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A continental-weathering control on orbitally driven redox-nutrient cycling during Cretaceous Oceanic Anoxic Event 2

Lookup NU author(s): Professor Simon Poulton, Dr Christian Maerz, Hannah Urquhart, Professor Thomas Wagner



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


The Cretaceous period (~145–65 m.y. ago) was characterized by intervals of enhanced organic carbon burial associated with increased primary production under greenhouse conditions. The global consequences of these perturbations, oceanic anoxic events (OAEs), lasted up to 1 m.y., but short-term nutrient and climatic controls on widespread anoxia are poorly understood. Here, we present a high-resolution reconstruction of oceanic redox and nutrient cycling as recorded in subtropical shelf sediments from Tarfaya, Morocco, spanning the initiation of OAE2. Iron-sulfur systematics and biomarker evidence demonstrate previously undescribed redox cyclicity on orbital time scales, from sulfidic to anoxic ferruginous (Fe-rich) water-column conditions. Bulk geochemical data and sulfur isotope modeling suggest that ferruginous conditions were not a consequence of nutrient or sulfate limitation, despite overall low sulfate concentrations in the proto–North Atlantic. Instead, fluctuations in the weathering influxes of sulfur and reactive iron, linked to a dynamic hydrological cycle, likely drove the redox cyclicity. Despite the potential for elevated phosphorus burial in association with Fe oxides under ferruginous conditions on the Tarfaya shelf, porewater sulfide generation drove extensive phosphorus recycling back to the water column, thus maintaining widespread open-ocean anoxia.

Publication metadata

Author(s): Poulton SW, Henkel S, Maerz C, Urquhart H, Floegel S, Kasten S, Sinninghe-Damste J, Wagner T

Publication type: Article

Publication status: Published

Journal: Geology

Year: 2015

Volume: 43

Issue: 11

Pages: 963-966

Print publication date: 01/11/2015

Online publication date: 24/09/2015

Acceptance date: 26/08/2015

Date deposited: 02/10/2015

ISSN (print): 0091-7613

ISSN (electronic): 1943-2682

Publisher: Geological Society of America


DOI: 10.1130/G36837.1


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Funder referenceFunder name
Natural Environment Research Council Research Fellowship
Royal Society-Wolfson Research Merit Award
SFB 754German Science Foundation