The Demonte terrace in the Stura Valley (Maritime Alps) between climatic changes and tectonic movements

Abstract

The lower part of the Stura valley, which from the Maritime Alps flows into the Cuneo plain, is characterized by several orders of fluvial terraces. This paper discusses the genesis and the subsequent erosion of the third order terrace (Demonte terrace) in relation to climatic changes due to succession of glacial and interglacial phases and to tectonic movements that have involved the study area. In order to understand the mechanisms that led to the aggradation of the Demonte terrace, the relations between this surface and the glacial deposits located in Stura Valley have been analysed. Stratigraphic relations and recent datings have identified the study surface as having a climatic genesis, temporally set in a typical paraglacial period, in particular in the passage from the last glacial period to the interglacial. As regards the incision of the Demonte terrace, longitudinal profiles of the terraces of the Stura Valley and the geometric relations between the Demonte terrace and the upper and the lower terraces have shown that the erosion of this surface cannot be exclusively due to climatic evolution, but are due above all to the tectonic movements that have acted on this area of the Maritime Alps. The tectonic activity that mainly influenced the fluvial pattern of the Stura di Demonte river is due to both the up-lifting of the Argentera massive and to the subsidence of the Cuneo plain. In particular the hydrographic disruption related to the capture of the Tanaro river due to the combined activity of anticlines, synclines and direct faults located in the Cuneo plain, is likely to have been responsible for the regressive mechanism that led to the progressive lowering of the Stura river base level. This is shown by the divergence of the terraces lower than third order.