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

International Geology Review2010, iFirst article, 1–33

ISSN 0020-6814 print/ISSN 1938-2839 online© 2010 Taylor & FrancisDOI: 10.1080/00206810903545493http://www.informaworld.com

TIGR0020-68141938-2839International Geology Review, Vol. 1, No. 1, December 2009: pp. 0–0International Geology ReviewAnatomy of the Ligure-Piemontese subduction system: evidence from Late Cretaceous–middle Eocene convergent margin deposits in the

Northern Apennines, ItalyInternational Geology ReviewM. Marroni et al. Michele Marronia,b*, Francesca Meneghinia and Luca Pandolfia,b

aDipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy; bIstituto di Geoscienze e Georisorse, CNR, Pisa, Italy

(Accepted 7 December 2009)

In the Northern Apennines, in contrast to the Western Alps and Alpine Corsica, upperstructural levels of the Late Cretaceous–middle Eocene subduction complex are stillpreserved and well exposed. This subduction complex developed in the Ligure-Piemontese basin since the Late Cretaceous time as a consequence of convergencebetween the Eurasia and Adria plates. Representative successions of this ancientsubduction complex are well preserved in the Ligurian units of the Northern Apen-nines, where turbidite and mass-gravity deposits showing pristine stratigraphic featuresare present. Three main domains, represented by different groups of tectonic units, canbe identified, each delineating a different domain of the subduction zone. In thisarticle, we first present a brief history of geological research in the Northern Apenninesduring the last half of the twentieth century and then a comprehensive picture of thestratigraphy and tectonics of the Ligurian units. A new interpretation of the relatedtectonostratigraphic units is proposed within the conceptual modern geodynamicframework of convergent margins.

Keywords: sedimentation; tectonics; subduction; accretionary prism; ophiolites;turbidites; Late Cretaceous–middle Eocene; Northern Apennines, Italy

IntroductionThe Apennines and the Western Alps, making up the structural framework of Italy, andthe Alpine sector of the island of Corsica, are all complexes classically regarded asconstructed during a long-lived geodynamic history, developed from the Late Cretaceous–middle Eocene closure of the Jurassic Ligure-Piemontese oceanic basin up to the lateEocene–Miocene continental collision. In the Apennine belt, different from the WesternAlps and the Alpine Corsica, the superstructure of this ancient subduction complex is stillintact. This uniquely qualifies the Apennines belt as a suitable complex to investigatecomplete sections of the upper part of the Late Cretaceous–middle Eocene subductioncomplex; the latter developed since the Late Cretaceous, as a consequence of plate conver-gence in the Ligure-Piemontese basin. These successions are well preserved in the Ligurianunits of the Northern Apennines, where turbidite and mass-gravity deposits showing pris-tine stratigraphic features can be studied. The sedimentary successions of the Ligurianunits have been intensively investigated in the past, and some of the concepts of modern

*Corresponding author. Email: [email protected]

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

2 M. Marroni et al.

sedimentary geology were developed and/or have been elaborated from those studies. Forexample, field observations that led to the definition of the turbidite concept wereperformed also in the Ligurian successions (Migliorini 1933). More recently, the conceptof olistostromes as a precursor of an advancing nappe (Elter and Trevisan 1973) wasdefined based on the evidence from the Ligurian units. Therefore, Ligurian units of theNorthern Apennines represent a natural laboratory where the shallow-to-mediumstructural levels of an accretionary prism can be studied and reconstructed.

In this article, we present a historical review of the research performed during the lasthalf of the twentieth century as well as an update of the data available for the Ligurianunits. Finally, we propose new interpretations of these related deposits based on modernconcepts regarding convergent margin tectonics.

Historical picture of the studies on the Ligurian units during the last half of the twentieth centuryThe Northern Apennines and the Western Alps are both collisional belts representing theAlpine sutures between the Europe and Adria plates during the Late Cretaceous toTertiary convergence (Figure 1). Despite their development in the same geodynamicsetting, and an apparent structural continuity visible in the tectonic maps (i.e. StructuralModel of Italy, CNR-Progetto Finalizzato Geodinamica 1992), these two collisional beltsshow striking differences. For instance, although the Western Alps expose the deepstructural levels, the Northern Apennines features a tectonic history characterized by a lowrate of exhumation. As a consequence, the highest structural levels of the Northern Apenninebelt, that is, the Ligurian units, are still well preserved, as testified by the widespreadoutcrops of very low-grade and unmetamorphosed sedimentary successions, mainly in theLigurian–Emilian Apennines.

The well-exposed sedimentary sequences as well as the great range of depositsrepresented the objectives of geological studies since the end of the nineteenth century.However, the first modern geological studies, with application of the concepts of alloch-tonous nappes, can be referred to the middle of the twentieth century, when Elter (1960),Elter et al. (1961), and Giannini et al. (1962) described the Northern Apennines as anorogenic belt consisting of an imbricate stack of tectonic units. At the top of this stack,these authors identified a group of tectonic units, i.e. the Ligurian units, belonging to apalaeogeographic domain, i.e. the Ligurian domain, located W of the present-dayApennine belt. Even though the allochtony of the Ligurian units was previously proposed,for instance, by Tillmann (1926), Zaccagna (1932), Rovereto (1939), and Teichmüller(1932), it was only from the 1960s that the idea of the Northern Apennines’ main structureas an imbricate stack of tectonic units was accepted by the whole scientific community.

This idea represented a strong impulse for new research in the Northern Apennines.From the 1960s up to the 1970s, numerous articles with significant data about the age,stratigraphy, and tectonics of the sedimentary successions from the Ligurian units, includ-ing also the first characterization of the mélanges (the so-called Complessi di base) as sed-imentary deposits in most of the successions from the Ligurian unit, were published. Thestate of the art for the research of that period is well outlined in the special issue of Sedi-mentary Geology edited by Sestini (1970).

On the basis of these new data, Elter et al. (1966) and Baldacci et al. (1967) proposeda complete reconstruction of the Cretaceous palaeogeography of the Ligurian domain. Inthis reconstruction, two different areas were first outlined: the internal basin, characterizedby the Late Cretaceous Monte Gottero Sandstone and Val Lavagna Shale, and the external

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 3

Figu

re 1

.(A

) G

eody

nam

ic s

ketc

h of

the

Med

iterr

anea

n ar

ea (

mod

ified

fro

m C

arm

inat

i et a

l. 20

04).

Dar

k gr

ey: p

ost 2

0 M

a oc

eani

c cr

ust;

light

gre

y: A

lpin

eor

ogen

ic b

elt.

