FIRST OSMIUM ISOTOPE DATA FROM THE IREVIKEN BIOGEOCHEMICAL EVENT IN THE ALTAJME CORE, GOTLAND, SWEDEN

The Ireviken Biogeochemical Event was a major perturbation to the global carbon cycle during the Silurian. In addition to carbon, other geochemical cycles including nitrogen and sulfur were also impacted with each of their signals showing that the inception of the perturbation took place during the onset of the biotic crisis. This extinction event affected conodonts, graptolites, chitinozoans, trilobites, and a range of other taxa and was followed by the carbon isotope excursion. Whereas it is becoming increasingly clear that the Ireviken Biogeochemical Event was a Paleozoic example of an Oceanic Anoxic Event (OAE) that included a significant expansion of reducing environments in the marine realm, the initial mechanism(s) that triggered this expansion remain unclear.

Here, we sampled the well-studied Altajme Core, which was drilled in Gotland, Sweden, to recover Osmium (Os) isotope data across the Ireviken Biogeochemical Event. A major perturbation in Os isotopes is present in several well-known Mesozoic OAEs, and are most often interpreted as evidence of the emplacement of a Large Igneous Province or other major volcanic complexes. Although our work remains ongoing, the initial results include some extremely unradiogenic values that approach mantle values during the event initiation. More data are forthcoming to improve sample density and resolution of the event, but it is clear that the Os isotopes from the sampled interval of the core are substantially lower than the modern oceanic values.