106 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

All students are encouraged to submit research to this poster session. Investigations from ANY geological subdiscipline are welcome. Presenters who are SGE members are eligible to compete for monetary awards distributed at the meeting.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Osmium Isotope Data from the Ireviken Biogeochemical Event in the Altajme Core, Gotland, Sweden

Paper number: 106-49
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

  • Anna McNally Presenting Author
    University of Iowa School of Earth, Environment, and Sustainability, Waterloo, IA
  • Alan Rooney
    Yale University, New Haven, CT
  • Bradley Cramer
    University of Iowa Earth & Environmental Sciences, Iowa City, IA

Abstract

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 impacted, with each of their signals showing that the inception of the perturbation took place during the onset of a 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 is most often interpreted as evidence of the emplacement of a Large Igneous Province (LIP) or other major mafic volcanic complexes. Our results show generally unradiogenic values that record little change across the entire interval. Prior to the onset of the Ireviken, Osi values were consistently under the median value of ~0.52, with a slight increase before the onset and then a decrease to 0.419. The lack of any clear negative excursion in Osi values across this interval is inconsistent with a LIP or other similar mafic complex emplacements during the Ireviken, similar to those of Mesozoic OAEs. However, Os isotopes from the sampled interval of the core are substantially lower than the modern oceanic values.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414261

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