Прикаспийская низменность
The basins' bottom and littoral sediments and their fossils contain geological evidence of the EEI. In the Caspian basin, bottom sediments attributable to the epoch differ from the under- and overlying layers in a number of ways and are called "chocolate clays" because of their reddish-brown color. The chocolate clays and related Khvalynean sediments are usually , occasionally exceeding . They are primarily limited to the Caspian Depression, from the modern Caspian coast to the foothills of the surrounding mountains.