On the origin of several heavy clay layers in solifluction deposits of the Belgian Condroz

Abstract

In many places in the Belgian Çondroz heavy solifluction clays occur on top of Tertiary sands. These deposits are generally found in conjunction with fair amounts of chert and silicified fossils. In order to determine the origin of the clays, investigation of the fossils (mainly brachiopods and corals) and the granulometric and mineralogical compositions were carried out. The fauna collected in the clay deposits is typical for the upper Tournaisian and lower Viséan (Lower Carboniferous). For comparison fossils were also collected from residual clays in situ on Viséan and Tournaisian limestones. No important differences between the fossil groups could be detected. The clay mineralogical analysis also indicates that the clays in the solifluction deposits are residues of soil formation on Carboniferous limestone.