The Atelian regression was a prolonged regression of the Caspian Sea in the middle of the Late Pleistocene. It occurred between the Khazarian transgression and the Khvalynian transgression. It is named after continental Atelian sediments identified by Pavel Pravoslavlev (1918) during his 1903-1932 work on Pleistocene geology of Sub-Caspian and Lower Volga regionsУсловия формирования Ательских пород Прикаспийской впадины и их инженерно-геологические особенности, 1984, Chapter 1Православлевъ П., Материалы к познанию Нижневолжских каспийских отложений, Ч.1. Варшава: Изд-во Варшавского ун-та, 1908. 464 с.Православлев П.А., "О значении вертикальных изменений в окраске песчано-глинистых пород в области нижнего течения р.р. Большого и Малого Узеней", Известия Российской Академии Наук, series VI, 1918, no. б, pp. 1843-1854. in cross-sections of Northern Caspian Depression, who grouped them into the Atelian formationАтельская регрессия In: Свиточ А.А., Большой Каспий: строение и история развития, 2014 The basin of the regression is called Atelian basin.Andrei L. Cheplyaga, "The Late Glacial Great Flood in the Ponto-Caspian Basin", In: The Black Sea Flood Question: Changes in Coastline, Climate and Human Settlement, p. 125 The term is derived from the historical name of Volga River (known in various local languages as Itil, Atil, Idel, Atel, etc.)T. Yanina et al., Paleogeography of the Atelian regression in the Caspian Sea (based on drilling data), Quaternary International, Volume 590, 20 July 2021, Pages 73-84,
Some researchers postulate that it was a deep regression (over -100 to -150m), but researchers differ considerably with respect to its depth, age, and duration, e.g., claiming it was at about -20m relative to the Khazarian maximum.Екатерина Бадюкова, Колебания уровня Каспийского моря в неоплейстоцене (была ли ательская регрессия?), Океанология, 2021, 61(1), pp.1-10,
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Further reading Попов Г.И., Плейстоцен Черноморско-Каспийских проливов (стратиграфия, корреляция, палеофаунистика, геологическая история), p. 22 describes Atelian layers