Aller d deposits at Zervynos on the ūla River: geology, geochronology and malacofauna

The paper contains results of new investigations of interstadial deposits at Zervynos on the ūla River in southeastern Lithuania regarding sapropelite occurence, radiocarbon dating and malacological analysis. Organic deposits belong to a lake formation. The age of lake deposits is the Aller d time. The Zervynos malacofauna consists of seven ecological groups, eurytopic water molluscs playing the main role (41%). Lake species and those of overgrowing and silting water make only 18%. Lake fauna is characterised by Gyraulus laevis (Alder) and Armiger crista (Linnaeus). Evolution of the ūla River valley is related to the development of glaciokarst depressions.