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Early Proterozoic (2.0 GA) Phosphorites from Pechenga Greenstone Belt and Their OriginThe period of 2500-2000 Ma is heralded by several other hallmark events, including onset and decline of the greatest positive excursion of Beta13Ccarb (Lomagundi-Jatuli Paradox), development of a significant seawater sulphate reservoir, abundant deposition of anomalously organic matter (OM)-rich sediments, the oldest known significant petroleum deposits (Shunga Event), and the appearance of first known marine phosphorites at 2000 Ma as reported here. They occur as numerous rounded, soft-deformed, clasts in fine-pebble intra-formational conglomerates, forming two separate c. 200 m-thick turbidite fans within the 1000 m-thick OM- and sulphide-rich turbiditic greywackes of the Pilgujaervi Formation in the Pechenga Greenstrone Belt, NW Russia. Carbonate-fluorapatite is the main mineral in the phosphorite clasts. OM, framboidal and micronodular pyrite as well as inclusions of quartz and chlorite are additional components. Many clasts show microlayering with a variable degree of soft-deformation, implying that they were derived from non-lithified, bedded phosphorites. Numerous samples revealed diverse microbial microstructures interpreted as cyanobacterial mats consisting of filamentous (1-3 micrometer in diameter, 20 micrometers in length), coccoidal (0.8-1.0 micrometers) and ellipsoidal or rod-shaped microfossils (0.8 micrometers in diameter, around 2 micrometers in length) which morphologically resemble modern Microcoleus and Syphonophycus, Thiocapsa, and Rhabdoderma, respectively, reported from alkaline or saline environments. No principle differences have been found between microfossils described from Cambrian and Phanerozoic and the 2000 Ma phosphorites. The sequence of the early Palaeoproterozoic events which point to a significant oxidation of the hydrosphere, now including formation of phosphorites and change in the phosphorous cycle, mimics the sequence which was repeated once again at the Neoproterozoic-Cambrian transition, implying that oxidation of the terrestrial atmosphere-hydrosphere system experienced an irregular cyclic development.
Document ID
20070037463
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Rozanov, A. Yu.
(Academy of Sciences (Russia) Moscow, Russian Federation)
Astafieva, M. M.
(Academy of Sciences (Russia) Moscow, Russian Federation)
Melezhik, V. A.
(Academy of Sciences (Russia) Moscow, Russian Federation)
Hoover, R. B.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Lepland, I.
(Academy of Sciences (Russia) Moscow, Russian Federation)
Date Acquired
August 24, 2013
Publication Date
August 26, 2007
Subject Category
Geophysics
Meeting Information
Meeting: SPIE Optics and Photonics 2007
Location: San Diego, CA
Country: United States
Start Date: August 26, 2007
End Date: August 30, 2007
Sponsors: International Society for Optical Engineering
Funding Number(s)
CONTRACT_GRANT: NSH-974.2003.5
CONTRACT_GRANT: RFBR-05-04-48088
CONTRACT_GRANT: RFBR-03-05-64499
Distribution Limits
Public
Copyright
Other

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