EPIGENETIC CHANGES IN THE MESOZOIC STRATA IN THE SOUTHEAST OF THE RUSSIAN PLATFORM

Epigenetic changes in Mesozoic strata are described on a comparative basis from the principal sections, Saratov (few hundred meter thick) and Novouzensk (3 km thick). Three epigenetic zones are recognized. An upper zone (down to 1,700 m) shows only normal diagenesis in the form of consolidation and crystallization of pore calcite. A transition zone (1,700 m-2,500 m) contains signs of alteration of sedimentary structures and recrystallization and replacement within the cement. The lower zone (below 2,500 km) shows abundant mosaic structure in the Sandy rocks and greater changes in the cements. Within the zones, epigenetic changes differ somewhat in siliceous arenites, carbonates, glauconitic sandy claystones and argillaceous siltstone. Finely divided clay, organic matter, and iron oxide hinders early epigenesie. Local development of chlorite and zeolites (sandstones) and sepiolite (limestones) is attributed to dislocation effects. R. C. Epis