Abstract

Clay with flints in the western part of the Paris Basin occurs in two different morphological contexts: the plateaus and the valley sides. The geometric study of the deposits and the lithological characterization of the clay with flints occurring in the valley sides, named "biefs a silex" in France, have enabled a typology of these materials. The typology depends on the slope of the valley sides. The analytical comparison (grain-size distribution, flint content and percentage of broken surfaces of flints) between the clay with flints of the plateaus and those of the valley sides ("biefs a silex") demonstrates that formations constitute two distinct facies. The clay with flints occurring on the valley sides is equivalent to "head" and "massive grazes". This facies results from periglacial reworking of the plateau clay with flints. The reworking process involved solifluction during the down-cutting of the valleys, in Quaternary. The geometry of the "biefs a silex" comprises either a single or double bevel; the latter case requires a minimum of two main stages of the reworking, which occurred between -800000 and -20000 years ago.

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