Introduction

The deformation history of mountain belts is characterised by alternating pulses of extension and contraction modulated through time according to a sequence known amongst geologists as the “Wilson cycle”. In these settings, extensional structures produced during episodes of pre-orogenic continental rifting and/or ocean opening are systematically overprinted by folding and thrusting developed during orogenic accretion or continental collision. The reverse is also common during more advanced evolutionary stages, when orogenic folds and thrusts are truncated and modified by the development of extensional structures produced during late- or post-orogenic extensional collapse (Wilson 1961; Dewey and Bird 1970). This cyclical repetition of kinematically alternating deformation events is recognised in fossil as well as in active orogenic domains, so that the evolution of a mountain belt can be reasonably predicted, at least to a certain extent, in terms of relatively simple models (Gutiérrez-Alonso et al. 2008).

The history of complete orogenic cycles is well recorded in the Southern Apennines fold-and-thrust belt of Italy and is generally inferred from numerous observations carried out at different localities scattered over wide areas, at regional scale. On the other hand, the documentation of repeated processes of inversion tectonics is rarely preserved in the same portion of a mountain chain, at local scale.

In this study, we identify the High Agri Valley (Fig. 1), in the central part of Lucanian Apennine, as a key area to study in detail the structural geology of each stage that characterises the life and tectonic history of a collisional mountain belt. We present an itinerary through the High Agri Valley aiming at illustrating its entire deformation record, focusing on multiscale geological structures representative of pre-, sin- and post-orogenic tectonic episodes. The geological sites of the itinerary were selected based on their scientific relevance. As a matter of fact, most of these represent case studies widely published in international geoscience journals. At the same time, the geological itinerary is designed in a spectacular scenery, mostly encompassed within the Appennino lucano val d’Agri Lagonegrese National Park, providing the opportunity to bridge scientific and cultural interest of the High Agri Valley, by examining its geological and structural features, which have been fundamental in determining its beauty, its vulnerability to natural hazards and its richness in geological resources (Bentivenga et al. 2017; Palladino et al. 2013).

Fig. 1
figure 1

Shaded relief for the Lucanian Apennines, Italy, with location of the High Agri Valley (inset (A)). a Geological sketch map of the High Agri Valley, with the geotouristic itinerary proposed in this study (in yellow) and the location of the geosites (1–12) described in the text. b Schematic stratigraphic columns of the main tectonic units copping out in the High Agri Valley. Af, Argille Varicolori and Flysch Rosso formations (late Cretaceous to Oligocene); AP, Apennine platform unit; CJl, Cretaceous and Jurassic limestone; Cs, Calcari Con Selce Formation (Late Triassic); Ga, Galestri Formation (Cretaceous); MF, Monte Facito Formation (Middle to Late Triassic); L1, Lagonegro I unit; L2, Lagonegro II unit; LU, Ligurian unit; OM, late Oligocene to Miocene sediments; Os, Oligocene shale and siltstone; Sm, Sorgente dell’Acero Member (Carnian); Ss, Scisti silicei (Jurassic); Td, Triassic dolomite; TL, Cretaceous to Tertiary Lagonegro sequence

Full size image

Study Area

The study area extends between 40° 20′ and 40° 29′ N, and 15° 43′ and 15° 52′ E (Fig. 1) in Southern Italy. It encompasses the NW–SE trending High Agri Valley, which is bounded to the northeast by the rough peaks of the Mt. Volturino - Il Monte di Viggiano range, reaching elevation of up to 1800 m a.s.l. (Fig. 1a). To the southwest, the Monti della Maddalena range separates the High Agri Valley from the Vallo di Diano basin to the west (Fig. 1a). The regional water divide runs along the Monti della Maddalena range. The High Agri Valley is axially drained by the Agri river, which flows 100 km eastwards into the Ionian Sea.

The NW–SE trending structural depression of the High Agri Valley is filled by Quaternary continental deposits that cover complex assemblages of pre-Quaternary sedimentary rocks (Fig. 1a, b) comprising Mesozoic to Cenozoic platform limestone deposited on top of Upper Triassic dolomite of the Apennine platform domain (Bonardi et al. 1988; Palladino et al. 2008). Clay and sandstone deposited in deep sea conditions (Liguride and Sicilide units; Cavalcante et al. 2012; Bonardi et al. 1988) tectonically overlie carbonate rocks of the Apennine platform domain, which in turn were thrust on top of coeval pelagic rocks of the Lagonegro domain (Cavalcante et al. 2011), and on younger Miocene synorogenic siliciclastic sediments (Pescatore et al. 1999, and references therein). The Lagonegro units tectonically overlie a 6–7-km-thick sequence of Mesozoic to Tertiary carbonates and Pliocene siliciclastic rocks that represent the westward continuation of the Apulia foreland. Between the Apulia carbonate rocks and the overlying Lagonegro units, a 1.5-km-thick mélange zone, consisting mainly of over-pressurized siliciclastic sediments of Miocene age (Butler et al. 2004), acts as a seal for oil reservoirs hosted in the buried Apulia carbonates.

The main tectonic contacts between the Apennine platform and the Lagonegro domains are exposed in the relief bounding the High Agri Valley. In the northern sector, the Marsico Nuovo thrust, a regional low-angle tectonic contact, duplicates rocks of the Lagonegro domain into two distinct tectonic units, the Lagonegro I unit below and the Lagonegro II unit above. In the western sector, the Lagonegro II unit is tectonically overridden by the Apennine platform rocks that crop out on the Monti della Maddalena ridge along the low-angle Monti della Maddalena thrust (Fig. 1a, b). In the central sector, the Monti della Maddalena Thrust and Marsico Nuovo Thrust were eroded on the Monte Lama and Monte Volturino ridge, where two main anticlines, the Monte Lama Anticline and Monte Volturino Anticline, separated by the Monte Volturino Syncline, are magnificently exposed. Both anticlines exhibit a distinct axial culmination and expose the deeper parts of the Lagonegro I unit (Scandone 1972; Bucci et al. 2012). In the eastern sector, scattered outcrops of Apennine Platform rocks (mainly limestone), and rocks of the Lagonegro II unit, are present along a low-angle tectonic contact, above the rocks of Lagonegro I Unit.

The abovementioned contractional architecture, related to the Late Oligocene–Early Miocene continental collision, was strongly modified by post-orogenic extensional tectonics, which resulted in a typical basin-and-range morphology, characterized by distinctive landform types, including horsts, grabens and fault-related slopes. The High Agri Valley is a fault-bounded intermountain basin that formed during the Quaternary in response to transtensional/extensional tectonics that dissected pre-existing Neogene folds and thrust structures of the Southern Apennines range (e.g. Tavarnelli and Pasqui 1998, 2000). The extensional tectonic regime is still active in the area and is responsible for the occurrence of strong historical earthquakes (Burrato and Valensise 2008).

The Itinerary

The geological itinerary includes 17 stops at as many geosites that can be reached through secondary roads, easily travelling by car (Fig. 2). The first seven stops (1a, 1b, 2, 3a, 3b, 4a, 4b) are designed to illustrate the contractional architecture of the Apennine tectonic pile through the presentation of regionally significant structures and associated meso-scale deformations. The subsequent ten stops focus on the effects of ancient (stops 5, 6a, 6b) and recent (stops 7, 8, 9, 10a, 10b, 11, 12) extensional deformations, illustrating the double switch in tectonic regime, from pre-orogenic drifting (through sin-orogenic thrusting) to post-orogenic extension. Each of the selected geosites contains multidisciplinary geological information, and when combined together provide an integrated view on the stratigraphy, the structural geology and the geomorphology of the High Agri Valley and surrounding ridges. In addition, and perhaps more significant, the stops illustrated along the proposed itinerary are relevant in that, collectively, help outline the main deformation episodes that led to the formation and then to the dissection of the Southern Apennines orogenic belt; therefore, they can be regarded as representative of the geological history of an important sector of Southern Italy.

