How Two Orogens Shaped and Filled a Foreland Basin: Plio-Pleistocene Tectonic and Climatic Controls on the Po Plain Basin (Italy)

This study presents a new regional-scale 3D reconstruction of the major Plio–Pleistocene tectonostratigraphic surfaces of the Po Plain Basin (Italy), providing new constraints on the deformation history of this key Mediterranean foreland basin. The model was constructed by interpreting several thousand 2D pre-stack time-migrated (PSTM) seismic profiles, calibrated with an extensive wellbore database. This approach enables a robust regional mapping of structural elements and defined Plio-Pleistocene unconformities.
The results show that the Plio-Pleistocene architecture of the Po Plain is controlled by the interaction of two different geodynamic systems, resulting in a complex source-to-sink system.  Since the Plio-Pleistocene, the advancing Northern Apennines (NA) thrust belt has mostly generated accommodation space, whereas most of the sediment supply came from the Southern Alps (SA). 
Isobath maps provide new temporal constraints on the timing and style of deformation, particularly in the central sector of the Po Plain, where the outermost buried fronts of the NA, belonging to the Emilian Arc fold system, are nearly in direct contact with the outermost fronts of the SA. Our reconstruction demonstrates that the evolution of the NA thrust front was strongly influenced by the presence of the buried SA to the north. Where the NA collided with the SA, out-of-sequence thrusting was triggered within the internal sector of the NA from the middle to late Pliocene, locally persisting until the late Pleistocene. In contrast, where this interaction did not occur, the NA thrust front evolved following a classical in-sequence style, highlighting significant along-strike variability in the structural evolution of the Northern Apennines.
The detailed 3D reconstruction of the entire Po Plain subsurface further allows a robust analysis of the progressive reorganization of basin depocenters through time via the calculation of isochore maps. Beyond providing a three-dimensional depiction of this evolution, these maps enable quantification of sediment volumes deposited between successive unconformities and, subsequently, the calculation of sedimentation rates across the basin.
Decompacted volume analysis reveals a marked increase in sediment accumulation during the Pleistocene, from approximately 31,041 km³ for the entire Pliocene, with a rate of 10.594 km³/Ma to about 60,646 km³ for the Pleistocene, with a rate of 25.269 km³/Ma, based on a 50% sand–50% shale decompaction model. This increase occurred despite an overall reduction in tectonic activity during the Pleistocene within the Alps, the primary sediment source region. This apparent paradox is interpreted as the result of strong climatic forcing associated with progressive climate deterioration and the onset of major Alpine glaciations, which dramatically enhanced erosion in the surrounding orogenic belts. The resulting increase in sediment flux, together with a major marine regression, drove rapid basin infilling and large-scale eastward progradation of the Po Basin system. These findings highlight the fundamental role of climate–tectonic coupling in controlling the evolution of the Po Plain over the last 5 Myr.