Quaternary drainage inversion driven by progressive extension in central Umbria, Italy.

Modification of rivers and their drainage basins is a poorly understood process associated with tectonically and/or climatically induced erosion, that strongly influence paleogeography, sediment budgets, and provenance. Such events may represents the geomorphological response to variation in rate, style, and locus of tectonic deformation, hence their identification and investigation is a key issue in active tectonic studies. We identify six orders of fluvial terraces and erosional surfaces associated with the evolution of the Puglia River, a tributary of the Tiber River, in central Umbria, Italy. Investigation of the highest terraces and erosional surfaces demonstrates southeastward flow of the Puglia River, until at least the middle Pleistocene, before reversal, erosion of the Ponte di Ferro Canyon, and deposition of the lowest terraces. Additional sedimentological evidences, including pebble imbrications, composition, dimension and roundness, confirm that the Puglia River reversed its course to northwestward flow in the recent geological past. Basing on an update geological survey, we document the structural control operated by low and high angle normal faults on the geometry of the ancestral Puglia River Basin and propose that the drainage inversion was driven by progressive extension, consisting with an eastward migration of fault activity. River reversal likely followed stream capture in response to enhanced fluvial erosion and uplift of the Puglia River basin, at the footwall of a NE dipping active normal fault. Future dating of the river terraces, will allow determine the timing of the inversion of the Puglia River, and will help to constraint the space-time changes of fault activity.