Fig. 2
figure 2

The geotouristic itinerary proposed in this study, with localities of the investigated geosites

Full size image

In the forthcoming sections, we describe the main features of each site of geological interest where the effects of orogenic contractional deformations are observed. A description of the sites of geological interest where effects of pre-orogenic and post-orogenic extension are visible will follow.

Contractional Tectonics

Monti della Maddalena Thrust (Stops 1a and 1b—View Points Along the SP273)

Location and Aim

The stop is located along the road SP273 Paterno-Mandrano that connects the High Agri Valley with the Vallo di Diano basin passing through the Mandrano plain on top of the Maddalena mountain range. This road intercepts the regional tectonic contact between the Mesozoic–Cenozoic platform and slope carbonates of the Monti della Maddalena unit, which overthrusts coeval pelagic rocks of the Lagonegro units. The analysis of the thrust represents the outcrop-scale focus of the stops. In addition, the stop 1b offers a spectacular view of the High Agri Valley, of both valley shoulders and of the alluvial plain, and offers a panoramic overview of most of the other stops located along the itinerary. For this reason, this stop provides an excellent opportunity for an introductory overview of the geology, geomorphology and tectonics of the High Agri Valley.

Outcrop Description

The stop 1a offers detailed view of the tectonic fabric associated with the regionally important Monti della Maddalena thrust (Fig. 3a). Along this thrust, intense shearing produced a brittle–ductile contractional shear zone that extends for tens of metres in the hanging wall, where it affects chiefly white Upper Triassic dolomite and subordinately Liassic limestone of the Apennine Platform unit (Fig. 3b). In the footwall of the Monti della Maddalena thrust, rocks of the Lagonegro units are also intensely deformed (Fig. 3c). The fault zone of the Monti della Maddalena thrust can be subdivided into three main domains, characterised by different fabrics and deformation features: (1) the footwall, (2) the fault zone, (3) the hanging wall. The main structures in the footwall rocks are represented by decimetre- to metre-size, ENE-verging asymmetric folds and associated cleavage fabrics. Near the thrust plane, where the largest deformation was accommodated, detached asymmetric folds are also present. WSW dipping reverse faults with metre-size displacements are also present. S–C shear fabrics are abundant in the footwall and are locally associated with synthetic, outcrop-scale faults that may be interpreted as C′ shear surfaces. The fault zone consists of up to 3 m of fault gouge. The gouge contains highly disrupted, millimetre- to centimetre-size fragments of limestone and dolomite of the hanging wall. A highly disrupted level is present close to the main slip surface. The level contains brown to red, marly limestone embedded in a deformed shale matrix derived from the shearing of the footwall rock materials. In the hanging wall, intensively fractured rocks affected by reverse faults and shear fabrics, including Riedel shear surfaces, characterise the deformation zone. The different structures and fabrics observed and measured in the three deformation domains are consistent with a single shear sense and are indicative of an ENE direction of movement. This is consistent with the regional tectonic setting and deformation history (Bucci et al. 2014). Several post-orogenic faults cut across the thrust assemblage. The effects of these post-orogenic faults are revealed from the multiple dislocation of the thrust contact, which is outlined by the strong colour contrast between the withe cataclastic carbonate of the hanging wall and the brownish terrigenous sediment of the footwall. The same post-orogenic faults make deca-metric morphologic steps in the slope, which are travelled downhill by the steep winding road linking the stop 1a to Paterno village. Between the stop 1a and Paterno village, the road intercepts the down-faulted thrust contact at stop 1b, where a population of meso-scale reverse faults combines locally to form complex thrust systems, imbricate fans or duplexes, in the cataclastic rocks of the hanging wall (Fig. 3b). Here, the fault planes are represented by mirror-like striated fault surfaces. In addition, the stop 1b offers a scenic view of the eastern flank of the High Agri Valley, where the itinerary is designed (Fig. 3d). There, rocks of the Lagonegro I units display ~N-S to NW-SE trending major folds (e.g. the Monte Lama and Monte Volturino folds) and are replaced toward NW by the rocks of the Lagonegro II unit along the NNE-SSW trending Marsico Nuovo thrust. Still observed from this stop, looking toward SE in panoramic view, rocks of the Apennine Platform unit constitute the carbonate massif of Il Monte di Viggiano. The valley flank displays a rectilinear trend of the mountain front, which is characterised by a mature staircase profile sloping toward the valley, generated by post-orogenic faulting (Fig. 3d). This mountain front is punctuated by two prominent alluvial fans, generated by the Molinara and Galaino creeks, which force the Agri river to flow close to the west side of the valley, in asymmetric position with respect to its axial sector.

Fig. 3
figure 3

Deformation structures in the Monti della Maddalena geosite (stops 1a and 1b). a The Monti della Maddalena thrust, along which carbonates of the Campano-Lucania platform unit override pelagic sediments of the Lagonegro II unit. b Mesoscopic deformation fabrics along the Monti della Maddalena thrust affecting platform carbonates in its hanging wall. c Mesoscopic folds in the footwall of the Monti della Maddalena thrust. d Panoramic view across the High Agri Valley toward its eastern flank. The Mt. Volturino-Mt. di Viggiano ridge, corresponding to the NE edge of the High Agri Valley, consists of a post-orogenic extensional fault system outlined by a mature staircase profile sloping toward the valley. Two main alluvial fans, generated by the Molinara and Galaino creeks, are also observed

Full size image

Mt. Lama–Mt. Calvelluzzo Anticline (Stop 2—Marsico Nuovo Dam)

Location and Aim

The stop is located at the northern end of the Marsico Nuovo village, along the SP16. Aim of this stop is to illustrate, from a panoramic scenic viewpoint, the geometry of a prominent, map-scale anticline in Lagonegro rocks and to discuss the nature of its western flank exposed along the Monte Lama-Monte Calvelluzzo ridge.

Outcrop Description

This stop offers a magnificent frontal view of one of the most impressive landforms of the High Agri Valley, namely the pentagonal facets of Monte Lama–Monte Calvelluzzo (Fig. 4a). These landforms have long been known and shown to researchers and students to represent a remarkable example of flat irons, developed upon steeply dipping beds of the Upper Triassic Calcari con Selce Fm. The tilted beds form the western limb of the Monte Lama–Monte Calvelluzzo anticline, a prominent N-trending fault-related structure in the Lagonegro thrust system (Mazzoli et al. 2001). The Monte Lama–Monte Calvelluzzo Anticline involves the Mesozoic succession of the Lagonegro I unit (Scandone 1972) or San Nicola unit (Mazzoli et al. 2001), and exposes the Upper Triassic Calcari con Selce Fm. in the core and the Jurassic Scisti Silicei Fm. in its limbs. The morphologic depression ringing the structure is floored by the Cretaceous Galestri Fm. The structure consists of a more than 8-km-long box fold with a marked northern plunge. The anticline shows a vertical western limb and a steep to overturned eastern limb, both offset by minor out-of-limb thrusts, and a double vergence of associated fold structures (Bucci et al. 2013). From this stop, the geometry of the fold can be clearly seen at Monte Lama along the flank of a lateral incision of the uppermost Agri river course (Fig. 4a). In spite of a good understanding of the thrust structure achieved in recent work, the tilted depositional contact between Calcari con Selce and Scisti Silicei has been represented in several papers and maps as a W-dipping fault, interpreted as a manifestation of the seismogenic tectonics of Quaternary age (Carbone et al. 1991; Pescatore et al. 1999). Benedetti et al. (1998) and Papanikolaou and Roberts (2007) propose that the mountain slope represents a 250-m-high Pleistocene fault-controlled escarpment, and claim that evidence for active faulting is present at the foot of the slope. More recent work, however (Bucci et al. 2007; Bucci et al. 2013), does not confirm evidence for a Quaternary fault at this mountain front; moreover, these authors document that a map-scale normal fault preserved in the crest of the present-day anticline is of Jurassic, e.g. pre-orogenic, rather than of Quaternary, e.g. post-orogenic, age (Bucci et al. 2006). Additional details about this inherited Mesozoic fault will be discussed in the description of the stop nos. 6a and 6b (see section “The Serra di Calvello Fault (Stops 6a and 6b—Laghetto Plain and Serra di Calvello)”).

