Прикаспийская впадина

Factual data has been analyzed on the unconformities at the Carboniferous-Permian boundary in the sections from the edge and the inner by-edge zones of the Pricaspian Depression; varieties of opinions on the unconformity formation mechanisms have been analyzed, as well.

In 1960–1980, the Elton and the Gremyachka deposits of potassium salts were discovered within the Permian halogen sequences in the Lower Volga Region, bischofite presence was recorded in the Privolzhskaya monocline, the conditions of halogen-bed formation were defined as those peculiar for typical evaporites. But in 1980-2010, halogenesis hypotheses emerged that denied the principal importance of climatic factor and the dominant role of oceanic waters in the brine composition of the salt-generating basin.

In connection with Carboniferous, Permian and Triassic rocks, marked by magnetic susceptibility of thousand and dozens of thousands (10-5 SI units) that are located in southern part of Precaspian Depression, samples of these rocks were studied in details, using strongly magnetic samples. The possible effects of anomalous magnetic field were counted on the base of received data.

The magnetic properties of igneous and sedimentary rocks of Lower Carboniferous and Upper Permian, were studied in the core samples from the boreholes, situated in the south of Precaspian depression. The volcanic rocks of Lower Carboniferous are characterized by low (first decades 10-5 SI units), and Upper Permian – by high (hundreds and first thousands 10-5 SI units) values of volume magnetic susceptibility.

The article presents the analysis of the inner structure of the salt-bearing series within the Caspian Depression. Certain salt-bearing complexes of various ages, compositions and plastic properties are distinguished. Their structural relations and the features of salt-tectogenesis manifestation are evaluated. Up to the present no subsalt uplifts have been confirmed in the Russian sector of the Caspian Depression and no HC fields have been discovered.

The detailed evaluation of the accumulated geological-geophysical data, particularly on the inner structure of the saltbearing series in the margins of the Caspian Depression, the mechanism of salt-tectogenesis manifestation, its reflection in the structure of the salt table and association with the structural inhomogeneities of the subsalt bed is presented.

The paper presents the results of a study of the insoluble residue of sylvinites and sylvin-halite rocks of the Lower Permian halogen formation, common within the Perelyubsky areas (Western and Eastern), promising for industrial development (Saratov Region) and the Gremyachinsky potash deposit (Volgograd Region). A technique for studying the insoluble residue of sylvinites is presented. The types of insoluble residue are distinguished according to the form of occurrence in sylvinites and its mineral composition is characterized.