UNIVERSITA’ DEGLI STUDI DI TORINO

This is an author version of the contribution published on: Questa è la versione dell’autore dell’opera: Barbero E., Festa A., Fioraso G., & Catanzariti, R. (2017) Journal of Maps, v.13 (2), 879-891 ttps://doi.org/10.1080/17445647.2017.1398114

The definitive version is available at: La versione definitiva è disponibile alla URL: http://www.tandfonline.com/loi/tjom20

Geology of the Curone and Staffora Valleys (NW ): field constraints for the Late Cretaceous – Pliocene tectono-stratigraphic evolution of Northern Apennines

Edoardo Barberoa,b, Andrea Festab, Gianfranco Fiorasoc and Rita Catanzaritid

aDipartimento di Fisica e Scienze della Terra, Università di Ferrara, Ferrara, Italy; bDipartimento di Scienze della Terra, Università di Torino, Torino, Italy; cIstituto di Geoscienze e Georisorse, CNR – Consiglio Nazionale delle Ricerche, Torino, Italy; dIstituto di Geoscienze e Georisorse, CNR – Consiglio Nazionale delle Ricerche, Pisa, Italy

ABSTRACT In the northwestern part of Northern Apennines, between Curone and Staffora Valleys, the tectonic superposition between the External Ligurian Units (i.e. the ophiolitic-bearing chaotic complex of the Groppallo Unit and the non-ophiolitic Cassio Unit), the Middle Eocene – Miocene wedge-top basin Epiligurian Units succession, and the Late Messinian – Pliocene Plain succession, records the multistage tectono-stratigraphic evolution from subduction to continental collision. Our geological map, at the 1:20,000 scale, allows us to define 6 main tectonic stages on the basis of (i) the crosscutting relationships between main faults and local to regional stratigraphic unconformities and (ii) the differentiation among different types of chaotic rock unit (olistostromes and broken formations) deposited since Late Cretaceous to late Messinian. This approach provides a new understanding on the tectono-stratigraphic evolution of this sector, and its meaning in the evolution of the northwestern part of Northern Apennines.

1. Introduction its meaning in the evolution of the northwestern part of Northern Apennines. In the hanging wall of the Apenninic thrust front, the On the basis of a new geological mapping at the northwestern part of Northern Apennines belt 1:5000 scale, detailed structural and stratigraphic (between Voghera and Piacenza) is characterized by observations, and targeted collection of biostrati- complex structural relationships among discontinuous graphic data, we present the ‘Geological map of the remnants of ophiolite-bearing chaotic units (e.g. Boc- Curone and Staffora Valleys (Northern Apennines, caletti & Coli, 1982) of Late Cretaceous age (i.e. Wes- Italy)’ (see Main Map) at the 1:20,000 scale. This Geo- tern External Ligurian Unit, see Marroni & Pandolfi, logical Map represents the northern prolongation of 2007), non-ophiolitic External Ligurian Units (e.g. the ‘Geological Map of the Villalvernia – Varzi Line Eastern External Ligurian Unit, see Marroni & Pan- between and Curone valleys (NW Italy)’ by dolfi, 2007), and the overlaying wedge-top basin Epili- Festa, Fioraso, Bissacca, and Petrizzo (2015). gurian Units (Figure 1). Although this sector is covered by different editions of the Geological Map of Italy (e.g. Bellinzona, Boni, Braga, & Marchetti, 1971; Boni, 1969; 2. Methods Vercesi et al., 2005, 2015), the understanding of the tec- tono-stratigraphic relationships between these differ- The geological map was produced from about four ent units is complicated by poor rock exposures and years (2014–2017) of fieldwork at the 1:5000 scale lack of continuous outcrops. A new detailed geological and accompanying detailed structural analyses and mapping, focused on (i) the crosscutting relationships stratigraphic observations. The definition of the struc- between main faults and local to regional stratigraphic tural setting of the sector was defined through the map- unconformities and (ii) the differentiation among ping of the crosscutting relationships between main different types of chaotic rock unit (i.e. olistrostromes faults and local to regional stratigraphic unconformi- and broken formations) of various age, provides ties that are documented in the attached geological further specific data covering the partial lack of geo- map at the 1:20,000 scale (see Main Map), using the logical information, allowing a new understanding on topographic maps ‘CTR – Carta Tecnica Regionale’ the tectono-stratigraphic evolution of this sector and of Regione Piemonte and Regione Lombardia. The dis-

Figure 1. Regional structural sketch map (a) of the northwestern part of Northern Apennines and Ligurian Western Alps (modified from Balestro, Festa, Dilek, & Tartarotti, 2015). (b) Location of Figure 1(a) (modified from Vezzani, Festa, & Ghisetti, 2010).

tinction among different types of chaotic rock units (i.e. accretionary stage has been recorded in the complex olistostromes and broken formations) followed specific evolution of the Ligurian accretionary complex, criteria defined in literature (e.g. Bettelli & Panini, which consists of different units containing tectono- 1989; Bettelli, Conti, Panini, & Vannucchi, 2006; sedimentary assemblages originally deposited in an Dilek, Festa, Ogawa, & Pini, 2012; Festa, Dilek, Code- ocean basin (i.e. Jurassic ophiolites and sedimentary gone, Cavagna, & Pini, 2013; Festa, Ogata, Pini, cover of the Internal Ligurian Units), ocean-continen- Dilek, & Alonso, 2016; Festa, Pini, Dilek, & Codegone, tal transition zone (External Ligurian Units), and 2010; Pini, 1999). The geological map was edited using thinned continental crust of the Adria margin (Subli- the methodological cartographic and representative gurian Units), respectively. During the Late Cretaceous criteria from the CARG Project (Project of Geological through Middle Eocene, these different units were Cartography) of Italy, at the 1:50,000 scale (see deformed and incorporated into the Alpine accretion- Pasquaré, Abbate, Bosi, et al., 1992; Pasquaré, Abbate, ary wedge, formed as consequence of the east-dipping Castiglioni, et al., 1992). ‘Alpine’ subduction (i.e. Elter, 1975; Marroni et al., 2010; Marroni, Molli, Ottria, & Pandolfi, 2001; Principi & Treves, 1984). Since the Middle Eocene, the thinned 3. Regional setting continental margin of Adria was involved in the W- The Northern Apennines (Figure 1) record the com- dipping Apennine subduction (e.g. Castellarin, 1994; plex evolution from Late Cretaceous subduction to Handy et al., 2010; Marroni et al., 2010; Molli et al., Cenozoic continental collision between the European 2010; Schmid, Kissling, Diehl, van Hinsbergen, & plate and Adria microplate and subsequent intra-con- Molli, 2017; Vezzani et al., 2010). The External Ligur- tinental deformation (e.g. Coward & Dietrich, 1989; ian Units underthrust below the Internal Ligurian Elter, Grasso, Parotto, & Vezzani, 2003; Festa, Pini, Units and together overlie the Subligurian Units, ulti- Dilek, Codegone, Vezzani, et al., 2010; Handy, Schmid, mately forming the frontal part of the advancing Ligur- Bousquet, Kissling, & Bernoulli, 2010; Marroni, Mene- ian accretionary complex, which, in turn, overthrust ghini, & Pandolfi, 2010; Molli, Crispini, Mosca, Piana, the deformed Adria continental margin. During the & Federico, 2010). The Late Cretaceous – Early Eocene progressive incorporation into the accretionary