Fig. 4
figure 4

The Mt. Lama-Mt. Calvelluzzo anticline (stop 2). a Panoramic view of the Mt. Lama-Mt. Calvelluzzo anticline from the Marsico Nuovo dam. The SW flank of Mt. Calvelluzzo is outlined by a prominent flat iron landscape, where flat iron structures I–IV are observed (see text for explanation). b Along-strike view of the flat iron-dominated landscape. c Detail of the wine glass rill channel between flat irons III and IV, where the contact between the bedrock and the roughly stratified debris is well exposed

Full size image

The Mt. Lama–Mt. Calvelluzzo Flatiron and the Lagonegro I Unit (Stops 3a and 3b—Camporeale)

Location and Aim

On the west flank of Mt. Lama–Mt. Calvelluzzo ridge, a light stroll will bring us at the base of the pentagonal facets presented in the previous stop. This will allow checking the nature of the pentagonal facets and discussing the debated evidence for active faulting.

Outcrop Description

From the hamlet of Camporeale, east of Marsico Nuovo, we have firstly a lateral view of the pentagonal facets (stop 3a, Fig. 4b). The main slope is formed by steeply (~ 50°–60 °) W-dipping limestones of the Calcari con Selce and the piedmont is floored by more erodible Scisti Silicei radiolarian argillites. The facets are separated by perched, “wine glass” canyons (Fig. 4b), which have been regarded as evidence for active faulting and footwall uplift (Benedetti et al. 1998). The knick-point is located at a marked lithological change from more erodible argillites to well-bedded limestone. In addition, the facets do not cut the bedding but form a bed-parallel envelope. At the base of the facet, the slope dips ~ 50°–60° being developed on single beds. Thus, a flat iron nature of the facets seems plausible, with the “wine glasses” being controlled by lithology. From the car stop, the trail leads to the north on gentle ground underlain by argillites of the Galestri Fm. The Galestri is highly incised and thus no subsidence (as expected in the hanging wall of a normal fault) is documented at this site. A first, some 10-m-high step occurs downhill the mountain slope at the lithological transition between radiolarite and limestone of the Scisti Silicei and more erodible argillites of the Galestri. Locally, asymmetric mesoscopic folds related either to parasitic folding (Z-type) or to out-of-limb shearing expose gently basinward-dipping beds. These outcrop-scale structures form 1–2-m-high scarplets which are laterally discontinuous and locally promote minor landslides. Further high, the Calcari con Selce limestones are affected by sub-horizontal or gently E-dipping fractures, which are thus almost orthogonal to bedding. The angular relations between beds and fractures can be interpreted as a result of wholesale tilting of beds and fabrics that was formed when beds were horizontal, i.e. before the folding event of Neogene age. Alternatively, the fractures orthogonal to bedding could develop later during the fold growth process, when the beds were already inclined. However, independently from their origin, the fractures are not affected by movements along bedding planes, suggesting that bedding-parallel slip did not occur in the area after the Neogene compressive events (Bucci et al. 2013). Conversely, no evidence for basinward-dipping fractures forming the damage zone of a recent normal fault, invoked by Benedetti et al. (1998), is observed. The trail finally reaches a gully at the base of the fourth facet (counting from S to N). Here (stop 3b), crudely bedded loose debris has been deposited at the mouth of the gully and is unconformably lying on a tilted limestone bed (Fig. 4c). The fan deposit is, itself, incised for a height of 3–4 m. The upper surface of the fan deposit continues into the bedrock until the thicker limestone of the facet is reached. The ~ 45° dipping surface is probably an erosional glacis formed during the last glaciation and subsequently incised. No evidence of faulting of the deposit and of the glacis is found at this site. In summary, the available evidence that can be observed at this site rules out the hypothesis of a Quaternary, large-displacement normal fault at this mountain front.

The Marsico Nuovo Thrust and the Pietra Maura Landslide (Stops 4a and 4b—Contrada Cognone)

Location and Aim

The stop 4 is located along the road SP16, a few kilometres north of Marsico Nuovo village. This road intercepts the regional tectonic contact between the Triassic limestone, shale and sandstone terrains of the Monte Facito Formation, pertaining to the Lagonegro II unit, which are thrust over Cretaceous pelagic rocks of the Galestri Formation, pertaining to the Lagonegro I unit. The stops 4a and 4b expose the Lagonegro terrains along a regionally important thrust contact, here named Marsico Nuovo Thrust, and illustrate the role of the thrust architecture in controlling the location and evolution of a large landslide.

Outcrop Description

The position of the Marsico Nuovo Thrust is poorly constrained because of the tectonic superposition of shale-dominated terrains that are present in the hanging wall (Monte Facito Formation of the Lagonegro II unit) and in the footwall (Galestri Formation of the Lagonegro I unit). According to the local geological cartography, the thrust contact separates the chaotic terrain of the hanging wall block and the thrust zone, from the thin-layered shale and subordinated calcilutite of the footwall. Beside, east of the stop 4a, the terrain appears chaotic in general, for a length in plane view (measured along the road) of about 400 m, that doubles up to 800 m if measured along the road, approaching the stop 4b. The zone of chaotic terrains is bounded by two streams, which result pushed far from each other toward lateral ridges. The stream drains a wide area upstream, which is characterised by a generalised hummocky topography, and locally by counterslope areas and periodically humid zones. Overall, the evidence is associated with a large landslide (Fig. 5a), namely the Pietra Maura landslide (Bentivenga et al. 2012). In plane view, the Pietra Maura landslide shows a NW-SE-oriented elongated shape with a large depletion zone (upstream of the stop 4) and a narrow channel (stop 4). The stop 4b provides a quite complete view of the Pietra Maura landslide, showing also its wide toe which deflects the Agri river and partially interacts with the Marsico Nuovo Dam. At the moment, the activity of the landslide seems to be mainly restricted to the depletion area and to a lesser extent to the lateral channel streams, while the resting part is dormant. Comparative analysis of landslide and geological maps reveals that the Pietra Maura landslide developed along the thrust zone. The landslide involves mainly weak rocks of Galestri (at the thrust footwall) and Monte Facito formations (at the hanging wall) and subordinately involves limestones pertaining to the overthrust block. The landslide is classified as a complex slide-earthflow and is characterised by an upper portion subject to multiple and compound slides (Fig. 5a) and rockfall and toppling phenomena (Fig. 5b), and a medium to lower part with a primary flow component. Instability conditions that lead to such failure can be attributed to the poor geomechanical behaviour of the sheared rock mass cut by numerous, closely spaced discontinuities (Bucci et al. 2016a, b) and to the peculiar hydrogeological setting due to the tectonic superposition of platform limestone, radiolarite and micaceous sandstones of the Monte Facito Formation over predominant marl and shale of the Galestri Formation.

