A deep boring (30 m), carried out at Watten (Nord, France) in 1990, has provided an opportunity to undertake palaeoecological studies based on stratigraphy, sedimentology, palynology, malacology and 14C datings on Early Weichselian and Holocene deposits. The location of the site in the inner zone of the coastal plain, extending in the Aa valley from the southernmost shores of the North Sea upstream to Watten, allows the comparison between interstadials recorded in a pure fluvial environment and the overlying Holocene sediments, in which alternation of marshy, fluvial and marine deposits are observed. The Early Weichselian sequence can be correlated with the Brørup and Odderade interstadials described in northwestern Europe, and belongs within the same palaeogeographical area. At that time the conditions were already continental at Watten. However, the last (Holocene) interglacial has been characterized, at least since the Boreal chronozone, by an oceanic climate and a progressive invasion of the sea, sometimes interrupted by stillstands and withdrawals.

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