Environmental Engineering Reference
In-Depth Information
Figure 6.3 shows a typical cross-section of the valley of the Somme river in
Northern France, showing local mechanisms of loess deposition in the early Upper
Weischel period (20-25,000 BP).
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Figure 6.3.
Local deposition mechanisms through a typical cross-section of the
Somme valley in Northern France [ANT 03]
In this area during that period, dominant winds were coming from a southwest to
west-southwest direction (see also Figure 6.4). The substratum in this area is
typically composed of chalk with upper clayey weathering.
The Aeolian loess deposit (number 6 in Figure 6.3) typically occurs on the west
side of the valley, which was protected from wind due to turbulence. Loess deposit
was also enhanced by snow. On the other hand, the opposite side of the valley was
submitted to wind erosion.
In Northern France, loess is widespread from Northern Brittany to Normandy
and the North, except on steep slopes exposed to the west or northwest and on the
narrow ridges of the Bocage Normand [ANT 03].
These regions are characterized by continuous or sub-continuous loess cover,
which is a very important component of the present-day landform (about 3 to 5 m
thick in Picardy and Northern France, and locally up to 8 m in the North-East).
The typical loess is also up to 8 m thick on the gentle leeside slopes (protected
from the dominant northwest-north-northwest winds) of asymmetrical valleys,
especially in Picardy. The main loess accumulations occur in the lower Seine valley,
the eastern Somme basin and in the North. Over the whole area the main typical
calcareous units are attributed to the Weichsel Upper Pleniglacial, between 15 and
25,000 years BP.