Fig. 5
figure 5

The Marsico Nuovo thrust and the Pietra Maura landslide (stops 4a and 4b) as seen from Contrada Cognone. a Panoramic view of the crown area and the depletion zone of the Pietra Maura landslide. b The Pietra Maura cliff. c Detail of the Pietra Maura carbonate buildup, stratigraphically covered by sandstone and siltite of the Middle Triassic Monte Facito Fm. d View of the limestone with chert ridge, stratigraphically underline by radiolarites and shales of the Middle Triassic Monte Facito Fm

Full size image

Pre-orogenic Extensional Tectonics

The Monte Facito Formation and the Signature of Syn-depositional Tectonics (Stop 5—Pietra Maura)

Location and Aim

From Contrada Cognone, the itinerary departs from the ordinary road, and it climbs up along a secondary road to the Pietra Maura location (stop 5). The stop 5 aims at illustrating the rocks of the hanging wall of the Marsico Nuovo thrust and in particular focuses on the stratigraphy of the Monte Facito Formation (Scandone 1967).

Outcrop Description

Several outcrops along the secondary road connecting Contrada Cognone to Pietra Maura (stop 5) illustrate the most significant litho-stratigraphic members of the Monte Facito Formation. This shows a very heterogeneous lithologic content that is mainly represented by variable amounts of sandstones, shales, radiolarites, marls and limestones and that reflects drastic environmental changes during deposition (Palladino et al. 2019). The lower portion of the sequence consists of some metres of tabular-shaped neritic limestone bodies predominantly made up of Dasycladales and Solenoporacean algae (Fig. 5b). Other associated faunas are represented by sponges, isolated corals, rare ammonites, gastropods, crinoids and benthonic foraminifers. Neritic limestones are stratigraphically covered by nodular calcareous breccias and siliciclastic sandstone and siltites (Fig. 5c). This interval marks the onset of subsidence and the sudden drowning of neritic limestones. Upward, lens-shaped brachiopod-rich calcarenite bodies interlayered with sandstones are interpreted as tentative re-colonization of the sandy substratum in a shallow water terrigenous environment. These levels have provided an abundant brachiopod fauna represented by Puncospirella fragilis and Anisactinella maurensis species (Bentivenga and Palladino 2013). In the same stratigraphic interval, micaceous sandstones with wave ripple marks are interpreted as a well-preserved Triassic submerged beach. Upward, radiolarites and marls with carbonate breccias and carbonate bodies testify the complete drowning of carbonate buildup elements, which anticipate the deposition of limestones with chert (Fig. 5d). The succession of these members, resulting in the sudden switch from shallow to deepwater deposits, reflects the Triassic tectonic evolution of the Lagonegro basin that experienced an ongoing rifting process. The tectonic subsidence and the consequence stratigraphic evolution of the Monte Facito Formation was related to the sin-sedimentary extensional tectonics affecting the Lagonegro basin during the middle Triassic time (230 MA), in the framework of the progressive Africa-Europe continental separation, and subsequent opening of the Neotethys Ocean.

The Serra di Calvello Fault (Stops 6a and 6b—Laghetto Plain and Serra di Calvello)

Location and Aim

The stop is located along the road SP16, in correspondence to the Laghetto plain and to the morphologic saddle between Monte Arioso and Monte Lama. The Laghetto plain hosts a seasonal small lake and is mainly filled by a thin continental deposit. The Laghetto plain is floored by the Galestri Formation that rings the periclinal termination of the Monte Lama anticlinal ridge and disappears northward under the Marsico Nuovo Thrust. Aim of this stop is to illustrate the diagnostic elements of a pre-orogenic extensional fault and to discuss its structural control during positive inversion tectonics (from pre-orogenic extension to syn-orogenic contraction).

Outcrop Description

The effects of pre-orogenic extension are preserved at the northern termination of the Monte Lama anticline, a major map-scale fold involving the sedimentary succession of the Lagonegro I unit (Fig. 6a). In the eastern limb of the anticline, the Jurassic Scisti Silicei Formation is thin (40–50 m), whereas in the western limb, the same formation is much thicker (100–150 m) and contains abundant slumping structures, an indication of intense seafloor mobility during deposition. These thickness variation in the Scisti Silicei are controlled by a major, Km-scale sin-sedimentary, pre-orogenic normal fault. The fault is sealed by the Cretaceous, post-rift sequence of the Galestri Formation, outcropping in the north side of the Laghetto plain (Fig. 6a, b). These relationships make it possible to unequivocally ascribe the normal fault activity to Jurassic time. During the Neogene orogenic event, this structure controlled the development of the Monte Lama fold in terms of orientation and thrust ramp location as revealed by the sub-parallel attitude of the Monte Lama anticline and the Jurassic fault. However, the map pattern at the northern termination of the Monte Lama anticline displays a continuous stratigraphic contact between the Galestri and Scisti Silicei that seals the Jurassic normal fault. Thus, no significant evidence for fault reactivation during positive tectonic inversion was observed at this site (Bucci et al. 2006). The strains produced during the Tertiary episodes of positive tectonic inversion were thus accommodated by mechanisms alternative with respect to the classical fault-reactivation style; these include buttressing effects, folding and wedge-type (or shortcut) thrusting (Butler 1987), which progressively modified the pre-existing normal faults. The south side of the Laghetto plain is characterised by the presence of a seasonal small lake (Fig. 6b). The lake is fed by an ephemeral water course flowing in a valley developed at the top of the Mt. Lama and Serra di Calvello anticlinal ridge, and trending parallel to the anticline axis. In spite of the locally poor exposure conditions, it seems probable that the valley hosts a relict of the pre-orogenic normal fault (Fig. 6c). The valley develops at the faulted contact between the Scisti Silicei and the Calcari con Selce formations, where differential erosion of intact bedrock and fractured rocks of the fault zone is expected. The evidence of the inherited normal fault preserved at the top of the Mt. Lama anticline is in good agreement with many natural and analogue examples that show major pre-orogenic faults controlling the nucleation and growth of anticlinal structures. Overall, these evidences confirm earlier interpretations of the Lagonegro basin as a domain that recorded a long and complex syn-rift evolution, similarly to other Mesozoic basins of the Adria Palaeo-margin (Karakitsios 1995). During the Mesozoic, intense extensional tectonics caused the deepening of the basin and the differentiation into an intermediate and a distal stratigraphic succession in a W-E direction. The overall basin architecture, at least during the Jurassic time interval, probably consisted in fault-bounded highs and depressions (roughly elongated with N-S trend in present-day coordinates) hosting syn-rift sequences characterised by different facies and thickness.

Fig. 6
figure 6

The Serra di Calvello fault (stops 6a and 6b). a Near along-strike panoramic view of the Serra di Calvello pre-orogenic normal fault (see text for explanation). b The Laghetto lake and its surrounding plain. c Along-strike view of the Serra di Calvello pre-orogenic normal fault that separates the Jurassic Scisti Silicei Fm. in its hanging wall, from the Upper Triassic Calcari con Selce Fm. in its footwall

Full size image

Post-orogenic Extensional Tectonics

East-Dipping Low-Angle Tectonic Contacts (Stops 7 and 8—Madonna di Monte Saraceno and Monte Torrette)

Location and Aim

The stops are located on the east flank of the Mt. Volturino ridge, in proximity of the SP16. Coming from the north, a light stroll departing from the main road leads to the stop 7, corresponding to the base of the carbonate relief on whose top is located in the Madonna di Monte Saraceno church. A visit to this site makes it possible to check the nature of the low-angle tectonic contact at the base of the carbonate relief. The stop 8 is located at the base of Mt. Torrette, along a secondary road linking the SP16 to the base of Monte Volturino. The stop 8 illustrates east-dipping, low-angle tectonic contacts affecting the sediments of the Lagonegro II unit.

