Clay minerals of clayey subsoils of Weichselian Age in the Zealand-Funen area, Denmark

Abstract

The distribution of clay mineral constituents of clay-size particles ( The regional distribution of each of these classes revealed a close association with the movement of the glaciers during the Weichselian glaciation. Post-depositional processes (oxidation and leaching) had formed two weathering zones; an upper brownish CaCO3-free zone down to depths of 1–3.5 m, and a lower brownish CaCO3-rich zone down to 3–6.5 m. The composition of the clay minerals of weathered CaCO3-rich clayey subsoils studied at a regional scale suggested a total-transformation process of chlorite, illite, and illite-smectite to smectite and vermiculite. The diversity of clay minerals, typically 5, impeded a more thorough characterization of the transformation of individual clay mineral constituents. Nevertheless, at the Havrebjerg site separate phases of the chlorite transformation were identified within a 0.6 m wide weathering sequence: lowest, a grey zone with unaltered inherited chlorite, followed by a greyish brown zone with slightly transformed chlorite, a brown zone with hydroxy-interlayered vermiculite/smectite, and a yellowish brown coloured zone with hydroxy-interlayered vermiculite/smectite and vermiculite/smectite (but no chlorite). Also, the weathering sequence reflected changes in the cation exchange capacities of the clay fraction and ratio of structural Fe(II) in clay minerals to total Fe.