Evidence of Soil-Forming Processes in the Early Proterozoic by the Example of Livvian Deposits (Karelia)

The paper deals with the fossil cyanobacterial films from the Lower Proterozoic (Livvian) shungite in Karelia, Russia. The films were previously described as a formal species Cyathotes nigoserica Makarikhin. They were formed by bacteria and possibly by fungi, which inhabited the littoral or supralittoral (the tidal zone). These organisms were adapted to the existence in temporally (possibly, long-lasting) dry conditions, which is proved by the development of dense coatings protecting their bodies from dehydration. This basically bacterial community influenced intensely the mineral substrate, changed its structure, and enriched it with biogenic constituents, thus forming an archaic soil microprofile. The research revealed the following signs of ancient soil formation: surface transformation of the mineral substrate texture by the vital activity of terrestrial organisms (bacteria, fungi) with the formation of a specific cellular topographic pattern,; changes in the internal structure of the substrate and the appearance of wedge-shaped fracture casts in the underlying matrix; redistribution of inorganic compounds during the formation of a paleosurface microprofile (the increasing content of silicon oxide in the upper part with a simultaneous reduction in the amount of iron oxides).