(B) T

ecto

nic

sket

ch m

ap o

f the

Wes

tern

Alp

s, N

orth

ern

Ape

nnin

es a

nd C

orsi

ca. T

he lo

catio

n of

the

stud

y ar

eas i

s ind

icat

ed. C

OPH

, Sch

isté

s Lus

trées

of C

orsi

ca; E

L, e

xter

nal L

igur

ian

units

; IL,

inte

rnal

Lig

uria

n un

its; O

PH, S

estri

Vol

tagg

io V

oltri

Gro

up P

iem

onte

se u

nits

; SA

B, S

outh

Alp

ine

base

men

t, in

clud

ing

Ivre

a an

d C

anav

ese

zone

s; S

AS,

Sou

th A

lpin

e se

dim

enta

ry c

over

; SZ

, Ses

ia z

one;

TM

, Ten

da M

assi

f; V

BC

, Var

isca

n B

asem

ent

of C

orsi

ca. T

he b

oxed

are

ain

dica

tes t

he lo

catio

n of

Fig

ure

7 (m

odifi

ed fr

om M

arro

ni a

nd P

ando

lfi 2

007)

.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

4 M. Marroni et al.

basin, characterized by Late Cretaceous–early Tertiary carbonate turbidites, reported asHelminthoid Flysch. The internal and external basins were separated by a ridge, known asRuga del Bracco, consisting of deformed and uplifted ophiolites (Figure 2). In the sametime span, the analysis of the relationships between tectonics and sedimentation producedsome notable definitions as chaotic complex (Abbate et al. 1970) or precursoryolistostromes (Elter and Trevisan 1973). The first term indicates a sedimentary and/ortectonic mixture of rock bodies of different size, age, and lithology set in a shaly matrix,generally associated with normal bedded deposits. The second one is referred to submarinelandslides derived from the front of an advancing nappe and sedimented within theforedeep deposits.

With the diffusion of the plate tectonic theory, the geological evolution of the NorthernApennines was reinterpreted. The first article placing the Ligurian domain in the frame ofplate tectonic theory was provided by Boccaletti et al. (1971) and represented a true mile-stone for the history of the geological studies in the Northern Apennines. This is the firstarticle where a subduction is proposed to explain the stratigraphic and tectonic features ofthe Ligurian units from the Northern Apennines. In the reconstruction proposed by Boccalettiet al. (1971), the internal and external Ligure-Piemontese basins, both characterized by aJurassic oceanic crust, are regarded as domains belonging to different geodynamicsettings, as subsequently suggested also by Baldacci et al. (1972). The internal domainwas involved in a first deformation stage (Late Cretaceous to Eocene), connected with aneast-dipping ‘alpine’ subduction, whereas the external domain was deformed successively(late Oligocene–Miocene) in a west-dipping ‘apennine’ subduction (Figure 3). This recon-struction implied a reversal of the subduction during late Eocene time. Reconstructionswith a subduction reversal have also been proposed subsequently by Haccard et al. (1972),Elter and Pertusati (1973), Grandjacquet and Haccard (1977), and Boccaletti et al. (1980),mainly differing in the age and the location of the ‘alpine’ and ‘apennine’ subductions.

A model with a single, west-dipping ‘apennine’ subduction was subsequently pro-posed by Ohnenstetter et al. (1976) and Abbate et al. (1980). Whereas Ohnenstetter et al.(1976) proposed a single subduction below the Adria plate, Abbate et al. (1980) depicted amodel where the subduction plane migrated progressively westward by multiple conver-gence zones (Figure 4). In this model, the Late Cretaceous–early Tertiary turbidites fromboth internal Ligurian (IL) and external Ligurian (EL) domains were interpreted as trenchdeposits related to the progressive migration of the deformation across the oceanic areas.

Figure 2. Proposed reconstruction of the Cretaceous palaeogeography of the Ligurian domainfollowing Elter et al. (1966).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 5

Figure 3. Proposed reconstruction (from Late Cretaceous to early Miocene) of the internal andexternal Ligure-Piemontese basins by Boccaletti et al. (1971). Schematic sequences of sectionsacross northern Corsica illustrating a model for the tertiary development of the Alps–Apennines struc-tures associated with trenches (no vertical scale). Black zone, oceanic crust; crosses, continental crust;large vertical hatched zone, upper mantle; white, asthenosphere; light stipple, ‘miogeosynclinal’ cov-ers; heavy stipple, ‘eugeosynclinal’ covers; dense vertical hatched zone: subligurian unit. 1, ApuanePalaeozoic units; 2, Massa zone; 3, Apuane autochthonous cover; 4, Tuscany nappe; 5, M. Cervarolaunit; 6, Umbro-Marchigiana zone; 7, Briançonnais and Sub-Briançonnais zone; 8, Canetolo zone;9, M. Caio unit; 10, Basal Complex of Ligurian flysches; 11, M. Cassio unit; 12, M. Spornounit; 13, Oligo-Miocene Ranzano Sequence; 14, M. Gottero unit; 15, M. Antola unit; 16, Bracco ophi-olitic unit; 17, Massiccio di Voltri ophiolitic unit; 18, Schistes lustrés unit; 19, Balagne Ligurian unit;20, Corsica autochthonous cover; 21, Po Valley post-orogenetic formations.

Western Ligurian Units

B

A

20 7

20 7 19 7 18 17 15 14 169 1013 11 13 12 8 4 8 2 3

19 18 17 15 16 1411 10 12 8 4 3sea level

Eastern Ligurian Basin Subligurian Basin

Subligurian Unit Tuscany Macigno basin

‘Scaglia’ basin

40 M.Y. (EOCENE)

25 M.Y. (Upper Oligocene–Lower Miocene)

Figure 4. Model proposed by Abbate et al. (1980) for the Alps–Apennines geodynamic systemduring the Late Cretaceous (from Abbate et al. 1980).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

6 M. Marroni et al.

The debate around these deeply different reconstructions promoted a new strong impulsefor detailed studies on the Ligurian units during the 1970s. Most of these studies focused on theJurassic ophiolites, detected at the base or as slide-blocks into the sedimentary basins in boththe internal and external domains. Fundamental is the paper by Decandia and Elter (1969) thatfirst interpreted the ophiolites of the Northern Apennines as a fossil Jurassic oceanic crust,located at the base of the sedimentary successions of the Ligurian domains. The features of theophiolites were analysed in numerous articles (Abbate et al. 1970; Bezzi and Piccardo 1970;Bortolotti and Passerini 1970; Decandia and Elter 1972; Gianelli and Principi 1974; Galbiati1976; Piccardo 1976; Abbate et al. 1980; Beccaluva et al. 1980; Cortesogno et al. 1987 andmany others) that proposed a detailed picture of the stratigraphy and the petrology of the ophi-olites as well as their comparison with the crust of the present-day oceanic basins.

Another fundamental contribution to the geological investigations of the Northern Apen-nines sedimentary succession is presented in the article by Mutti and Ricci Lucchi (1972),who applied the facies association concept to the analyses of the turbidites from the Ligurianunits. On the same lines, the articles by Aiello et al. (1977), Martini et al. (1978), Sagri(1979, 1980), Casnedi (1982), Nilsen and Abbate (1983–1984), and many others describedthe sedimentological features of the turbidite deposits of both the IL and EL units. Anothercrucial contribution was provided by Pertusati and Horremberger (1975), who first appliedthe techniques of structural geology to the successions of IL units.

The first articles interpreting the Ligurian units as remnants of an accretionary prismare those by Treves (1984) and Principi and Treves (1984), where, for the first time, thesedimentation and the deformation of the sedimentary deposits are discussed according tothe data from modern subduction zones. The proposed model considers the deformeddeposits with different ages as sediments accreted at different time in an accretionaryprism developed in a westward subduction zone (Figure 5).

