Geologicheskii Vestnik

In the Kungurian Age of the Early Permian during the continent collision and growth of the Ural orogen in the Western Urals evaporite formation was formed. In Belsk basin of the Ural Foredeep, on the territory of the Toratau Geopark, section of the Kungurian evaporites with thickness ranging from 500 to 1200 m is composed of three horizons — salt, gypsum, anhydrite and the transition horizon. Salt bearing horizon in the submerged parts of the Foredeep consists of rock salt alternating with anhydrite, in places interbedded with saline grey clays. Subordinate polyhalite is present. Brief information on the lithology of the Kungurian evaporites in sections, located in different parts of the Ural Foredeep is presented: along Seleuk river, where they overlay reef limestone; along Teyruk river, near Smakaevo village, located closer to the central part of the Foredeep, where they overlay depressional sediments; and at the Eastern part of the Foredeep, along Zilim river near Aktashevo village where the sulfates overlay deep-water fl ysch deposits. The evaporite rocks show signs of plastic fl owing, the result of which is the formation of diapir structures, fi rst described in this area in the 40s of the last century (near Smakaevo village). For the “Aktashevo” section, the structure and primary, perfectly preserved, sedimentological features are considered in detail. Flysch terrigenous-sulfate rhythms with graded bedding and convolute lamination, which are overlapped by storm sedimentation deposits with HCS (hummocky) type stratifi cation, are established. Secondary, epigenetic, signs associated with tectonic impact on rocks are expressed by the formation of anhydrite nodules, enterolitic intra-layer microfolds, as well as small clay-crystalloclastic diapirs — structures of interlayer fl ow and brecciation. The general model of sedimentation of Kungurian evaporites provides for a catastrophic increase in salinity and salt loss from seawater, caused by the abrupt termination of the connection of the marine basin with the world ocean, like the Messinian salinity crisis. The difference from the latter is in the overlap of salts not by sea, but by continental deposits of the Upper Permian.

Preuralian Foredeep, Kungurian stage, evaporite, deformation of sulphate strata, diapir, Kungurian salinity crisis

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