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| Titel |
Reconstructing the redox conditions of Paleoproterozoic oceans: Insights from the Zaonega Formation |
| VerfasserIn |
Neel Patel, Aubrey Zerkle, Gareth Izon, Alexander Romashkin, Dmtriy Rychanchik, Kärt Upraus, Kalle Kirsimäe, Boswell Wing, Aivo Lepland |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104592
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| Publikation (Nr.) |
 EGU/EGU2015-4018.pdf |
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| Zusammenfassung |
| The Paleoproterozoic is marked by profound changes in global tectonics, climate and
biogeochemical cycling of redox sensitive elements. Determining the redox state of marine
environments at this point in Earth’s history is fundamental in understanding the
connections between the geosphere and biosphere, including possible microbially-assisted
phosphogenesis. One hypothesis suggests that oxidative weathering following Earth’s first
significant rise in atmospheric oxygen, resulted in an increased supply of sulfate and
phosphate to the oceans, culminating in the first significant phosphorite deposits some
300–400 Ma later (Lepland et al., 2013). Thus Paleoproterozoic ocean structure
has been envisaged as stratified, through mildly oxygenated shallow water and
anoxic deep water, with temporally and spatially variable phases of euxinia possibly
linked to transient changes in the size of the seawater sulfate reservoir (Scott et al.,
2014).
New cores obtained from the upper part of the Â2 Ga Zaonega Formation in the Onega
Basin of Karelia, NW Russia, have recovered a variety of organic-rich mudstones and
carbonate rocks, containing several discrete mm–cm scale P-rich beds that may represent
seep or hydrothermally-influenced depositional settings (Lepland et al., 2013). Here we
present new Fe-speciation data and pyrite derived S–isotope data spanning one of these new
cores in order to: i) evaluate the redox state of the water column, determining the extent of
water column euxinia, and ii) assess the potential influence of S–cycling on phosphogenesis.
Preliminary Fe extractions show that total Fe is broadly dictated by lithology, but
generally lower in samples where the P–rich intervals occur, possibly supporting
extensive sulfate reduction and the formation of a euxinic water column. Further
S–isotope analyses on associated pyrites will determine the extent to which additional
biogeochemical S–cycling (e.g., sulfide oxidation) could also have contributed to the P–rich
intervals.
References:
Lepland, A., Joosu, L., Kirsimäe, K., Prave, A.R., Romashkin, A.E., Crne, A.E., Martin,
A.P., Fallick, A.E., Somelar, P., Üpraus, K., Mänd, K., Roberts, N.M.W., van Zuilen, M.A.,
Wirth, R., Schreiber, A., 2014. Potential influence of sulphur bacteria on Palaeoproterozoic
phosphogenesis. Nat. Geosci. 7 (1), 20–24.
Scott, C., Wing, A.B., Bekker, A., Planavsky, N.J., Medvedev, P., Bates, S.M., Yun, M.,
Lyons, T.W., 2014. Pyrite multiple-sulfur isotope evidence for rapid expansion and
contraction of the early Paleoproterozoic seawater sulfate reservoir. Earth Planet. Sci. Lett.
(389), 95–104. |
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