Several contributions followed Treves (1984) and Principi and Treves (1984), in whichfurther analyses of the Ligurian successions and the reconstruction of the structural historyof the IL units provided clear evidence that the deformation is coherent with an involvementof sediments in an accretionary prism setting (Van Wamel et al. 1985; Van Zupthen et al.1985; Meccheri et al. 1986; Marroni et al. 1988; Marroni 1991; Marroni et al. 2004; Hooger-duijn Strating 1994; Leoni et al. 1996; Marroni and Pandolfi 1996; Ducci et al. 1997).

In addition, calcareous nannofossil biostratigraphic analyses have provided a refiningof the age for most of the formations of the Ligurian sedimentary successions (Rio andVilla 1983, 1987; Rio et al. 1983; Marroni and Perilli 1988, 1990; Villa 1991; Cobianchiand Villa 1992; Marroni et al. 1992; Cobianchi et al. 1994; Gardin et al. 1994).

More recently, the finding by different authors of a tight association betweenophiolites and fragments of the lower and upper continental crust in sedimentary mélangesallowed refinement of the configuration of the EL and IL domains. Although the IL unitsderived from an oceanic basin, the EL domain can be divided into two areas: the western-most domain characterized by an ocean–continent transition crust consisting of a subcon-tinental mantle topped by continental extensional allochthonous, and the easternmostdomain characterized by a thinned, continental crust (Marroni and Tribuzio; 1996; Molli1996; Montanini 1997; Marroni et al. 1998, 2001; Montanini and Tribuzio 2001; Piccardoet al. 1990, 2002, 2004).

The improvement of the geological knowledge of the Ligurian units stimulated newgeodynamic models for the closure of the oceanic basin in the Late Cretaceous–earlyTertiary time span. Most of these models, as for instance those of Bettelli et al. (1989),Elter and Marroni (1991), Castellarin (1992), Marroni and Treves (1998), Vescovi et al.(1999), and Laubscher (1988, 1991), proposed a deformation of the Ligurian units in an

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 7

oblique subduction setting, where strike-slip faults perpendicular and/or parallel to the beltstrike were active from the intraoceanic subduction up to continental collision.

In the last 10 years, further contributions on both structural (Pini 1999; Corsi et al.2001; Ellero et al. 2001; Bettelli and Vannucchi 2003; Marroni et al. 2004; Levi et al.2006; Meneghini et al. 2007; Dellisanti et al. 2008) and stratigraphic features (Marroniand Pandolfi 2001; Zuffa et al. 2002; Argnani et al. 2004; Bracciali et al. 2007) have beenpublished. Contemporaneously, several models of pre- (Marroni et al. 2001; Piccardo et al.2004; Principi et al. 2004; Marroni and Pandolfi 2007) and syn-convergence evolution(Daniele and Plesi 2000; Marroni et al. 2002; Del Castello et al. 2005; Molli et al. 2006;Nirta et al. 2007; Molli 2008; Vignaroli et al. 2008) have been proposed. The various syn-convergence models mainly debate the Late Cretaceous–early Tertiary dipping of the

Figure 5. Model proposed by Principi and Treves (1984) for the Alps–Apennines geodynamic sys-tem during the Late Cretaceous–early Miocene time span (modified from Principi and Treves 1984).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

8 M. Marroni et al.

subduction by proposing different solutions. However, the problem is still open and repre-sents the target of future research.

The Ligurian units of the Northern Apennines: the state of artGeological backgroundThe Ligurian units crop out with good continuity in the Ligurian–Emilian Apennines.Therefore, the data reported in this article refer to this area, although extensive out-crops of Ligurian units occur also in Southern Tuscany (Nirta et al. 2007 and quotedreferences). The Ligurian units consist of an assemblage of tectonic slices interpretedas tectonic fragments of a Jurassic oceanic area, i.e. the Ligure-Piemontese basin, andits transition to the continental margin. During Jurassic time, this basin was locatedbetween the Adria plate, to the SE, and the Europe plate, which included at this timealso the Corsica–Sardinia microplates, to the NW (Figure 6).

According to the scheme proposed by Elter et al. (1966), the Ligurian units can bedivided into two main groups, the IL and EL units, on the basis of their structural andstratigraphic features. The IL units include a Jurassic ophiolite sequence, still preserved atthe base of a sedimentary succession characterized by mainly siliciclastic turbidites ofLate Cretaceous–early Palaeocene age. In contrast, the EL units are characterized by thewidespread occurrence of the Late Cretaceous carbonate Helminthoid Flysch. Despite theubiquitous occurrence of Late Cretaceous Helminthoid Flysch, the EL units have beenfurther subdivided by Marroni et al. (2001), according to the lithostratigraphic features oftheir basal complexes. The first EL group (‘western successions’) includes all the succes-sions characterized by the occurrence of sedimentary mélanges with both oceanic andcontinental slide-blocks, whereas the second group (‘eastern successions’) displayssuccessions showing a Triassic–Jurassic sedimentary base derived only from the thinned

Figure 6. Geodynamic sketch of the Tethyan domain during the Jurassic time (modified afterCavazza et al. 2004).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 9

Adria continental margin. According to these features, the first group is considered to beplaced ‘oceanward’, near the Ligure-Piemontese oceanic domain, whereas the secondgroup can be located ‘continentward’ at the distal edge of the Adria continental margin(Marroni and Pandolfi 2007 and references therein).

In summary, three groups can be distinguished into the Ligurian units, hereafterreferred to and described as IL, ‘oceanward’ western EL (WEL) and ‘continentward’ east-ern EL (EEL) units (Figure 7). Each group of units is representative of a specific palaeoge-ographical domain and, hence, records a different sedimentary history.

The internal Ligurian unitsThe IL units are arranged in a stack of tectonic units cropping out in the LigurianApennines, from the Sestri-Voltaggio line to the Ottone-Levanto-Carrara line (Figure 7).Along the N–S trending Sestri-Voltaggio line, these units are juxtaposed against the VoltriGroup, represented by Jurassic ophiolite sequences and related sedimentary cover,metamorphosed up to eclogite facies. The Sestri-Voltaggio line has been regarded as aneast-dipping, low-angle normal fault of early Tertiary age successively reworked in theOligo–Miocene time (Hoogerduijn Strating 1994). Very recently, Capponi et al. (2009)and Federico et al. (2009) have provided evidence for a dextral transpression along theSestri-Voltaggio line during the Oligo–Miocene, interpreted as related to the indenter ofAdria into the Western Alps arc. Despite the different interpretations, a pressure gap ofabout 8 kbars can be detected across the Sestri-Voltaggio line between the Voltri Groupand the IL units. Elsewhere in the Ligurian Apennines, the IL units are thrust over the ELones along the Ottone-Levanto-Carrara line, a steep tectonic surface, interpreted as a pre-Oligocene east-verging thrust by Elter and Pertusati (1973). However, Elter and Marroni(1991) and Marroni and Treves (1998) proposed a different interpretation of this line as asinistral strike-slip fault, developed during the northwestward indenter of the Adria plate.The IL units, as well as the adjacent alpine units, are unconformably overlain by post-orogenic succession of the Tertiary Piedmont Basin whose older deposits are mainlyrepresented by the late Eocene Monte Piano Marls and by the early Oligocene,continental/marine conglomerates (Mutti et al. 1995).