wedge, a consistent part of the External Ligurian Units Figure 2(c)) also represent a highly disrupted broken (i.e. the Lower to Upper Cretaceous ‘Basal Complex’) formation with blocks (limestones, sandstones, and was strongly deformed by tectonic processes forming manganiferous siltstones), deriving from stratal disrup- broken formations and tectonic mélanges (e.g. Bettelli tion of the primary lithostratigraphic unit, embedded & Panini, 1989; Codegone, Festa, Dilek, & Pini, 2012; in a varicolored (gray, red, and purple) clays and shales Festa et al., 2013; Festa, Pini, Dilek, Codegone, Vezzani, matrix. Tens of meters thick body of Salti del Diavolo et al., 2010; Pini, 1999; Remitti et al., 2011). Since the Conglomerate (AVV1 in the Main Map, Figure 2(d)), Middle – Late Eocene, different episutural and with clasts consisting of prevailing carbonate rocks wedge-top basins (i.e. Tertiary Basin and and minor micaschist, gneiss, quartzite, granulite, Epiligurian Units, respectively) unconformably cov- pinkish granite and diorite, are interbedded within ered the Ligurian accretionary complex (Figure 1) the Argille Varicolori. The latter are overlain by the and the N- to NE-verging thrust-related structures late Campanian Monte Cassio Flysch (MCS in the (e.g. Mosca, Polino, Rogledi, & Rossi, 2010; Mutti Main Map, Figure 2(e)), which consists of alternating et al., 1995; Ricci Lucchi, 1986). beds of clayey marls and carbonate-rich calcareous- Different mass-transport deposits, including olistos- marly turbidites, dm to m thick. The Viano Clay tromes (i.e. sedimentary mélanges), occur at different (AVI in the Main Map, late Maastrichtian – Late Paleo- stratigraphic levels within both the External Ligurian cene), consisting of alternating layers of claystones and Units and Epiligurian Units, representing excellent less abundant limestones in dm thick beds, closes markers of tectonic events (e.g. Festa et al., 2016; see upward the stratigraphic succession of the Cassio Unit. also Bettelli & Panini, 1989; Codegone et al., 2012; The Groppallo Unit consists of a chaotic complex Festa et al., 2013; Festa, Fioraso, et al., 2015; Ogata, with a block-in-matrix fabric (the Pietra Parcellara Mountjoy, Pini, Festa, & Tinterri, 2014; Piazza, Artoni, Complex – CPP in the Main Map), up to 150 m (or & Ogata, 2016; Pini, 1999; Remitti et al., 2011). more) in thickness, in which heterogeneous blocks, up to hundreds of m in size (Figure 2(f)), are randomly dis-

tributed in a matrix of coarse-grained ophiolitic sand- 4. Data stones (Figure 2(g,h)) and polymictic argillaceous The study sector (Figure 1), which is located between breccias. Huge blocks (olistoliths) are represented by Curone and Staffora Valleys, is characterized by com- mantle ultramafic rocks (i.e. spinel-lherzolites) locally plex tectono-stratigraphic relationships between two intruded by small gabbro bodies, while clasts consist different units of the External Ligurian Succession, rep- of lherzolites, gabbros, bed fragments of Calpionella resented by the Groppallo Unit (e.g. Vercesi et al., Limestone and Palombini Shale, minor basalts, cherts 2015) and the Cassio Unit (e.g. Elter, Elter, Sturani, (i.e. Radiolarites) and granitoids. It is worth noting & Weidmann, 1966; Vescovi, Fornaciari, Rio, & Val- that, although the nature of blocks and clasts of this loni, 1999). These units are unconformably overlain Unit closely resemble that one of the Casanova Com- by the Middle Eocene – Miocene Epiligurian Succes- plex Auct. (sensu Bertotti, Elter, Marroni, Meccheri, & sion. To the north, this complex tectono-stratigraphic Santi, 1986; Elter, Marroni, Molli, & Pandolfi, 1991; setting is sealed by the late Messinian – Early Pliocene Marroni et al., 2001) rather than the classical one succession. described for the Pietra Parcellara Complex (see, e.g. Marroni et al., 2010; Vercesi et al., 2015), we prefer to maintain this last formational name because its struc- 4.1. Stratigraphy tural position is well consistent with that of the Gropallo 4.1.1. External Ligurian Units Unit described in the Northern Apennines (e.g. Vercesi The stratigraphic succession (Chronostratigraphic et al., 2005; 2015). Analyses of calcareous nannofossils Scheme in Main Map) of the Cassio Unit shows a com- show an early Campanian age (CC18 zone of Sissingh, plete transition from the ‘Basal Complex’ (Scabiazza 1977)r fo the uppermost part of this chaotic complex. Sandstone and Argille Varicolori) to the late Maas- trichtian – Late Palocene Viano Clays. The Scabiazza 4.1.2. Epiligurian Succession Sandstone (SCB in the Main Map, late Albian– Santo- The Epiligurian Succession starts with the Baiso Argil- nian) consists of a strongly disrupted chaotic succes- laceous Breccias (BAI in the Main Map, Lutetian – Bar- sion (broken formation sensu Hsü, 1968) with bed tonian) (Figure 3(a)), which consist of a lenticular and fragments of whitish micaceous sandstones, embedded laterally discontinuous mass-transport chaotic deposit into a pelitic- to argillaceous matrix (Figure 2(a,b)). (olistostrome) sourced from the downslope dismem- The analysis of calcareous nannofossils shows mixing berment of the ‘Basal Complex’ and Monte Cassio of late Albian, Aptian-Albian, Early Cretaceous and Flysch. They pass upward (and local laterally) to hemi- Early Jurassic taxa, and few taxa younger than Conia- pelagic clays and marls of the Monte Piano Marls cian. The Argille Varicolori (AVV in the Mainp Ma , (MMP in the Main Map, Lutetian – Priabonian) Varicolored scaly clays; Santonian – Campanian; (Figure 3(b,c)), which are overlain through an erosive

Figure 2. Field occurrence of the External Ligurian Succession (a– e: Cassio Unit; f–h: Groppallo Unit): (a) strongly disrupted chaotic succession (broken formation) of the Scabiazza Sandstone, showing a preferred alignment (i.e. pseudo-bedding) of sandstone bed fragments (west of Ca de’ Franchini); (b) close-up view of the Scabiazza Sandstone with bed fragments of whitish micaceous sand- stone embedded into a pelitic-to argillaceous matrix; (c) noncylindrical and asymmetrical folds deforming alternating grey and red- dish to purplish shale and minor black manganiferous siltstones in the Argille Varicolori (east of San Lorenzo). Hammer for scale; (d) close-up of the Salti del Diavolo Conglomerate (Cascina Sighera). Hammer for scale; (e) alternating bed of calcareous turbidites and grey marls of the Monte Cassio Flysch (Barca); (f) panoramic view of a serpentinite block, hundreds of m wide, embedded in the poorly outcropping argillaceous matrix of the Pietra Parcellara Complex (east of Zebedassi); (g,h) clast-supported debris flow of polymictic rounded to angular clasts of ultrabasic rocks (dark green to reddish in color) and oceanic cover succession (whitish in color) of the Pietra Parcellara Complex (north of Zebedassi). Hammer for scale in (g).

unconformity surface (Figure 3(b)) by turbidites of the stratigraphic position and petrographic composition Ranzano Formation. The latter, which is locally depos- of lithic fragments (see, e.g. Cibin, Di Giulio, & Mar- ited directly above the External Ligurian Succession, is telli, 2003; Martelli, Cibin, Di Giulio, & Catanzariti, subdivided in three superimposed members (Pizzo 1998; Mutti et al., 1995). The succession continued, d’Oca Member – RAN1 in the Main Map – of late Pria- through an unconformity surface, with the slope fine- bonian age, Val Pessola Member – RAN2 – of late Pria- grained hemipelagic deposits of the Antognola For- bonian – early Rupelian age, and Varano de’ Melegari mation (ANT and ANT1a in the Main Map, late Rupe- Member – RAN3 – of middle – late Rupelian age; lian – Aquitanian), which includes olistostromal Figure 3(b), (d), and (e)), which differ for the lenticular bodies, up to 60 m thick, of the Val

Figure 3. Field occurrence of the Epiligurian Succession (a–h) and Messinian-Pliocene Succession (I): (a) panoramic view of the Baiso Argillaceous Breccias, showing the typical block-in-matrix fabric characterized by the random distribution of polymictic blocks sourced from the ‘Basal Complex’ and Helminthoides Flysch in argillaceous matrix (east of Cascina Galuzia); (b) panoramic view of the unconformable contact between the Monte Piano Marls (MPP2) and conglomerates and turbidite sandstone of Varano de’ Melegari Member (RAN3; Ranzano Formation) (near Giarella); (c) alternating whitish and reddish clayey marl of the Monte Piano Marls (MMP1, East of Cascina Galuzia); (d) grey to greenish coarse grain turbiditic sandstone and matrix-supported conglom- erates of the Val Pessola Member (RAN2a, Ranzano Formation) (near Piumesana). Note that the attitude of bedding is subvertical; (e) thick bed (up to 2 m) of grey sandstone, interbedded within alternating greyish pelite and arenite, in dm thick beds, of the Varano de’ Melegari Member (RAN3, Ranzano Formation) (South of Giarella); (f) panoramic view of the contact between clayey marl of the Antognola Formation (ANT) and the Val Tiepido – Canossa Argillaceous Breccias (ANT1b) (close to Moglia). The latter are character- ized by the random distribution of blocks, sourced from the ‘Basal Complex’ of the External Ligurian Succession and the Epiligurian Succession, within a clayey matrix, according to mass-transport processes of formation; (g) well-bedded whitish calcareous marls of the Contignaco Formation (east of Piumesana); (h) close-up of the bioclastic sandstone of the Monte Vallassa Sandstone (Serra del Monte), showing fragments of bivalve (coin for scale); (i) detail of the matrix-supported conglomerates and sandstones of the Cas- sano Spinola Conglomerate (close to Guagnina).

