A new location of stromatolites in the Middle Timan: their morphological and structural features

The paper presents the results of macroscopic and microscopic study of Riphean stromatolites of the Pavyuga Formation from a new locality on the left bank of the Vorykva River (Middle Timan). The stromatolites form a stromatolite bioherm. The microstructure of the stromatolite assemblages is characterised by layering of different composition and granularity; traces of organogenic formations of clotted and filamentous type were found in microgranular interlayers. Numerous traces of secondary transformations, such as pyritization, dolomitization on shells, and fenestra formation, were noted. The taxonomic affiliation of the stromatolites to the species Gimnosolen sp. and Inseria djejimi Raab. allows dating to the Late Riphean. A similar association is known from the upper part of the Pavyuga Formation, but the colonies of stromatolites are orientated disorderly in that association, which indicates the environment of the organogenic buildup margins.