Lithology and facies of the Burtasian and Khvalynian sediments in Manych

Results of study od the lithofacies structure of the Burtasian and Khvalynian sediments in the Manych Depression are discussed. The sediments are similar in the grain size and mineral compositions. They are mainly represented by clayey silt, as well as silty and sandy-silty clay with subangular fragments of crystalloclasts and lithoclasts. They are characterized by a low content of heavy fraction dominated by transparent minerals (apatite, garnet, biotite, chlorite, hornblende, and others). Ore minerals (limonite and magnetite) are subordinate. The Burtasian sediments are marked by thin-horizontal bedding. Bedding of the Khvalynian sediments is more diverse: horizontal, gentle-horizontal, and alternation with gentle crossbedded-diagonal (trough-like), crisscross-wavy, and other types of bedding. The lithological composition and fossil plant seeds found in the Burtasian and Khvalynian sediments make it possible to distinguish facies formed under calm (Burtasian) and calm flow (Khvalynian) hydrodynamic regimes of sedimentation in closed (lakes) and open (channels of the Khvalynian Strait) reservoirs.