Архив метки: Late Pleistocene

BIODIVERSITY OF MALACOFAUNA IN THE CASPIAN-MANYCH-PONT SYSTEM DURING THE LAST INTERGLACIAL EPOCH

Arid Ecosystems

UDC 551.41

Yanina T.A.,  Semikolennykh D.V.,  Sorokin V.M. BIODIVERSITY OF MALACOFAUNA IN THE CASPIAN-MANYCH-PONT SYSTEM DURING THE LAST INTERGLACIAL EPOCH // Arid Ecosystems. 2024. Vol. 30. № 2 (99). P. 119-135. | PDF

The conditions of the biodiversity formation and their comparative analysis at individual stages of development of the Ponto-Caspian basins in the MIS 5 epoch have been identified. The work was carried out based on the results of studying materials from many years of field research in the Caspian, AzovBlack Sea regions and the Manych Depression. The biodiversity of malacofauna in the Caspian-ManychPont system under the climatic conditions of the MIS 5 epoch was closely linked with the basin’s history. Two transgressive basins, Late Khazarian and Hyrcanian, have been reconstructed in the Caspian Sea. The Late Khazarian malacofauna of the northern part of the paleo-Caspian Sea is represented by 26 species. The majority of the Late Khazarian species belongs to the Cardiidae family and are Caspian endemics. The main species is Didacna surachanica Andrusov, 1910. The Hyrcanian malacofauna includes 22 species, the majority of which are also Caspian endemics. The main species are Didacna subcatillus Andrusov, 1910 and Didacna cristata Bogachev, 1932. The malacofauna composition is influenced by factors such as inheritance from the previous basin, aquatic environment’s salinity and temperature, and the introduction of freshwater fauna with river runoff. The significant impact of unexpected catastrophic events, such as the sudden break of a periglacial lake and the subsequent flow of its waters into the Caspian Sea, has led to a sharp change in the biodiversity of the Hyrcanian basin in comparison to the Late Khazarian basin. The Pont’s Karangatian transgression occurred in three stages. In the northeastern part of the Pont, the malacofaunal composition consists of 37 species, mostly Mediterranean species, both
euryhaline and stenohaline. Each stage is characterized by its malacofaunal complex, which includes varying degrees of euryhaline or stenohaline elements. The second complex, corresponding to the maximum stage of transgression, was characterized by the greatest diversity and the presence of the most halophilic elements. An important feature of the third complex is the presence of Caspian species characteristic of the Hyrcanian transgression of the Caspian Sea. The events that occurred in the Manych Depression, which are closely associated with the evolution of the Caspian and the Pont, have been reconstructed: the ingression gulf of the Karangatian transgression of the Pont in the second stage of its development; reduction in the length of the bay, with the simultaneous advance of waters of the Hyrcanian transgression and their discharge into the bay; complete release of the Manych Depression from the Karangatian waters and the discharge of the waters of the Hyrcanian transgression into the Karangatian basin in the third stage of its development. The Pont’s species diversity was determined by the malacofauna composition that migrated from the Mediterranean Sea. At the final stages of the development of the Karangatian transgression its faunal composition was influenced by Caspian invasive species that penetrated the Pont with the waters of the Hyrcanian transgression through the Manych Strait. The composition of malacofauna in the Caspian Sea was primarily the result of evolutionary processes. Migration was the main factor in the formation of the Black Sea malacofauna, without any evolutionary influence.

Keywords: Late Pleistocene, climate change, Late Khazarian transgression, Hyrcanian transgression, Karangatian transgression, species evolution, malacofauna migration.

Acknowledgments. This study was financially supported by the Russian Science Foundation, project No. 22-27-00164 (2022-2023) “Environmental evolution of the Ponto-Caspia region during the last interglacial epoch”.

Funding. The study was carried out with support of the Russian Science Foundation project No. 22-27-00164 (2022-2023) «Evolution of the natural environment of the Ponto-Caspian Sea in conditions of the last interglacial epoch».

DOI: 10.24412/1993-3916-2024-2-119-135
EDN: NVDSVE

THE GEOMORPHOLOGICAL INTERACTION BETWEEN THE TERRAIN OF THE BAER KNOLLS AND THE VOLGA PALAEODELTAS AT THE END OF THE KHVALYNSK TIME

Arid Ecosystems

UDC 551.79; 551.351.2(262.81); 551.89; 551.468.6

Lobacheva D.M., Badyukova E.N., Makshaev R.R. THE GEOMORPHOLOGICAL INTERACTION BETWEEN THE TERRAIN OF THE BAER KNOLLS AND THE VOLGA PALAEODELTAS AT THE END OF THE KHVALYNSK TIME // Arid Ecosystems. 2023. Vol. 29. № 3 (96). P. 15-23. | PDF

Many geological sections in the ledge of the Lower Volga valley have been actively studied since the end of the 19th century. Results of many years of field work showed that alluvial sediments of the Khvalynsk time (end of the late Pleistocene – early Holocene) are absent in all the studied quaternary sections along the valley. Numerous literary sources, maps and descriptions of wells were used for this research. We conducted geomorphological mapping in ArcGIS using the SRTM DEM and studied many outcrops and wells and carried out field surveys along the Volga valley and in the Baer’s knolls, the giant underwater dunes of the Northern Caspian region. We consider that in the Khvalynsk time the Volga River probably did not run through the site of its current location. In this regard, the question arises of where the Volga channel was located in the North-Western Caspian region. Thus, we propose that the western branch of the Volga ran along the foot of the Eastern Yergeni slopes and eroded the surface of the marine plain, which resulted in the formation of the Sarpinsko-Davanskaya Hollow. Meanwhile, its eastern branches ran into the Khaki Saline, which was one of the estuaries of the Northern Caspian region, where one of the eastern channels of the Paleo Volga probably were flowing into. In the Khvalynsk time, in the lower reaches of the Volga channel there were multiple terminal distributary channels. The large branching delta was much larger (about 200-210 km wide) than the modern delta and somewhat reminiscent of the modern delta of the Lena river in size. Where the modern Volga-Akhtuba floodplain is located now, there was probably a small central branch, in the west there was a Sarpinsky branch, and in the east, an Elton-Khaki branch. They were interconnected by an extensive system of branches, the relief of which is still preserved. At the very end of the Late Khvalynsk time, the Sarpa and Khaki branches began to die off, and most of the water began to run along the central branch, forming the modern Volga-Akhtuba valley.

Keywords: Volga Delta, Caspian Sea, Lower Volga, Baer’s knolls, geomorphology and paleogeography, Late Pleistocene, Khvalynsk time, giant river dunes.

Financing. This work was supported by a grant No. 20-05-00608 “Evolution of the Natural Environment of the Middle Volga Region in the Late Pleistocene: Chronology, Climatorythmics and Correlation with the Events of the Caspian Region”.

DOI: 10.24412/1993-3916-2023-3-15-23

EDN: VTESSF