Tiepido–Canossa Argillaceous Breccias (ANT1b in the & Valleri, 2003; see Festa, Ogata, Pini, Dilek, & Code- Main Map, i.e. ‘Complesso caotico pluriformazionale’ gone, 2015). Blocks embedded within the olistostrome of Gelati, Bruzzi, Catasta, & Cattaneo, 1974; Figure 3 are sourced from both the External Ligurian Succession (f)) of Late Chattian age (planktonic foraminiferal and Epiligurian Succession (Monte Piano Marls and zone IFP22 (P22) of Mancin, Pirini, Bicchi, Ferrero, Ranzano Formation). The siliceous marls of

Contignaco Formation (CTG in the Main Map, late of the BST is deformed by E- to ENE-trending open Aquitanian – Burdigalian; see Figure 3(g)) drape both folds, which involve the Epiligurian Succession up to the Ranzano Formation and Antognola Formation. the Monte Vallassa Sandstone. Here, the Cassio Unit The stratigraphic contact with Ranzano Formation depicts a roughly SE-dipping monocline, with local (Colletta sector) corresponds to an angular unconfor- open folds with NE-to ENE-striking fold axis. Two mity, which passes laterally to a correlative conformity main fault systems (ENE- and N-directed) dissect the (Case Cucchi sector) where the Contignaco Formation hanging wall succession. The ENE-striking faults mainly overlies the Antognola Formation. In the latter sector, define a deformation zone (Momperone – Vignola locally, the lower part of the Contignaco Formation is Deformation Zone – MVDZ hereafter), several km long characterized by slumping structures. The Monte and hundreds of m wide, formed by the interlacing of Lisone Chaotic Complex (CML in the Main Map, E- and ENE-striking fault segments. In detail, the latters Late Burdigalian – Langhian?), which represents show transpressive left- and right-lateral movements, another mass-transport chaotic deposit (olistostrome), respectively (Figure 4(a)). In the Colletta sector, the rests unconformably on both the uppermost part of the MVDZ is unconformable sealed by the Contignaco For- External Ligurian Succession and the Antognola For- mation and, to the south (Vignola sector), by the Monte mation. It differs from the above described olistros- Vallassa Sandstone (see cross section 3 in Main Map, tromes on the basis of the nature of blocks, Figure 4(b)). The N-striking faults show normal kin- consisting of only disrupted bed fragments of Hel- ematics, as outlined by cartographic evidences such as minthoides Flysch, and to the South of the studied sec- the displacement of stratigraphic contacts among differ- tor it is overlain by the Monte Vallassa Sandstone (see ent members of the Monte Piano Marls and the Ranzano Festa, Fioraso, et al., 2015 for major details). The Epi- Formation (see Main Map). Particularly, the Val Pessola ligurian Succession continues through a regional Member and Varano de’ Melegari Member show E-W unconformity with the shallow and coarse shelf depos- directed change of thickness in sector bounded by those its of the Monte Vallassa Sandstone (AMV in the Main faults (see cross section 1 in Main Map). Left-lateral reac- Map, Gelati & Vercesi, 1994) of the Bismantova Group, tivations of this fault system are documented by slicken- Langhian – Serravallian in age (Figure 3(h)). In the lines on fault surfaces (Figure 4(a)). northern sector of the studied area, late Messinian In the footwall of the BST, the Groppallo Unit (post-evaporitic) chaotic deposits (i.e. Valle Versa defines a tectonic window overthrust by the Cassio Chaotic Complex – CTV in the pMain Ma – sensu Unit along a thrust folded by a NW-striking, open to Dela Pierre et al., 2003) and the Cassano Spinola Con- gentle anticline, with SE-fold axis plunge (see Main glomerates (CCS in the Main Map; Figure 3(i)), which Map). The thrust dips to NE and SW in the northeast- are followed by shelf deposits of Argille Azzurre (FAA ern and southwestern sides of the tectonic window, in the Main Map; Piacenzian) and Asti Sandstone (AST respectively, superposing the Scabiazza Sandstone in the Main Map; Zanclean), unconformably overlie (northestern side), the Monte Cassio Flysch and the both the External Ligurian Succession and the Epiligur- Scabiazza Sandstone (southwestern side) onto the Pie- ian Succession. tra Parcellara Complex (see cross section 2 in Main Map). Along the northeastern side of the tectonic win- dow, the Scabiazza Sandstone is locally involved by 4.2. Tectonic setting thrust splays and imbricated with the Pietra Parcellara The tectonic setting is characterized by the ENE-trend- Complex, forming lenticular tectonic slices, hundreds ing of tectonic structures (thrusts, strike-slip faults, and of m in length. To ENE, the footwall of the BST is regional scale folds), which are rotated to WNW-trend- characterized by a hundreds of meters wide and 5 km ing to the West of Curone Valley, being displaced by long deformation zone (San Desiderio Deformation WNW- to NW-striking strike-slip faults (see Main Zone – SDDZ hereafter), which is about WNW-ESE Map and related Structural scheme). and ENE-WSW oriented to the West and East sectors In the north-central part of the studied sector, the of the Staffora Valley, respectively (Figure 4(c)). Barca-Sala Thrust (BST hereafter), ENE-striking and Mesoscale structural associations (S–C shears; Figure SSE dipping, superposes the Cassio Unit and Epiligurian 4(d)) and fault striations (slikenlines) show transpres- Succession onto a composite tectonic unit, characterized sive right-lateral movements, according to the carto- by the tectonic relationships among the Cassio Unit, the graphic displacement of stratigraphic contacts Middle Eocene to Burdigalian part of the Epiligurian Suc- observed in the Map. This deformation zone juxtaposes cession, and the Groppallo Unit (see cross sections 3 and the Monte Cassio Flysch and the Argille Varicolori to 4 in Main Map). The BST, which is splitted into two main different terms of the Epiligurian Succession (i.e. sub-parallel surfaces bounding an elongated slice of Baiso Argillaceous Breccias, Monte Piano Marls and Argille Varicolori, shows a gradual decrease of offset Ranzano Formation; see cross sections 2, 3 and 4 in toward WSW where it is truncated by a NW-striking Main Map; Figure 4(c)). Far from faults bounding fault located along the Curone Valley. The hanging wall the SDDZ, the Argille Varicolori preserve an earlier

Figure 4. (a) Diagrams showing mesoscale data (Schmidt net, lower hemisphere) of main fault systems and fold axes described in the text. Right- and left-lateral fault kinematics are indicated with red and black colors, respectively; (b) panoramic view and sche- matic sketch of the Vignola sector, showing the unconformable overlain of the Monte Vallassa Sandstone (Langhian – Serravallian, AMV) onto the ENE-striking Momperone – Vignola Deformation Zone (MVDZ, red lines), which tectonically juxtaposes the Antog- nola Formation (late Rupelian – Aquitanian, ANT) and the Val Tiepido Canossa Polygenetic Argillaceous Breccias (ANT1b). In the sketch, dark and shadow colors indicate outcrops and interpreted areas, respectively; (c) panoramic view of the San Desiderio Defor- mation Zone (red lines) close to Monticelli, displacing and juxtaposing with transpressive right-lateral displacement the Cassio Unit (Argille Varicolori – AVV, Late Cretaceous), different terms of the Epiligurian Succession (Monte Piano Marls, MMP1, Middle – Late Eocene, and the Varano de’ Melegari Member of the Ranzano Formation – RAN3, middle – late Ruperlian), the Cassano Spinola Conglomerate (late Messinian), and Argille Azzurre (Early Pliocene); (d) detail of the San Desiderio Deformation Zone (SDDZ), show- ing the tectonic contact between the Baiso Argillaceous Breccias (BAI), the Monte Piano Marls (MMP1), and the Argille Varicolori (AVC) along a transpressive right-lateral faults (red lines), ENE-striking (east of Cascina Galuzia). S-C shears are indicated by dotted white line; (e) isoclinal and transposed folds with fold axes displaying WNW- and ESE-oriented maxima in the Argille Varicolori (close to Cascina Galuzia), showing stretching and thinning of the limbs; (f) block-in-matrix fabric in the Argille Varicolori, showing the alignment of elongated blocks (i.e. pseudo-bedding) and the scaly fabric of the shaly matrix (South of Guagnina).

