La rappresentazione cartografica della successione continentale pliocenico-quaternaria delle aree collinari piemontesi nel Progetto CARG

Abstract

Forno M. G., Fioraso G. & Boano P., Cartography of the plio-quaternary continental succession of Piedmont hilly area in
the CARG project. (IT ISSN 0394-3356, 2009).
Before the CARG project, the plio-quaternary continental succession of Piedmont hilly area was prevalently omitted by a geological
map. The continental deposits are, in fact, difficult to identify and to interpret because of their preservation in discontinuous relicts
which are slightly thick. In detail, the scarcity of significant outcrops, the ambiguous morphological expression and the numerous erosional discontinuities further handicap the cartography and the interpretation of successions. The diffusion of discontinuities implies the use of Unconformity Boundary Stratigraphic Units.
The widespread colluvium, connected with the reworking of different terms of succession, and the frequent landslides create further
remarkable problems of mapping. The convergence of some quaternary terms with the later marine units or with the recent colluvium,
further complicates the cartography.
During the mapping of the “Trino” and “Torino Est” sheets of the CARG project the Unconformity Bounded Stratigraphic Units (UBSU)
are used for mapping the quaternary continental succession. The presence of some superimposed sedimentary bodies, separated by
evident erosional discontinuities, and the necessary differentiation of various alimentation basins impose to introduce an articulate
legend, to the detriment of un immediate understanding of maps. The fluvial succession connected with an ancient trend of the Po
River (paleoPo) is described in the southern slope of the Torino Hill. The fluvial terraced succession connected to ancient alpine watercourses (paleoDora Riparia, paleoStura di Lanzo, paleoOrco and paleoDora Baltea) is instead mapped on the western and northern slopes. Both the successions are strongly uplifted. The sediments connected with ancient tributary watercourses are also represented, in both the areas, and distinguished from the current fluvial sediments.
The cartography of succession in areas of distribution of different sedimentary units outcropping in a small sector, separated by erosional discontinuities, was particularly complex.
A part from the interpretative difficulties, the importance of continental deposits is pointed out in order to reconstruct the recent geological history: the anomalous altimetrical distribution suggests a remarkable deformation of the hilly area, connected with the evolution of important pre-existent or new tectonic structures and with the differential uplift of the different areas.
The difficulty in the individuation of chronological elements in the sediments, often only of pedostratigraphic nature, represents an
unresolved aspect. The only exception is the fossiliferous villafranchian succession that allows a detailed chronological reference.