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Durham University

Department of Earth Sciences


Publication details for Dr Darren R. Gröcke

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. (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.

Author(s) from Durham


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.