Clay minerals in cave sediments and terra rossa soils in the Montagnola Senese karst massif (Italy)

Reddish mud-rich sediments are common in several karst areas, in the form of red surface soils and clastic cave infilling. The origin and significance of red surface soils have been largely debated over the last years, whilst clastic mud-rich sediments in cave environments have received less attention by geoscientists. The genetic relation between these two materials still remains uncertain. In fact, these sediments are mainly constituted by fine materials, therefore, their study has been generally focused on the clay fraction only.This paper compares the clay fraction of red surface soils and mud-rich cave sediments in the Montagnola Senese massif. Previous studies have demonstrated that in this area red cave muds originate from the erosion of the red surface soils and their consequent re-deposition in the cave environment. Despite these well-established genetic relations, notable differences in the clay fraction of these two materials have been recognized in the present study. These differences are likely to be attributable to the different grades of pedogenetic alteration that affected the two materials. This study demonstrates that the genetic relations between mud-rich cave sediments and red surface soils can be misinterpreted when the clay mineral fraction only is considered.