ИСТИНА

At the present time the stages of the Caspian sea-level evolution during the largest Late Quaternary Khvalynian transgression remains open. There have been attempts to establish an absolute chronology based almost entirely on radiocarbon dating, often of individual shells. This approach is of course limited to <50 ka but in any case has given very conflicting results; as a result, no consensus view of the transgression/regression history has evolved. In an attempt to resolve these problems, a major project (IGCP-481) was established to re-date the more recent transgressions using radiocarbon. Unfortunately, most ages were again unexpectedly young and stratigraphically inconsistent (Yanina, 2014). Existing radiocarbon chronology does not allow resolving two transgressions (Early and Late Khvalynian). Based on clear palaeontological and geomorphological evidence, these must be very different in age, but shells associated with both transgressions gave very scattered ages of between 8 and 50 ka (Arslanov et al, 2015). It is presumed that these difficulties arose because of reservoir effects and the very thin shell developed by many fauna during cold periods. Another controversial issue is the stage between Early and Late Khvalynian – Enotaevka regression. Firstly identification at the Enotaevka section of Lower Volga was made in the middle of XX century and based on the description of thin subaerial strata between two marine horizons containing Khvalynian marine fauna. Unfortunately later the particular described section was lost during Volga erosion and construction on the coasts. Thus for the long time this important event describing deep regression phase of the Caspian sea had no available section with clearly related horizon of subaerial sediments.