Details
Original language | English |
---|---|
Article number | 105583 |
Journal | Precambrian research |
Volume | 338 |
Early online date | 19 Dec 2019 |
Publication status | Published - Mar 2020 |
Abstract
The invention of photosynthesis was a key interval in Earth's history, initiating major changes in the evolution of the oceans and atmosphere. Many studies suggest that oxygen levels were already enhanced before the Paleoproterozoic Great Oxidation Event (GOE, 2.45–2.32 Ga). However, the timing of the onset of photosynthetic oxygenation, as well as spatio-temporal fluctuations of atmospheric and oceanic oxygen levels are highly debated. Here, we present a new and substantial uranium (U) isotope dataset comprising marine sediments, e.g. black shales, carbonates and iron-rich sedimentary rocks, from the Hamersley Basin (Western Australia), Kaapvaal and Zimbabwe Cratons (both southern Africa) with depositional ages ranging from 3.4 to 2.2 Ga. Sub-recent U mobilization was monitored by analyzing 234U along with δ238U, and detrital U contribution was monitored with [Al]/[U] or [Th]/[U] ratios. Samples with significant authigenic U enrichment (EFU > 2), relative to post-Archean Australian Shale (PAAS), exhibit authigenic δ238U ranging from −0.96 to −0.02‰ (±0.05‰, 2 s.d. long-term reproducibility), which deviates markedly from typical δ238U of the continental crust (−0.40 to −0.20‰). Remarkably, we find increased δ238U variability in the upper Ghaap Group (2.50–2.47 Ga, carbonates and black shales) and the lower Pretoria Group (2.42–2.32 Ga, Duitschland Formation, shales) of the Kaapvaal Craton. The predominantly light U isotope composition of those samples is likely explained by U isotope fractionation related to the onset of partial U mobilization during slow oxidative weathering of uraninite shortly before and during the GOE. The lack of low δ238U values in the Timeball Hill Formation (overlying the Duitschland Formation) indicate the onset of quantitative U mobilization during (modern-style) oxidative weathering of uraninite and other U-bearing minerals with limited U isotope fractionation. These limited U isotope variations measured in the Paleoproterozoic Timeball Hill Formation further suggest that, in contrast to modern oceans, in the period following the GOE, U was largely quantitatively reduced and removed from the water column of the Transvaal basin which remained mainly anoxic at depth.
Keywords
- Archean, Early Proterozoic, Great Oxidation Event, Modern-style weathering, Oxidative weathering, Uranium isotope fractionation
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
Sustainable Development Goals
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In: Precambrian research, Vol. 338, 105583, 03.2020.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The onset of oxidative weathering traced by uranium isotopes
AU - Brüske, A.
AU - Martin, A. N.
AU - Rammensee, P.
AU - Eroglu, S.
AU - Lazarov, M.
AU - Albut, G.
AU - Schuth, S.
AU - Aulbach, S.
AU - Schoenberg, R.
AU - Beukes, N.
AU - Hofmann, A.
AU - Nägler, T.
AU - Weyer, S.
N1 - Funding Information: Ingo Horn (Leibniz University of Hannover) is thanked for help and guidance during (MC-) ICP-MS measurements of U isotopes and trace elements. Vanessa Sutterer (University of T?bingen) is thanked for assistance with X-ray fluorescence analyses of samples from core DP-16. Funding for SW, SS, ANM, ML, and AB was provided by the Deutsche Forschungsgemeinschaft (DFG) priority program SPP-1833 ?Building a habitable Earth? and is thankfully appreciated (to SW grant WE2850-15/1 and to SS grant SCHU2695/4). Part of this study was funded by the Deutsche Forschungsgemeinschaft (DFG) grant AU356/7 to SA. NJB and AH received research funding from the DST-NRF Centre of Excellence for Integrated Mineral and Energy Resource Analysis (CIMERA). Drilling of core GKP-01 was funded by the Agouron Institute in Pasadena during 2002-03 and that of BARB-3 and 5 by the ICDP in 2010. Core BH-1 (SACHA-W216) was drilled by the Council of Geoscience in Pretoria and cores DP-16 and KMF-5 by Gold Fields Limited. We thank the editor and reviewers for constructive comments that helped to improve the manuscript.
