERY-WENLOCK BOUNDARY OF GOTLAND, SWEDEN

The Ireviken Biogeochemical Event (IBE) is one of several major biogeochemical events in the Silurian and occurs across the Llandovery-Wenlock boundary. This event consists of a major positive carbon isotope excursion, increased biotic turnover, and significant perturbations within other biogeochemical cycles, such as sulfur. More recently the IBE has been hypothesized to coincide with the expansion of reducing marine conditions which allowed for a global increase in organic carbon burial rates, and lead to the Ireviken positive carbon isotope excursion.

One of the highest resolution carbon isotope datasets through this interval is in the Altajme core from Gotland, Sweden which offers an exceptionally well preserved and expanded stratigraphic section. New Sulfur isotopic data including δ³⁴S_pyr (pyrite) and δ³⁴S_CAS (carbonate-associated sulfate) from the Altajme core are indicative of a local signal of increased microbial sulfate reduction (MSR). The δ³⁴S_pyr signal provides evidence for a local expansion of reducing marine environments coincident with the IBE and when combined with data from the Baltic and distant basins the δ³⁴S_CAS data from this study may suggest a global expansion of reduced marine environments.