Anna d’Atri

Fragments of the Western Alpine Chain as Historic Ornamental Stones in Turin (Italy): Enhancement of Urban Geological Heritage through Geotourism

In Piemonte, stone has always been the most widely used raw material for buildings, characterizing the architectural identity of the city of Turin. All kinds of rocks, metamorphic, igneous, and sedimentary, are represented, including gneisses, marbles, granitoids, and, less commonly, limestones. The great variety of ornamental stones is clearly due to the highly composite geological nature of the Piemonte region related to the presence of the orogenic Alpine chain and the sedimentary Tertiary Piemonte Basin. This paper provides a representative list of the most historic ornamental stones of Piemonte, which have been used over the centuries in buildings and architecture. The main stones occurring in Turin have been identified and described from a petrographic and mineralogical point of view in order to find out the corresponding geological units and quarry sites, from which they were exploited. This allows the associated cultural and scientific interest of stones to be emphasized in the architecture of a town which lies between a mountain chain and a hilly region.

Geology of Piemonte region (NW Italy, Alps–Apennines interference zone)

ABSTRACT The geological map of Piemonte Region (Italy) is a graphic representation of the geology of the region, grounded on a large geodatabase, that can be also browsed as an interactive scalable map (GeoPiemonte Map) using a WebGIS application. The Map, produced at 1:250,000 scale, is the first original release of the ‘GeoPiemonte Map’ project. The geological data represented on the map derive from a thorough revision of available geological maps and literature, integrated with unpublished original data. The revision and harmonisation of existing and new data have been based on explicit criteria used for the classification of geologic units and their representation on the Map. These criteria firstly aimed at providing a lithostratigraphic, hierarchic subdivision of Piemonte geologic units and describing them using shared concepts and vocabularies, consistent with IUGS Descriptive Standards for the Geosciences.

New data on post-Eocene tectonic evolution of the External Ligurian Briançonnais (Western Ligurian Alps)

A new structural setting for the central part of the External Ligurian Brianconnais (CELB) is proposed. CELB is divided into km-scale tectonic units that still preserve pre-Alpine geological features at several stratigraphic levels. Macro-, meso- and microscale primary features, such as paleoescarpments, unconformities and depositional or diagenetic fabrics are thus well preserved and can be still mapped and studied in detail at many stratigraphic levels. Significant transposition of bedding is recorded only in Upper Cretaceous and Eocene marly limestones and shales and in major km-long shear zones, where intense development of closely spaced tectonic foliations occurred. Several features indicate that the CELB tectonic evolution took place at shallow crustal levels: 1) strong localization of deformation along the weakest stratigraphic levels; 2) absence of diffuse recrystallization of rocks; 3) minor occurrence or absence of transposition of bedding; 4) kinematic evolution of fold axial plane foliations into frictional slip cleavages. A gradual decrease in the intensity of deformation from the Internal Ligurian Brianconnais to CELB and Dauphinois Domain is observed, although the boundaries of these three domains correspond, in the study area, to several Km-long, transpressive shear zones whose kinematic role in the evolution of the southern termination of the Western Alps should be carefully considered.

Geological setting of the southern termination of Western Alps

A revision of the stratigraphic and tectonic setting of the southern termination of the Western Alps, at the junction of the Maritime Alps with the westernmost Ligurian Alps, is proposed. In response to the Alpine kinematic evolution, a number of tectonic units formed on the deformed palaeo-European continental margin and were arranged in a NW–SE striking anastomosed pattern along the north-eastern boundary of the Argentera Massif. Because these tectonic units often cut across the palaeogeographic subdivision of the Alpine literature and show only partial affinity with their distinctive stratigraphic features, new attributions are proposed. The Subbriançonnais domain is here intended as a “deformation zone”, and its tectonic units have been attributed to Dauphinois and Provençal domains; furthermore, the Eocene Alpine Foreland Basin succession has been interpreted, based on the affinity of its lithologic characters and age, as a single feature resting above all the successions of the different Mesozoic domains. The Cretaceous tectono-sedimentary evolution of the studied domains was characterized by intense tectonic controls on sedimentation inducing lateral variations of stratigraphic features and major hydrothermal phenomena. Since the early Oligocene, transpressional tectonics induced a NE–SW shortening, together with significant left-lateral movements followed by (late Oligocene–middle Miocene) right-lateral movements along E–W to SE–NW striking shear zones. This induced the juxtaposition and/or stacking of Briançonnais, Dauphinois and Ligurian tectonic units characterized by different metamorphic histories, from anchizonal to lower greenschist facies. This evolution resulted in the arrangement of the tectonostratigraphic units in a wide “transfer zone” accommodating the Oligocene WNW-ward movement of portions of the palaeo-European margin placed at the south-western termination of Western Alps and the Miocene dextral shearing along SE striking faults that bound the Argentera Massif on its NE side.

