Soil evolution and origin of landscape in a late Quaternary tectonically mobile setting : the Po Plain-Northern Apennines border in Lombardy (Italy)

The interactions among Quaternary (paleo-) soil-forming, erosion, re-deposition and geomorphic processes at the origin of the present-day landscape are discussed at three isolated tectonic reliefs of the Southern Po Foredeep Basin of Lombardy (San Colombano, Casalpusterlengo and Zorlesco reliefs, Italy). These sites offer the possibility to combine different scales of geopedological, geomorphological, stratigraphic and structural ob- servations, to unravel the contribution of climate and tectonics to the Quaternary geological evolution and to the origin of the landscape. Field surveys, laboratory analyses and soil micromorphology were used to characterize the Late Quaternary pedogenic processes acting on different (paleo)-surfaces, in combination with the detailed study of seven se- lected soil profiles. Pedo-stratigraphic correlations revealed that two alluvial/loess-paleosol sequences, which originated from the Late Pleistocene to Holocene glacial/interglacial fluctuations, are differently preserved throughout the present-day hill landscape. In situ paleosols allowed to localize the paleo-topographic surfaces of geomorphic, tectonic and sedimentary stabilization; redeposited paleosols, occurring systematically close to the main faults and/or at the erosional bottom of paleo-valleys, allowed to mark the stages of tectonic instability. The integrated approach contributed to unravel the composite nature and rank of the stratigraphic boundaries. Polycyclic loess-soil aggradation characterized the stable paleo-highs, uplifted during different phases of active thrusting of the northernmost Emilian arcs of the Apennine, while valley incision, fluvial terracing, soil truncation and redeposition occurred in the intervening structural lows. In the San Colombano hill area, Late Pleistocene transtensional faulting induced changes of the drainage network and enhanced redeposition of pa- leosols in colluvial wedges on the hangingwalls, along the fault scarps. LGM loess was preserved above different dissected remnants of the paleo-topography composing the hilltops. These new constraints permit to refine the Late Quaternary tectono-depositional history and landscape evolution at the southern margin of the Po Basin.