ШОКОЛАДНЫЕ ГЛИНЫ СЕВЕРНОГО ПРИКАСПИЯ (РАСПРОСТРАНЕНИЕ, УСЛОВИЯ ЗАЛЕГАНИЯ И СТРОЕНИЕ)

Аннотация

“Chocolate” clay is one of the most common facies of Lower Khvalynian sediments of Northern Caspian and Lower - Middle Volga region. After more than a hundred years of research, there are still many unresolved issues related to the conditions of its bedding, structure, facial composition and coloration. “Chocolate” clay is confined solely to pre-Khvalynian relief depressions: terraces, paleo-incisions and tributary junctions, different paleo-ravines, estuaries, saline-dome depressions (Elton, Baskunchak), and ancient aeolean depressions at watersheds (Kalmykia). The roof of chocolate clay gradually decreases from the north to the south according to the general slope of the surface of the Lower Volga and Northern Caspian regions. The highest level of clays occurrence in the Caspian depression usually amounts to 20-25 m a.s.l. To the north, within the valley of the Volga, this level rises to 35 m and higher. There are two types of chocolate clay distribution: continuous and spotted (mosaic) one. Continuous distribution prevails in the Volga River valley and is observed in ancient estuaries and major tributaries junctions: the Large and Little Irgiz, Large and Little Karaman, Torgun etc. Spotted distribution is typical for Kalmykia and the Volga delta. Analysis of the “Chocolate” clays reference sections showed that several subfacies of clays may be distinguished: monoargillaceous, stratified, sand-clay and silt-clay. The most common monoargillaceous subfacies has entirely clay composition. It’s massive unstratified or hidden-stratified dark chocolate-brown clay with a large block jointing, sometimes interbedded with lighter silt varieties.

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