A Trip Through Deep Time in the Rock Succession of the Marguareis Area (Ligurian Alps, South Western Piemonte)

The multidisciplinary research project “PROGEO-Piemonte” aims to achieve a new conceptual and operational discipline in the management of the geological heritage of the Piemonte Region. To this end, an itinerary is proposed to illustrate the most significant steps in the geological evolution through time of the stratigraphic successions exposed in the Marguareis area (south western Piemonte). Volcanic and sedimentary rocks crop out here representing continental alluvial plain, carbonate tidal flat, and deep sea basin environments, spanning 200 million years from Permian to Eocene times. Together, they record the main stages of the geological evolution of the European margin related to the opening and closure of the Alpine Tethys ocean and consequent genesis of the Alpine chain. The proposed itinerary reveals stratigraphic successions with prolonged discontinuities and ancient faults documented by the geometrical relationships between rock bodies.

The Stone Bridges on the Po River at Turin (NW Italy): A Scientific Dissemination Approach for the Development of Urban Geological Heritage

This paper presents a minero-petrographic study of the rocks employed in the building of stone bridges over the Po River in the city of Turin (Piemonte Region—NW of Italy). In all the bridges, the dimension stones are present in different quantities and elements, either representing the only building material or associated with several artificial materials. The total number of bridges on the Po River is six, three of which are made of natural stones (Princess Isabella Bridge, King Umberto I Bridge and King Vittorio Emanuele I Bridge) and three are built with artificial materials with minor dimension stones (Balbis Bridge, Queen Margherita Bridge and Sassi Bridge). The lithologies of the six bridges have been identified in order to find out the corresponding geological units and the original quarry site. The stones mainly consist of rocks from the western Alps, with a prevalence of metamorphic rocks such as gneisses, as well as intrusive igneous rocks. Sedimentary rocks are minor represented.

TOURinSTONES: a Free Mobile Application for Promoting Geological Heritage in the City of Torino (NW Italy)

The Piemonte mountains surrounding the city of Torino comprise a wide variety of rocks, characterized by a multitude of minerals, structures and colors. The Alps, because of their long and complex history, have produced a wide variety of ornamental stone used in the town, over the centuries, for both esthetic and structural reasons. TOURinSTONES is an application for mobile phones that allows geotourists to walk in the center of Torino, where the visitor can find Alpine rocks used in palaces and historical monuments as witnesses and tangible symbols of the city. The application consists of 26 historical sites of interest in each of which ornamental stones of historical and scientific interest can be observed in detail. The sites are grouped in four thematic itineraries through which the user can discover the city from the cultural and architectural point of view. By a numbered list of the stones used in all the described monuments, the user can access specific data on each rock including quarry location, petrographic description and utilization in Torino. The mobile application can be downloaded free from the App Store or Google Play respectively for Apple and Android devices.

Geology of the Colle di Tenda – Monte Marguareis area (Ligurian Alps, NW Italy)

ABSTRACT The 1:25,000 geological map of the Colle di Tenda – Monte Marguareis area covers an area of about 130 km2 in the Italian Ligurian Alps, between the Vermenagna and Tanaro valleys. It is a detailed geological map of a sector of the Ligurian Alps of renewed scientific interest, and represents the eastern continuation of a recently published geological map of the Entracque-Colle di Tenda area. In addition to the increased detail and scale, the more relevant new contents of this map are represented by: a map of all the tectonic elements making up the Limone-Viozene Zone and the Refrey Unit, which represent the south-eastern portion of a major regional transfer zone developed at the southern termination of the Western Alps arc; the representation of km-scale Cretaceous palaeoescarpments previously overlooked or interpreted as Alpine faults; a new interpretation of some dark shales with interbedded sandstones, which were previously mapped as Helminthoides Flysch tectonic remnants, as belonging to the Annot Sandstone unit, the uppermost term of the Alpine Foreland Basin succession; and a map legend designed following the same criteria of the 1:250,000 Map of the Piemonte Region.

STRATIGRAPHY, SEDIMENTOLOGY AND SYNDEPOSITIONAL TECTONICS OF THE JURASSIC-CRETACEOUS SUCCESSION AT THE TRANSITION BETWEEN PROVENÇAL AND DAUPHINOIS DOMAINS (MARITIME ALPS, NW ITALY)

The Provencal and Dauphinois Mesozoic successions cropping out at the southeastern margin of the Argentera Massif (Maritime Alps, NW Italy) were deposited at the transition between the Provencal platform and the Dauphinois basin, marked in the study area by a partly preserved Mesozoic palaeoescarpment. These successions show important lateral variations occurring over relatively short distances, probably related to syndepositional tectonics. Different stratigraphic intervals of the pelagic-hemipelagic Dauphinois succession contain resedimented deposits, made up of both intra- and extrabasinal material, which provide a twofold evidence of syndepositional tectonics indicating both tectonically-triggered gravitational processes and a tectonically-driven evolution of the source areas. Two stages of syndepositional tectonics have been recognized: the first in the earliest Cretaceous, which is related to the deposition of carbonate breccias in the Dauphinois succession and to hydrothermal dolomitization of the Middle Triassic-Jurassic Provencal carbonates, and the second in the Late Cretaceous, which triggered the deposition of different detrital lithozones in the Upper Cretaceous Puriac Limestone. The cited evidence indicates that syndepositional tectonics continued to influence the evolution of the Alpine Tethys European passive margin long after the Late Triassic-Early Jurassic syn-rift stage, which caused the differentiation between the Dauphinois basin and the Provencal platform.