PY - 2020/3
Y1 - 2020/3
N2 - The invention of photosynthesis was a key interval in Earth's history, initiating major changes in the evolution of the oceans and atmosphere. Many studies suggest that oxygen levels were already enhanced before the Paleoproterozoic Great Oxidation Event (GOE, 2.45–2.32 Ga). However, the timing of the onset of photosynthetic oxygenation, as well as spatio-temporal fluctuations of atmospheric and oceanic oxygen levels are highly debated. Here, we present a new and substantial uranium (U) isotope dataset comprising marine sediments, e.g. black shales, carbonates and iron-rich sedimentary rocks, from the Hamersley Basin (Western Australia), Kaapvaal and Zimbabwe Cratons (both southern Africa) with depositional ages ranging from 3.4 to 2.2 Ga. Sub-recent U mobilization was monitored by analyzing 234U along with δ238U, and detrital U contribution was monitored with [Al]/[U] or [Th]/[U] ratios. Samples with significant authigenic U enrichment (EFU > 2), relative to post-Archean Australian Shale (PAAS), exhibit authigenic δ238U ranging from −0.96 to −0.02‰ (±0.05‰, 2 s.d. long-term reproducibility), which deviates markedly from typical δ238U of the continental crust (−0.40 to −0.20‰). Remarkably, we find increased δ238U variability in the upper Ghaap Group (2.50–2.47 Ga, carbonates and black shales) and the lower Pretoria Group (2.42–2.32 Ga, Duitschland Formation, shales) of the Kaapvaal Craton. The predominantly light U isotope composition of those samples is likely explained by U isotope fractionation related to the onset of partial U mobilization during slow oxidative weathering of uraninite shortly before and during the GOE. The lack of low δ238U values in the Timeball Hill Formation (overlying the Duitschland Formation) indicate the onset of quantitative U mobilization during (modern-style) oxidative weathering of uraninite and other U-bearing minerals with limited U isotope fractionation. These limited U isotope variations measured in the Paleoproterozoic Timeball Hill Formation further suggest that, in contrast to modern oceans, in the period following the GOE, U was largely quantitatively reduced and removed from the water column of the Transvaal basin which remained mainly anoxic at depth.
AB - The invention of photosynthesis was a key interval in Earth's history, initiating major changes in the evolution of the oceans and atmosphere. Many studies suggest that oxygen levels were already enhanced before the Paleoproterozoic Great Oxidation Event (GOE, 2.45–2.32 Ga). However, the timing of the onset of photosynthetic oxygenation, as well as spatio-temporal fluctuations of atmospheric and oceanic oxygen levels are highly debated. Here, we present a new and substantial uranium (U) isotope dataset comprising marine sediments, e.g. black shales, carbonates and iron-rich sedimentary rocks, from the Hamersley Basin (Western Australia), Kaapvaal and Zimbabwe Cratons (both southern Africa) with depositional ages ranging from 3.4 to 2.2 Ga. Sub-recent U mobilization was monitored by analyzing 234U along with δ238U, and detrital U contribution was monitored with [Al]/[U] or [Th]/[U] ratios. Samples with significant authigenic U enrichment (EFU > 2), relative to post-Archean Australian Shale (PAAS), exhibit authigenic δ238U ranging from −0.96 to −0.02‰ (±0.05‰, 2 s.d. long-term reproducibility), which deviates markedly from typical δ238U of the continental crust (−0.40 to −0.20‰). Remarkably, we find increased δ238U variability in the upper Ghaap Group (2.50–2.47 Ga, carbonates and black shales) and the lower Pretoria Group (2.42–2.32 Ga, Duitschland Formation, shales) of the Kaapvaal Craton. The predominantly light U isotope composition of those samples is likely explained by U isotope fractionation related to the onset of partial U mobilization during slow oxidative weathering of uraninite shortly before and during the GOE. The lack of low δ238U values in the Timeball Hill Formation (overlying the Duitschland Formation) indicate the onset of quantitative U mobilization during (modern-style) oxidative weathering of uraninite and other U-bearing minerals with limited U isotope fractionation. These limited U isotope variations measured in the Paleoproterozoic Timeball Hill Formation further suggest that, in contrast to modern oceans, in the period following the GOE, U was largely quantitatively reduced and removed from the water column of the Transvaal basin which remained mainly anoxic at depth.
KW - Archean
KW - Early Proterozoic
KW - Great Oxidation Event
KW - Modern-style weathering
KW - Oxidative weathering
KW - Uranium isotope fractionation
UR - http://www.scopus.com/inward/record.url?scp=85077239124&partnerID=8YFLogxK
U2 - 10.1016/j.precamres.2019.105583
DO - 10.1016/j.precamres.2019.105583
M3 - Article
AN - SCOPUS:85077239124
VL - 338
JO - Precambrian research
JF - Precambrian research
SN - 0301-9268
M1 - 105583
ER -