Outcrop Description

The stop 7 coincides with the church of Madonna di Monte Saraceno, which is built on one of the several wide isolated outcrops of platform carbonates located east of the Monte Volturino ridge (Fig. 7a). They represent the easternmost fringes of the Monti della Maddalena thrust sheet. These scattered outcrops of platform carbonates are generally interpreted as thrust remnants, or klippen, in the official cartography (Servizio Geologico d’Italia 1969) as well as in other geological maps (Lentini et al. 1990). However, the results of recent investigations (Bucci et al. 2012, 2014) document east-dipping, low-angle tectonic contacts (Fig. 7a) carrying out the klippen on top of deformed rocks of the Lagonegro I and II units. The low-angle tectonic contacts are locally responsible for the omission of parts of the stratigraphic sequence and for a remarkable structural truncation of bedding planes in the upper and lower blocks. In addition, the basal tectonic contact of the klippe truncates folds, thrusts and related structures in the footwall and exhibits distinct extensional characteristics. The geometry, fabrics and deformation features differ from those observed in the rocks at the base of the frontal ramp of the thrust that crops out along the western margin of the upper Agri Valley. These relationships have been interpreted as indicators of the post-thrusting emplacement of the klippen by low-angle normal faults. However, kinematic indicators are poorly preserved in the footwall of the klippen, which is mainly characterised by slivers of Oligocene–Miocene sediments associated with chaotic terrains, consisting of a highly disrupted tectonic levels where the original sedimentary features and rock fabrics are obliterated. Mesoscopic structures associated with basal low-angle tectonic contacts are better preserved in the rocks of the hanging wall, which will be presented in the subsequent stop 10.

Fig. 7
figure 7

East-dipping low-angle tectonic contacts (stops 7 and 8—Madonna di Monte Saraceno and Monte Torrette). a Low-angle normal-fault array affecting carbonates of the Campania-Lucania platform unit at the Madonna di Monte Saraceno sanctuary. b Mesoscopic, low-angle normal fault array affecting pelagic carbonates of the Upper Triassic Calcari Con Selce Fm. (belonging to the Lagonegro II tectonic unit) along the S flank of Mt. Torrette (location indicated in c). c Panoramic view of the Mt. Volturino-Mt. Torrette ridge, with indication of the location of the mesoscopic low-angle normal fault array illustrated in detail in b. d Panoramic view of the Mt-Volturino-Mt. Torrette-Madonna di Monte Saraceno ridge illustrating the mesoscopic and macroscopic low-angle normal fault arrays that determine the superposition of the limestone of the Campania-Lucania platform tectonic unit onto pelagic carbonates of the Lagonegro II tectonic unit (visible in the centre and in the NE side of the image). Toward the SE, the low-angle normal faults are bounded by a right-lateral strike-slip fault, whose trace coincides with the SW-NE-oriented morphologic saddle separating Monte Volturino and Monte di Viggiano. The picture also illustrates that low-angle extensional tectonic contacts are truncated by a SW-dipping, high-angle normal/extensional fault that controls the steep SW flank of Mt. Volturino. The point of view of c is also indicated

Full size image

In the stop 8, meso-scale east-dipping low-angle tectonic contacts are present in the Calcari con Selce Formation of the Lagonegro II unit (Fig. 7b). These meso-scale structures rest at the hanging wall of a major, poorly exposed, low-angle tectonic contact developed within the sheared rocks of the Monte Facito Formation, at the base of a large klippe of rocks of the Lagonegro II unit, which constitutes Monte Torrette (Fig. 7c). A specific structural analysis was performed at these sites (Bucci et al. 2014). The analysis focused on striated, meso-scale low-angle fault planes present in the Calcari con Selce Formation and revealed that along the transport direction, the low-angle tectonic contacts cut mesoscopic folds propagating locally along mechanically favourable shale layers and are linked to steeper (40°–60°), NNW–SSE-trending normal faults in the hanging wall. In addition, fault slip kinematic data for the low-angle tectonic contacts in the Lagonegro II unit are entirely compatible with the similar kinematic data obtained for such contacts in the Apennine platform domain. We consider this as evidence of a common and coeval origin of the low-angle tectonic contacts in the two lithological types. Field evidence confirms the presence of at least two shallow low-angle tectonic contacts in the Monte Volturino and surrounding areas, located at the contact between the Apennine platform unit and the Lagonegro II unit, and at the contact between the Lagonegro I and the Lagonegro II units (Fig. 7d). In this context, the deformation of the Lagonegro units that crop out at Mt. Torrette have been interpreted as the results of tilting and possibly reactivation as low-angle, foreland-directed normal faults of pre-existing west-dipping thrust surfaces.

The Signature of the Post-orogenic Extensional Tectonics in the Landscape (Stop 9—Il Monte di Viggiano)

Location and Aim

The stop is located at the top of the Monte di Viggiano, at the end of a delightful, steep walkway starting from the parking at the end of the paved road. Along the trail, several outcrops of rudist-rich portion of Apennine platform carbonate, which are beautifully exposed, merit additional stops. The potential for conservation of these outcrops have been discussed in a recent paper, to which the reader is referred for additional information (Bentivenga et al. 2017). The trail stops at the sanctuary of Madonna di Viggiano offering a superb 360° view. Aim of this stop is to discuss, from a panoramic viewpoint, the signature of the post-orogenic extensional tectonics in the landscape.

Outcrop Description

The Monte di Viggiano offers a panorama view of the southern side of the Monte Volturino. Here, the east-dipping low-angle tectonic contacts developed at the base of the Madonna di Monte Saraceno relief and of other scattered, isolated outcrops of apenninic platform rocks (Scarrone di Mezzo relief) and Lagonegro II rocks (Monte Torrette) are visible east of the Monte Volturino ridge (Fig. 7d). Toward SE, the low-angle normal faults are bounded by a right lateral strike-slip fault, whose trace coincides with the SW-NE-oriented morphologic saddle separating Monte Volturino and Monte di Viggiano (Fig. 7d). A further minor relief constitute by carbonate platform rocks, named Serritello, rests west of Monte Volturino, where it overlies the Lagonegro rocks along an east-dipping low-angle normal fault, having the same attitude, and occupying the same structural position of the low-angle normal faults detected east of the Monte Volturino ridge (Fig. 8a). The low-angle normal fault abruptly stops against the steep western slope of Monte Volturino, which is clearly controlled by a high-angle normal fault, down-dipping toward the High Agri Valley (Figs. 7d and 8a). The evidence suggests a common origin for the low-angle normal faults detected west and east of the Monte Volturino ridge, which formed along the same detachment zone during a first episode of extensional tectonics affecting mainly the upper portion of the tectonic pile, and in the specific case the rocks of the Lagonegro II, and apenninic platform unit. In contrast, the subsequent high-angle normal faulting affected the entire tectonic pile, truncating all the pre-existing, inherited structures. The high-angle normal faulting produced hundreds of metres of cumulate offset as demonstrated by the down-throwing of the low-angle normal fault at the base of the Serritello relief (Fig. 8a), whose possible prosecution can be found east of Monte Volturino, at the base of the Madonna di Monte Saraceno isolated outcrops of platform carbonate rocks (Fig. 7d). The same high-angle normal fault also cuts across the Monte Volturino fold, which was down thrown toward SW of about 600 m, where the same structure is recognisable in the SW face of the Monte Corno relief (Fig. 3d). The stop offers also a scenic view of the opposite margin of the High Agri Valley, which is dominated by the platform carbonate rocks of the Monti della Maddalena ridge, ranging in elevation between 1000 and 1300 m. The same rocks constitute the Monte di Viggiano massif, where the present stop is located, which has a maximum elevation of 1727 m, about 1000 m higher than the Agri alluvial plain. Under the Agri alluvial plain, the platform carbonate rocks are found in boreholes under the continental infill, at a depth ranging between 300 and 600 m under the topographic surface. This means that the High Agri Valley boundary faults record a maximum cumulative throw ranging between 1200 and 1600 m, respectively, estimated for the fault system bounding the valley toward the west and the east.

