Le Tardiglaciaire des fonds de vallée du Bassin Parisien (France) [The Late-Glacial from the Paris basin floodplains (France)]

Abstract

The Paris Basin floodplains provide contrasted Late-Glacial records closely connected to climatic changes. Extensive study of morpho-sedimentary evolution associated with palynological and malacological data allows palaeoenvironmental reconstructions which fit well with what is known for N-W Europe. The transition between the Pleniglacial and the Late-glacial remains poorly documented. It is represented by sand and silt deposits sedimented by a braided river network. The Bølling begins with a significant incision related to a meandering system evolving from several channels to a single one. Whereas the second part of the Bølling and the Older Dryas show episodes of recurring sedimentation, the Allerød appears relatively stable. A key-horizon paleosol, and local peat formation, which started locally during the Bølling, illustrate the vegetation development and a significant decrease in alluvial dynamics. During the Younger Dryas a major erosion crisis induces an important phase of marly silt deposition, preceeding a further incision at the beginning of the Holocene. Three regional pollinic zones are defined. Zone 1 , with Juniperus, Betula and Artemisia is allocated to the Bølling ( 1 a) and the Older Dryas (lb). Zone 2, which corresponds to the Allerød is marked by a rise in Betula (2a), followed by the expansion of Pinus (2b). Zone 3, allocated to the Younger Dryas, shows a decrease in Pinus and an extension of Artemisia. The oldest Late-glacial malacological assemblages (Oldest Dryas and/or Balling) are characterized by abundant Vallonia and appearance of some mesophilous species. Species diversity increases during the Allerød. The Allerød paleosol yields open-ground assemblages including some xerophilous species. The climatic degradation of the Younger Dryas results in a significant fall of diversity and number of specimens. Although, the records still remain partially lacunar, their response to the climatic variations modulated by vegetation, give good information about catchment evolution and fluvial dynamics trends in this plateau region of N-W Europe.