LA SUCCESSIONE FLUVIALE TERRAZZATA PLEISTOCENICA DEI VERSANTI OCCIDENTALE E NORDOCCIDENTALE DELLA COLLINA DI TORINO

Abstract

Forno M. G. & Lucchesi S., The fluvial pleistocenic terraced succession of W and NW slopes of the Collina di Torino. (IT
ISSN 0394-3356, 2005).
Previous studies about the Quaternary evolution of the Collina di Torino put in evidence in a preliminary way traces of a Pleistocenic
hydrographic net, suspended and with a different pattern from the watercourses now developed in the relief. The geological survey of the Western and Northwestern slopes carried out during the present study, synthesized in the attached geological map at 1:20.000 scale, allows a more detailed reconstruction of the distribution of the fluvial terraced succession preserved on the secondary watersheds.
The identification of the various relics of the succession, distributed with different elevations, is suggested by its morphology: they correspond to terraced surfaces with an extension between some thousands and some tens of thousands of m2, often underlined by ancient buildings, and locally to wider remains of embedded meander. The local manmade modifications of the area and the loess and
colluvial covers are instead obstacles for the field work.
Despite these difficulties the extreme detail used for the geological survey allows the recognition of fluvial sedimentary bodies, some
meters thick, associated with the main described shapes: locally the terraced surfaces appear modelled directly on the Tertiary marine
sediments.
The different shapes are identified and correlated by the elevation and the alteration degree of the sediments, suggesting the chronological reference to the Middle and Upper Pleistocene.
The present elevation of the remains, suspended from 20 to 400 m on the plain, their distribution in the present ridges along strips
parallel to the main watershed and their elongation, different from the present watercourses, suggest a link with a very different
morphological and geological situation of the relief. In particular it can be supposed the trend of watercourses parallel to the main
watershed: the extremely recent setting of the present River Po along the Northern boundary of the relief, already known by literature,
shows that the examined remains are instead connected to a previous trend of the hydrographic net; mineralogical analysis, still in progress, suggest an alimentation particularly from the Stura di Lanzo and Dora Riparia basins.
The anomalous elevation of the fluvial succession and the presence of scarps some tens of meters high between the different orders of terraces suggest a succession of erosional deepening episodes of the hydrographic net, connected to the uplifting of the Collina di Torino.
The examined terraced succession represents the result of the deformation of the distal sector of the alpine fluvial aprons, involved in
the uplift of the Turin Hill and in the Northwestern migration of its external margin, and their embedding in the hilly area. It can be supposed that this deformation, still in action, had a rate of uplift of the order of 1mm/yr from the Middle Pleistocene to the Holocene.