Alleröd deposits at Zervynos on the Ūla River: geology, geochronology and malacofauna

Th e 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. Th e age of lake deposits is the Allerod time. Th e 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.