Unravelling the tectono-stratigraphic link of buried and exposed structural fronts of the Northern Apennines through integrated geological mapping (CARG Sheet 160 Pavia, Italy)

Understanding the structural and stratigraphic connection between the exposed sectors of collisional belts and their external thrust front buried beneath foreland basin sediments remains a long-debated issue, largely due to the need for integration of heterogeneous surface and subsurface datasets. This research focuses on the Northern Apennines front, at the transition between the exposed Oltrepo Pavese hillslopes and the buried thrust front beneath the Po Plain, investigated within the Italian Geological Mapping Project (CARG, Pavia Sheet - 160). Detailed field mapping resulted in an original 1:10.000 scale geological map of the exposed belt, supported by petrographic and biostratigraphic analyses. These surface data were integrated with seismic profiles and deep well data, from a regional 3D model of the central Po Plain, which reconstruct the geometry of the buried thrust system displacing the Plio-Pleistocene sequence in the Po Plain, in order to link the exposed and buried stratigraphic units. The integration of surface and subsurface data allows the recognition of structures otherwise hided beneath vegetation and Quaternary colluvial covers in the hillslopes. In particular, seismic interpretation allows to localize buried structures and constrains their geometric relationships with respect to the attitude of the outcropping units.

The stratigraphic record in the exposed area includes Paleocene to Lower Eocene turbiditic succession of the Val Luretta Formation, which thrusts over a Tortonian to Piacentian sequence. This latter records a progressive shallowing upward trend in the environment, from a deep-sea setting to shallow marine, deltaic and then continental environments associated with the Messinian Salinity Crisis, followed by the Pliocene marine transgression.

Interpretation of subsurface dataset allows the recognition of a south-dipping, north-verging thrust system affecting both the exposed and the buried units, with multiple splays and blind thrusts active until the Lower Pleistocene.

These results provide new constraints on the geometry and the evolution of this sector of the Northern Apennines front, demonstrating the effectiveness of combining field-based geological data with subsurface data to link outcropping and buried portions of orogenic belts