ИСТИНА

The Early Khvalynian chocolate clays from key sections in the Middle and Lower Volga region were studied to obtain mineralogical and geochemical data for sediment provenance reconstruction. The results show that the main clay mineral of chocolate clays is illite. Geochemical composition of chocolate clays is characterized by high concentration of iron oxide (Fe2O3). The potential sediment source of illite is the Pleistocene marine complex of the East-European plain. Deglaciation after LGM and rapid melting of permafrost along with solifluction processes could predetermine the supply of illite-rich sediments to the Early Khvalynian basin. Subsequently, illite-rich sediments were deposited under oxic conditions and formed chocolate clays in the Middle and Lower Volga River valley.