Evolution of the Northern Caspian Sea Region and the Volga delta in the late Pleistocene-Holocene

On the basis of geologic-geomorphologic studies, an alternative concept regarding the evolution of the Northern Caspian Sea Region and the adjacent areas in the boundary of the Pleistocene-Holocene is presented. A supposition is made about the existence of a large lagoon in the North Caspian Region that the Volga River emptied into forming a delta. Later, water from the lagoon flowed as a “stratum” stream into the Black Sea through the Manych Strait. A conclusion is reached that the Baer mounds were formed on the bottom of this stream.     

Geological structure of the Curonian Spit (of the Baltic Sea) and its evolution history (revised)

The origin and evolution history of the Curonian Spit in the Baltic Sea are discussed based on geological and geomorphologic data. Evidence of the correlation between the spit formation stages and the Holocene sea level oscillations is presented. The ledges of moraine basement and marine accumulative features formed a single barrier. Its subsequent transformation occurred under the influence of the wave-related lithodynamic and eolian processes.     

Dependence of the types of coasts and coastal eolian relief on the variations of the sea level using the example of the Caspian Sea

In this work, the history of the development of the Turali area (the Dagestan coast of the Caspian Sea) in the Late Holocene is under consideration. The analysis of the geological structure of the bay bar that separates the Bolshoy Turali lagoon from the sea, the granulometric analysis of the coastal deposits, and the data of geo-radar profiles make it possible to assert that the large eolian relief forms were formed during the New Caspian (Novokaspiyskoe) transgression of the Caspian Sea.     

Caspian Sea Level Fluctuations in the Neopleistocene (Was There an Atelian Regression?)

The article deals with deposits exposed in sections along the rivers of the Caspian lowland and on the eastern slope of the Ergenei. The conclusion is made about the lagoonal origin of chocolate clays lying on high-capacity subaerial and alluvial–deltaic deposits. The impact of the Caspian Sea level rise on coastal processes is examined. Taking into account the regularities in the behavior of the coastal zone during sea level rise, subaerial deposits with such thickness in the outcrops could not have been preserved during the early Khvalynian transgression from –100 m. Another curve of Caspian Sea level fluctuations is proposed, where there is no deep Atelian regression between the Khazarian and Khvalynian transgressions. It is concluded that the Khazarian transgression was one of the largest in the history of the Caspian Sea. Its level was slightly less than that of the Khvalynian transgression. The rise of the level of the latter began not from –100 m, but from about 5–15 m; i.e., this transgression was in fact an oscillation of the Caspian Sea against its gradual regression after the Khazarian transgression. Sea level oscillations contributed to the formation of lagoonal-transgressive terraces, in which chocolate clays accumulated.

     

Age of Khvalynian transgressions in the Caspian Sea region

As follows from a geomorphologic analysis of the Khvalynian sediments in the North Caspian region, radiocarbon dating of their molluskan and plant remains provided more or less reliable age estimates, according to which the Khvalynian transgression occurred approximately 11–20 ka B.P. This value corresponds, however, to the terminal transgressive-regressive phase of the latter, i.e., rather to the Late Khalynian transgression than to its Early Khvalynian peak. It is inferred that the high terraces that formed during the maximal Early Khvalynian transgression are unambiguously older, being 70 to 40 ka in age.     

The geological-geomorphological structure of the Baltic (Vistula) spit

A model of Holocene evolution for the coastal zone is discussed using the example of the geological-geomorphological structure of the Vistula spit. The conclusion is drawn that there is a significant role played by the aeolian factor in the formation of the studied area. The entire spit, excluding beaches, the near-gulf terrace, and several remnants of the ancient deltaic plain, is mostly composed by aeolian sands. One of these remnants is found in the near-gulf part of the spit near Cape Vysokii.     

Development of barrier-lagoon systems in the southeastern Baltic Sea

A comparative study of the geological structure and evolution of the Curonian and Vistula spits representing large barrier-lagoon systems in the southeastern Baltic Sea reveals some geological and geomorphologic differences against the background of their general similarity. It is shown that morphological structures in the Vistula Spit are smaller. The grain-size analysis of the spit sediments demonstrates that eolian sands constitute all the structures of the spits down to the water level and below it (down to depths of 2 m), except for beaches and low lagoonal terraces. This means that the eolian relief on the maritime plain started forming when the sea level was approximately 4 m below its present-day position. Subsequently, they were growing beyond the wave influence. The sea-level rise resulted in the erosion of the coasts of the spits on both the sea and the lagoon sides and provided an intense landward transport of eolian material.     

Large accumulative forms of relief on the southeastern coast of the Baltic Sea

The paper describes the conditions of formation of large accumulative forms on the southeastern coast of the Baltic Sea and presents the results of a comparative analysis of these structures. It has been established that Baltic barrier–lagoon systems have a complex geological and geomorphologic structure. Sandy barriers, which are, in general, marine accumulative formations, often comprise various fragments of different genesis (moraine remnants, glaciolacustrine and deltaic plains, etc.). The formation and development of large accumulative forms in the southeastern Baltic occurred against the background of sea level fluctuations in the Littorina time following a unified scenario for the entire coast.