Geology of the Entracque–Colle di Tenda area (Maritime Alps, NW Italy)

Abstract

The 1:25,000 geological map of the Entracque -Colle di Tenda area covers an area of about 130 km 2 in the Italian Maritime Alps, between the Gesso and Vermenagna valleys. The map area is of great relevance since the Alpine units of this region sampled a geological nodal point in the Mesozoic, at the transition between two different sedimentation domains of the Alpine Tethys European palaeomargin (the Dauphinois basin to the NW and the Provençal platform to the SE). During the Cenozoic, this palaeogeographic hinge was progressively incorporated along multiple shear zone systems developed at the southern termination of the Western Alps arc.

Geological setting of the southern termination of Western Alps

“…2), it consists of deep-water facies (Carraro et al 1970) whereas in the Tenda Pass (Fig. 2) it is composed of a thick platform limestone succession, locally dolomitized (Barale et al 2013(Barale et al , 2015. The Cretaceous interval, mainly made up of marly limestones, also shows important lateral variations in thickness, from more than 100 m (Roaschia Valley, Zappi 1960) to nil in the Tenda pass area and NW of Valdieri in the Gesso Valley (Fig.…”

“…6c) and mainly SW-vergent thrusts (Barale et al 2015). Regional foliations did not develop during D3, apart from a cm-spaced dissolution cleavages that became, along syn-D3 reverse shear zones, a pervasive slip cleavage that can locally transpose the primary rock fabric (Fig.…”

“…In the study area, the Dauphinois succession continues with an Upper Cretaceous unit composed of several hundred metres of hemipelagic marly limestones including platform-derived bioclastic layers in the western sector (Sturani 1962;Bersezio et al 2002) and layers rich in siliciclastic or dolomite clasts in the eastern sector (Malaroda 1963; Barale et al 2015). In the Provençal domain, the Upper Cretaceous hemipelagic marly limestones bear very scarse detrital levels (Lanteaume 1968;Varrone 2004;Varrone and d'Atri 2007).…”

“…This paper, although supported by a revision of the geological setting of the whole Maritime-West Ligurian Alps junction (e.g. Barale et al 2015), focuses mainly on the geometry and kinematics of the boundaries of the several newly defined tectonic units (see below). This choice was made not only for the sake of brevity, but also because the present setting of the study area is essentially due to syn-D2 and D3 shear zones or shear planes, generally steep, that are responsible for alignement of the units along an average WNW-ESE direction (with a slightly anastomesed pattern, Fig.…”

“…The Briançonnais domain represents a portion of the European continental margin located between the Mesozoic Barale et al (2015). Ligurian-Piemonte basin and the Dauphinois and Provençal domains.…”