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Basinal hydrographic and redox controls on selenium enrichment and isotopic composition in Paleozoic black shales

Kipp, Michael A. and Algeo, Thomas J. and Stüeken, Eva E. and Buick, Roger (2020) Basinal hydrographic and redox controls on selenium enrichment and isotopic composition in Paleozoic black shales. Geochimica et Cosmochimica Acta, 287 . pp. 229-250. ISSN 0016-7037. doi:10.1016/j.gca.2019.12.016.

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Mass-dependent variations in selenium stable isotope ratios have recently been developed as a paleo-redox proxy. Since the reduction of selenium oxyanions occurs at a relatively high redox potential, this system holds promise for probing conditions relevant to the evolution and diversification of eukaryotic and animal life, which required substantial dissolved oxygen levels. Although several studies have identified selenium isotopic variability during oxygenation events in Earth’s distant past, we still have only a broad understanding of the mechanisms controlling this isotopic variability. This currently limits the robust interpretation of selenium isotope variability to first-order mechanisms driving large-magnitude changes. Here, we explore selenium isotope variability within and among Paleozoic black shales deposited on the North American craton that have been well-studied using a variety of other paleo-environmental proxies. Using this combined dataset, we attempt to unravel the controls on selenium abundance and isotope ratios in organic-rich ancient marine sedimentary rocks. We find that in the Late Pennsylvanian units, an estuarine nutrient trap on the Midcontinent Shelf enabled vigorous selenium recycling, leading to very high concentrations in sediments and enrichment of heavy isotopes in the aqueous selenium reservoir. In contrast, we find that among the Late Devonian units, differences in local basinal hydrography led to a gradient in selenium abundance and isotopic fractionation, with the more restricted basins depleting their selenium reservoirs and causing enrichment of heavy isotopes in the residual aqueous reservoir. In both of these case studies, the additional context provided by complementary paleo-environmental proxies was critical for distinguishing between possible drivers of selenium isotopic variability. When extending such studies to other paleo-environmental settings, we suggest that the continued use of complementary datasets will enable the most robust use of the selenium paleo-redox proxy. Moreover, further development of techniques for high-precision and phase-specific selenium isotope measurements will greatly improve the ability to deduce subtle redox fluctuations with this proxy.

Item Type:Article
Related URLs:
URLURL TypeDescription
Kipp, Michael A.0000-0003-1844-3670
Algeo, Thomas J.0000-0002-3333-7035
Stüeken, Eva E.0000-0001-6861-2490
Additional Information:© 2019 Elsevier Ltd. Received 14 July 2019, Accepted 13 December 2019, Available online 23 December 2019. We thank Scott Kuehner, Fang-Zhen Teng, Bruce Nelson, Yan Hu and Andy Schauer for technical support. This work was supported by an NSF Graduate Research Fellowship to MAK (DGE-1256082) and a NASA Exobiology grant to RB (NNX16AI37G). TJA thanks the state geological surveys of Ohio, Kentucky, Tennessee, New York, Illinois, Kansas, Oklahoma, and North Dakota for providing access to cores sampled for studies of Upper Pennsylvanian and Upper Devonian black shales, and Jeff Over for providing samples from three locales of the Woodford Formation. Three anonymous reviewers are thanked for comments that substantively improved this manuscript. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1256082
Subject Keywords:Selenium isotopes; Epicontinental seas, late Paleozoic; Basin hydrography; Redox proxies; Redox-sensitive trace elements
Record Number:CaltechAUTHORS:20201001-124645034
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Official Citation:Michael A. Kipp, Thomas J. Algeo, Eva E. Stüeken, Roger Buick, Basinal hydrographic and redox controls on selenium enrichment and isotopic composition in Paleozoic black shales, Geochimica et Cosmochimica Acta, Volume 287, 2020, Pages 229-250, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105724
Deposited By: Tony Diaz
Deposited On:01 Oct 2020 20:18
Last Modified:16 Nov 2021 18:45

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