Han, Z., Hu, X., Newton, R.J. orcid.org/0000-0003-0144-6867 et al. (5 more authors) (2023) Spatially heterogenous seawater δ³⁴S and global cessation of Ca-sulfate burial during the Toarcian oceanic anoxic event. Earth and Planetary Science Letters, 622. 118404. ISSN 0012-821X
Abstract
The early Toarcian of the Early Jurassic saw a long-term positive carbon-isotope excursion (CIE) abruptly interrupted by a significant negative excursion (nCIE), associated with rapid global warming and an oceanic anoxic event (T-OAE, ∼183 Ma). However, the detailed processes and mechanisms behind widespread ocean deoxygenation are unclear. Here, we present high-resolution carbonate-associated sulfate sulfur-isotope (δ³⁴SCAS) records spanning the late Pliensbachian–Toarcian (Pl–To) interval from the Tibetan Himalaya. We observe a large positive sulfur-isotope excursion (SIE) from ∼20‰ (around the Pl–To boundary) to ∼40‰ (around the end of the T-OAE nCIE), attributed to large-scale burial of reduced sulfur (pyrite and sulfurized organic matter) under widespread anoxic/euxinic conditions. Importantly, high δ³⁴SCAS values were maintained into the mid–late Toarcian, even when global anoxic conditions diminished. The δ³⁴S data confirm significant spatial heterogeneity in seawater δ³⁴S compositions during the whole of the Toarcian, and provide strong evidence for a two-phase pattern of ocean deoxygenation. Upwelling of ³⁴S-enriched equatorial deep water, affected by significant reduced-sulfur burial, likely caused the greatly amplified SIE in the formerly adjacent Tibetan area. By contrast, the dampened magnitude of the Toarcian SIE in Europe is attributed to a smaller, local reduced-sulfur sink. Box-modeling results indicate that the persistent post-T-OAE positive δ³⁴S values were likely maintained because of a global reduction in Ca-sulfate (gypsum and anhydrite) burial driven by declining and continuously low seawater sulfate concentrations during and after the T-OAE. This geochemical pattern, albeit markedly reducing the total amount of global pyrite sequestration, increased the proportion of reduced to oxidized sulfur burial needed to generate the observed positive δ³⁴S values.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2023 Elsevier B.V. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License (CC BY-NC). |
Keywords: | Toarcian Oceanic Anoxic Event; CAS sulfur isotopes; heterogenous δ³⁴S ocean; stepwise deoxygenation; negligible Ca-sulfate deposition |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Earth Surface Science Institute (ESSI) (Leeds) |
Funding Information: | Funder Grant number NERC (Natural Environment Research Council) NE/N018559/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 10 Oct 2023 09:03 |
Last Modified: | 26 Oct 2023 14:38 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.epsl.2023.118404 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:203350 |