The recent discovery of foraminifera shells [morphologically close to the Aral-Caspian species of Retroelphidium shochinae (Mayer)] in the Holocene sediments of the brackish water in the Chany Lake system (southern West Siberian Plain), raises the question of explaining this phenomenon. Previously, no findings of foraminiferae were reported from this region. The distinct feature of foraminiferae from the Chany Lake section is the fairly large proportion of pathology (up to 30%), such as “twin” accretion of shells and numerous cone-like outgrowths on the shell chambers. Along with the foraminiferae, ostracod and gastropod shells were also found. The ostracod dominant species is Cyprides littoralis (Brady), which is typical for regions located south of Western Siberia. The most prevalent gastropod species are of “Tajikistan” (Caspiahydrobia coniformis Star. et Izzat., C. laurica, and C. elongata) and “Aral” types (C. sagniana Star. et Andr., C. bergi, and C. nikitinski) (S. I. Andreeva, Omsk Pedagogical University, Omsk, Russia; pers. comm. 2004). The AMS 14C dating of foraminiferae, ostracods, and gastropods was conducted at the NSF-Arizona AMS, Facility (University of Arizona). In Sargul Lake (54°34' N, 78°47' E), depth 1.20 m: Retroelphidium shochinae chanicum: 6375 ± 40 BP (AA-59219); 1.15 m, Caspiahydrobia spp.: 5480 ± 40 BP (AA-59220); 1.10 m, Cyprideis littoralis: 5270 ± 40 BP (AA-59221). In Zharkol Lake (50°01' N, 64°05' E), 0.85 m: Planorbis spp., Cyprideis littoralis: 4010 ± 40 BP (AA-59326). No reservoir correction value is known for West Siberian freshwater; we can assume it to be equal to ca. 400 years using the Caspian Sea value. The results of dating show clearly that the R. shochinae chanicum shells have a mid-Holocene age, at least ca. 6000 BP. The presence of elements of the Aral-Caspian foraminiferae in Western Siberia allows us to suggest that the Aral Sea waters invaded this region at the time of the Holocene Climatic Maximum. This is supported also by the study of lake sediments in the Turgai Depression, which connects the river system of the West Siberian Plain with Central Asia. The same species of foraminifera was found in the Holocene deposits of the Zharkol Lake (Kazakhstan), and dated to ca. 4000 BP (table). Thus, this phenomenon is very important for understanding the development of river networks and palaeohydrology of Central Asia and neighboring regions.
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