Late Alpine tectonics in the Ligurian Alps: constraints from the Tertiary Piedmont Basin conglomerates

Abstract

The Tertiary Piedmont Basin (TPB) is a syn-tectonic Neoalpine–Apennine basin with an upper Eocene–upper Miocene sedimentary succession. It has an inner position with respect to the arcuate belt of the Western and Ligurian Alps, in northwestern Italy. In the area north of Genova, the Scrivia Valley separates two distinct sectors where the TPB basal conglomerates display a differentiated clast provenance: in the western sector conglomerates are fed by the metamorphic units of central Liguria, whereas in the eastern sector most of the conglomerate clasts come from the Antola flysch Unit. Observations on clast lithology demonstrate that the transition between the two types of conglomerates is abrupt and roughly coincides with the Scrivia River Valley. An explanation of the different clast provenance as due to a progressive deepening of the erosional level appears to be possible in the eastern sector, but it is not feasible in the western sector, where the flysch units appear to have been protected from erosion. We propose that the northwards thrusting of the Ligurian Alps metamorphic units onto the Antola flysch units, made the latter not available to erosion and led the Scrivia Fault and other equivalent tectonic lineaments to act as tear faults. Field data suggest that the Tertiary geodynamics of the Ligurian Alps was dominated by the Corsica–Sardinia anticlockwise rotation, that caused the northwards backthrusting of the Ligurian Alps, accommodated by a complex strike-slip fault system, that segmented the TPB, affecting the sedimentation and the clast provenance of the conglomerates

Stratigraphic vs structural contacts in a late orogenic basin: the case of the Tertiary Piedmont Basin in the Sassello area (Ligurian Alps, Italy)

“…These types of contacts are a consequence of the Aquitanian-Burdigalian late-alpine/apennine tectonics, which caused the back-folding and back-thrusting of the alpine units toward E-NE. Due to this back-thrusting, the TPB underwent local uplift and evolved as a piggy-back basin (Capponi et al, 2001(Capponi et al, , 2009, and references therein). In the study area, thrust faults are associated to a roughly E-W striking sinistral strikeslip zone (Federico et al, 2014).…”

“…The TPB is a late-to post-orogenic basin that has an inner position with respect to the arcuate belt of the Western and Ligurian Alps (Capponi, Crispini, Federico, Piazza, & Fabbri, 2009;Capponi, Crispini, Piazza, & Amandola, 2001;Gelati & Gnaccolini, 1988;Giglia, Capponi, Crispini, & Piazza, 1996;Mutti et al, 1995). The basin fill unconformably overlies the collisional stack of tectonic units resulting from the main alpine orogenic deformation phases (Paleocene-Eocene; Federico, Capponi, Crispini, Scambelluri, & Villa, 2005 with references therein).…”

“…The depositional history of the TPB was controlled by tectonic and eustatic events (Capponi et al, 2001(Capponi et al, , 2009Gelati & Gnaccolini, 1988;Ghibaudo, Massari, Chiambretti, & d'Atri, 2014;Giglia et al, 1996;Mutti et al, 1995).…”

“…Both folds and thrusts pertain to the back-folding and back-thrusting event of the Ligurian Alps, Aquitanian -lower Burdigalian in age, recognized both at the eastern side of the Voltri massif (Capponi et al, 2009) and in the Sassello area (Capponi et al, 2001). Different thrust/fold segments are separated by ENE-WSWstriking tear faults (see the geological map and the map of the types of contacts).…”

Anatomy of the Ligure-Piemontese subduction system: evidence from Late Cretaceous–middle Eocene convergent margin deposits in the Northern Apennines, Italy

“…The Sestri-Voltaggio line has been regarded as an east-dipping, low-angle normal fault of early Tertiary age successively reworked in the Oligo-Miocene time (Hoogerduijn Strating 1994). Very recently, Capponi et al (2009) and Federico et al (2009) have provided evidence for a dextral transpression along the Sestri-Voltaggio line during the Oligo-Miocene, interpreted as related to the indenter of Adria into the Western Alps arc. Despite the different interpretations, a pressure gap of about 8 kbars can be detected across the Sestri-Voltaggio line between the Voltri Group and the IL units.…”