The analysis of the history of the development of the relief of the Aral Sea region allows to conclude that it was possible for Cardium edule to penetrate into the Aral Sea in the Holocene along a wide and deep paleovision developed earlier during the flow of water from Western Siberia along the Turgai trough, then along the Turan and PaleoUzboy into the Caspian Sea.

This valley functioned until the Holocene, when subaerial conditions were established on the territory. During the Novocaspian transgression, the waters of the Caspian Sea with Cardium edule penetrated far inland through this paleochannel, forming a long bay. Subsequently, the Amu-Darya formed the Aral delta, dividing the Aral and Sarykamysh basins. The Syr-Darya and the Amu-Darya flowed into the Aral Sea at this time.

The arrival of the river waters contributed to the rise of the Aral Sea level after the penetration of the Cardium edule. For example, the calibrated age of shells from the core at the bottom of the Aral Sea (wellhead 26.5 m abs.) is 6,600-7,000 years ago; from a core whose wellhead is 48 m abs. the age of shells is 4300-4700 cal. (Krivonogov S. K., et al., 2014). The age of shells from the terrace on the Kulandinskaya Spit (54, 5 m abs.) is much younger — 2860 ±80 years B.P. (Weinbergs et al., 1980). So, the shells selected at the depth of the sea, which were the first entered to the Aral Sea, have more ancient age compared to those selected on high sea terraces.

Following many researchers of the XVIII-XIX centuries, the author is sure that the Amu Darya flowed into the Caspian Sea in the Middle Ages. In addition to historical evidence, this conclusion can be confirmed by some geological and geomorphological data. Thus, Ogurchinsky Island is a fragment of a barrier-lagoon system that exists on the edge of the Amu-Darya delta plain. The rise of the Caspian Sea level after the last (Derbent) regression led to catastrophic consequences – the flooding of the coastal plain and the destruction of villages and cities located on it.

Literature

Krivonogov, S.K., Burr, G.S. et al. The fluctuating Aral Sea: A multidisciplinary-based history of the last two thousand years // Gondwana Research. – 2014. – Vol. 26. – № 1. – P. 284-30.

Weinbergs I.G. Stelle V.Ya. Late Quaternary stages of the development of the Aral Sea and their relation to changes in the climatic conditions of this time / Fluctuations in the moisture content of the Aral-Caspian region in the Holocene. - Moscow: Nauka, 1980. - p. 175-181.