Fig. 8
figure 8

Effects of post-orogenic extensional tectonics (stops 10a, 10b, 11 and 12). a Panoramic view of the Mt. Volturino-Monte di Viggiano ridge. Serritello and the Mt. Copone graben are observed. b Detail of the SW flank of Mt. Volturino, where a low-angle normal fault is truncated by high-angle mesoscopic extensional faults. c Detail of the Mt. Copone graben boundary normal fault. Slickensides exposed on the fault surface indicate dip-slip kinematics. d The high-angle High Agri Valley boundary extensional fault and associated damage zone. A detail of the fault surface indicates oblique-slip kinematics. A steeply dipping deformed breccia is stratigraphically covered by gently to moderately dipping undeformed breccia. The contact between the deformed and the overlying undeformed breccia is overprinted by a regularized topographic profile. e Evidence for recent and/or active faulting at NE margin of the High Agri Valley. Recent high-angle faults affecting the colluvium wedge lying above the substratum determine steps in the topographic profile. f Evidence for controlled hydrocarbon upward migration at the confluence of the Torrent Fossatello and the Rio Cavolo, few hundred metres west of the Tramutola Pool

Full size image

From Low-Angle to High-Angle Normal Faulting (Stops 10a, 10b and 11—Serritello, Sorgente Copone, Barricelle)

Location and Aim

The stops are located in the Marsico Vetere area (Fig. 8a), where different fault systems with extensional and transtensional kinematics, and their crosscutting relationships, are particularly evident and well exposed. The stop 10a illustrates outcrop-scale, east-dipping low-angle tectonic contacts in the sediments of the Apennine platform domain. The stop 10b shows two high-angle fault systems and their crosscutting relationships. The stop 11 provides insight into the most recent faulting episode recognised along the Marsico Vetere fault array.

Outcrop Description

The stop 10a illustrates the low-angle tectonic contacts cutting rocks of the Apennine platform domain, and developed primarily at the boundary between the Jurassic limestone and the Triassic dolomite, which results in a “younger-on-older” tectonostratigraphic relation (Bucci et al. 2012). Cataclastic zones are well developed in the dolomite rocks and locally exceed a few tens of metres in thickness. The cataclastic shear zones are associated with, and represent evidence for, the presence of east-dipping low-angle tectonic contacts (Fig. 8b). The tectonic contacts are low-angle (20°–40°), NE-dipping fault zones. Kinematic indicators on the fault surfaces include primary corrugations and asymmetrical dome structures with a long axis parallel to the transport direction, and slickensides (Bucci et al. 2014), both in the hanging wall and in the footwall blocks. Analysis of the kinematic indicators reveals a NE, top-down displacement along shallow shear zones. Based on these lines of evidence, these structures have been interpreted as low-angle normal faults that are commonly developed in an extensional regime (Novellino et al. 2015; Brozzetti 2011).

The stop 10b shows two younger fault systems, respectively, trending NE-SW and NW-SE, cutting across and clearly offsetting the older low-angle normal faults. Several exposures of NE-SW-trending normal faults are located between Monte Volturino and Il Monte di Viggiano, and define a morphostructural depression named Sorgente Copone graben. Two main normal faults, the Pietra Liscia fault (Fig. 8c) and the Marsico Vetere fault, respectively, bound to the north-west and to the south-east of the Sorgente Copone graben for a length of about 4 km. Southward, both faults terminate against the eastern border fault of the High Agri Valley and are covered under the Quaternary breccias and sediments. Northwards, they terminate against the uppermost strand of the East Val d’Agri Fault System (EAFS; according to Bucci et al. 2013). Both the Pietra Liscia fault and the Marsico Vetere fault have been dissected in several segments by Quaternary NW-SE oblique-to-strike slip faults with left-lateral kinematics. The fault system strongly affects roughly stratified talus breccias of early-to-middle Pleistocene age (Di Niro et al. 1992), which appear faulted against the Mesozoic bedrock (Fig. 8d).

The stop 11 is located in an abandoned quarry along a fault strand close to the valley flat, belonging to the NW-SE-trending high-angle fault system. The faults are marked by 10–20-cm-thick cataclastic shear bands and by a polished and planar slip surface. Two sets of slip lineations are observed on these surfaces. The first set indicates left-oblique slip on northwest-striking surfaces and characterises the main fault morphology and presumably the larger slip accommodated by the fault. The second set of slip lineations indicates dip-slip motion. The second slip event is marked by short (dm-scale) and variably developed lineations, which are ostensibly superposed on the first set and on the main fault morphology, though without erasing the imprint of the older motion. It is likely that these slips occurred in the near surface in recent times. As a matter of fact, on the topographic surface, the traces of one of such reworked faults are locally documented by a sub-metric-scale step in the slope profile suggesting active deformation in very recent time (Fig. 8e).

Fault-Controlled Hydrocarbon Migration (Stop 12—Tramutola Pool)

Location and Aim

This is the last stop of the itinerary. It is located close to the Tramutola Pool, along the west margin of the High Agri Valley, few kilometres S of the first geosite of the itinerary. The stop is designed to show an oil superficial manifestation, resulting by the migration of hydrocarbon in the vertical direction along fault-related fractures and hydraulic connections.

Outcrop Description

The natural hydrocarbon springs of the Tramutola Pool geosite are liquid manifestations. They consist of a free drip of oil due to the rising from shallow levels (the superficial reservoir is about 300–400 m deep) along rock fractures. Oil is associated with water and natural gas (mainly methane, carbon dioxide and hydrogen sulphide). The natural hydrocarbon springs consist essentially of oil more or less oxidised that do not evaporate, dark or blackish, very viscous or even pasty (Van Dijk et al. 2013). Such spontaneous manifestations are evident at the confluence of the Torrent Fossatello and the Rio Cavolo, few hundred metres west of the Tramutola Pool. They are found within marly-arenaceous silicoclastic terrains, near the tectonic contact with the Mesozoic apenninic platform carbonate, that form the hill on the west bank of the stream. The hydrocarbons and sulphidic water mix with the clean water of the stream until it enters the main stream of the Rio Cavolo (Fig. 8f), a tributary of the Agri river, which contributes to the recharge of the artificial Pietra del Pertusillo lake. Apart the scientific and education values, this geosite is historically important, since, during the first half of the ‘900, the growing interest around the Tramutola oil spring triggered the first hydrocarbon exploration activities in the High Agri Valley, targeting the scattered, mainly unproductive, superficial oil traps. Only after the exploration of the deep oil traps, at the beginning in the 1980s, the richness of the hydrocarbon resource in the subsoil of the Agri Valley was demonstrated.

