Recent advances in the stratigraphy of the Upper Pleistocene of Westernmost Europe: La Haute Ville and Brehat Cliffs (Northern Brittany, France)

摘要

A description of the different layers deposited in La Haute Ville and Brehat sites is given. Methodological considerations and comparisons with Russian, French and Netherlands stratigraphic scales are summarized. Malacological study shows the existence of shells deposited during the Early, Middle and Late Weichselian. In La Haute Ville, the upper part of the Lower and Middle Weichselian contains four soils which developed above an aeolian dune. Four malacozones have been separated. The groups of molluscs were classified according to their modern ecological preferences. The upper part of La Haute Ville Formation is observed in the lower part of the La Haute Ville cliff. This aeolian accumulation is completely decalcified. There is no fauna. The presence of colored quartz implies the existence of a warm climate. By comparison with other dunes of Brittany, it could be dated to the Early Weichselian. Comparison between the onshore and offshore data shows that the dune has never been as rich in carbonates as the loess or loess-like deposits. The Port Morvan Formation consists of four different soils interlayered with loams. All the soils are located at the level of the dome-like top of the dune. The disappearance of the soils towards the west and the east is associated with an undulation of the dune. The existence of four soils and the presence of molluscs living under broad leaved forests suggest a moderate climate. The cooling of the climate started at the end of the Port Morvan formation. These data allow correlation of this formation with the Middle-Lower Weichselian. The formation of Sables d'Or les Pins corresponds with true loess. It was deposited above the Port-Morvan formation which displays a clear erosion of its top. The top of this formation was affected by the development of a Holocene soil. A light grey layer represents a podzolic horizon. The lower boundary of these layers is affected by thermokarst. Because of their location, their aeolian origin, the existence of thermokarst, the mollusc assemblage and the dating already obtained elsewhere, this section is attributed to the Upper Weichselian. The Holocene deposits are represented by a podzolic soil and slope deposits, which formed during moderately humid conditions. It covers a dark grey soil made of colluvium containing charcoal and prehistoric to recent artifacts, which possibly formed in a forest or bush environment.