Geologicheskii Vestnik

The article deals with the features of calcification development in carbonate deposits of the Upper Famen stage of the fenestral lithotype within the south-western part of the East Orenburg arch-shaped uplift. Calcification is developed mainly in layered fenestration microbioliths and is represented by block calcite. There is also a separate type of calcification — croustification. This process is common, reducing the capacitance properties of rocks. According to literature sources and lithological studies of the core material of several wells, calcification depends on a complex of factors such as sedimentation rate, structural complexity of sediments, hydrodynamic activity, frequency of drainage and the presence of organogenic films. Since the shallow water conditions of the sedimentation basin are favorable for the development of a wide range of groups of organisms, primarily microbes, calcification is often closely interrelated with the vital activity of organisms. The biological control of calcification in the core is indicated by characteristic laminar, wavy micrite interlayers (microbialites) and an abundance of clumps of calcareous algae, well observed at the microscopic level. Thus, calcification is a typical post-sedimentation process for carbonate deposits of the Upper Famen stage, among the microbial layers of the fenestral lithotype.

East Orenburg arch-shaped uplift, Famen stage, fenestra, calcification, croustification

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