The Evolution of Alluvial Fans in the Umbria-Marche-Romagna Apennines (Italy).

Several wide middle-upper Pleistocene piedmont landforms and deposits preserved on the Adriatic side of the Umbria-Marche-Romagna Apennines, indicate stages of pedimentation and related alluvial fan building and successive dissection. Both the terraced ancient alluvial fans and the related pediments correspond with the best-known valley terraces. The widest and best examples of alluvial fans and related pediments belong to the middle Pleistocene cold morphogenetic stages; the depositional bodies often show the typical fan-shapes. Instead, the alluvial fans of the upper Pleistocene are confined within deeper entrenchments, thus being almost always restricted from developing true fan shapes. During this latter stage, no significant areal erosion occurred around the fan-like bodies and, consequently, no significant erosional glacis could form after the end of the middle Pleistocene. We interpret this tendency for stream entrenchment and confinement of alluvial fan bodies as depending from an increasing rate of the tectonic uplift which became particularly significant at the end of the middle Pleistocene.