The group of the IL units includes several units known as, from SE to NW, Colli-Tavarone (including Lizza-Serò), Bracco-Val Graveglia, Gottero, Due Ponti, Vermallo,Portello, Cravasco/Voltaggio and Monte Figogna units. Despite the complexity derivedfrom a great number of local names, all these units are quite homogeneous from a strati-graphic point of view. In fact, all these units contain part of a general succession thatconsists of a Jurassic ophiolite sequence capped by the Middle Jurassic/early Palaeocenesedimentary cover.

A stratigraphic log of the IL succession (Figure 8) can be fully reconstructed by theintegration of data available from the different tectonic units. The ophiolites are character-ized by a reduced sequence, not thicker than 1 km, consisting of a basement made up ofmantle lherzolites, intruded by gabbros and covered by a volcano–sedimentary complex,where sedimentary breccias, basaltic flows and radiolarites are complexly intermixed(Abbate et al. 1980 and quoted references). This stratigraphy has been interpreted asrepresentative of an ophiolite sequence developed into a slow-spreading ridge (Treves andHarper 1994 and quoted references). The ophiolite sequence is capped by pelagic/hemipelagicdeposits represented by Radiolarite Formation (Callovian–Tithonian), CalpionellaLimestone (Berriasian-Valanginian) and Palombini Shale (Valanginian–Santonian). TheRadiolarite Formation mainly derived from the reworking of pelagic siliceous ooze by

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

10 M. Marroni et al.

Figu

re 7

.Te

cton

ic s

ketc

h m

ap o

f the

Nor

ther

n A

penn

ines

with

inte

rpre

tativ

e cr

oss-

sect

ion.

Inse

t: EL

, ext

erna

l Lig

uria

n un

its; E

MS,

Epi

mes

oalp

ine

succ

essi

ons;

IL, i

nter

nal L

igur

ian

units

; PP,

Plio

-Ple

isto

cene

dep

osits

; TU

, Tus

can

and

Um

bria

n un

its. T

he lo

catio

n of

the

geol

ogic

al se

ctio

n of

Fig

ure

9 is

indi

cate

d as

A–A

’.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 11

turbidites and oceanic bottom currents, whereas the Calpionella Limestone and the Palom-bini Shale derived from distal carbonatic and mixed siliciclastic-carbonatic turbidites,mainly reworking a source area located in the uppermost part of the Europe/Corsicacontinental margin (Pandolfi 1997; Bracciali et al. 2007). The Palombini Shale gradesupward to siliciclastic turbidites, ranging from Campanian to early Palaeocene (theManganesiferi Shale, the Monte Verzi Marl and the Zonati Shale, which form the ValLavagna Shale Group, the Ronco Formation, the Canale Formation, and the MonteGottero Sandstone), interpreted as a complex turbidite fan system fed by the Europe–Cor-sica continental margin (Nilsen and Abbate 1983–1984). The Manganesiferi Shale (earlyCampanian) is composed of siliciclastic, coarsening-upward basin plain turbidites andgrades up to mixed siliciclastic–carbonatic turbidites known as Monte Verzi Marl (early tolate Campanian). This formation is represented by siliciclastic basin plain turbidites inter-bedded with carbonatic megaturbidites. The upper part of the turbidite system is an overall

Figure 8. Reconstruction of the succession of the internal Ligurian units (redrawn from Marroniand Pandolfi 2007). Details of the ophiolite sequences are shown in the boxed areas.D

ownloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

12 M. Marroni et al.

siliciclastic sequence showing a thickening and coarsening upward trend, represented bythe Zonati Shale (late Campanian–early Maastrichtian) and the Monte Gottero Sandstone(early Maastrichtian–early Palaeocene). The Zonati Shale, which can be correlated withthe Ronco Formation and the Canale Formation, is made by thin-bedded turbidites,interpreted as basin plain deposits, and grades upward to the Monte Gottero Sandstone,composed of coarse-grained siliciclastic turbidites and interpreted as the proximal portionof the deep-water fan. According to Abbate and Sagri (1982), Nilsen and Abbate (1983–1984) and Pandolfi (1997), the turbidite sequences recognizable in the IL succession arecharacterized by turbiditic facies indicative of a connection between continental marginand deep-sea deposits. The arenites from Val Lavagna Shale Group, Gottero Sandstone,and Bocco Shale are arkoses and subarkoses characterized by an almost completesiliciclastic framework and by a metamorphiclastic composition of the fine-grained lithicfragments (Valloni and Zuffa 1984; van de Kamp and Leake 1995; Pandolfi 1997). Thearenite framework is dominated by the presence of mono- and polycrystalline quartz,plagioclase, and K-feldspar. Lithic fragments of volcanic nature are common and includeporphyritic rhyolite and dacite fragments. Intrusive coarse-grained fragments such asgranitoids are also common. Metamorphic rock fragments include low-grade schists andmicaschists. Carbonate extrabasinal fragments are scarce and they are represented byoolitic and peloidic grainstones and mudstones. According to these data, the source area ofthe sedimentary cover of the IL units can be placed on the upper part of a continental crustbelonging to the Corsica–Europe continental margin (Valloni and Zuffa 1984).

The youngest formation of the IL units is represented by the early Palaeocene coarse-grained deposits known as the Bocco Shale (see also Giaiette Shale or Colli/Tavaroneformations), characterized by the occurrence of thin-bedded turbidites, where ophiolite-bearingslide, debris flow, and high-density turbidity current-derived deposits are imbedded. Faciesanalysis and provenance studies indicate, for the last deposits, a formation by small andscarcely evolved flows that reworked a typical oceanic lithosphere and its sedimentarycover. These sedimentary processes can be interpreted as the downcurrent evolution ofsubmarine landslides developed along a steep slope. The thin-bedded turbidites are insteadindicative of a different facies association derived from more evolved low-density turbid-ity currents. The composition and the stratigraphic features of the thin-bedded turbiditesindicate a source area different from that of the slide and debris flow deposits. Particu-larly, the source was the same area that supplied the Gottero Sandstone and the ValLavagna Shale, i.e. the uppermost part of a continental crust. It is worth to noting that, inall the investigated area, the Bocco Shale lies on top of the sedimentary succession, fromthe Gottero Sandstone to the Palombini Shale, by means of a well-preserved unconform-ity. Marroni and Pandolfi (2001) have interpreted this formation as lower slope and trenchdeposits related to the frontal tectonic erosion of the accretionary prism.

On the whole, the described sedimentological features of this succession, in particularthe transition from pelagic to turbidite deposits, have been interpreted as reflecting thetrenchward motion of an area belonging to the Ligure-Piemontese oceanic lithosphere.

