Substantial incorporation of isotopically heavy reduced U species into marine carbonate sediments
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Substantial incorporation of isotopically heavy reduced U species into marine carbonate sediments. / Yuan, Yan; Chen, Tianyu; Zhang, Feifei; Liu, Yuanyuan; Xiong, Guolin; Wei, Guang-Yi; Dahl, Tais W.; Yan, Wen; Ling, Hong-Fei; Cheng, Hai; Shen, Shu-Zhong.
In: Geochimica et Cosmochimica Acta, Vol. 358, 2023, p. 27-37.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Substantial incorporation of isotopically heavy reduced U species into marine carbonate sediments
AU - Yuan, Yan
AU - Chen, Tianyu
AU - Zhang, Feifei
AU - Liu, Yuanyuan
AU - Xiong, Guolin
AU - Wei, Guang-Yi
AU - Dahl, Tais W.
AU - Yan, Wen
AU - Ling, Hong-Fei
AU - Cheng, Hai
AU - Shen, Shu-Zhong
N1 - Publisher Copyright: © 2023 Elsevier Ltd
PY - 2023
Y1 - 2023
N2 - The uranium (U) isotope ratio (238U/235U, reported as δ238U) in marine carbonates is an important proxy for reconstructing changes in past oceanic redox conditions, based on the essential assumption that U in carbonates originates from dissolved U(VI) in seawater. However, diagenetic processes may induce the addition of isotopically heavy U(IV) into the carbonates, complicating the application of the U isotope proxy. So far, the valence states of trace amounts of U and its relation with U isotope composition in marine carbonate sediments have not been directly studied. In this study, we have calibrated an ion-exchange chromatographic method to separate U(IV) from U(VI) in geological carbonate samples (e.g., modern and fossil corals, stalagmites, cold seep carbonates) and quantified their contents by mass spectrometry. Our study confirms that modern coral carbonates are faithful archives of U(VI) sourced from seawater. Surprisingly, drill core samples from a modern coral carbonate platform, which bear no sign of alteration inferred from conventional diagenetic proxies (e.g., Mn/Sr), show significant positive correlation between U(IV) fraction and bulk carbonate δ238U, suggesting U(IV) is present in the marine carbonates and drives δ238U toward higher values than that of seawater. We therefore suggest that coupled valence and isotope analyses of U in marine carbonates could provide critical constraints toward reliable reconstruction of marine redox evolution in the Earth's history.
AB - The uranium (U) isotope ratio (238U/235U, reported as δ238U) in marine carbonates is an important proxy for reconstructing changes in past oceanic redox conditions, based on the essential assumption that U in carbonates originates from dissolved U(VI) in seawater. However, diagenetic processes may induce the addition of isotopically heavy U(IV) into the carbonates, complicating the application of the U isotope proxy. So far, the valence states of trace amounts of U and its relation with U isotope composition in marine carbonate sediments have not been directly studied. In this study, we have calibrated an ion-exchange chromatographic method to separate U(IV) from U(VI) in geological carbonate samples (e.g., modern and fossil corals, stalagmites, cold seep carbonates) and quantified their contents by mass spectrometry. Our study confirms that modern coral carbonates are faithful archives of U(VI) sourced from seawater. Surprisingly, drill core samples from a modern coral carbonate platform, which bear no sign of alteration inferred from conventional diagenetic proxies (e.g., Mn/Sr), show significant positive correlation between U(IV) fraction and bulk carbonate δ238U, suggesting U(IV) is present in the marine carbonates and drives δ238U toward higher values than that of seawater. We therefore suggest that coupled valence and isotope analyses of U in marine carbonates could provide critical constraints toward reliable reconstruction of marine redox evolution in the Earth's history.
KW - Carbonates
KW - Isotopes
KW - Redox
KW - Tetravalent uranium
U2 - 10.1016/j.gca.2023.07.023
DO - 10.1016/j.gca.2023.07.023
M3 - Journal article
AN - SCOPUS:85168373398
VL - 358
SP - 27
EP - 37
JO - Geochimica et Cosmochimica Acta. Supplement
JF - Geochimica et Cosmochimica Acta. Supplement
SN - 0046-564X
ER -
ID: 363439974