How did the Caspian Depression get its low elevation?

The Caspian Depression is a vast, flat lowland situated at the north end of the Caspian Sea, much of which lies below sea level. Its low elevation is primarily the result of its geologic structure as a vast downwarp, or tectonic depression, within the ancient structural block known as the Russian Platform.12

This northern portion of the Caspian region is characterized by a continental-type crustal structure that dates back to Precambrian times. Over millions of years, the area has been shaped by complex tectonic processes, including the sagging of ancient structural edges and the accumulation of sedimentary layers. Additionally, the region's landscape has been influenced by the historical expansion and contraction of the Caspian Sea, which left behind peripheral terraces and sedimentary deposits as glaciers advanced and retreated across the Russian Plain during the Pleistocene Epoch.2