Case study of the Kоpanovka reference section made it possible to investigate the structure of Upper Pleistocene deposits to verify the Hyrkanian horizon in the Lower Volga region. At the moment the synthesis of data on stratigraphy and malacofauna analysis, obtained by comparing our own field materials and published data, doesn’t allow identifying the Hyrkanian deposits in the Kopanovka section. Suggestions about the age of the Hyrkanian deposits in the area of the Tsagan-Aman section do not agree with numerous data on stratigraphy and the absolute chronology of the Upper Pleistocene deposits of the Lower Volga region. The Hyrkanian deposits were found only in the Manych River deposits and the northern part of the Caspian Sea; the age of their accumulation correlates with the MIS 5 stage.

Pleistocene key sections of the Northern Caspian Lowland are characterized by the incompleteness of the geological record, which is presented in depositional breaks, their duration, causes, and types. Depositional breaks occurred in all periods of the Middle and the Late Pleistocene and occupied various time intervals, usually quite continuous – from ∼180 ka (Cherny Yar) to 100–110 ka (Alexandrov Gay, Gorky Erik, Kopanovka, Enotaevka), rarely shorter – about 15–40 ka (Seroglazovka, Mergenevo). Period of accumulation in these sections is small (3.5–44 ka) and covers only 1.2–9% (average 3–4%) for presented deposits and less than 10% from all chronological record. The total chronological assessment of the geological record incompleteness in all studied sections estimated as more than 90%. In all studied sections accumulation rates for Holocene, Upper Khvalynian, Lower Khvalynian, Upper Khazarian, Chernoyarian, and Lower Khazarian are lower than the average for this region. Incompleteness is usually characterized by erosion of river waters of the Volga and Ural system, but more often by abrasion of the Khvalynian and the Khazarian transgressive waters. Another cause of incompleteness of the geological record is long continuous periods without significant deposition. This is often observed in subaerial conditions in the vast watershed area.

During the second half of the late Pleistocene, the Caspian experienced repeated transgressions (Early and Late Khvalynian) and regressions (Enotaevsk and Mangyshlak) with an oscillation amplitude of 120-150 m. The question about the age of the Khvalynian deposits is controversial. The investigation presents the age chronology of the Khvalynian deposits of the Caspian coasts on the basis of marine terrace stratigraphy and C-14 and Th-230/U-234 dating conducted in the Laboratory of the Saint-Petersburg State University. Forty samples of mollusc material from Khvalynian deposits were dated. For dating, the shells of index-genus Didacna from the deposits of marine terraces with different elevations were sampled. Besides shells, a fragment of bone from Equus sp. was dated. The analysis of dating showed that during the maximum of the Late Valdai (Wurm) glaciation the Khvalynian basin was in a regressive situation. The maximum stage (+48 to +50 m) of the Early Khvalynian transgression was not dated. Transgressive stages of the Early Khvalynian basin with sea levels of +35 and +22 m occurred during the period of deglaciation approximately 16 ka cal BP and 14 ka cal BP. The transgressive stages of the Late Khvalynian basin with sea level at about 0 m and -12 m occurred 14-12 ka cal BP. Probably, the age of deposits of Makhachkala stage with level about 0 m reflected an Allerod warming, and the age of deposits of Sartassy stage with level about -12 is associated with warming at the end of Younger Dryas. Under cold climate conditions of Younger Dryas the level of the Late Khvalynian basin fell. Increasingly continental climatic conditions during the Boreal period of the Holocene resulted in the Mangyshlak regression. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.

The Late Pliocene–Quaternary Great Caspian, in addition to the positive transgressive rhythmics shows regressions of different scales: balakhanskaya, domashkinskaya, tyurkyanskaya, venedskaya, chelekenskaya, chernoyarskaya, atel’skaya, enotaevskaya, mangyshlakskaya, and izerbashzkaya. In these periods, large-scale natural phenomena took place on the Caspian shelf, coasts, and adjacent inundated territories, including sea level drop, drying of a part of seabed, and change of landscapes and the sedimentation character. The neaped water area showed changes in water salt composition and temperature regime, along with a change in faunistic complexes. Different hierarchic state of sea level and different correlation with climate events on the surrounding territories was shown to take place during the regression with predominance of warm (interglacial) periods among them.

