Hydrostratigraphy of Pleistocene alluvial fan and river plain deposits of the Po foreland basin

In the southern active margin of the Po river foreland basin the Middle Pleistocene-Holocene basin fill is controlled by thrust faults and subsidence affecting the front of the advancing Apennines chain and by glacioeustaic climatic cycles. The extensive study of cored boreholes allowed the recognition of bipartite depositional units constituting the building elements of the basin fill. In Middle-Late Pleistocene times the stacking of these stratigraphic elements was basically controlled by tectonics modulated by climate over the astronomically driven 100 ka cycles. In the southern margin of the Po river basin these building elements average 30 m thickness and are neatly subdivided in a lower portion representing the alluvial fan gravels and an upper portion representing the overbank muds. The age constraints provided by radiocarbon dates indicate the development of coalescent alluvial fans in cold climatic phases, destined to become aquifers, and the aggradation of the alluvial plain in warm climatic phases, with river-channel avulsion and overbank sedimentation forming the laterally continuous fine-grained deposits destined to become permeability barriers. Aggradation during interglacials is of the utmost importance to hydrostratigraphy since river channels build up topographically elevated alluvial ridges causing river avulsion and the ultimate draping of aquifer bodies by a laterally continuous confining layer.