Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 115, Issue 26, Pages 6596-6601Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1803478115
Keywords
Toarcian Oceanic Anoxic Event; Early Jurassic; thallium isotopes; carbon isotope excursion; large igneous province
Categories
Funding
- Florida State University Arts and Sciences Postdoctoral Fellowship
- Geological Society of America
- American Association of Petroleum Geologists
- Society for Sedimentary Geology
- Virginia Polytechnic Institute and State University
- National Science Foundation (NSF) [EAR-1324752]
- NSF [OCE-1624895, EAR-0719911, DMR-1157490]
- NASA [NNX16AJ60G]
- State of Florida
- Directorate For Geosciences
- Division Of Ocean Sciences [1624895] Funding Source: National Science Foundation
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For this study, we generated thallium (TI) isotope records from two anoxic basins to track the earliest changes in global bottom water oxygen contents over the Toarcian Oceanic Anoxic Event (TOAE; similar to 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 TI 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 TI 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.
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