Morphotectonic study of the lower Sangro River valley (Abruzzi, Central Italy)

Abstract

This work analyses the morphotectonic setting of the Adriatic piedmont of Central Italy, in order to outline the role of tectonics in the development of the fluvial landscape in this area. Particularly, it focuses on the Sangro River, which flows in the southern Abruzzi, from the Apennines, through the piedmont, to the Adriatic coast. The piedmont area developed in a marine environment from the Pliocene to the Early Pleistocene resulting in the deposition of a clayey-sandy sequence. Afterwards, regional uplift processes with NE tilting led to the deposition of a regressive conglomeratic sequence, as the area evolved into a continental environment. This work is based on the qualitative and quantitative study of drainage patterns and on the analysis and correlation of selected morphological evidence of tectonics on fluvial terraces, in order to define the role of tectonics in the geomorphological evolution of the lower Sangro River valley. The drainage network and its statistical azimuthal distributions are analysed; the distribution and the transverse and longitudinal profiles of fluvial terraces are investigated and the morphological evidence for tectonics is then assessed: river bends, linear valleys, beheaded and hanging valleys, counterflow confluences of streams. Space and time correlation of these features allows us to highlight the effects of regional uplift, tilting, and local tectonics on drainage development. Following the emergence of the piedmont area (Middle Pleistocene), uplift and tilting determined a SW–NE consequent and parallel drainage. Progressive incision shaped the Sangro valley as a consequent valley. Local tectonics along NNW–SSE and WNW–ESE faults and fractures resulted in the incision of linear valleys, beheading the previous SW–NE drainage, and controlled the development of a rectangular drainage network (late Middle Pleistocene). The drainage network was then rearranged by selective erosion processes, maintaining a strong inheritance from of its Middle Pleistocene configuration.