Krewer, C., Poulton, S.W. orcid.org/0000-0001-7621-189X, Newton, R.J. et al. (3 more authors) (2024) Controls on the Termination of Cretaceous Oceanic Anoxic Event 2 in the Tarfaya Basin, Morocco. American Journal of Science, 324. 11. ISSN 0002-9599
Abstract
Oceanic Anoxic Event 2 (OAE2) has been the focus of considerable research, but biogeochemical dynamics during the recovery from the carbon cycle disturbance largely remain unknown. Here, we present a high-resolution reconstruction of water column redox and nutrient cycling across the final stages of OAE2, in order to assess controls on the termination of widespread ocean anoxia. We focus on calcareous black shales deposited on a subtropical shelf at Tarfaya, Morocco, representing a location prone to water column anoxia beyond the temporal extent of the OAE itself. Our multi-proxy approach combining iron-sulfur systematics with redox-sensitive trace metal (U and Mo) concentrations documents persistent anoxia, with cyclic fluctuations between weakly euxinic (or possibly ferruginous) conditions and more intense euxinia. During the end of the carbon isotope plateau phase, elemental weathering ratios indicate muted variability in chemical weathering intensity, although fluctuating redox conditions may have been driven by changes in continental weathering inputs of sulfate and reactive iron. By contrast, during the recovery phase, changes in chemical weathering intensity appear to have exerted a strong control on redox fluctuations. Overall, the recovery phase documents progressively less reducing conditions and less intense chemical weathering, which resulted in decreased P recycling and intervals of P drawdown, as indicated by P phase partitioning results. These trends were interrupted by the Holywell Event, during which more intense euxinia and enhanced P recycling transiently returned during an interval of particularly low chemical weathering. Nevertheless, the general trend towards lower P bioavailability in the water column, due to both sequestration of P in the sediments and a likely progressive decrease in P supply via continental weathering, appears to have exerted a major control on the recovery from oceanic anoxia in this shelf setting, and potentially on a global scale.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | This item is protected by copyright. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License (CC BY-4.0). View this license’s legal deed at http://creativecommons.org/licenses/by/4.0 and legal code at http://creativecommons.org/licenses/by/4.0/legalcode for more information. |
Keywords: | carbon cycle, chemical weathering, Iron, Oceanic Anoxic Event 2 (OAE2), Phosphorus recycling, Redox changes, Trace elements |
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) |
Depositing User: | Symplectic Publications |
Date Deposited: | 30 May 2024 12:49 |
Last Modified: | 11 Sep 2024 14:58 |
Status: | Published |
Publisher: | American Journal of Science |
Identification Number: | 10.2475/001c.118797 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:212890 |