layer-parallel extensional block-in-matrix fabric, which and asymmetrical boudinaged limbs by R and C’ is deformed by rootless and transposed folds (Figure 4 shears along NE-SW cross sections, commonly dis- (e,f)). The latters are characterized by curviplanar axial placed by localized shear zones. surfaces, with fold axes displaying a broad girdle with The tectonic setting above described is cut by two WNW- and ESE-oriented maxima (Figure 4(a,e)), main fault systems, NW- and N-striking. The former

corresponds to pluri-km long faults, which cut with affecting unconsolidated sediments in the latest left-lateral movements, reactivated by right-lateral stages of accretion (e.g. Bettelli & Vannucchi, ones as shown by fault striations (slickenlines) on 2003; Festa et al., 2013; Festa & Codegone, 2013; fault surfaces (Figure 4(a)) and S–C shears, both the Pini, 1999). Although the time for tectonic superpo- BST and the SDDZ (see Main Map). From East to sition of the Cassio Unit onto the Groppallo Unit is West of the NW-striking fault of the Curone Valley, difficult to constrain because of the lack of a detailed the main fold axes, bedding surfaces, and stratigraphic stratigraphic marker, the lack of involvement of Epi- boundaries are gradually rotated from ENE-WSW to ligurian Succession suggests it occurred earlier than WNW-ESE directions and cut by NE-striking faults Middle Eocene time (Figure 5(a,b)). Regarding the to the West of that Valley (see Main Map). Cassio Unit, it is worth noting that the age of the The N-striking fault system shows best exposures Scabiazza Sandstone (late Albian – Santonian) is only in the northeaster sector of the studied area similar to that one observed in the Media Val Taro (East of Mt. Treno), representing the southern pro- Unit (see, Vescovi et al., 2002; see also Ostia Sand- longation of the Pliocene Schizzola Valley Fault of Per- stone of Vescovi et al., 1999) and in the Cabella otti and Vercesi (1991) and Vercesi et al. (2015). The Ligure sector (see, Marroni, Ottria, & Pandolfi, latter defines a hundreds of meters wide deformation 2015), and younger than that one commonly zone, with left-lateral kinematics (e.g. Vercesi et al., described for the classical Cassio Unit (i.e. Cenoma- 2015), bounded by interlaced subvertical faults with nian – Turonian). Although additional investi- anastomosed geometry. gations are needed, these data suggest the deposition of this Formation in an outer sector of the Cassio basin (with respect to the West-verging 5. Conclusions ‘Alpine’ accretionary wedge), providing new con- The crosscutting relationships between mapped faults straints for a more detailed reconstruction of the and stratigraphic unconformities, and the distinction internal physiography of the depositional environ- of different types of chaotic rock unit, allow describing ment of the External Ligurian Succession. a detailed tectono-stratigraphic evolution of this sector . Middle Eocene (Lutetian – Bartonian): the wide of the Northern Apennines. Six main tectonic stages occurrence of the Baiso Argillaceous Breccias have been defined from Late Cretaceous to Pliocene along the SDDZ, ENE- to WNW-oriented, and (Figure 5(a,b)). their increase in thickness away from it, suggest that this deformation zone was active at least since . Late Cretaceous – Early Eocene: this tectonic stage Middle Eocene (Figure 5(a,b)), favoring mass-trans- preserves the record of both gravitational (i.e. olis- port processes triggered by the tectonic uplift of the tostrome) and tectonic-induced (i.e. broken for- ‘Basal Complex’ and Monte Cassio Flysch. Unfortu- mation) deformation related to the evolution at nately, a detailed description of Middle Eocene kin- shallow structural levels of the External Ligurian ematics of the SDDZ is hampered by late Messinian wedge during the subduction stage. The random dis- – Early Pliocene right-lateral reactivations of main tribution of polymictic blocks within the matrix of faults (see below ‘Late Messinian – Early Pliocene’ the Pietra Parcellara Complex (Groppallo Unit) is stage). This mass-transport event marks an impor- consistent with mass-transport processes occurred tant stage of the regional scale instability of the at the wedge front during Campanian time (Figure External Ligurian wedge (e.g. Bettelli & Panini, 5(b), Eoalpine Phase of Elter et al., 1966; see also, 1989), which can be related to the early stage of con- Bertotti et al., 1986; Elter et al., 1991). On the con- tinental collision (Mesoalpine stage or Ligurian trary, far from the main faults of the SDDZ, the Phase, e.g. Cerrina Feroni, Ottria, & Ellero, 2004; orientation and distribution of fold axes (with Elter, 1975; Marroni et al., 2010; Mutti et al., WNW- and ESE-oriented maxima) within the 1995). The uppermost temporal constrain to this Argille Varicolori is consistent with the tectonic tectonic stage is represented by the unconformable deformation related to NE-SW to NNE-SSW short- deposition of the Ranzano Formation (Late Eocene ening directions, which are commonly attributed – Early Oligocene) onto both the Baiso Argillaceous (e.g. Cerrina Feroni, Ottria, Martinelli, & Martelli, Breccias and External Ligurian Succession (Figure 5 2002; Elter & Marroni, 1991; Levi, Ellero, Ottria, & (a,b)). Pandolfi, 2006) to the Paleocene – Early Eocene . Late Priabonian – Rupelian: the NE-and N-striking European verging overthrust (Figure 5(b)) of the normal faults, which displace the lower portion of Helminthoides Flysch nappe onto the ‘Basal Com- the Epiligurian Succession, controlled the physio- plex’. The characteristics of mesoscale deformation graphy of Late Eocene – Early Oligocene deposi- within the Argille Varicolori (see ‘Tectonic setting’) tional basin as suggested by both the E-W change well agree with deformation occurred in the frontal in thickness of the Val Pessola Mb. and Varano and shallower levels of the External Ligurian wedge, de’ Melegari Mb. of the Ranzano Formation (see

Figure 5. (a) Structural scheme of the studied sector, showing the crosscutting relationships between different faulting stages (indi- cated with different colors) and stratigraphic unconformities (see text for complete explanation). (b) These relationships allow to define six tectonic stages as summarized in the time column (see Legend of the Main Map for acronyms). Main mass-transport deposits and main unconformities surfaces are evidenced (black asterisk and dotted blue line, respectively).

cross section 1 in Main Map, Figure 5(a)). At the (1995) and Faulting stage A of Piana (2000) and regional scale, this stage is close associated with Festa et al. (2005, 2013), Festa, Fioraso, et al. faulting along the Villalvernia – Varzi Line, which (2015), which are related to the opening of the controlled the depositional settings of both the Ter- Balearic Sea. The deposition of the Antognola For- tiary Piedmont Basin and Epiligurian Succession mation (late Rupelian – Aquitanian), which uncon- (e.g. Di Biase, Marroni, & Pandolfi, 1997; Di Giulio formably overlains different terms of the Ranzano & Galbiati, 1995; Felletti, 2002; Festa, Fioraso, et al., Formation and External Ligurian Succession, pro- 2015; Marroni et al., 2002; Mutti et al., 1995), and vides the temporal constrain for this tectonic stage corresponds to the Ligurian phase II of Mutti et al. (Figure 5(a,b)).

