Abstract

A diverse assemblage of exceptionally well-preserved microorganisms, including several previously unknown taxa, has been discovered in stromatolitic black chert from the ca. 680-790 Ma-old Min'yar Formation (Suite) of the southern Ural Mountains, USSR. Like most ancient and modern stromatolitic communities, the Min'yar microflora is dominated by filamentous and unicellular cyanobacteria. Geologic evidence indicates that the microbial community inhabited a shallow water, presumably marine environment. The microfossils occur in two interlaminated and thinly interbedded sedimentary fabrics ; 1, flat to wavy-laminated Stratifera-like stromatolitic laminae that presumably were deposited during periods of little wave action; and 2, intraclast grainstone that formed as a result of desiccation and (or) wave agitation. The microfossils are both better preserved and more abundant in the intraclasts than in the Stratifera-like laminae. The occurrence of probable pseudomorphs after replacement of sulfate minerals provides additional evidence for a shallow water, periodically emergent depositional environment for the Min'yar microbial mats.--Modified journal abstract.

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