Geologicheskii Vestnik

The article discusses the features of the Devonian section, which makes up the zone of junction of the East Ural anteclise with the Caspian syneclise and the Pre-Ural regional trough. The Devonian section was studied by deep wells drilled in the territory of the Sol-Iletsk uplift and in the adjacent border part of the Caspian depression. The absence of most of the Devonian section within the Orenburg rampart, which complicates the northern part of the Sol-Iletsk uplift, is noted. The Devonian deposits here are represented only by the Zavolzhskaya Formation, which rests on the Ordovician terrigenous stratum. To the south and west the Devonian section increases, and more ancient Devonian formations appear from under the surface of the pre-Zavolzhsky erosion. In the extreme eastern part of the Sol-Iletsk uplift, on the southern flank of the Orenburg block, the Devonian section is reduced and is represented only by the Vyazovsko-Koyvenskoi and Zavolzhskoi formations. In the southwestern part of the Sol-Iletsk uplift and in the adjacent area of the Caspian Depression, all the stages from the Emski stage are distinguished. In the extreme eastern part of the Sol-Iletsk uplift, on the southern flank of the Orenburg block, the Devonian section is reduced and is represented only by the Vyazovsko-Koyvenskoi and Zavolzhskoi formations. In the southwestern part of the Sol-Iletsk uplift and in the adjacent area of the Caspian depression, all stages from the Emsian to the Famennian are distinguished. The structure of the sections exposed by deep wells within the Sol-Iletsk uplift and the marginal part of the Caspian Depression is described. The facies variability of the Devonian deposits is noted. The Zhivetsko-Fransky relatively deep-water type of the section of wells 20 Peschanaya, 35 Chiliksaiskaya, 1 and 2 Kainsayskaya, and 1 Burannaya is considered to be part of the Kainsayskaya formation, which was identified during the compilation of the third-generation State Geological Map-1000 sheet M-40 with valve M-41 (published in 2013). The sub-synchronous section, which was discovered by the Nagumanovskaya 1 well and is characterized by a shallower sedimentation pattern, has been identified as the Akbulak section. It has been indicated that this type of section also characterizes the eastern part of the East Orenburg arched elevation, which means that the lithofacies variability of the Zhivets-Frasnian part of the Devonian section is characterized by submeridional zonation.

stratigraphy, Devonian section, formation, stratum, well, Sol-Iletsk uplift, Caspian Depression

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