This interpretation is coherent with the pre-Oligocene (Di Biase et al. 1997) polyphasedeformation history described and summarized for the IL units by several authors(Meneghini et al. 2007 and quoted references) and interpreted as achieved during progres-sive underthrusting (D1a), underplating (D1b and D1c), and later exhumation (D2a andD2b) in an accretionary prism. The folding phase related to the main underplating event(D1b) is predated by extensive dewatering and rapid fluid escape (D1a event) andfollowed by the development of shear zones (D1c). The D1b folds show similar geometryand westward vergence, associated with a slaty cleavage developed under P/T conditions

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 13

ranging from to low-grade blueschists in the lowermost units to very low grade in theuppermost one (Leoni et al. 1995; Ellero et al. 2001). The D1c subphase, characterized bywest-verging thrusts, is particularly meaningful for the understanding of the dynamics ofthe Ligure-Piemontese accretionary prism because it testifies active shortening of the ILunits during and after their accretion. In addition, the D1c thrusting event represents thetransition from the accretion-related deformation to extensional tectonics, characterized byparallel folds (D2a) and low-to-high-angle normal faults (D2b). The extensional tectonics isinterpreted as the consequence of the thickening of the Ligure-Piemontese accretionary prism,produced by either the continuous underplating at its base or the shortening of the previouslyunderplated units. Finally, the extensional tectonics resulted in the exhumation of the ILunits up to the surfaces during the early Oligocene, when its sedimentary succession repre-sented one of the source areas of the conglomerates deposited in the Tertiary PiedmontBasin (Di Biase et al. 1997).

The western external Ligurian unitsThe WEL unit group includes Bettola, Caio, Orocco, Ottone, Monte delle Tane, andGroppallo units. As for the IL units, all WEL units show part of a more general successioncomprising sedimentary mélanges at the base and two, Late Cretaceous and Tertiary,flysch deposits. All successions are detached from their original base. The tectonic settingof the WEL units is quite complex. They are generally juxtaposed between the IL units,through the Ottone-Levanto-Carrara line, and the EEL units, onto which they areoverthrust in the Emilian Apennines. However, in some areas, the EEL unit group isoverthrust by the WEL units as a result of the Oligo–Miocene east-verging deformations.

Concerning the stratigraphy, the most typical deposit of the western successions is rep-resented by the sedimentary mélanges cropping out extensively in the Ottone, Monte delleTane, and Groppallo units and known as Casanova, Monte Ragola, and Pietra Parcellaracomplexes, respectively. Among them, only the Casanova complex is stratigraphicallyoverlain by the Helminthoid Flysch, whereas the Monte Ragola and Pietra Parcellaracomplexes are bounded by thrusts, and their original stratigraphic relationships with theHelminthoid Flysch can be only suggested.

Although distinguished by their tectonic position, all basal complexes show the samestratigraphic and sedimentological characteristics. They are all detached from their strati-graphic base and consist of huge slide-blocks enclosed in a matrix made of clast-supportedbreccias and coarse-grained, turbidite-derived rudites and arenites. The most significativedifferences among these mélanges arise from the lithologies represented as slide-blocks orclasts.

The best exposed and preserved sedimentary mélange is represented by the Casanovacomplex (Passerini 1965; Naylor 1982; Elter et al. 1991), an up to 1500 m-thick successionthat consists of monomict-to-polymict pebbly-mudstones, polymict pebbly sandstones andhuge slide-blocks showing a transition to well-bedded, coarse-grained arenites andrudites, known as Casanova Sandstone (Figure 9).

The slide-blocks, generally monolithologic, and the clasts in the breccias are com-posed by various lithologies. The most representative are probably the mantle ultramafics,consisting of spinel-lherzolites with common pyroxenite bands, deformed and partlyrecrystallized in the plagioclase stability field, with the formation of tectonite-mylonitefabrics (Piccardo et al. 2004). The ultramafic slide-blocks are interpreted as slices ofsubcontinental mantle, emplaced at low structural levels during the early stages of riftingof the Jurassic Ligure-Piemontese basin (Piccardo et al. 2002). The rare slide-blocks of

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

14 M. Marroni et al.

Figu

re 9

.G

eolo

gica

l cro

ss-s

ectio

n al

ong

the

uppe

rmos

t par

t of t

he A

veto

Val

ley

(Lig

uria

n–Em

ilian

Nor

ther

n A

penn

ine)

show

ing

the

rela

tions

hips

am

ong

inte

rnal

Ligu

rian

unit,

wes

tern

ext

erna

l Lig

uria

n un

its a

nd S

ublig

uria

n un

its. T

he s

ucce

ssio

n of

the

Otto

ne u

nit i

s ov

ertu

rned

. The

abb

revi

atio

ns u

sed

are

acco

rdin

g to

the

Italia

n 1:

50,0

00 m

appi

ng p

roje

ct (

CA

RG

). Ex

plan

atio

n: A

PA, P

alom

bini

Sha

le; C

CV

a, C

asan

ova

Sand

ston

e; C

CV

b, m

atrix

sup

porte

d pe

bbly

-mud

ston

e of

the

Cas

anov

a co

mpl

ex; b

, slid

e-bl

ocks

of b

asal

t; ∑

, slid

e-bl

ocks

of s

erpe

ntin

ites;

MV

E, M

onte

Ver

i com

plex

; OTO

, Otto

ne F

lysc

h; O

RO

, Oro

cco

Flys

ch (m

odifi

edfr

om E

lter e

t al.

2005

).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 15

gabbros, locally characterized by the occurrence of ductile shear zones, consist of trocto-lite- to olivine-bearing gabbro derived from low-pressure fractional crystallization of mid-ocean ridge (MOR)-type melts (Montanini et al. 2008). Slide-blocks of basalts, sometimeswith preserved stratigraphical relationships with late Callovian to early Oxfordian radiolar-ites (Conti et al. 1985), frequently occur as pillow lava and massive bodies, but basalticdikes are also widespread in lherzolites, gabbros, and massive basalts. They are normal totransitional MOR basalts, generated by a few per cent of fractional melting of a slightlydepleted astenospheric mantle in the spinel stability field (Vannucci et al. 1993; Montaniniet al. 2008). Slide-blocks of sedimentary rocks also occur, corresponding to the PalombiniShale (Valanginian–Late Cretaceous), the Calpionella Limestone (Berriasian-Valanginian),and the Radiolarite (Late Jurassic) Formation. All these lithologies belong to the same suc-cession, which is the typical sedimentary cover of the Jurassic ophiolites from the Ligure-Piemontese basin (Decandia and Elter 1972).

Continent-derived rocks are also recognized, consisting mainly of slide-blocks of grani-toids of late Palaeozoic age (310–280 Ma; Ferrara and Tonarini 1985), commonly affectedby a cataclastic deformation younger than Middle Triassic (Marroni et al. 1998). Whereprimary relationships with basalts are well preserved, the granitoids are intruded by basaltdikes, although basaltic flows stratigraphically covering the granitoids and their brittle struc-tures are also found (Molli 1996). Other continent-derived rocks, found as clasts in polymictbreccias, mainly consist of micaschists, orthogneisses, and garnet-bearing paragneisses.

One of the most striking feature recognized in the sedimentary rock-derived slide-blocks is the presence of a pre-brecciation deformation recognized inside the clasts ofCalpionella Limestone and Chert. The deformation is represented by folded veins in theCalpionella Limestone clasts and by a well-developed foliation (confined inside the clasts)in the siliceous shales associated with the Chert-derived clasts.

