a stratigraphic subdivision of the Middle and Upper Pleistocene around the Caspian Sea. The horizon was established by the Russian geologist N. I. Andrusov and described by P. A. Pravoslavlev (1913). It is composed of sands, clays, and coquinas that were deposited in an isolated saltwater basin.
The horizon is subdivided into the Lower Khazar, or Giurgian, strata, which contain Didacna subpyramidata, D. paleotrigo-noides, and D. nalivkini (Middle Pleistocene), and the Upper Khazar layers, which contain D. surachanica (the lower part of the Upper Pleistocene). It is found on all shores of the Caspian Sea, in the valley of the Manych River, and in the Lower Volga Region. The Giurgian strata were associated with several transgressions of the Caspian Sea and corresponded to the cold and moist epochs of the Middle Pleistocene. In the course of the transgressions, the water covered the Caspian, Western Turkmen, and Kura lowlands and reached the Avoz-Black Sea Depression through the Manych River valley. The Upper Khazar strata correspond to a minor transgression that occurred in the second half of the last interglacial period.