(from Khvalyn Sea, the ancient Russian name for the Caspian Sea), a stratigraphical subdivision of the Upper Pleistocene of the Caspian Sea region. Established by the Russian geologist N. I. Andrusov and described (1913) by P. A. Pravoslavlev, the Khvalyn horizon is represented by sands, clays, and coquinas deposited in a saltwater isolated basin. It is subdivided into Lower Khvalyn strata, which contain Didacna cristata and D. ebersini, and Upper Khvalyn strata, which contain D. praetrigonoides.
The Khvalyn horizon is found on all the shores of the Caspian Sea and in the adjacent lowlands and extends into the valley of the Vostochnyi Manych River. Its deposits are connected with two transgressions of the Caspian Sea—the early Khvalyn, which is the most extensive transgression in the Upper Pleistocene and corresponds to the age of the melting of the first Würm (Kalinin) glaciation, and the late Khvalyn transgression, which is associated with the degradation of the latest Würm (Ostashkov) glaciation. The waters of the first transgression passed through the valley of the Manych into the Azov–Black Sea Depression, in which a deep post-Karangat regression was observed at the time.