The matrix of these slide-blocks is mainly represented by the Casanova Sandstone,regarded as an early Campanian complex deep-sea turbidite system characterized by theassociation of coarse-grained and poorly evoluted high-density turbidites with thick tovery thick fine-grained low-density turbidites. The Casanova Sandstone shows a litho-arenitic composition where the rock fragments are mainly represented by serpentinites,basalts, cherts, Calpionella Limestone, and Palombini Shale (Di Giulio and Geddo 1990).Granitoids, low-grade metamorphic rocks, and arkosic arenites fragments are also present.According to Di Giulio and Geddo (1990), a petrofacies characterized by an arkosic con-tinental block-derived composition (sensu Dickinson 1985) can also be recognized in thearenites of the Casanova Sandstone, although it is only found in the fine-grained low-den-sity turbidites. The Casanova Sandstone, generally 300–600 m thick, shows a gradualtransition to the late Campanian Ottone Flysch. Moreover, in the lower part of the OttoneFlysch, several intercalations of debris flow deposits (known as Monte Veri complex), asthose recognized in the Casanova complex, are widespread (Elter et al. 1991).

The Monte Ragola complex (Marroni and Tribuzio 1996) exhibits a 600 m thicksuccession assigned to Santonian–early Campanian by nannofossil assemblages (Elteret al. 1997). Differently from the Casanova complex, the Monte Ragola complex is char-acterized by the prevalence of mantle ultramafics, the scarce presence of basalts, and theabsence of gabbro bodies, but the main feature is the occurrence of slide-blocks of maficand acid granulites. According to Marroni and Tribuzio (1996) and Montanini (1997), themafic granulites can be interpreted as remnants of an igneous complex, derived fromcrystallization at moderate pressure of tholeiite-derived and crustally contaminatedliquids. The relics of igneous textures, and mineral and whole-rock mineral variationsindicate that the granulites intruded at deep structural levels into extending continental

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

16 M. Marroni et al.

lithosphere and re-equilibrated in subsolidus conditions at 0.6–0.9 GPa and at 810–920°Cunder granulite facies in the Late Carboniferous–Early Permian time (Meli et al. 1996).The mafic granulites show a subsequent metamorphic history younger than the MiddleTriassic (Meli et al. 1996), commonly accompanied by a deformation changing from plas-tic to brittle, during their exhumation along an intermediate P/T gradient from granulite toamphibolite and greenschist facies conditions to upper crustal levels, probably in associationwith the subcontinental mantle (Marroni et al. 1998). In addition, slide-blocks of garnet-bearing acid granulites showing primary contacts with the mafic granulites have been distin-guished. They are interpreted as granulite facies metasediments showing a post-late Palae-ozoic retrograde metamorphic history from granulite to amphibolite and greenschist faciesassociated with mylonite and cataclasite development (Marroni et al. 1998).

The Pietra Parcellara complex (Elter et al. 1997), probably of Santonian–early Campa-nian age, crops out in the eastern areas of the Northern Apennines. The slide-blocks recog-nized in the Pietra Parcellara complex show features similar to that recognized in theCasanova and Monte Ragola complexes even if the continent-derived rocks, that is, thegranulites, the granitoids and the associated metamorphic rocks, are absent.

In summary, all the sedimentary mélanges recognized in the western successions seemto be derived from a source area corresponding to an ocean–continent transition at the mar-gin of the Adria plate (Marroni and Pandolfi 2007 and quoted references). According to thereconstruction proposed by Marroni et al. (2001), this area was characterized by a basementof subcontinental mantle and lower continental crust, covered by extensional allochtons ofupper continental crust and intruded by basalts (Figure 10). Even if characterized by somedifferences, mainly consisting of the occurrence of the granulites and the other continent-derived rocks, the overall characteristics, as, for instance, the widespread occurrence of sub-continental mantle ultramafics, suggest that the mélanges probably belonged to the samegeodynamic setting, with the differences only reflecting heterogeneities in the source area.

By contrast, other WEL units display successions represented mainly by HelminthoidFlysch with no or small remnants of sedimentary mélanges at their base. The HelminthoidFlysch consists of calcareous turbidites characterized by rhythmic alternation of calcare-ous-marl, marly-limestone, and marl layers showing medium-to-very thick beds with fine-to-medium arenitic base. One of the main features of these layers consists of an a:p ratio <<1which, in some layers, can reach values >20. This feature, together with the presence ofincomplete Bouma sequences, the lack of erosive structures, the parallel plane geometry of

Figure 10. Simplified model of the ocean–continent transition at the Adria continental marginbased on data from the external Ligurian units during the Middle–Late Jurassic during the radiolaritesedimentation (from Marroni et al. 1998).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 17

the strata, and the carbonate-free hemipelagic background sediments, indicates a depositionby low-density turbidity currents in a deep-sea environment located below the local CaCO3compensation level. The arenites show an arkosic composition characterized by monominer-alic fragments of quartz, feldspar, and rock fragments derived from granitoides and low-grade metamorphites. Close to the stratigraphic transition with the Casanova complex, fewstrata with lithoarenitic composition, comparable to that of the underlying ophiolitic sand-stone from the Casanova complex, can be recognized. This evidence is together with theabsence of carbonate in hemipelagic background sediments, is indicative of an abyssal plainenvironment located below the local CaCO3 compensation level (Scholle 1971). TheHelminthoid Flysch reveals the same stratigraphic setting in both the WEL and EEL units.

The most complete succession in the WEL units (Figure 11) can be identified in the Caiounit (Vescovi et al. 1999), where a late Campanian–Maastrichtian Helminthoid Flysch istypically characterized, at the base, by thin intercalations of mafic and ultramafic fragment-bearing debris flows. The Monte Caio Flysch is overlain by Palaeocene–middle Eocenecarbonate flysch, that is, the Marne Rosate Formation. The Bettola unit (Marroni et al. 2001)displays a well-preserved succession where a late Cretaceous Helminthoid Flysch, i.e. theBettola Flysch, is overlain by a Palaeocene–middle Eocene carbonate flysch, i.e. the ValLuretta Flysch. The successions of the Caio and Bettola units show close similarities and arereported together in the geological sketch map of Figure 7. Even if consisting only of a LateCretaceous Helminthoid Flysch devoid of its basal complex, the Orocco unit (Elter and Mar-roni 1991) is included in this group by its tectonic setting, similar to that of the Caio unit.

