Geometry and kinematics of a landslide surface in tertiary clays from the Duero Basin (Spain)

The Peñalba roto-translational landslide is one of the large landslides that can be observed in the central area of the Duero Basin (Spain). Its present morphology is a semicircular-shaped depression in which more than 6 m of vertical movement have been measured. The erosion of the banks of the Duero River affecting the slope of the Peñalba Hill has incised vertical cliffs where a slip surface outcrops and can be observed. Currently, the incision level of the Duero River is located 22 m below this surface. The slip surface, on the translational zone within a large roto-translational landslide, developed within the Dueñas Facies in a single bed with a high PI (39.0–47.8) and lower carbonate contents, would have behaved as low-shear strength surfaces (ϕ′R = 18°–21.8°).At Peñalba, the slip surface and the deformation structures related to it have been exceptionally well preserved. The structures observed are similar to those usually described in shear zones of tectonic origin: an S–C fabric, related to progressive simple shear, and C′ planes, called extensional crenulation cleavage. These similarities suggest that analogous kinematic processes would have taken place in completely different geodynamic environments. In the present work, we have adopted a structural geological–kinematic approach to explain the development of the features in this roto-translational landslide.