The level of the Caspian Sea, the largest inland sea in the world, has fluctuated capriciously in history, with amplitudes up to 3 m in the last century, to 25 in in the last millennium, and to over 150 in since the Last Glacial. There is little consensus about the causes, and forecasts are contradictory, mainly due to a lack of solid data about past sea levels before 1837 AD, when instrumental observation started.We studied the Holocene Turali barrier complex along the western Caspian shore in Dagestan, Russia. Barrier dynamics during the last 3 m sea-level cycle in the past century show that only lagoonal deposits overridden by highstand barriers are suitable for dating former highstands. In the Holocene barrier complex, we selected the most suitable sites for dating using ground penetrating radar (GPR) profiles, outcrops and gravel pits. We obtained 14 accelerator mass spectrometry (AMS) (14)C data on in situ double-valved molluscs from highstand lagoonal deposits.The results suggest that the last major highstands occurred around 2600 BP and in the Little Ice Age and coincide with global cooling events associated with minima in solar activity. This suggests that millennial precipitation changes in the Volga River drainage basin are also forced by solar activity. (c) 2007 Elsevier Ltd and INQUA. All rights reserved.

The chocolate clays commonly comprise a part of the Lower Khvalynian sequence in the northern Caspian Lowland and in the Volga region. The mode of occurrence varies from continuous to patchy mosaic. All the clay deposits are confined to Pre-Khvalynian depressions of various origins. There are several sub-facies distinguishable within the chocolate clay facies: mono-clayey (typologic), stratified sandy-clayey and silty-clayey. Judging from specific features of lithology, geomorphic position, mode of occurrence, mollusc fauna composition, and radiocarbon dates, the chocolate clays represent a specific facies of the Lower Khvalynian sediments and cannot be considered as an individual stratigraphic unit.

The Pliocene-Pleistocene marine sediments of the Great Caspian region host various lithological fossil facies, which reflect specific sedimentation conditions caused by different structural-geomorphologic settings, tectonic regimes, climates, and hydrologies. The facies of shelf, epicontinental basins, ingression gulfs and estuaries, intermontane and mountainous basins, and deep-sea depressions form a hierarchy of geological bodies from types to subtypes. Paragenetic associations of fossil facies, which form various series in space and along the section, are typical of marine sediments.

Marine Holocene deposits of the coast of Iran are represented by the Upper Khvalinian and New Caspian beds. Upper Khvalinian sediments are faunistically barren, whereas the New Caspian beds contain abundant fossil molluscs that allow subdivision into the Daghestan, New Caspian and modern layers. The only fossil species found in the Daghestan layer is Didacna cristata. The New Caspian sediment layer is characterized by a taxonomically diverse molluscan assemblage dominated by Cerastoderma glaucum. It is subdivided into the Upper and Lower New Caspian sub-layers. Modern sediments are lithologically diverse. Besides the New Caspian fauna, they also contain the valves of the species Mytilaster lineautus which is known to have immigrated from the Black Sea.

The paper considers setting and history of the Pleistocene straits in the Manych Trough and estimates their role in the development of the Ponto-Caspian basins. The system of the straits is located in the lowermost part of the Manych Trough. As viewed from above, it presents a broken knee-shaped line, probably due to the tectonic control. A characteristic feature of the strait morphology is that landforms in the younger straits are mostly inherited from older ones. The maximum depths of the straits are confined to the central part of the depression. The very small gradient of the strait bottom, together with fine composition of the marine deposits, suggests the water flow in the straits was slow and quiet. The Manych impact on the evolution of the adjacent sea basins – Pontian and Caspian – differed considerably depending on whether a continuous waterway (a system of straits and lakes) existed within the depression or if it was interrupted by land bridges of a kind. The opening of the straits resulted in the Caspian Sea level drop, while in the Black Sea the input of the Caspian water caused a rise of the regressive basin level. The water entering the Black Sea had the Caspian type of salinity, which accounts for practically one-way migration of the Caspian malacofauna into the Pontian basin where it mixed with the Black Sea and Mediterranean aboriginal species.