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| Titel |
Sulphur bacteria mediated formation of Palaeoproterozoic phosphorites |
| VerfasserIn |
Lauri Joosu, Aivo Lepland, Kalle Kirsimäe |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091729
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| Publikation (Nr.) |
 EGU/EGU2014-6037.pdf |
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| Zusammenfassung |
| Modern phosphorite formation is typically associated with high productivity in upwelling
areas where apatite (Ca-phosphate) precipitation is mediated by sulphur oxidising bacteria
[1]. They inhabit the oxic/anoxic interface within the upper few centimetres of sediment
column, accumulating phosphate in their cells under oxic conditions and releasing it rapidly
when conditions become anoxic. Sulphur bacteria are known to live in close association with
a consortium of anaerobic methane oxidising archaea and syntrophic sulphate-reducing
bacteria.
Paleoproterozoic, c. 2.0 Ga Zaonega Formation in Karelia, Russia contains several P-rich
intervals in the upper part of 1500 m thick succession of organic-rich sedimentary rocks
interlayered with mafic tuffs and lavas. Apatite in these P-rich intervals forms impure
laminae, lenses and round-oval nodules which diameters typically range from 300 to 1000
μm. Individual apatite particles in P-rich laminae and nodules commonly occur as cylinders
that are 1-8 μm long and have diameters of 0.5-4 μm. Cross-sections of best preserved
cylindrical apatite particles reveal a thin outer rim whereas the internal parts consist
of small anhedral elongated crystallites, intergrown with carbonaceous material.
During recrystallization the outer rim thickens towards interior and cylinders may
attain hexagonal crystal habit, but their size and shape remains largely unchanged
[2].
The sizes of Zaonega nodules are similar to giant sulphide-oxidising bacteria known from
modern and ancient settings [3, 4]. Individual apatite cylinders and aggregates have shapes
and sizes similar to the methanotrophic archaea that inhabit microbial mats in modern
seep/vent areas where they operate in close associations with sulphur-oxidising microbial
communities [5]. Seep/vent influence during the Zaonega phosphogenesis is indicated by
variable, though positive Eu anomaly, expected in magmatically active sedimentary
environment experiencing several lava flows. Moreover, P-rich intervals in the Zaonega
Formation are found in organic-rich sediments exhibiting strongly negative δ13Corg values
(-37 to -34 per mil) which is interpreted to reflect the methanotrophic biomass.
We conclude that modern-style phosphogenesis, mediated by sulphide-oxidising
bacteria living in consortium with methanotrophs, was established at least 2 Ga
ago.
[1] Schulz and Schulz (2005) Science 307, 416-418 [2] Lepland, Joosu, Kirsimäe, Prave,
Romashkin, Ärne, Martin, Fallick, Somelar, Üpraus, Mänd, Roberts, van Zuilen, Wirth,
Schreiber (2014) Nature geoscience 7, 20-24 [3] Bailey, Joye, Kalanetra, Flood, and
Corsetti (2007) Nature 445, 198-201 [4] Schulz, Brinkhoff, Ferdelman, Marine,
Teske and Jorgensen (1999) Science 284, 493-495 [5] Knittel, Losekann, Boetius,
Kort and Amann (2005) Applied and Environmental Microbiology 71, 467-479. |
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