GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 36-3
Presentation Time: 9:00 AM-5:30 PM


GOVERT, Daniel J.1, YOUNG, Seth A.1, KALJO, Dimitri2, HINTS, Olle2, NOBLE, Paula J.3, MARTMA, Tonu2 and OWENS, Jeremy D.4, (1)Earth, Ocean, and Atmospheric Science, Florida State University, 108 Carraway Building, Tallahassee, FL 32306, (2)Department of Geology, Tallinn University of Technology, Tallinn, 19086, Estonia, (3)Department of Geological Sciences & Engineering, University of Nevada, MS 172, Reno, NV 89557, (4)Department of Earth, Ocean & Atmospheric Science, Florida State University, 1017 Academic Way, Tallahassee, FL 32306

The Silurian Ireviken carbon isotope excursion (CIE) was a large-magnitude positive shift in δ13C values that occurred across the Llandovery-Wenlock boundary (~430 Ma). The Ireviken CIE has been documented from many worldwide localities and several paleocontinents. This study analyzes two localities that preserve deeper basinal mudstone and shale sequences: the Baltic Basin (Latvia) and the Franklinian Basin (Bathurst Island, Arctic Canada). Both localities preserve a maximum magnitude CIE of +3‰ respectively, suggesting an increase in organic carbon burial associated with the known marine mass extinction, termed the Ireviken Event. Approximately 80% of conodont and graptolite fauna during this event went extinct along with a ~50% decrease in trilobites, and brachiopods, as well as a decline in chitinozoans and acritarchs. Previous sea-surface temperature studies have suggested the Ireviken CIE and mass extinction were caused by global shifts in temperature which drove climate conditions to icehouse conditions. However, eustatic sea-level records and glacial sedimentary records are not consistent with this hypothesis and a definitive mechanism for this mass extinction is not well-constrained. For the first time this study will analyze a suite of local and global shale-based paleoredox proxies (δ34Spyr, Fe speciation, [Mo,V, U], ε205Tl) from these two deeper water mudstone sequences to test the hypothesis that an expansion of oceanic anoxia, and possibly euxinia (anoxia and sulfidic water-column), caused the Ireviken extinction event and drove increased organic carbon burial which affected the globally recognized CIE. Constraining the redox state of the local and global oceans during the Ireviken mass extinction event can illuminate the causes, consequences, and patterns of extinction related to this event through integrating new geochemical data with biotic records from deeper basinal settings.