. Chattian – Early Miocene: the former extensional (Figure 5(b); e.g. Festa, Fioraso, et al., 2015 and regime was inverted to a compressional one that reference therein. accompanied the deposition of the Antognola For- . Late Messinian – Early Pliocene: tectonic defor- mation. This stage is mostly recorded along the mation triggered the mass-transport emplacement MVDZ, developed by the interlacing of ENE-strik- of the Valle Versa Chaotic Complex. NW-striking ing transpressive right-lateral faults and E-striking transtensional faults cut both the SDDZ and the transpressive left-lateral ones, and the widespread BST (Figure 5(a,b)). At the northern boundary of occurrence of olistostromes of the Val Tiepido – the SDDZ, this caused the juxtaposition of the Canossa Argillaceous Breccias, which sourced Argille Varicolori to the late Messinian – Early from denudation of uplifted External Ligurian Suc- Pliocene succession, while across the Curone Val- cession and the lower part of Epiligurian Succes- ley it separates sectors characterized by a gradual sion. In the southwestern sector of the study reorientation of both the late Priabonian – Rupe- area, submarine structural highs formed during lian faults (from N- to NE-striking; Figure 5(a)) the Middle Eocene – Rupelian stage were sealed and the main fold axes (from ENE- to NW-strik- by the unconformable deposition of the Con- ing; Figure 5(a)). This reorientation suggests a tignaco Formation (Colletta sector; see cross sec- refolding of earliest main tectonic features, during tion 3, Figure 5(a,b)). Toward east (e.g. Case which the NW-striking fault of the Curone Valley Cucchi sector), the occurrence of slumping in the acted as transfe r fault, accommodating part of lower part of the Contignaco Formation marks this deformation (Figure 5(a)). To the West of the paleo-scarp connecting the structural highs the Curone Valley, the displacement of fold axial with a seafloor basinal low, where the unconfor- plane along NE-striking faults also suggests the mity surface at the base of the Contignaco For- reactivation of those faults, which controlled the mation passes gradually to a correlative deposition of the Ranzano Formation during the conformity. A second pulse of gravitational late Priabonian – Rupelian stage. At the regional instability occurred in the Burdigalian – Lan- scale, this stage is related to the N-S shortening ghian(?) as suggested by the mass-transport that caused a further northward migration of the emplacement of the Monte Lisone Chaotic Com- Apenninic frontal thrust (Faulting Stage D of plex. This tectonic stage was definitively sealed Festa et al., 2005; see also Artoni et al., 2010; by the Monte Vallassa Sandstone, which uncon- Festa, 2011; Mosca et al., 2010). Finally, the N- formably overlain faults associated with the striking Schizzola valley fault, which cuts the MVDZ (Figure 5(a,b)). At the regional scale, this SDDZ, probably represents a fault system younger stage is related to the migration toward NE of the than Early Pliocene as suggested by Perotti and Apenninic thrust front (Ligurian Phase III of Vercesi (1991) and Vercesi et al. (2015).

Mutti et al., 1995; Faulting Stage B of Festa et al., 2005, 2013; Piana, 2000; see also Piazza et al., 2016). Software . Late Serravallian – Tortonian(?): The NNW-ver- The geological map and map inclusions were digitized ging migration of BST, ENE-striking, and the and edited with Adobe Illustrator CC. deformation of the Epiligurian Succession with

ENE-directed fold axis, well agree with this tec- tonic stage. The left-lateral NW-striking faults, Acknowledgements which displace the lateral continuity of the BST, We thank G. Balestro, S. De Caroli, G. Codegone, L. Papani probably worked as transfer faults (Figure 5(a,b)) and A. Succo for passionate discussions on the geology of the as documented to the south of the study area for studied sector, and we would like to express our sincere the left-lateral Sarizzola Fault Zone, NW-striking, thanks to H. Apps, A. Artoni, and L. Pandolfi for their con- which cuts the Vill alvernia – Varzi Fault Zone structive and thorough reviews and useful comments, from (see Festa, Fioraso, et al., 2015). At the regional which we have benefited greatly in revising both our manu- script and geological map. scale, this tectonic stage is related to the north- westward propagation of Apenninic thrust system (e.g. Festa et al., 2005; Mosca et al., 2010; Piana, Funding 2000), during which left-lateral NW-faults rep- Research has been supported by ‘Ricerca Locale (ex 60%) resented transfer faults (Costa, 2003). Although 2013, 2014, 2015, 2016’ of the Università degli Studi di Tor- only minor evidences are preserved in the mapped ino (grants to A. Festa), and the Italian Ministry of area, the uppermost temporal constrain to this University and Research (Cofin-PRIN 2010/2011, grants n. tectonic stage is represented by the unconformity 2010AZR98L_002 – G.A. Pini, to A. Festa). at the base of the late Messinian Valle Versa Chaotic Complex immediately to the south

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Tectonic evolution of the Central-Southern Apennines, Freiburg: International Association of Sedimentologists Italy. Geological Society of America Special Paper 469, Special Publication 8, Blackwell. pp. 58, accompanying by a CD-ROM including the Schmid, S. M., Kissling, E., Diehl, T., van Hinsbergen, D. J. J., “Geological-Structural Map of the Central-Southern & Molli, G. (2017). Ivrea mantle wedge, arc of the Western Apennines (Italy)” at 1:250.000 scale, Sheets 1 and 2. Alps, and kinematic evolution of the Alps–Apennines doi.org/10.1130/2010.2469 08°59' Longitude East of Greenwich (Geographic Coordinate System) 09°00' 09°01' 09°02' 09°03' 09°04' 09°05' 09°06' 09°07' 09°08' 09°09' 09°10' 11 Scientific supervision, geological editing, LEGEND cartographic and mapping editors: RAN1 s 1-2 2 3 4 CCS CTG 1-2 2 REGIONAL SCHEME p BAI Edoardo BARBERO and Andrea FESTA l D QUATERNARY DEPOSITS E. BARBERO , A. FESTA , G. FIORASO & R. CATANZARITI 4’ ANT A i n BW - Bobbio Tectonic Window A a MF - Monferrato Regional p A r Cairo Montenotte Synthem Field mapping scheme e d i CMT3 Ld OLL - Ottone-Levanto Line r d 1-2 PTF - Padane Thrust Front n ia e Rocchetta Cairo Subsynthem (CMT ). Clast-supported gravelly and gravelly-sandy fluvial deposits, fresh or slightly Edoardo BARBERO (2014-2017, Pre-Quaternary n tic s 3 MEA RFDZ - Rio Freddo Deformation Zone S weathered, covered by dm to m thick overbank deposits, consisting of sands with planar to wavy lamination or massive silts 3 in e succession) SVZ - Sestri-Voltaggio Zone a 2 e s and silty sands (Holocene - Present) Ld Andrea FESTA (2006-2015, Pre-Quaternary succession) TH - Torino Hill GEOLOGICAL MAP Ld 66 Tyrrhenian 3 VVL - Villalvernia-Varzi Line CMT 84 Gianfranco FIORASO (2010-2015, Quaternary MEA Merana Synthem 3 ANT Sea 3 succession) Main tectonic boundary Pian del Gatto Subsynthem (MEA ). Fluvial deposits consisting of clast-supported sandy-gravels, moderately weathered, MPP Main thrust fault Ionian 3 57 1 Ld CTG Sea N locally covered by m thick (3-4 m) overbank of sandy silty sediments with planar lamination. Deposits form terraces perched CTG 44 Main buried tectonic boundary CMT3 RAN1 Calcareous nannofossils analyses 10-20 m above the streambed of the Staffora and Curone Rivers (Late Pleistocene) OF THE CURONE AND STAFFORA VALLEYS 44 4 Main buried thrust fault 52 54 48 88 s MEA MCS Rita CATANZARITI (2015-2016) Main buried normal fault la 2 MEA t 250 km 3 Map A Madonna della Neve Subsynthem (MEA ). Fluvial deposits consisting of clast-supported sandy gravels, moderately 77 2 BAI Ld 1 - Dipartimento di Fisica e Scienze 08°00’ E 09°00’ E ANT 20 weathered. Deposits form terraces perched 25 m above the streambed of the Staffora and Curone Rivers (Late Pleistocene) 87 51 RAN della Terra Università di Ferrara (Northern Apennines, Italy) Ld 1 Via Saragat, 1

51’00’’ Ld 441222 Ferrara (Italy) PTF Piandendice Synthem (PND) 3’ 63 RAN1 PND

44° Ld e-mail: [email protected] Pavia Scala 1:20.000 MPP PO PLAIN Fluvial deposits consisting of clast-supported sandy-gravels, highly weathered, permeated by veinlets of iron-manganese MF 44° CCS 1 RFDZ oxides. Deposits form terraces perched 30-75 m above the streambed of the Staffora, Curone and Nizza Rivers (Middle m 250 0 500 1.000 1.500 2.000 2.500 m MCS 2 - Dipartimento di Scienze della Terra TH 11 MEA BAI Ld Piacenza Pleistocene) 51’00’’ 35 3 RAN Università di Torino 69 1 56 Via Valperga Caluso, 35 Torino PTF 44 Voghera Unconformity

