ИСТИНА

During the Late Quaternary dramatic changes in relative sea-level are known to have occurred in the Caspian Sea. However, all previous attempts at resolving the uncertainty associated with the timing of these transgressive/regressive events using standard dating methods have produced inconclusive or controversial results. In the Lower Volga River region, Early Khvalynian marine deposits are situated between the modern soil and Atelian subaerial strata (MIS 3-5), and are represented by readily identifiable marine silty-clays with clear specific characteristics: fissile mudrock, in general with a well-developed stratified fabric, consisting of interbedded sub-mm laminae of silt. These laminated layers break into small blocks, which, together with a red-brown colour, gives the material a characteristic ‘chocolate’ appearance – hence the widely-used name “Chocolate Clays”. In general, this type of facies in the Northern Caspian is found in topographic depressions of various configurations and size, the largest of which is the Lower Volga River valley. As a result, the relative position of Chocolate Clays in the Lower Volga River sequence may vary: in the northern part of the region, close to Volgograd, they are underlain by subaerial loess-soil sequences (Yanina et al. 2017) with a clear erosional contact.