Eventi geomorfologici nelle Alpi italiane e nella pianura occidentale del Po: Inquadramento cronologico in base a radiodatazioni 14C

Abstract

Radiocarbon-dated episodes of landslide reactivation, debris flow deposition, fluvial sediment accretion in northwestern Italy, are reported. New findings of subfossil trunks buried in valley subsoil or debris slope deposits date mass movements occurred at intervals on the high valley slopes, and torrential deposits; the former started 9500 years BP, the latter took place since 5800 years BP. Some of these processes, which caused also valley floor damming, are documented up to 900/1000 AD, and have been indirectly ¹⁴C dated by wood or peat remains contained in upstream overflooding sediments. A peaty horizon, in the time span from 36,000 to 18,000 years BP, so far only identified in the subsoil of the Po River western alluvial plain area (southern Piedmont plain), has also been found at least up to the Ticino River inflow area. This horizon should be considered as a boundary marker between Upper Pleistocene (Pleniglacial) and Holocene fluvial deposits. Previously reported data on average Holocene sediment accretion rates in the range of 0.5÷5 mm/yr and with modal value of 2 mm/yr, are confirmed. A southward migration of a Po River reach in the order of 1.5 mm/yr over the last 1500 years, has been identified.