CLAYS IN PALEOWEATHERING PROCESSES - STUDY OF A TYPICAL WEATHERING PROFILE IN THE HERCYNIAN BASEMENT IN THE MONTES-DE-TOLEDO (SPAIN)

A series of weathered Paleozoic slates was studied in an area southwest of the Montes de Toledo mountain range where the weathered slates are overlain by a rana formation and show three weathering levels. The fresh slate (at 30 m depth) is composed of ferrous chlorite, mica, quartz and feldspars. In the lowest part of the weathering profile the ferrous chlorite begins to evolve to smectite, and in the intermediate level, all the chlorite has been transformed into smectite. In the upper level (in contact with the rana formation), the smectites evolve to kaolinite, and the micas, which are unaffected at greater depths, begin to evolve to vermiculite, and there has been segregation of the free iron oxyhydroxides producing red, ochre and white zones. Two principal weathering processes, separated in time but superimposed, have been identified.