Drainage system adjustment in response to the opening of the Rieti intermontane basin (Central Italy): geostatistical reconstruction of the PaleoFarfa River alluvial plain

Abstract

The Rieti intermontane basin is one of the western tectonic depressions of the Central Apennines. Its infilling deposits are currently cut by the Farfa River, a left tributary of the Tiber River with a 132 km2 wide drainage basin. It currently flows from the Sabini Mts. (Central Apennines) into the Tiber River to the WSW. In the upper basin, the river cuts fluvial conglomerates and sands, which are Gelasian in age. Downstream, on the left side of the Tiber Valley, the facies show deltaic to clearly marine characteristics that indicate the presence of the Gelasian paleo-shoreline, which is also indicated by the finding of Lithodomus holes in the calcareous bedrock at an elevation of 260–277 m a.s.l. The shape of the Gelasian alluvial plain and delta has been outlined and redrawn via GIS techniques. We herein underline that during the Gelasian, the shoreline was located at the foot of the Fara in Sabina Mts. and that the alluvial plain of the PaleoFarfa River was much wider (approximately 700 km2) than the present, extending to the foot of the Reatini Mts. The reconstruction of both the basal and top surfaces of the old alluvial body provides evidence that the activity of Quaternary faults, responsible for the formation of the Rieti intermontane basin, strongly influenced the deposition of the alluvial body and finally caused the adjustment of the PaleoFarfa drainage system. Finally, from the shoreline elevation, a Pleistocene averaged uplift rate of 0.12/0.14 mm/year has been calculated for this sector of the Apennines.