Deep gullies entrenchment in valley fills during the Late Holocene in the Basento basin, Basilicata (southern Italy)

Abstract

Deeply entrenched channels namely badland gullies occur on the gently sloping valley floors of any alluvial basins in the semi-arid environments of Fossa Bradanica, Basilicata, southern Italy. Valley fills in this region consist of predominantly Holocene alluvium; late Pleistocene deposits occur as terraces above the present flood plain or as eroded benches buried beneath younger alluvium. Historical fluvial deposition began before 7000 a cal. BP and ended at around 120 a cal. BP. In this study, we focus on the channel entrenchment (badland gullies incision) in the last 4500 years, based on a detailed study of chronostratigraphic alluvial sequences of Basento River. Four main phases of incision have been recorded at around 4500-4350, 1500, 900-800, and 120 a cal. BP. The formation of late-Holocene badland gullies can be related to changes in climate, vegetation and groundwater conditions. Environmental history mainly derived from the high-resolution pollen record of Lago Grande di Monticchio. Badland gullies formation appears to be linked to repeated dry-wet cycles. During dry periods, water tables significantly dropped and vegetation cover decreased with increase in runoff and water discharge from rainfall, leading to deepening and widening of stream channels.