Linking the exposed belt to the buried one: preliminary data and results in the framework of the project CARG 160 Pavia

The study of complex transition zone between the outcropping front and the buried one of collisional belts usually faces some challenges due to the difficulty in homogenization and correlation of field and subsurface data. An attempt to unravel this complicated relationship, aiming to understand the spatial and evolutionary connection of outcropping units and buried structures, is being pursued in a sector of the Northern Apennines (namely in the central part of the Emilian arc), within the activities for the implementation of the “Foglio 160 – Pavia”, as part of the CARG Project. The study area is specifically located at the southeastern portion of the Pavia Sheet, between Casteggio and Stradella (Oltrepo Pavese), where the units exposed in the Northern Apennines outcropping chain slopes rapidly below to the Po alluvial plain. The hill sector includes a Paleocene to Pleistocene sedimentary succession, involved in the SW-NE oriented thrusts and folds of the Apennines front, which can be traced along the western flank of the Emilian arc, currently buried below the Quaternary deposits of the Po Plain where it controlled the syntectonic sedimentation of the Plio-Quaternary sequence (Amadori & al., 2019; Maesano et al., 2024). In the hill sector, the 1:10.000-scale geological survey activity for the CARG project allowed the collection of a dataset regarding the outcropping units, implemented by the integration with shallow well data provided by local public administrations (Provincia di Pavia, Regione Lombardia), due to the scattered distribution of outcrops and the extensive development of alteration profiles and soils. By contrast, the spatial arrangement of folds and thrusts forming the buried front of this sector of the Northern Apennines below the Po Plain deposits was obtained by a comprehensive 3D reconstruction of the regional scale structures and Plio-Pleistocene unconformities, derived from the integration of well logs and available seismic data (ongoing PHD project by Daniel Barrera Acosta, University of Pavia). Based on this integrated data set, it is possible to carry out several geological cross sections, showing the geometry and mutual relationship of structures and geological units moving from the exposed belt to the buried one. This work presents a preliminary attempt to correlate and homogenize field and subsurface data, in order to set up a conceptual model of the transition zone between topographic front of the Apennines with its tectonic front and, in perspective, to evaluate the flexural response of the foredeep to the emplacement of the Northern Apennines buried fronts. The obtained conceptual geological model is expected to provide a more complete knowledge of the structural and stratigraphical evolution of the Apennine border, as well as the understanding of the dynamics of frontal chain uplift and foreland basin subsidence and their time/space correlations.