Stromatolites as Indicators of Hydrocarbon Enrichment (in Riphean Sediments of the Volga–Ural Region Platform)

Scanning electron microscopy revealed fossilized remains of microorganisms (filamentous microfossils) in stromatolites from the borehole core from the Lower Riphean Kaltasy Formation and Upper Riphean Leuza Formation of the Volga–Ural region. It has been established that the dark color, uncharacteristic of carbonate biogenic structures, is due to their significant enrichment in carbon, the distribution of which in its biogenic and abiogenic components, as well as in the host rocks, differs significantly. The possible causes of this event are discussed, and the host rocks are compared with phosphate stromatolites. The prospect of using the results of a microscopic study of stromatolite structures for identification of hydrocarbon accumulation in deep-lying Riphean series is considered.