10125 Torino (Italy) N 45°00’ MPP1 RAN ANT e-mail: [email protected] 1a 1b Ld Alessandria PRE-QUATERNARY SUCCESSION 12 CTG Map AST 31 79 47 FAA AVV 62 38 3 - Istituto di Geoscienze e Georisorse Asti Sandstone (AST). Yellowish homogeneous sands and silts, compacted and locally cemented, with slightly planar-parallel 85 CNR - Consiglio Nazionale delle VVL 70 82 21 Ld bedding and occurrence of ripple structures. Thickness: > 50 m (Late Pliocene) 57 2’ BAI 63 RAN Ricerche 33 58 3a 13 MPP1 Via Valperga Caluso, 35 FAA N 30 23 10125 Torino (Italy) BW Argille Azzurre (FAA). Brownish-to greyish fine-grained sands, locally with planar parallel bedding, interbedded by dm thick CCS AVV AVV 56 37 24 RAN3 63 CTV RAN e-mail: [email protected] levels of greyish marly-clays and medium-to coarse grained sandstones. Fossil remains consist of gasteropods, bivalves, 75 MPP 3 Antola AST 75 2 31 84 63 37 RAN Tertiary brachiopods, echinoids, and plant fragments. Thickness: 100-150 m (Early Pliocene) 61 86 ANT 2 77 MPP1 74 4 - Istituto di Geoscienze e N Piedmont OLL AVI BAI Ld Ld Unconformity 89 66 65 Ld Georisorse CNR - Consiglio Basin

44°30’ N 44°30’ Voltri Ld 79 Nazionale delle Ricerche Gessoso - Solfifera Group CMT3 73 31 65 MPP1 SVZ CCS 24 61 Ld Via Moruzzi, 1 Cassano Spinola Conglomerate (CCS). Matrix-to clast supported conglomerates, in tabular to lenticular up to m thick beds, 38 AVV 49 BAI 56124 Pisa (Italy) AVI AVV Ld 19 48 e-mail: [email protected] Genova alternating with yellowish-to brownish well-sorted sandstones. Fossil remains consist of plant fragments. Thickness: 0-50 m Ld RAN RAN2 ANT RAN MPP Ld 3 (late Messinian) 3 2 13 25 km MEA 19 36 Ld Ligurian Sea Gottero 3 51 Unconformity Ld 39 MEA 29 3 Ld Pliocene - Quaternary LIGURIAN - PIEDMONT OCEAN 49 MPP1 CTV Ld 34 Ld 34 Ld deposits Ligurian Units (N-Apennines) Valle Versa Chaotic Complex (CTV). Chaotic complex with block-in-matrix fabric, consisting of polymictic blocks, dm to 52 BAI MPP Ld Ld 43 1 Epiligurian Units and Tertiary Antola Unit some m in size, randomly distributed within clayey marls with brecciated texture. Blocks are composed of vuggy dolomitic Ld Piedmont Basin limestones and brecciated limestones. Thickness: 0-30 m (late Messinian) 31 40 External Ligurian Units MCS MEA CMT 61 BAI a 3 3 ADRIA PLATE (a: blocks of ophiolite) 31 Unconformity 21 58 Internal Ligurian Units SCB 39 71 26 Northern Apennines 30 41 38 Mesozoic-Cenozoic a (a: ophiolite) SCB 39 83 EPILIGURIAN UNITS Ld RAN2 sedimentary cover 25 Piedmont Units (Alps) RAN2a (Subligurian and Tuscan Units) Bismantova Group MEA Ld Blueschist-facies 3 61 Ld 21 Ld 45 Ld Ld ophiolites Monte Vallassa Sandstone (AMV). Yellowish and fossiliferous arenites, in dm thick beds, locally with cross-bedding, passing MCS AVI 57 Ld AMV CTV Ld Ld CTG a Eclogite-facies to microconglomerates. Fossil content consists of rodolites of red algae, bryozoan, corals, echinides, lamellibranchies (Pectini- SCB 75 metasediments (a), 50’00’’ Ld b AVV SCB 47 34 62 dae sp.), brachiopods (Terebratula sp.), and gastropods. The basal part of the succession is characterized by a discontinuous 29 Ld ophiolites (b) 44° horizon of conglomerates with lithodome holes, representing a trasgressive lag deposits. Thickness: >150 m (Langhian? - SCB RAN3 Ld

EUROPEAN PLATE 44° 56 27 19 Ld MPP1 RAN 49 Serravallian?) Ld CMT3 3a Undifferentiated 64 50’00’’ AVV MEA3 Western Alps Units Unconformity CPP 67 AVI AVV 30 48 Ld CML 61 BAI RAN Ld MPP 2 MPP2 Monte Lisone Chaotic Complex (CML). Chaotic complex with block-in-matrix fabric (olistostrome), consisting of tabular to 20 43 2 55 Ld 68 31 MCS 45 irregular shaped blocks, dm in size, randomly distributed within a clayey marl matrix. Blocks are mainly composed of 31 52 Ld RAN SCB 2 marly-limestones and calcarenites sourced from Helmintoides Flysch. Thickness: 10-30 m (late Burdigalian - Langhian) ∑ 20 27 20 40 45 MCS MPP RAN 45 4 24 Unconformity AVV ∑ Ld 2 2a 59 64 12 1 RAN MPP γ 2 RAN 36 2 44 ap 33 47 3a RAN CTG 1’ 70 20 3 Contignaco Formation (CTG). Whitish calcareous marls and greysh-to greenish silty marls, interbedded by silicified marls 23 32 66 RAN 30 RAN 3 with brownish-orange weathered surfaces. Locally (Case Cucchi) the basal part of the succession is characterized by volcano- 23 SCB 72 RAN Ld 3 cc CPP 29 CPP 73 3a clastic, cinerite beds and slumping structures. Fossil content consists of sponge spicula, radiolarians, rare planktonic foramin- SCB Ld 63 MEA ifera and pteropods. Thickness: 0-200 m (late Aquitanian - Burdigalian) 25 39 40 3 MCS Ld AVI ∑ cc Unconformity 34 23 Γ MCS 65 MEA AVV ∑ 88 3 27 Ld 71 ANT Antognola Formation (ANT). Grayish-to brownish silty-marls intercalated with dm thick graded and laminated sandstones AVV RAN3a ANT RAN 46 ∑ 1b (ANT ). Plaktonic foraminifera assemblage characterized by Catapsydraz dissimilis, Paragloborotalia opima opima, Globigeri- 40 3a cc 51 63 51 1a CMT 1a noides primordius. Thickness: >200 m (late Rupelian - Aquitanian). Lenticular chaotic-rock bodies or olistostromes (”Val ap 45 57 53 3 ANT MCS 21 CTG 1b CTG Tiepido – Canossa Argillaceous Breccias”, ANT ), up to 50-60 m thick, are interbedded within the unit (late Chattian). 19 SCB AVI 49 1b 1b Ld They consist of highly disrupted polymictic assemblage of blocks sourced from the “Basal Complex” of the External Ligurian 43 Ld 34 CMT3 38 39 RAN Units (Argille Varicolori, Scabiazza Sandstone, Palombini Shale), Monte Cassio Flysch, and Epiligurian Units (Monte Piano Marls 30 Ld 2 PND ANT MCS and Ranzano Formation). Ld 69 21 38 34 MEA PND Unconformity MCS 31 60 RAN 30 3 MEA3 7 Ld 3 31 51 Ld Ld Ld Ld MPP 56 71 32 Ranzano Formation (RAN) 40 Ld 2 32 41 31 57 45 31 CMT RAN3 Varano de’ Melegari Member (RAN ). Alternating dark gray pelites and light gray arenites (a/p 1) in tabular beds, intercalat- AVI 35 Ld 36 3 39 3 ≤ 21 54 73 51 ANT 70 1b 3b ed by thick lenticular beds (RAN3b) of pelitic-arenitic intervals (a/p>1). Lithic component of pelites sourced from Helmintoides 42 MCS AVV Flysch of External Ligurian Units. The base of the member is characterized by lenticular bodies of conglomerates and 29 66 41 Ld RAN3a 43 19 25 coarse-grained sandstones (RAN ), tens of m thick (up to 90 m), with clasts sourced from sedimentary successions of 24 3a 3a 40 MEA3 78 60 41 PND 40 External Ligurian Units. Thickness: 100-500 m (middle – late Rupelian)

