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Ocean redox conditions between the Snowballs – geochemical constraints from Arena Formation, East Greenland

Scheller, Eva L. and Dickson, Alexander J. and Canfield, Donald E. and Korte, Christoph and Kristiansen, Kasper K. and Dahl, Tais W. (2018) Ocean redox conditions between the Snowballs – geochemical constraints from Arena Formation, East Greenland. Precambrian Research, 319 . pp. 173-186. ISSN 0301-9268.

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The emergence of animal ecosystems is largely believed to have occurred in increasingly oxygenated oceans after the termination of the Sturtian and Marinoan glaciations. This transition has led to several hypotheses for the mechanism driving ocean oxygenation and animal evolution. One hypothesis is that enhanced weathering increased oceanic nutrient levels, primary productivity and organic carbon burial, and ultimately oxygenated the atmosphere and oceans. Another hypothesis suggests that an animal-driven reorganization of the marine biogeochemical cycles might have oxygenated the oceans. Through molybdenum (Mo), carbon (C), sulfur (S) isotopes and iron (Fe) speciation results from the Arena Fm, East Greenland, this study constrains ocean redox conditions during the Cryogenian, after the Sturtian deglaciation and before the major radiation of animals. Carbon and sulfur isotope stratigraphy is used to correlate the Arena Fm with other formations worldwide between the Sturtian and Marinoan glaciations (∼720–635 Ma). The lower part of the Arena Fm (∼25 m) consists of black shales deposited under locally euxinic conditions as evidenced by high proportions of highly reactive iron (Fe_(HR)/Fe_T > 0.38) and pyrite (Fe_(PY)/Fe_(HR) > 0.7). These black shales display small Mo enrichments (<3 ppm) and low Mo/TOC compared to overlying shales and Phanerozoic euxinic sediments. The maximum δ^(98)Mo value is observed in the basal Arena Fm (1.5‰). Many samples display lower δ^(98)Mo than typical oceanic input fluxes, which can be explained by Mo isotope fractionation from a marine Mo pool with δ^(98)Mo ∼ 1.3‰, similar to that inferred from other Cryogenic euxinic basins. The combination of low [Mo] and δ^(98)Mo suggests that widespread anoxia prevailed in the oceans at this time. Our data are consistent with most other studies from this time suggesting that ocean oxygenation was not linked to Snowball Earth deglaciation, but was delayed until animals effectively entered the scene.

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Additional Information:© 2017 Published by Elsevier B.V. Received 5 July 2017, Revised 29 October 2017, Accepted 3 December 2017, Available online 8 December 2017. Thanks H. Grøn Jensen and B. Petersen for laboratory assistance. KKK thanks the organizers and field assistance of Bjørn Buchardt and Svend Stouge during fieldwork in August 2005. TWD acknowledges Minik Rosing for field assistance during field work in 2011 and Christian Bjerrum for use of handheld X-Ray Fluorescence analyzer. This project was funded by the Villum Foundation to TWD (1168439, VKR023127). Field trip to East Greenland in 2007 was funded by the Carlsberg Foundation, and the 2011 field campaign with expedition ship, S/V Activ led by Captain Jonas Bergsøe was funded by Skibsreder Carsten Brebøls Almenyttige Fond and Dr. Frederik Paulsen. We thank the Carlsberg Foundation Distinguished Associate Professor Fellowship (TWD), Independent Research Fund Denmark (TWD, CK) and the Villum Foundation (DEC) for financial support.
Funding AgencyGrant Number
Villum Foundation1168439
Villum FoundationVKR023127
Carlsberg FoundationUNSPECIFIED
Skibsreder Carsten Brebøls Almenyttige FondUNSPECIFIED
Independent Research Fund DenmarkUNSPECIFIED
Subject Keywords:Ocean oxygenation; Ocean anoxia; Neoproterozoic; Molybdenum; Molybdenum isotopes; stable isotope fractionation; Snowball Earth; Cryogenian
Record Number:CaltechAUTHORS:20171212-132912679
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Official Citation:Eva L. Scheller, Alexander J. Dickson, Donald E. Canfield, Christoph Korte, Kasper K. Kristiansen, Tais W. Dahl, Ocean redox conditions between the snowballs – Geochemical constraints from Arena Formation, East Greenland, Precambrian Research, Volume 319, 2018, Pages 173-186, ISSN 0301-9268,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83831
Deposited By: Tony Diaz
Deposited On:12 Dec 2017 21:37
Last Modified:26 Nov 2018 18:35

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