Discussion

Scientific and Touristic Motivations for the Geological Itinerary

The complete geological history of the Southern Apennines of peninsular Italy can be reconstructed through observations carried out at sparse outcrops across the orogenic system. Only occasionally it is recorded within, and can be inferred from, analysis of rather exceptional, single, metric outcrops (e.g. see Tavarnelli and Prosser 2003; Tavarnelli et al. 2003). In addition to these rare situations, the geological heritage across the looping route of the itinerary described above represents a wellspring of knowledge on the geological history of the Southern Apennine chain, as it makes it possible to recognise and analyse in great detail several structures of different ages and scales, from mesoscopic to macroscopic, related to the main tectonic events that shaped the geological foundation of Southern Italy; these include pre-orogenic extension related to the Mesozoic rifting events, the Neogene orogenic contraction and the Quaternary late/post-orogenic strike-slip events that were followed by extensional deformations responsible for recent uplift and for intense seismic activity of the area. Compared to known examples of geological itineraries scattered elsewhere around the world, our itinerary has the peculiarity to illustrate the cyclical, recurrent character of the geological processes, their role in shaping the natural landscape and their interaction with the human impact. These issues are rarely addressed by geological itineraries (Bentivenga et al. 2017), which commonly link geosites sharing particular characteristics. The most represented itineraries in the geological literature include the following: (i) geosites of the same origin and type (Migoń et al. 2018; Bertok et al. 2015); (ii) geosites located in the same parks or protected area (Costantini et al. 2015a; Balestro et al. 2016); (iii) geosites of city, province and region (Pica et al. 2016; Costantini et al. 2015b); (iv) geosites placed along historical (Niculiţă and Mărgărint 2018) and cultural paths (Sabato et al. 2018).

The present geological itinerary consists of 17 stops at as many geosites, which preserve remarkable evidence for past deformation events and allow the visitor to recompose the tectonic puzzle that led to the growth of a mountain belt from a marine environment, to its emersion and, later, to its dissection and collapse to achieve its present-day physiography. The geosites contain multiple geological information, including structural, stratigraphic and geomorphological ones. Several recent research papers are based on these information, providing a documentation of the scientific value of these geosites. In addition, the itinerary interconnects with other geological field trip routes in the High Agri Valley. It seems appropriate to stress here that field trip routes and geological itineraries across the High Agri Valley were designed and/or accomplished as parts of international congresses and conferences open to stratigraphy, palaeontology, geomorphology, structural geology, seismology, archaeology and hydrocarbon experts (e.g. see Ferranti et al. 2007), or of more general educational programmes of geoscience schools, documenting the interest of broad, varied and multidisciplinal communities on the area, as well as the educational value of the visited geosites.

The itinerary also presents a number of non-geological issues that yet, coupled with the remarkable geological interest of the area, will hopefully and potentially result in positive feedback on geotourism.

  1. (I)

    Trip (Fig. 2) may be done by car, going round the Monte Lama–Monte Volturino ridge clockwise, including short but delightful walking tours. Geosites 1a, 1b, 2, 3a, 4a, 4b, 6, 8, 11 and 12 are exposed along the paved road; geosites 5, 7 and 10a are reachable following a secondary road. Geosites 3b, 9 and 10b can be reached in 15 min thanks to well indicated walkways or pathways.

  2. (II)

    Risk conditions along the route of the itinerary are extremely reduced. These are limited to the sites 3b (Fig. 4c) and 4b (Fig. 5b), where tens of metres of high rocky walls exposing sub-vertical rock beds and layers are prone to rockfall and toppling. Further potential risk conditions are limited to the vertical rock walls of sites 10b (fault planes, Fig. 9a), 10a and 11 (dismantled quarries, Fig. 9b) and along the trails approaching site 10b (rockfall, Fig. 9c) and site 7 (rockfall, Fig. 9d). At these locations, it is recommended to avoid leaving the main, indicated path during the visit, and to avoid climbing, maintaining a safe distance of a few metres from the vertical rocky walls.

  3. (III)

    Several geosites geographically coincide with sites of cultural and natural heritages. Geosites 7 and 9 coincide with notable places of worship and religious architecture: the church of Madonna di Monte Saraceno and the sanctuary of Madonna di Monte di Viggiano (Fig. 10a), which is considered one of the symbols of the historical and cultural identity of the Basilicata region. The sanctuary is located at the top of the Monte di Viggiano, at the end of a delightful, steep walkway offering spectacular view points (Fig. 10b). Geosites 10a and 10b rest just in front (and few hundreds of metres far) to the archaeological site of La Civita, displaying the ruin of a palaeo-Christian temple (Fig. 10c). Moreover, in the opposite (western) side of the valley, the Roman town of Grumentum (Fig. 10d) is located just few kilometres south of the geosite 12. Grumentum is also overlooking the Pietra del Pertusillo lake (Fig. 10e), which is one of the main naturalistic attractions of the High Agri Valley.

  4. (IV)

    The itinerary develops within the territory of the Appennino lucano val d’Agri Lagonegrese National Park, and many geosites are located along the official trails (Fig. 10f), which cross the most interesting naturalistic areas of the park.

Fig. 9
figure 9

Risk conditions along the post-orogenic extensional fault arrays on the NW margin of the High Agri Valley, at the foot of the Mt. Volturino-Mt. Torrette-Madonna di Monte Saraceno carbonatic ridge. a Steep fault surface exposed at Sorgente Copone graben, at geosite 10a. b The dismantled Arenata quarry walls, at geosite 11. c Rockfall along a trail of the itinerary at Sorgente Copone. d Rock avalanche at the foot of the Madonna di Monte Saraceno sanctuary, corresponding to the geosite 7

Full size image
Fig. 10
figure 10

Images and views of points of high cultural heritage in the High Agri Valley. a The Madonna del Monte di Viggiano, sanctuary, located on top of the omonymous mountain, seat of seasonal pilgrimage. b A view of the paved pedestrian trail leading to the summit of Il Monte di Viggiano, location of the Madonna del Monte di Viggiano sanctuary. c Panoramic view of the archaeological site of La Civita, with the ruins of a palaeo-Christian temple. The Marsico Vetere village is observed in the background. d Remains and ruins of the Roman town of Grumentum, located few kilometres south of the geosite no. 12 described in this study. e Panoramic view of the Pietra del Pertusillo artificial lake, one of the main attractions of the High Agri Valley. f Direction signs of a dense foot-pathway network punctuate the itinerary proposed in this study

Full size image

Overall, the coincidence of sites of relevant geological interest with other natural and cultural heritage sites is vital for educational purposes, as they offer a firsthand way for people to approach the world of geology through integrated itineraries, exploring the geodiversity and its interconnection with the natural and cultural heritages (Coratza et al. 2016).

Despite its potential for geotourism, the geological itinerary here presented is marginal respect to the main geotouristic routes of the Southern Apennine (e.g. Cilento e Vallo di Diano Geopark) and remains unknown to the visitors of the Appennino lucano Val d’Agri Lagonegrese National Park due to the lack of adequate information for non-specialists. Parallel to the scientific characterisation of the geosites along the itinerary, we acknowledge the need to promote their educational contents through outreach activities. For example, we consider the strategy adopted for the promotion of the geological itinerary of Sasso di Castalda (PZ), 10 km north of the High Agri Valley (Palladino et al. 2013). The itinerary was inaugurated in 2009, through a public meeting (Fig. 11a), followed by a walk along a path through the sites of geological interest (Fig. 11b). Explicative panels showing the relevant geological features of the geosites were placed at each stop and are still present in good condition (Fig. 11c). In the Sasso di Castalda case, the cooperation between university, local associations and municipality has guaranteed high educational and scientific standards, active citizen involvements and the long-term maintenance of the panels. The example of Sasso di Castalda can be followed to promote the geological itinerary of the High Agri Valley, also opening at further initiatives as (i) the publication of a field trip guide, (ii) the publication of the trail map and (iii) the digital development of the trail tracks and their geological contents, making them suitable for mobile technologies. However, the designing and realizing of geoheritage promotion actions should be subordinated to a scientific agreement, that is lacking at the moment, with the Appennino lucano Val d’Agri Lagonegrese National Park authority and other subjects in charge of regional and local land management.

figure 11

Geosites as a Tool for Enhancing the Geological Education to Natural Hazards

It is essential to keep in mind that to forge a connection between the visitors and the object visited, it is crucial to relate what is shown with something in the personality or experience of the visitors (Rabal-Garcés et al. 2017), for instance, by using examples taken from everyday life. This transforms the object visited into something closer to their own human experience and thus makes it more meaningful to them. Several geosites included in the geological itinerary give the opportunity to discuss common human experiences of geology, represented by geological and geomorphological hazards, such as, primarily, earthquake and landslides (Niculită et al. 2016; Coratza and De Waele 2012). This makes it possible not only to convey a sense of the object’s scientific value but to raise awareness in the population about its relevance and need for protection (Magagna et al. 2013). Along the geological itinerary, important landmarks produced by geological hazards are detectable from the Il Monte di Viggiano (stop 9), Sorgente Copone (stops 10b), Camporeale (stops 3a, 3b) and Pietra Maura geosites (stops 4a and 4b). All these geosites have an aesthetical appeal and are ideals to promote geological education.

