Continentally-derived solutes in shallow Archean seawater: Rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa
The chemical composition of surface water in the photic zone of the Precambrian ocean is almost exclusively known from studies of stromatolitic carbonates, while banded iron formations (IFs) have provided information on the composition of deeper waters. Here we discuss the trace element and Nd isoto...
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ftgfzpotsdam:oai:gfzpublic.gfz-potsdam.de:item_236540 2023-05-15T16:30:26+02:00 Continentally-derived solutes in shallow Archean seawater: Rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa Alexander, B. Bau, M. Andersson, P. Dulski, P. 2008 https://gfzpublic.gfz-potsdam.de/pubman/item/item_236540 unknown info:eu-repo/semantics/altIdentifier/doi/10.1016/j.gca.2007.10.028 https://gfzpublic.gfz-potsdam.de/pubman/item/item_236540 Geochimica et Cosmochimica Acta 550 - Earth sciences info:eu-repo/semantics/article 2008 ftgfzpotsdam https://doi.org/10.1016/j.gca.2007.10.028 2022-09-14T05:57:06Z The chemical composition of surface water in the photic zone of the Precambrian ocean is almost exclusively known from studies of stromatolitic carbonates, while banded iron formations (IFs) have provided information on the composition of deeper waters. Here we discuss the trace element and Nd isotope geochemistry of very shallow-water IF from the Pongola Supergroup, South Africa, to gain a better understanding of solute sources to Mesoarchean shallow coastal seawater. The Pongola Supergroup formed on the stable margin of the Kaapvaal craton not, vert, similar2.9 Ga ago and contains banded iron formations (IFs) that represent the oldest documented Superior-type iron formations. The IFs are near-shore, pure chemical sediments, and shale-normalized rare earth and yttrium distributions (REYSN) exhibit positive LaSN, GdSN, and YSN anomalies, which are typical features of marine waters throughout the Archean and Proterozoic. The marine origin of these samples is further supported by super-chondritic Y/Ho ratios (average Y/Ho = 42). Relative to older Isua IFs (3.7 Ga) from Greenland, and younger Kuruman IFs (2.5 Ga) also from South Africa, the Pongola IFs are depleted in heavy rare earth elements (HREE), and appear to record variations in solute fluxes related to sea level rise and fall. Sm–Nd isotopes were used to identify potential sediment and solute sources within pongola shales and IFs. The epsilon (Porson)Nd(t) for Pongola shales ranges from −2.7 to −4.2, and epsilon (Porson)Nd(t) values for the coeval iron-formation samples (range −1.9 to −4.3) are generally indistinguishable from those of the shales, although two IF samples display epsilon (Porson)Nd(t) as low as −8.1 and −10.9. The similarity in Nd isotope signatures between the shale and iron-formation suggests that mantle-derived REY were not a significant Nd source within the Pongola depositional environment, though the presence of positive Eu anomalies in the IF samples indicates that high-T hydrothermal input did contribute to their REY signature. ... Article in Journal/Newspaper Greenland GFZpublic (German Research Centre for Geosciences, Helmholtz-Zentrum Potsdam) Greenland Geochimica et Cosmochimica Acta 72 2 378 394 |
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GFZpublic (German Research Centre for Geosciences, Helmholtz-Zentrum Potsdam) |
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ftgfzpotsdam |
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unknown |
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550 - Earth sciences |
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550 - Earth sciences Alexander, B. Bau, M. Andersson, P. Dulski, P. Continentally-derived solutes in shallow Archean seawater: Rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa |
topic_facet |
550 - Earth sciences |
description |
The chemical composition of surface water in the photic zone of the Precambrian ocean is almost exclusively known from studies of stromatolitic carbonates, while banded iron formations (IFs) have provided information on the composition of deeper waters. Here we discuss the trace element and Nd isotope geochemistry of very shallow-water IF from the Pongola Supergroup, South Africa, to gain a better understanding of solute sources to Mesoarchean shallow coastal seawater. The Pongola Supergroup formed on the stable margin of the Kaapvaal craton not, vert, similar2.9 Ga ago and contains banded iron formations (IFs) that represent the oldest documented Superior-type iron formations. The IFs are near-shore, pure chemical sediments, and shale-normalized rare earth and yttrium distributions (REYSN) exhibit positive LaSN, GdSN, and YSN anomalies, which are typical features of marine waters throughout the Archean and Proterozoic. The marine origin of these samples is further supported by super-chondritic Y/Ho ratios (average Y/Ho = 42). Relative to older Isua IFs (3.7 Ga) from Greenland, and younger Kuruman IFs (2.5 Ga) also from South Africa, the Pongola IFs are depleted in heavy rare earth elements (HREE), and appear to record variations in solute fluxes related to sea level rise and fall. Sm–Nd isotopes were used to identify potential sediment and solute sources within pongola shales and IFs. The epsilon (Porson)Nd(t) for Pongola shales ranges from −2.7 to −4.2, and epsilon (Porson)Nd(t) values for the coeval iron-formation samples (range −1.9 to −4.3) are generally indistinguishable from those of the shales, although two IF samples display epsilon (Porson)Nd(t) as low as −8.1 and −10.9. The similarity in Nd isotope signatures between the shale and iron-formation suggests that mantle-derived REY were not a significant Nd source within the Pongola depositional environment, though the presence of positive Eu anomalies in the IF samples indicates that high-T hydrothermal input did contribute to their REY signature. ... |
format |
Article in Journal/Newspaper |
author |
Alexander, B. Bau, M. Andersson, P. Dulski, P. |
author_facet |
Alexander, B. Bau, M. Andersson, P. Dulski, P. |
author_sort |
Alexander, B. |
title |
Continentally-derived solutes in shallow Archean seawater: Rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa |
title_short |
Continentally-derived solutes in shallow Archean seawater: Rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa |
title_full |
Continentally-derived solutes in shallow Archean seawater: Rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa |
title_fullStr |
Continentally-derived solutes in shallow Archean seawater: Rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa |
title_full_unstemmed |
Continentally-derived solutes in shallow Archean seawater: Rare earth element and Nd isotope evidence in iron formation from the 2.9 Ga Pongola Supergroup, South Africa |
title_sort |
continentally-derived solutes in shallow archean seawater: rare earth element and nd isotope evidence in iron formation from the 2.9 ga pongola supergroup, south africa |
publishDate |
2008 |
url |
https://gfzpublic.gfz-potsdam.de/pubman/item/item_236540 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
Greenland |
genre_facet |
Greenland |
op_source |
Geochimica et Cosmochimica Acta |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1016/j.gca.2007.10.028 https://gfzpublic.gfz-potsdam.de/pubman/item/item_236540 |
op_doi |
https://doi.org/10.1016/j.gca.2007.10.028 |
container_title |
Geochimica et Cosmochimica Acta |
container_volume |
72 |
container_issue |
2 |
container_start_page |
378 |
op_container_end_page |
394 |
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1766020159391137792 |