Mineralogical characterization of fibrous clays near Pecharroman (Segovia. Southern part of the Duero Basin)

Forty-eight samples from selected boreholes belonging to sedimentary deposits from the Duero Basin (Pecharroman, Segovia Province) have been studied. Results point out the presence of two kind of clays: with fibrous minerals and without them. These two clays occur in four different associations, established according to the content in phyllosilicates and their composition. In this way, sepiolite and palygorskite are interpreted as neoformed and transformed fibrous clays, respectively. On the other hand, illite, smectite and kaolinite are considered inherited minerals. The situation of the different mineralogical assemblages, allows us to establish two sequences linking the clay mineral assemblages and lithofacies. The aim is a better understanding of the formation mechanisms and evolution of these fibrous clay minerals.