The geological site of Il Monte di Viggiano (stop 9) offers a scenic view on the entire High Agri Valley and allows recognising distinct landmarks in relation to the geological and structural features. Different morphologies for the eastern and western shoulders of the valley are recognisable. To the west, the Maddalena Mountain range is characterised by a “hat-like” topography produced by small depressions perched along its crest. These basins are aligned NW–SE for over 15 km from Mandranello–Mandrano southwards to Magorno. A second subparallel, and topographically lower, alignment of smaller basins is found to the east for about 10-km stretch, between the villages of Tramutola and Moliterno (Maschio et al. 2005). No obvious range-bounding fault outcrops along this side of the valley. On the contrary, to the east, the valley flank displays a rectilinear trend of the mountain front, which is characterised by a mature staircase profile sloping toward the valley, generated and controlled by post-orogenic faulting. Geomorphological evidence for active tectonics provides an opportunity to stimulate discussion on hazard and seismic risk (Mirabella et al. 2018; Bucci et al. 2016a, b). Most of the observations made from the panoramic viewpoint of the Monte di Viggiano geosite can be explored in detail at the Sorgente Copone geosite, where faults with different kinematics and age are remarkably well exposed. Outcrops of exhumated faults, now inactive, are important because these provide a rare opportunity to illustrate the anatomy and size of a fault zone, highlighting the deformation state of the involved rocks. Outcrops of recent faults make it possible to observe the effects of active faulting on the youngest deposits and morphology, highlighting landmarks as triangular facets, break in slopes and fault-related ruptures of the topographic surface, which can interact with human-related structures and infrastructures (Vignaroli et al. 2019).

In contrast, the Camporeale geosite (stops 3a and 3b) shows an example of morphological convergence, where landmarks similar to those produced by the activity of recent faults (triangular facets) are actually attributable to selective erosion on very inclined layers (flatiron). These particular morphologies are prone to mass wasting processes, including rockfall, toppling and debris flow, mainly concentrated along V-shaped valleys separating sub-vertical slopes. The geosite is ideal for discussing the nature and mechanism of different types of landslides and related hazard and risk condition. In addition, the geosite provides a vantage point of view on the opposite side of the valley, where a large slide-earthflow, the Pietra Maura landslide, marginally involves the homonymous geosite.

The Pietra Maura landslide (stops 4a and 4b) develops in correspondence with the tectonic contact between the Lagonegro units. The geosite provides an understanding on the instability conditions that lead to a large failure, which can be attributed to the poor geomechanical behaviour of the sheared rock mass along a regionally important thrust (Guzzetti et al. 1996). In addition, this site is particularly interesting because it makes it possible to observe the progressive infill of the Marsico Nuovo dam by the Pietra Maura landslide, stimulating the discussion on the underestimation of geological hazards for the design and construction of engineering works.

Geosites as Georesources

A further common experience of geology in daily life of people is represented by the direct or indirect use of geological resources, such as hydrocarbons. Hydrocarbons are mainly known because of their industrial derivatives. However, it is rarely possible to observe the raw material in the natural environment, as it is normally trapped underground. The Tramutola Pool geosite (stop 12) is important because it represents a window in the subsoil of the High Agri Valley. It is the only place in the area where one can clearly observe a natural hydrocarbon spring, verifying the colour, texture and smell of crude oil. The geosite helps to understand the genesis of the surface manifestations of hydrocarbons, which are found in correspondence of fault and fracture systems draining oil from the most superficial underground traps. The geosite also helps to imagine a subsoil rich in hydrocarbons, whose clues on the surface are otherwise only witnessed by engineering infrastructures, as wells and subsurface pipelines, and industrial oil centre. Such subsoil richness is closely linked to the geological history experienced by the High Agri Valley, which is responsible for the formation of both the oil and the natural traps in which it accumulates. This particular geological condition makes the High Agri Valley the largest onshore oil field of continental Europe and a strategic area for the oil industry as well. However, the increasing richness produced by the oil industry has not driven a balanced development of the territory. On the contrary, the territory has undergone a growing industrialisation not counterbalanced by adequate investments to support the local economy, failing to setup a sustainable geoconservation plan, which includes geotourism issues. Because of its double vocation of industrial and natural area, strongly linked to geology issues, the High Agri Valley would be a rare and ideal experimental laboratory for reconciling economic and environmental values of georesources, based on the enhancement of the geological heritage, and its integration into natural park systems, historical routes and cultural networks for touristic promotion. Recently, significant steps have been taken by the Basilicata region, which has issued a regional law that provides for the possibility of recognising geosites as areas to be protected, which is the basis for a policy of enhancing the geological heritage. However, the law applies to portions of territory that have not yet been officially defined. The lack of an official geosite inventory makes the regional law inapplicable. For the reason, we maintain that an official geosite inventory at regional scale, based on scientific criteria and reproducible methods of identification, evaluation and mapping, should be realized as soon as possible.

Conclusions

The proposed geological itinerary may be used for different purposes, targeting a diverse public or audience ranging from non-specialists to academic geologists. It is particularly suitable as a geotouristic trail and for didactic field trips at an undergraduate level for two reasons: its location within a protected area and the remarkable scientific value of this sector of the Southern Apennine. The itinerary is in a mountain environment and is mostly contained within the Appennino lucano val d’Agri Lagonegrese National Park. This means that there are both wide outcrops of substrate rocks favouring observation of the geological features and that most of the areas are protected and crossed by a network of well-maintained trails.

The geological itinerary retraces the progressive geological and tectonic evolution of the High Agri Valley and highlights, through observations at each proposed stop, the key elements that can be generalised at the scale of the Southern Apennine chain. The study of the geosites included in the itinerary makes the Val d’Agri a remarkable area of prime geological interest, as it provides an opportunity and makes it possible to discuss the implications that the geological history has on the natural landscape, geological resources and natural hazards of this precious “open-air laboratory”. The connection of different geosites in the geological itinerary represents a concrete strategy of development of the territory, which is explored, observed and understood as a dynamic environment that has changed in the past and changes at present. In this way, the beauty, charm and appeal of the visited places are increased, as well as the awareness of the value of the geological heritage and the importance of its protection.

Our contribution presents a possible way to promote the geological heritage, based on a trip back in the geological time, exploring different sedimentary and tectonic environments recognised in the geological record of the High Agri Valley. In a general perspective, we expect the same strategy applicable in other areas of prime geological importance, where the effects of alternating tectonic pulses modulated through time are preserved. At local scale, our goal is to shed a light on the need for mapping, protection and promotion of high-value geosites, and to stimulate the interest of local administrators, stakeholders, and public and private organizations, on the geological heritage of the High Agri Valley, triggering potentially fruitful cooperation for setting-up a sustainable geoconservation plan, which includes geotourism issues.