Space-time geological model of the Quaternary syntectonic fill of a foreland basin (Po basin, Northern Italy)

Quantitative models of large and widely populated Quaternary foreland basins, which host relevant resourceslike groundwater, heat, and fertile soils, may be computed if space–time models of the basinfills are available.The paper presents the combination of geometrical (space) and evolutionary (time) constraints to modelQuaternary stratigraphy in the southern Po basin in Lombardy, disentangling the tectonic and climatic controls.Five Quaternary high-rank unconformities and seven intermediate-rank unconformities were recognised, down-traced, and correlated from surface to subsurface. Within this framework, the surface facies associations of high-,intermediate-, and low-rank stratigraphic units were compared to the litho-textural associations of their subsur-face equivalents obtained from borehole logs and published geophysical images, to draw the bestfitting model,which was constrained to the Quaternary geological evolution.Discrete, long-term thrusting, wrenching, folding, and extensional collapsing stages are inferred to have shapedthe Gelasian, intra-Calabrian, Early–Middle Pleistocene, Middle–Late Pleistocene and Latest Pleistocene–Holocene high-rank composite unconformities. These surfaces are cut into synsedimentary, polyphasic, buriedanticlines and correspond to conformable boundaries in the adjacent depocentres. The intermediate-rank, low-angle unconformities composing the high-rank ones, bound the stratigraphic units forming the overall regressivefill of the basin. These surfaces might correspond to steady tectonic uplift/subsidence periods when depositionwas mostly controlled by Pleistocene climate changes since the Gelasian.The hierarchic space/time structure, translated into hard geometrical constraints (a fence diagram of cross-sec-tions) and relative chronology of the stratigraphic relationships (intersect/erode, onlap and offset) allows com-puting the geological quantitative model using a potentialfield interpolation method. The model buildingphase and subsequent inspection permit critically analysing the current interpretations on the evolution of thePo basin during the Quaternary compared with other foreland settings. The 4-D model integrates the surface–subsurface geometry with the tectono-sedimentary evolution in a multi-scale structure that may be exportedfor hydrogeological, geothermal and environmental modelling.