’ 57 49 50 80 51 RAN RAN3 30 25 2 51 32 Val Pessola Member (RAN2). Tabular beds, dm thick, of grayish-to green pelite, alternating with greenish arenites (a/p≤1) and 49’00’ RAN 53 RAN2 45 70 3b 30 77 PND 2a intercalated by conglomerates, microconglomerates and coarse-grained arenitic intervals with thick lenticular beds (RAN2a). 44° 41 MPP 37 Ld 1 79 Lithic composition of arenites sourced from denudation of ophiolitic Ligurian Units and related sedimentary covers. Thickness: 36 39 21 44° 28 33 Ld 60 22 CMT3 0-500 m (late Priabonian - early Rupelian)

67 49’00’’ 46 AVI 51 RAN 69 3 30 RAN AVI 65 CMT AMV 1 Pizzo d’Oca Member (RAN ). Tabular beds, decimeters thick, of grayish-to whitish arenites, alternating with pelites (a/p<1) 61 3 1 RAN MPP 39 interbedded by conglomerates and coarse-grained arenitic intervals with thick lenticular beds (RAN1a). Lithic composition of 3a RAN 2 43 3a RAN 41 1a arenites is characterized by fragments of metamorphic and magmatic continental-derived rocks. Thickness: 0-100 m (late 3 CTG RAN3 51 Priabonian) 33 ANT 46 38 32 CMT Unconformity RAN3a 3 MMP 43 CTG 21 Monte Piano Marls (MMP). Pinkish-to reddish marls and clayey marls (MMP ), passing upward to gray-to greenish calcare- 61 1 2 ous marls and badly stratified marls (MMP ) with abundant plaktonic foraminifera (Acrina brooki, Globigerinatheka mexicana, Ld 2 1 Turborotalia cerroazulensis). Thickness: 0-80 m (Middle – Late Eocene) 71 30 ANT 25 RAN 35 50 MEA 24 Ld 3a MPP MEA 20 3 34 2 3 BAI Baiso Argillaceous Breccias (BAI). Lenticular chaotic bodies (olistostromes) consisting of highly disrupted polymictic assem- 37 34 22 2 MEA 31 blage of blocks sourced from the “Basal Complex” of External Ligurian Units (Argille Varicolori, Scabiazza Sandstone, Palombi- 3 ANT 75 MEA 1a ni Shale) and Monte Cassio Flysch, embedded in a brecciated argillaceous matrix. Locally (S of Sala Superiore) this unit shows 18 40 RAN3a 3 Ld lateral heteropy with Monte Piano Marls. Thickness 20-100 m (Lutezian – Bartonian) Ld AMV RAN 21 32 Unconformity 3 10 24 Ld 20 19 BAI RAN 50 Ld EXTERNAL LIGURIAN UNITS 3a 1 59 21 47 Cassio Unit RAN 35 AVI 2 CMT 41 25 3 32 61 Viano Clay (VIA). Clayey-marls alternating with brownish-to reddish pelites, fine-grained arenites and pinkish calcarenites in 25 45 28 41 20 cm-to dm thick beds. Grayish calcareous turbidites and calcarenites, in dm to one m thick beds, are interbedded in the basal RAN 27 63 19 3 Ld 83 part of the succession. Thickness: 250-300 m (late Maastrichtian - Late Paleocene). CC25/26, NP9-CNP11 MEA 31 82 23 61 47 RAN2 2 39 AVI 45 47 MCS 26 Ld 30 73 48 RAN 80 Monte Cassio Flysch (MCS). Thick grayish to light brown marly-calcareous turbidites made of siliciclastic calcarenites, marls, 34 75 3 17 RAN ANT Ld calcareous marls, and marly-shales alternating with decimeters beds of clayey-marls, in dm to m thick beds (Helmintoides 2 25 ANT ANT 88 60 ANT CTG CMT 1b Flysch Auct.). Thickness: 250-400 m (late Campanian). CC21/23 20 53 Ld 3 22 38 PND 25 MEA 35 MEA 20 AVV Argille Varicolori (AVV). Chaotic rock unit (broken formation) of red, green and grayish claystones and shalestones with 2 RAN 51 3 Ld 75 3b RAN3b Ld 48’00’’ block-in-matrix fabric. The matrix consists of alternating cm-dm layered deformed beds affected by a pervasive scaly cleavage. 68 CML RAN 49 72 AVV1 44° RAN 3b The blocks, dm to m in size, are made of limestones, sandstones and manganiferous siltstones, tabular to lenticular in shape. 20 2 40

50 RAN 44° CMT 2 48 Thickness: about 150 m (Santonian – Campanian). NW of Barca, a lenticular body, about 100 m thick and hundreds of m 26 30 39 3 RAN ANT long, of conglomerates passing upward to coarse-grained arenites and microconglomerates is interbedded within the Argille 48’00’’ 2 41 Ld 1b MEA 31 80 25 2 Varicolori (Salti del Diavolo Conglomerate, AVV1, Campanian, CC16/19). Clasts consists of prevailing carbonate rocks and 51 MEA minor micaschist, gneiss, quartzite, granulite, pinkish granite and diorite. 20 MEA3 3 41 MPP SCB MEA 1 AVI 30 3 Scabiazza Sandstone (SCB). Disrupted unit (broken formation) consisting of dm to m thick bed fragments of whitish micace- CMT RAN Ld RAN RAN 3 3 ous sandstones, embedded into a pelitic- to argillaceous matrix. Thickness: 150 – 200 m (late Albian – Santonian). CC9/14 2 35 3 CML CTG MPP BAI Ld Ld 80 54 2 45 PND MEA 69 3 GROPPALLO UNIT CPP Ld 65 CML 62 Pietra Parcellara Complex (CPP). Chaotic rock unit with a block-in-matrix fabric, consisting of “exotic” huge blocks Castello di Cross Section 3 ANT ANT 1b ∑ (olistoliths) randomly distributed in a sedimentary matrix (olistostrome). The blocks, up to hundreds of m in size, are made of Val Curone Pozzol Groppo 50 66 ANT 22 serpentinite (∑), grabbros (Γ), Calpionella Limestone (cc), Palombini Shale (ap), granitoids (γ) and not mappable tens of m in ANT Γ WSW ENE W EW GroppoMPP superiore NE 1b size olistoliths of basalts and radiolarian cherts. The matrix, which consists of different lithofacies alternating without any 20 2 cc RAN 54 fromLd relevant stratigraphic order, is made of coarse-grained ophiolitic arenites (medium-to coarse-grained ophiolite dominant m 500 3a 48 500 m Ld ap RAN 85 MPP AGE Catanzariti et al., 1997 CHRONOSTRATIGRAPHIC lithoarenite), matrix-to clast-supported polymictic breccias (mainly of basalts, limestones, serpentinites, gabbros, radiolarites, RAN 3 1 3a 55 30 RAN (Ma) Fornaciari and Rio, 1996 3 γ granitoids), and varicolored argillaceous breccias. Thickness: about 150 m (early Campanian). CC18/19 Ld Epoch Sissingh, 1977 RAN3a CTG STAGE SCHEME RAN PERIOD 2 BAI 36 Martini, 1971 RAN 87 RAN CHRONOZONE CMT 2 RAN RAN 3 81 RAN 3 3a RAN 3a 3a >50 MPPCMT 3 RAN PIACENZ. EPILIGURIAN UNITS SYMBOLS 1 3 RAN 2 35 AST 1 RAN MEA 3 RAN 1’ 2 3 3a 38 ZANCL. Strike-slip fault (horizontal arrow