In the WEL units, as well as in the EEL ones, polyphase deformation history associ-ated with metamorphism typical of diagenesis zone can be observed. These deformations,whose structures are sealed by uppermost middle Eocene deposits of the Epiligurian basin,affected also the lowermost middle Eocene deposits of the EL successions; thus, the age ofall of these deformations can be confined to the middle Eocene (Ligurian phase of Elter 1975).In all the EL units, this polyphase deformation history includes a D1 phase consisting of

Figure 11. Reconstruction of the western and eastern successions of the external Ligurian units(redrawn from Marroni et al. 2001).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

18 M. Marroni et al.

west-verging isoclinal to close parallel folds (Levi et al. 2006) associated with a cataclas-tic shear zone (Marroni et al. 1999), which generally represent the present-day boundaryof the recognized tectonic units. The relationships between the WEL and the EEL units areacquired during this phase. The subsequent D2 phase is, in turn, represented by east-verging close to open large-scale folds with about NW–SE axis and subhorizontal axialplanes (Meccheri et al. 1982; Cerrina Feroni et al. 1989; Costa et al. 1991, 1995; CerrinaFeroni et al. 1994; Corsi et al. 2001; Marroni et al. 2002; Levi et al. 2006). As a whole,the structures of the D2 phase, which include not only overturned folds with subhorizontalaxial planes, but also shear surfaces cutting down in the stratigraphic sequence and passiverotation of the linear structural elements, are coherent with the gravitational spreading andtectonic transport of both WEL and EEL units towards the easternmost areas.

The eastern external Ligurian unitsThe second group of EL units is represented by the Media Val Taro, Cassio, Farini,Antola, and Sporno units, showing thick, well-preserved basal sequences where, in con-trast to the WEL units, the mafic and ultramafic slide-blocks are totally lacking. Althoughthe Antola unit is found at the top of the IL units, the Media Val Taro, Cassio, Farini, andSporno units are generally located at the top of the WEL units, even if this occurrence islocally modified by both middle Eocene and Oligo–Miocene east-verging deformations.

Whereas the Farini and Sporno units (Cerrina Feroni et al. 1994) are characterized bysuccessions that include Palaeocene–middle Eocene carbonate flysch, all other EEL unitsshow well-preserved basal complexes below the flysch deposits. The Media Val Taro unit(Vescovi et al. 1999) consists of a basal complex represented by the Palombini Shale, theS. Siro varicoloured Shale, and the Ostia Sandstone formations.

The Cassio unit shows the most representative succession of the EEL domain, with acomplete transition from the basal complex, to Late Cretaceous Helminthoid Flysch, up toearly Tertiary, predominantly shaly, deposits. The basal complex includes the PalombiniShale (Early Cretaceous), arenites correlated to the Ostia Sandstone (Case BaruzzoSandstone of Vescovi et al. 1999 and Scabiazza Sandstone), and varicoloured, hemipe-lagic shales (Cenomanian–late Campanian).

The varicoloured, hemipelagic shales are characterized by intercalations of conglomer-ates, known as Salti del Diavolo conglomerate. Pebbles feature intrusive, volcanic, low- tomedium-grade metamorphic, siliceous and carbonate sedimentary rocks (cfr. Baldacci et al.1972). Intrusive rocks are represented by medium- to coarse-grained syeno- and monzogran-ites. Volcanic rocks are characterized by dacites and rhyolites. Pebbles of metamorphicrocks are common. Low- to medium-grade metamorphic rocks such as phillites, schists,muscovite-biotite- and garnet-bearing micaschists and gneisses are recognized, as well ascordierite-bearing gneisses. Pebbles of carbonate (mainly limestones and dolostones notolder than Barremian-Hauterivian age) and siliceous rocks can be also recognized, with thecarbonate pebbles mainly made of mudstones, radiolarian-bearing wackestones and pack-stones, peloidic grainstones, and Calpionella-bearing mudstones. Recrystallized dolostonesand arenites made up of carbonate platform fragments are also observed. Siliceous rocks arered and green radiolarites, silicified radiolarian-bearing mudstones and siltstones, radiolar-ian-bearing packstones, and cherty-limestones.

Arenites from Ostia Sandstone, Varicoloured Shale, and Salti del Diavolo conglomerateare sublitharenites characterized by a mixed siliciclastic-carbonate framework compositionand by a mixed composition of the fine-grained lithic fragments (Bracciali et al. 2007 andquoted references). The extrabasinal siliciclastic-arenite framework is characterized by

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 19

mono- and polycrystalline quartz, plagioclase, and K-feldspar grains. Coarse-grained lithicfragments of granitoids are common. Metamorphic rock fragments include low-gradeschists, micaschists, and minor fragments of medium-grade cordierite- and garnet-bearinggneisses. Siliceous rock fragments are represented by radiolarian-bearing cherts, cherty-limestones, siliceous mudstones, and siliceous siltstones. Carbonate mudstones, radiolarian-bearing wackestones, and medium- to coarse-grained dolostones are the most commonextrabasinal carbonate rock fragments. Calpionella-bearing mudstones, oolitic grainstones,and radiolarian-bearing packstones are also found.

According to Bracciali et al. (2007), the geochemical data relative to the siliciclasticfraction of these deposits indicate an ultramafic source standing out also from the mafic-felsic components contributing as well to the sediment. This is in agreement with theoccurrence of millimetre-sized Cr-spinel fragments in the corresponding arenitic fraction(Mezzadri 1964 and Wildi 1985), typically derived from mantle coarse-grained ultramaficrocks and indicative of a source area characterized by the presence of mantle rockscropping out below the continental crust. The source area was located in correspondencewith the Adria continental margin where the metamorphic and magmatic rocks belongingto the basement were exposed (Elter et al. 1966). In this picture, the presence of mantlerock exposed at the sea floor can be also hypothesized.

The Varicoloured Shale grades upward to the late Campanian-Maastrichtian MonteCassio Flysch, showing arenites with a hybrid composition (Fontana et al. 1994),characterized by the presence of an extrabasinal arkosic to lithic-arkosic assemblage withfragments of granitoids, low-grade metamorphic rocks, dolostones, Early Cretaceousmicritic limestones, and cherts, associated with coeval intrabasinal debris made up ofplanktonic and benthonic bioclasts and glaucony. At the top of the succession, thePalaeocene Viano Shale (Laccarino and Rio 1972), consisting of red and grey shalesalternating with carbonate turbidites, occurs. On the whole, the entire succession from theCassio unit is characterized by deposits supplied by a continental margin where ophiolites arelacking, even if the presence of mantle rock exposed at the sea floor can be hypothesized.

Locally, an assemblage of tectonic slices has been recognized at the base of the Cassiounit succession (Vercesi and Cobianchi 1998). Even if dismembered in multiple tectonicslices, the original succession can be fully reconstructed. It consists of Middle Triassicdolomitic limestones with stromatolitic structures, capped by sedimentary breccias withDiplopora-bearing dolomitic clasts (Late Triassic). On top of the sedimentary breccias liecherty-limestones (Lias) and marls (Dogger-Malm), showing a transition to cherts(Malm), Aptychus-bearing calcareous red marls (Malm), and Calpionella-bearing pelagiclimestones (Early Cretaceous). The pelagic limestones, similar to the Maiolica Formationof the Southern Alps and Tuscany, are characterized by intercalations of sedimentarybreccias with dolomitic and cherty clasts. This sequence can be interpreted as the rem-nants of the continental substratum of the succession from the Monte Cassio unit and canbe probably extended to the other WEL successions (Marroni et al. 2001) (Figure 11).

