Thallium isotopes reveal protracted anoxia during the Toarcian (Early Jurassic) associated with volcanism, carbon burial, and mass extinction

Them, Theodore R.; Gill, Benjamin C.; Caruthers, Andrew H.; Gerhardt, Angela M.; Gröcke, Darren R.; Lyons, Timothy W.; Marroquín, Selva M.; Nielsen, Sune G.; Trabucho Alexandre, João P.; Owens, Jeremy D.

Abstract

For this study, we generated thallium (Tl) isotope records from two anoxic basins to track the earliest changes in global bottom water oxygen contents over the Toarcian Oceanic Anoxic Event (TOAE; ∼183 Ma) of the Early Jurassic. The T-OAE, like other Mesozoic OAEs, has been interpreted as an expansion of marine oxygen depletion based on indirect methods such as organic-rich facies, carbon isotope excursions, and biological turnover. Our Tl isotope data, however, reveal explicit evidence for earlier global marine deoxygenation of ocean water, some 600 ka before the classically defined T-OAE. This antecedent deoxygenation occurs at the Pliensbachian/Toarcian boundary and is coeval with the onset of initial large igneous province (LIP) volcanism and the initiation of a marine mass extinction. Thallium isotopes are also perturbed during the T-OAE interval, as defined by carbon isotopes, reflecting a second deoxygenation event that coincides with the acme of elevated marine mass extinctions and the main phase of LIP volcanism. This suggests that the duration of widespread anoxic bottom waters was at least 1 million years in duration and spanned early to middle Toarcian time. Thus, the Tl data reveal a more nuanced record of marine oxygen depletion and its links to biological change during a period of climatic warming in Earth’s past and highlight the role of oxygen depletion on past biological evolution.

Citation

Them, T. R., Gill, B. C., Caruthers, A. H., Gerhardt, A. M., Gröcke, D. R., Lyons, T. W., Marroquín, S. M., Nielsen, S. G., Trabucho Alexandre, J. P., & Owens, J. D. (2018). Thallium isotopes reveal protracted anoxia during the Toarcian (Early Jurassic) associated with volcanism, carbon burial, and mass extinction. Proceedings of the National Academy of Sciences, 115(26), 6596-6601. https://doi.org/10.1073/pnas.1803478115

• Journal Article Type: Article
• Acceptance Date: May 16, 2018
• Online Publication Date: Jun 11, 2018
• Publication Date: Jun 11, 2018
• Deposit Date: Sep 4, 2018
• Publicly Available Date: Dec 11, 2018
• Journal: Proceedings of the National Academy of Sciences
• Print ISSN: 0027-8424
• Electronic ISSN: 1091-6490
• Publisher: National Academy of Sciences
• Peer Reviewed: Peer Reviewed
• Volume: 115
• Issue: 26
• Article Number: 6596
• Pages: 6596-6601
• DOI: https://doi.org/10.1073/pnas.1803478115
• Public URL: https://durham-repository.worktribe.com/output/1321269