Fault-propagation folding, fluvial dynamics, gravitational deformation and rock slope failures: mutual relationships in the Poggio Baldi area (Northern Apennines)

Folding of sedimentary rock sequences as inherited from past tectonics events can control various aspects of rock slope stability, including the development of DSGSD (Deep-seated Gravitational Slope Deformation) and large landslides. In these cases, the knowledge of fold geometry and its complexity is much important for deriving conceptual/evolutionary models of gravity-driven deformations and understanding slope failure mechanisms. This work provides further insights into the relationship between slope-scale gravitational processes and fold-related morphostructural features. We present a case study where the kinematic evolution of a complex fault-propagation fold within the Marnoso-Arenacea turbiditic sequence in Northern Apennines has preconditioned the formation of a DSGSD and the onset of the large and still-active Poggio Baldi landslide, with failure episodes documented in 1914 and 2010. An inventory of gravity-driven geomorphological features was realized and their distribution within different sectors of the fold structure analysed to conceive a multiple-step geological, conceptual model for the development of the DSGSD. While fold geometry, characterized by breaking-through thrusts and panel rotations, and the lithological anisotropies within the flysch sequence played the role of predisposing factors, the Quaternary entrenchment of the Bidente River along the fold back-limb was considered as the main cause for the onset of gravitational deformation. Finally, the reconstruction of the original slope topography in the Poggio Baldi area and the results of remote sensing analyses allowed for the size calculation of the wedge-shaped rock block which detached in 1914, an event that occurred in the wider frame of the DSGSD.