CATTUTO C., GREGORI L., MELELLI L., TARAMELLI A. & BROSO D.
I conoidi nell’evoluzione delle conche intermontane umbre – The alluvial fans in the evolution of the umbrian intramontane basins
Pages 89-95
Abstract
An extensional tectonic ph ase from the Late Pliocene to prese nt with a maximum value in Lower-Middle Pleistocene stron gly cont rolled the evolut ion of the central Apennines area and the Umbria region as well. Toge ther with this exten sional condition , isostatic uplift occurred in Lower Pliocene. As a consequence two large and cont inuous basins crossed the area from NW to SE. Along the eastern margin of the region, paral lel to the first ones, other smaller basins are present. The depressions are recognizable as intramont ane basins crossed by superficial dra inage networks belonging to River Tevere catchment. Alluvial and colluvial deposits, ero ded from neighb ou ring slopes, fill the basins. Alluvial fans are one of the most common deposition landforms in th is environment . In thi s paper , we started from a mapping inventory of alluvial fans in Umbria region . Id entification and mapping of fans were carried out in the field, by using top ographic maps and interpr eting two sets of black and white aeri al ph oto graph s. Th e bound aries of the fans were also crosschecked using a digital derivate hillshade from the 90 m DEM. The fan boundaries were dr awn interactively on the shaded relief map based on the spa tial distributions of slope, local relief and curvature. The fans are divided in inactive delta and fan delta and in active alluvial fans. Alluvial fans in tectonically active areas are related to the ratio of sedime nta – tion to uplift rate. Geometri c and sedimentary char acteristics of the fans allow to understand the fault activity distribution in the region . We suppose d a more recent evoluti on of the fans going from west to east , according to the extension al stress field migration.