Microstructure of deposits in Baer’s mounds at the lower course of the Volga River

Abstract

Results of the microscopic study of sandy rocks from the Bugrovaya and lower Khvalynian sequences at the lower course of the Volga River are discussed. The terrigenous material of these deposits represents a mixture of clasts of two types: argillic (clayey) and nonargillic. The argillic component (clasts of chocolate clays) predominates in the clastic material and imparts the brownish red color to sands and sandstones of the Bugrovaya sequence. The nonargillic component includes fragments of crystals and rocks, the assemblage of which is similar to the clastic material of the underlying Khvalynian sand. The combination of clay clasts, which are not prone to long-range transport, with redeposited crystallo-and lithoclasts indicates the presence of different provenances. Their thin banding (lamination) related to differentiation of the clastic material by composition and grain size and the presence of glauconite grains testify to the aqueous origin of the Bugrovaya sequence.