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THE SILURIAN FRONTIER OF EMERSION STAGE IN THE TERRITORY OF SOUTH CIS-TIMAN (PERM REGION)

At the base of the Silurian deposits in the Southern Rassolnaya Deposit, ventfacts considered as an indicator formations of deserts with a predominance of wind erosion (corrosion) processes were first discovered. In this work, the systematization of the found ventfacts was carried out, their morphology was revealed, and it is concluded that the most numerous group among the Aeolian polyhedra is the group of pyramidal ventfacts. Among the latter, the pyramidal trihedrons, otherwise known as dreikanters, are the most common. From the point of view of lithology, ventfacts are quartzite sandstones with relics of hydromicas cement, the structure of which is dominated by a cementless contact connection of quartz grains and fragments of various rocks. According to the structural position of the layers of rocks containing windmills, deposits of the Ordovician and Silurian systems are distinguished in the geological section. A mineralogical study of this section was conducted analyzing the mineral associations of the heavy fraction of lithological samples. The conclusion about possible ventfacts formation time as the border of the Ordovician and Silurian was made. To denote the time and facies boundaries of the emersive phase, the concept of the emersive frontier (or boundary) is introduced by analogy with the term mineralogical boundary. This frontier is taken by the author as the upper (Silurian) emersive boundary, after which there is a drastic change in the tectonic situation in the region. Based on the results of the study, a paleogeographic reconstruction of the Eastern margin of the East European platform on the Silurian emersive frontier is proposed, which may be associated with the Aeolian type of diamond placers of the Silurian intermediate reservoir in the Southern Cis-Timan.