Tufa deposits in the Seine and the Avelasse Valleys have yielded numerous molluscs assemblages belonging to the Lyrodiscus Biome. These malacofaunas, primarily indicative of forest which developed under a warm climate, have no present-day counterpart. The biostratigraphical study of several localities based on new investigations at Vernon (Seine Valley) and Arrest (Avelasse Valley) and a reexamination of the faunas from St Pierre-les-Elbeuf suggests the allocation of a Holsteinian age. This is supported by U/Th dates for Vernon and the stratigraphy of the loess sequence of St Pierre-les-Elbeuf Similar assemblages yielded by tufas of the same age in England and Germany indicate that the Lyrodiscus Biome was widespread. The warm climate recorded by the molluscs of the tufa deposits is in agreement with pollen and marine analysis for the isotopic stage 11 (362-423 kyr B.P.). In this way, the Lyrodiscus Biome appears as an interesting marker for the continental Quaternary in Western Europe. If the occurrence of these particular molluscan assemblages is due to climate, refuges from the declined Tertiary biota, from which i.e R. (Lyrodiscus) could have emigrated, also needed to exist.
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