Pietra di Nava quarry, Pornassio, Imperia Province, Liguria, Italyi

Regional Level Types
Pietra di Nava quarry	Quarry (Abandoned)
Pornassio	Commune
Imperia Province	Province
Liguria	Region
Italy	Country

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The Pietra di Nava quarry, active for about 50 years, ceased operations following the death of its owner, leading to a complete stop in extraction and processing activities.

The activity was organized into two main areas:
an upper area (this locality), intended for the extraction of stone material;
and a lower area, dedicated to processing, equipped with specific plants and machinery.

At the peak of its development, the site employed about 20 workers, a number that gradually decreased over time due to the introduction of more advanced technologies.

The quarry develops within both a sedimentary carbonate succession known as the Val Tanarello Limestones and calcareous schists belonging to the Caprauna Formation. However, only the Val Tanarello Limestones were extracted, as they are characterized by low porosity, high CaCO₃ content, and high mechanical strength, ensuring resistance to weathering, frost, and aggressive (including saline) environments.

The Val Tanarello Limestones succession is attributed to the Upper Jurassic and consists of light grey micritic limestones, overlain by pink nodular limestones (“marbres de Guillestre”). The pink nodular limestones contain rare belemnites and isolated ammonite aptychi, indicating a pelagic depositional setting. The uppermost levels yield a Tithonian microfauna, constraining the age of the sequence to the uppermost stage of the Upper Jurassic Series.

The transition to the Caprauna Formation (Upper Cretaceous), which is composed of calcareous schists (“calcschistes planctoniques”), is marked by a phosphatic hardground, which in this outcrop is always dark red due to the high content of Fe oxides. In other outcrops, it may appear variably ferruginous, chloritic, or siliceous, with a thickness ranging from a few millimeters to a few centimeters. This discontinuous layer sometimes contains a diverse fossil assemblage, including selachian teeth, belemnites, bivalves, brachiopods, crinoids, and is overlain by a level with stromatolitic structures. It is interpreted as spanning the Aptian–Cenomanian interval (mid-Cretaceous), representing a major stratigraphic hiatus between the Upper Jurassic and Upper Cretaceous deposits.

The quarry exposure, together with the opposite valley slope, reveals a large-scale duplication of the stratigraphic succession produced by an early deformation phase, involving both the Jurassic limestones and the Upper Cretaceous calcareous schists.

The main structure is a synclinal antiform, interpreted as a kilometric parasitic fold developed on the right limb of a larger south-verging structure. The axial plane dips southward at approximately 40°. The discontinuous presence of the hardground horizon on both limbs provides a key marker for reconstructing the structure.

At the landscape scale, this duplication is expressed by abrupt morphological breaks on both sides of the valley, corresponding to steep cliffs formed by resistant Malm limestones. A strong ductility contrast between Malm limestones and calcareous schists controls deformation: calcareous schists are often thinned into meter-scale layers during the main tectonic phase, while fold hinges are rounded in limestones and sharp in schists.

Later deformation phases include a fracture cleavage with NNE orientation, irregularly developed, and locally decimetric kink bands trending approximately NW.

Mineral List

2 valid minerals.