Early Proterozoic (2.04 GA) phosphorites of Pechenga Greenstone Belt and their origin

Abstract

No principal differences have been found between microfossils described from Cambrian and Phanerozoic and the 2000 Ma phosphorites. Numerous samples revealed diverse microbial microstructures interpreted as cyanobacterial mats consisting of filamentous (1-3 µm in diameter, 20 µm in length), coccoidal (0.8-1.0 µm) and ellipsoidal or rod-shaped microfossils (0.8 µm in diameter, around 2 µm in length) which morphologically resemble modern Microcoleus and Siphonophycus, Thiocapsa, and Rhabdoderma, respectively, reported from alkaline or saline environments. The sequence of the early Palaeoproterozoic events which point to a significant oxidation of the hydrosphere, including the formation of phosphorites and changes in the phosphorous cycle, mimics the sequence which was repeated at the Neoproterozoic-Cambrian transition, implying that oxidation of the terrestrial atmospherehydrosphere system experienced an irregular cyclic development.

The early Earth and its environments

“…?Pyrite framboids ( fig. 10b) and structures resembling glycocalyx are met as well (Rozanov, Astafieva, Hoover, 2007;Rozanov, Astafieva, 2008a).…”