Investigating the Role of Marine Redox Conditions and Orbital Forcings in an Early Silurian Mass Extinction (Ireviken Event): A Deeper Water Perspective

• Other Authors: Govert, Daniel J. (Daniel John) (author), Young, Seth A. (professor directing thesis), Owens, Jeremy D. (committee member), Parker, William C. (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean and Atmospheric Science (degree granting department)
• Format: Master Thesis
• Language: English
• Published: Florida State University 2020
• Subjects: Geology; Mathematics; Arctic; Bathurst Island; Canada; Cape Phillips; Phytoplankton
• Online Access: https://diginole.lib.fsu.edu/islandora/object/fsu%3A781661/datastream/TN/view/Investigating%20the%20Role%20of%20Marine%20Redox%20Conditions%20and%20Orbital%20Forcings%20in%20an%20Early%20%20%20%20%20%20%20%20%20%20Silurian%20Mass%20Extinction%20%28Ireviken%20Event%29.jpg

The Ireviken carbon isotope excursion (CIE) was a large-magnitude positive shift in δ13C values that is recorded in early Silurian (~432 Ma; Llandovery-Wenlock boundary) strata globally. Associated with this CIE is a marine mass extinction, the Ireviken Event (murchisoni Event in graptolites), during which approximately 80% of conodont and graptolite fauna went extinct, along with a ~50% reductions in trilobites and brachiopods, as well as a decline in corals, chitinozoans, and acritarchs (organic-walled phytoplankton group). Previous paleoredox studies of carbonate sequences throughout the Ireviken CIE and extinction event intervals have shown evidence for widespread euxinic (anoxic + sulfidic) conditions during this time in the Silurian oceans providing a possible causal mechanism for both of these linked biogeochemical events. This study investigates two localities that preserve deeper marine basinal mudstone/shale sequences to further test this redox-based hypothesis: the Baltic Basin (Latvia) and the Cape Phillips Basin (Bathurst Island, Arctic Canada). A set of local paleoredox proxies for both sites (34Spyr, [Mo, V, Mn], Fe-speciation) are utilized to constrain local marine water column conditions throughout the study interval. Additionally, samples were analyzed from both sections for thallium isotopes (205Tl), a global paleoredox proxy for Mn-oxide burial in the oceans. Local paleoredox proxy records (Fe-speciation and [Mn]) indicate both deeper water sections were reducing throughout the Ireviken CIE interval. Pyrite sulfur isotopes from multiple paleocean basins co-vary with previous 34SCAS datasets, both records indicate global pyrite burial initiated at the onset of the Ireviken CIE and continued throughout the peak carbon isotope interval. The new thallium isotope data presented herein suggest the global oceans were more reducing prior to the CIE interval and during the early stages of the marine extinction event, subsequently this interval was followed by a brief oxic event during the rising ...