PEDOGENESIS BY CLAY DISSOLUTION ON ACID, LOW-GRADE METAMORPHIC ROCKS UNDER MEDITERRANEAN FORESTS IN SOUTHERN TUSCANY (ITALY)

Pedogenesis on acid, low-grade metamorphic rocks under well-developed forests was studied in the meso-mediterranean climatic zone. To that p urpose three representative soil profiles on phyllite and sandstone un der sclerophyllous oak, pine and heathland were selected. The major so il forming processes consisted of transformation of part of the K-mica (muscovite) to (hydroxy-interlayered) vermiculite and smectite, impov erishment both in major elements (Al, K, Mg and Fe) and fine particles , and redistribution of sesquioxides as organic complexes. These proce sses indicate clay hydrolysis under acid conditions and subsequent rem oval of solutes by lateral subsurface now. The resulting impoverishmen t of the soil profiles could be mainly attributed to hydrolysis under acid conditions brought about by slow decomposition of organic matter. The proposed mode of pedogenesis deviates strongly from the current c oncept of fersiallitisation, and is probably restricted to acid parent materials in mediterranean climates where lateral removal of soluble weathering products is ensured throughout the largest part of the year .