MMP 41 29 54 PLIOC. 2 MMP RAN2 MPP1 RAN RAN 5 MEA FAA ~100-150 Stratigraphic boundary a b 2 22 2 2a MESSIN. 2 indicates the movement component) MEA3 35 Ld AVI AVI 11 CCS ~50 Unconformity 82 defined (a), inferred (b) 68 76 MMP MMP TORTON. CTV ~30 RAN 2 2 MNN RAN2 2 MMP 54 AMV 10 8 910 arrow indicates the dip of fault surface MPP AVI 2 2 39 MMP BAI RAN Ld MNN7 MMP 2 2 Ld 54 a b m 0 AVI 2 MMP 0 m SERRA -VAL. MNN6 Ld 40 30 Attitude of bedding a b Thrust or reverse fault (triangles on the 1 AVI BAI Ld ANT AMV AMV AMV > 150 > 150 1b MEA > 150 c (a: normal; b: overturned; c: vertical) hanging wall) defined (a), inferred (b) MCS AVI MNN5 3 73 LAN- GHIAN arrow indicates the dip of fault surface AVI 43 AVI Ld CML CML MCS 49 Ld15 MNN4aANT 10-30 b MCS 39 Ld 1b 40 Attitude of bedding of isolated a Undetermined fault 75 MNN3 MEA 28 Ld 3 blocks within the CPP defined (a), inferred (b) 20 BURDIGA- LIAN b MPP ANT1b 49 MNN2 a arrow indicates the dip of fault surface 2 EARLY MIDDLE LATE AVI Ld A- CTG CTG 30 3 ~ 200 10-30 ~ 200 42 Ld Ld Landslide deposits (Ld) a MPP QU IT Buried fault thrust or reverse (a), normal

68 A NIAN 1 35 MNN1 b 47’00’’ 40 86 RAN3 ab c d or strike-slip (b) 25 63 ANT ANT a b 44° ANT MNP25 1b 1b Alluvial fan 1 Trace of fold axial planes; anticline (1), 44° LATE > 200 81 ANT ANT > 200 ANT a b CHATTIAN 54 syncline (2); defined (a), inferred (b) 47’00’’ AVI 60 AMV > 200 2 CMT 35 San Desiderio MNP24 a b Normal fault (ticks on the hanging wall) San Lorenzo Cross3 Section 3 30 SSW Barca Zebedassi NNE SW C.na Galuzia NE LIAN defined (a), inferred (b) 1 1’ NNW SSE NW SE MNP23 ~500 Trace of geological cross-section T. Curone CTG San Giovanni RAN3 ~400 RAN3 60 arrow indicates the dip of fault surface OLIGOCENE MIOCENE 34 EARLY MNP22 RAN2 ~200 SAV m 500 500 m m 500 74 San Desiderio Deformation Zone 500 m RUP E MNP21b RAN2 RAN the base of MCS MNP21a ~500 3a Tecto contact at Barca-Sala Thrust nic AVI 64 Val Ardivestra MNP20 RAN1 ~100 MMP1 35 MNP19 MMP2 ~30-50 MMP2 ~30-50 late Messinian - Early Pliocene San Desiderio Deformation Zone RAN3a RAN2 SCB MCS RIABO- 8 right-lateral faults

MMP LATE 3 50 ANT P NIAN NP18∞ 5 2 CCS CMT CTG BAI RAN STRUCTURAL SCHEME AVI MCS 3 MEA3 2 RAN1a late Serravallian - Tortonian(?) CMT3 MMP1 MMP MMP 6 2 AVV CCS 2’ 4 BAI 2 1 4’ TO- NP17∞ MMP1 MMP1 thrust and strike-slip faults ~ 30-50 40 ~ 30-50

45 RAN BAR NI AN CPP 3 1 km 1 SF CPP AVV NP16" Chattian - Early Miocene AVV CTV MCS 6 SCB ANT AVI 3 7 left-lateral and right lateral 20 7 8 Z 5 transpressive fault BAI BAI 45 DD SCB CTG 15 MIDDLE NP15* BAI S Mt. Treno m 0 MCS AVV FAA 0 m 2 Monticelli 7 SDDZ 8 late Priabonian - Rupelian m 0 3a 0 m ~ 20-100

30 EOCENE 6 extensional fault MCS AVV 3b 8 LUTE ZIAN 1 C.na Galuzia 7 45 MCS MCS 7 8 Late Cretaceous - NP14 San Desiderio ? 50 NP13 San Lorenzo 9 San Giovanni Early Eocene AVV1 CPP 8 AVV SI AN CPP MEA C.na Colombera BST thrust faults 3 MMP RAN NP12 7 ANT AVV MMP1 2 1a 9 CTG EARLY 3 7 RAN1 SCB NP11* Temporal AVV SCB BAI YP RE CASSIO UNIT BST 5 undetermined MMP NP10 Cusinasco 9 8 1 SCB CPP 55 Piumesana or reactivated NP9 Monastero 7 NP8 9 7 fault

THANE- TIAN 10 NP7NP6

LATE 8 SDDZ

LAN- NP5* Biagasco BST 9 5 6 San 60 SE DIAN NP4* Zebedassi 1 Desiderio Simplified symbol of unconformity in cross sections NP3* AVI Deformation

NI AN 7 7

EARLY Zone PALEOCENE NP 2 ~ 250-300 DA Cross Section 1 Cross Section 2 65 NP1 Barca 8 BST Castello di CC26* 5 T. Staffora Valley NNW SSE NW Serra del Monte SE Cecima Barca-Sala CC25 Pozzol Groppo Colletta TRICHTI AN Thrust

Latitude North 8 4 C.na Galuzia 1 Ca’ dell’Armarolo 70 CC24* Giarella 1 MVDZ Montemerlano MAAS Colletta 8 Vignola ANT Montemarzino T. Curone Valley 6 46’00’’ MVDZ Momperone- MMP 7 Vignola 44° Barca-Sala Thrust RAN AMV CC23* 3 ANT 1 MVDZ Deformation RAN3a RAN ANT 44° 3b RAN 2 75 6 Zone m 500 San Desiderio Deformation Zone CTG 2 500 m CC22* GROPPALLO 7 Lavasello San Ponzo NI AN 46’00’’ CTG ~ 250-400 MMP MMP2 BAI AVI MCS BAI 2 ANT CC21 Scrimignano Momperone Semola FAA AVI UNIT 7 SF ANT CC20 9 8 5 5 MCS AVI 9 6 Schizzola Latitude North 80 CC19 Continental deposits Valley Fault CCS CPP 1 5 MMP1 (Pleistocene - Present) 6 6 CAMPA 3 FAA 3b 3’ CC18 AVV1 ~150 Unconformity a b Trace of fold axial plane; RAN2 3b Serra del Monte AVV RAN ACE OUS CC17

3 MCS ~ 150 anticline (a), syncline (b) CC16 AVV Argille Azzurre and Asti Sandstone RAN NTO 3a 85 CC15 2 RAN SA -NIAN (Early - Late Pliocene) AVI 3b MCS LATE 4 Stratigraphic unconformity CCS AVV AVV MCS BAI CC14 Thickness (in meters) of Unconformity SCB NIA- Buried thrust AVV lithostratigraphic units Gessoso Solfifera Group Antognola Formation FAA CO CI AN CC13 3 CTV SCB RAN2 BAI 6 m 0 CTG 0 m (late Messinian) (late Rupelian - Aquitanian) Buried normal to 90 CC12 Unconformity strike-slip fault Biostratigtraphic data Unconformity ? MCS MMP2 RAN AVI CPP 2a BAI CC11 EPILIGURIAN UNITS AVI The mapped area is located onto the “CTR - Carta Tecnica Regionale” (this paper) and from Ranzano Formation EXTERNAL LIGURIAN UNITS CRET CPP TURONIAN Festa et al. (2015a, b) Monte Vallassa Sandstone 7 MMP MMP ~150-200 4 (late Priabonian - late Rupelian) 1 2 Regione Piemonte, at 1:10,000 scale in sections 177120, 177160, 178090, CC10 (Langhian? - Serravallian?) Cassio Unit

SCB 95 MA- SCB MCS 178130 and onto the “CTR - Carta Tecnica Regionale” Regione Lombardia, Unconformity 9 (Late Cretaceous - Late Paleocene) at 1:10,000 scale in sections B8A5, B9A1, B9B1,B9A2 and B9B2 Biostratigtraphic data Unconformity Monte Piano Marls and from literature Monte Lisone Chaotic Complex Tectonic contact NI AN CENO CC9 8 Baiso Argillaceous Breccias 5 and Contignaco Formation (Lutetian - Priabonian) Groppallo Unit Momperone - Vignola (late Aquitanian - Langhian?) 10 100 Unconformity Deformation Zone E Unconformity Unconformity (early Campanian) © Journal of Maps, 2017 ALBI- AN CC8*

08°59'Longitude East of Greenwich (Geographic Coordinate System) 09°00' 09°01' 09°02' 09°03' 09°04' 09°05' 09°06' 09°07' 09°08' 09°09' 09°10'