Morphostratigraphy and sediment provenance of a Late Holocene succession from the central Po Plain (northern Italy)

The description of fluvial landforms is rarely accompanied by the 3D geometry of associated alluvial deposits. In this study, based on integrated geomorphological, stratigraphic and sediment provenance analysis, we examined the combined geomorphic and sedimentary expression of the central Po Plain and its Late Holocene evolution. Ten morphostratigraphic units were mapped and dated to the last four millennia. The timing of formation of each unit was assessed combining radiocarbon and archeological data. Each unit includes a system of fluvial ridges and associated crevasse splays and floodplains. Morphostratigraphic units appear in the subsurface as lens-shaped sediment bodies marked at the base by swamp deposits. Upsection, fluvial-channel deposits grade laterally into levee, crevasse and floodplain facies associations. The Late Holocene evolution of the Po River network records the seaward migration of the Po Delta apex and the progressive increase in anthropic impact on the geomorphic evolution of the area, with substantial modifications of the river network since Renaissance. Morphostratigraphic units are arranged in a compensational stacking pattern that records avulsion processes. Increased frequency of avulsions during the Middle Ages resulted from political and social disorder in the Italian peninsula after the fall of the Western Roman Empire and from an overall increase in precipitations. The location of Late Holocene paleochannels controlled the local response to seismic perturbation during the 2012 earthquake sequence, co-seismic liquefaction occurring mostly along paleochannel axes.