Similar to the Cassio unit, the Antola unit displays an up to 3000 m-thick successionthat can be roughly subdivided into three main parts: the lower basal complex (MontoggioShale and Gorreto Sandstone), the middle carbonatic turbidite deposits (Monte AntolaFlysch), and the upper mixed siliciclastic-carbonatic turbidite deposits (Bruggi–Selvapi-ana Formation and Pagliaro Shale) (Catanzariti et al. 2007 with quoted references). Thepart of the basal complex represented by the Montoggio Shale has been further subdi-vided. The lowermost portion is made up of black manganiferous, carbonate-free, hemipe-lagic shales, interlayered with fine-grained turbiditic sandstones, showing an arenite/peliteratio >1 and a thickness of at least 100 m. The uppermost portion consists of 200–300 m of

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

20 M. Marroni et al.

varicoloured hemipelagic shales, followed by the turbiditic succession of the Gorreto Sand-stone, characterized by thin-bedded turbidites of mixed siliciclastic/carbonatic composition.The basal complex grades upward to the Monte Antola Flysch, consisting of calcareous tur-bidites and megaturbidites, showing a siliciclastic-arenite composition (Rowan 1990; Fon-tana et al. 1994), interlayered with rare siliciclastic beds and thin hemipelagic, carbonate-free shales, indicating sedimentation below the calcite compensation depth (Scholle 1971).The Monte Antola Flysch is overlain by the carbonatic megaturbidite sequence of theBruggi–Selvapiana Formation, partly corresponding to the Bruggi and Selvapiana membersof Abbate and Sagri (1967). This formation is characterized by the alternation of turbiditic,marly megabeds with thin-bedded siliciclastic turbidites and shales. The top of the Antolaunit succession, the Pagliaro Shale (Bellinzona and Boni 1971), mainly consists of thickshale beds alternating with siliciclastic, thin-bedded turbidites and minor calcareous tur-bidites (corresponding to the Cabella Member of Abbate and Sagri 1967) (Figure 12).

Also, the Late Cretaceous succession of the Solignano unit, characterized by varicol-oured shales and a Maastrichtian Helminthoid Flysch, known as Solignano Flysch, is hereregarded as belonging to the eastern domain, according to the modal analyses of the arenites ofthe Solignano Flysch, which reveal a hybrid composition characterized by dolostonefragments without any evidence of ophiolite fragments (Fontana et al. 1994).

Figure 12. Stratigraphic log of the Antola unit according to Catanzariti et al. (2007).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 21

Location of the Ligurian succession in the Late Cretaceous–early tertiary palaeogeography of the Ligure-Piemontese basinAccording to the described geological features, some considerations about the location ofthe successions preserved in the Ligurian units, in the framework of the Late Cretaceous–early Tertiary palaeogeography, can be attempted.

The IL units are characterized by an oceanic basement topped by a thick sedimentarycover, spanning from Late Jurassic to early Palaeocene. In this sedimentary cover, atransition from pelagic (cherts, Calpionella Limestone, Palombini Shale Formation) toturbidite (Val Lavagna Shale Group and Monte Gottero Sandstone Formation) and lowerslope deposits (Bocco Shale) has been outlined by several authors (Marroni et al. 1992and quoted references). This transition has been interpreted as achieved during thetrenchward motion of an oceanic lithosphere (Treves 1984; Marroni and Pandolfi 2001).Matching with this reconstruction are the contrasting sedimentary features shown by thepelagic versus trench plus lower slope deposits (Marroni and Perilli 1990). In fact, whilethe pelagic deposits show a very low sedimentation rate, as demonstrated by their longtime span of sedimentation (about 80 Ma) and reduced thickness (about 1000 m), thetrench and lower slope deposits are characterized by a short time span of sedimentation(about 20 Ma) but a relevant thickness (about 3000 m). The interpretation of the transitionfrom pelagic to trench and lower slope deposits as achieved during a trenchward motion iscoherent with the subsequent structural and metamorphic evolution, typical of unitssubjected to underplating into an accretionary prism (Meneghini et al. 2007 and quotedreferences). Thus, the IL units can be regarded as a fragment of the accretionary prismdeveloped during subduction of the Ligure-Piemontese oceanic basin in the LateCretaceous–early Tertiary. Regarding the palaeogeographic location of the IL successions,clear evidence is provided by the Monte Gottero Sandstone, whose arenite compositionindicates that the source area is represented by the crystalline basement of the Europe/Corsica plate (Valloni and Zuffa 1984). Thus, the IL domain can be interpreted as located in anarea characterized by oceanic lithosphere bounded by the Corsica continental margin in itsnorthwestern side, whereas the opposite side is represented by the accretionary prism, fromwhich the ophiolite-bearing deposits of the Bocco Shale were derived (Figure 13).

A different picture can be drawn for the EL units, mostly characterized by a successionthat includes late Campanian–middle Eocene carbonate turbidites. It is crucial to highlightthat the turbidites are represented by a monotonous sequence of beds without evidence ofsin-sedimentary deformations as slumps, intraformational breccias, or unconformities, asalso stated by Marroni and Treves (1998). This is particularly evident for the MonteAntola unit succession where Catanzariti et al. (2007) have recognized a continuoussedimentation from late Campanian to late Palaeocene. Also, the Caio unit displays asuccession continuous from late Campanian to middle Eocene (Rio et al. 1983). Thus, thebasin from which the EL successions were derived is lacking any evidence of deformationfrom late Campanian until the above described lowermost middle Eocene deformationevent. As previously discussed, the slide-blocks preserved in the basal sedimentarymélanges from WEL, and the arenite composition from the Cenomanian to Campanianturbidite from EEL units, indicate that the EL domain was located along the western edgeof the Adria plate, in correspondence with the ocean–continent transition (WEL units) andthe adjacent thinned continental margin (EEL units). Thus, whereas the IL units experi-enced the Late Cretaceous–early Tertiary subduction-related sedimentary and tectonicevents, the EL domain escaped deformation until the middle Eocene, i.e. until the incep-tion of the continental collision. This feature can be explained only by placing the basin,

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

22 M. Marroni et al.

from which the EL units derived, in a suprasubduction setting, located between the Adriathinned continental margin and the rear of the accretionary prism.

However, both the WEL and EEL units are characterized by the sedimentary evidenceof a Santonian–early Campanian tectonic pulse, as testified by the occurrence of the basalsedimentary mélange of the WEL units, which suggests a tectonic-controlled deposition,according to the huge size of the slide-blocks and the evidence of brittle deformation ofthe slide-blocks before their inclusion in the mélange. The occurrence of Santonian–Campanian tectonics is also testified by radiometric data on the continental crust slide-blocks. The partial annealing of fission tracks in zircons from quartzo-feldspathic granu-lites indicates that the temperature must have exceeded 200°C at about 80 Ma during athermal event of Late Cretaceous age (Balestrieri et al. 1997). This is consistent with themetamorphic overprint under subgreenschist facies conditions responsible for the develop-ment of chlorite and sericite in the quartzo-feldspathic granulites. In addition, the maficgranulites provided an 40Ar/39Ar age around 80 Ma (Meli et al. 1996), which can be relatedto the development of a metamorphic overprint in the pumpellyite-actinolite facies (Marroniand Tribuzio 1996; Montanini 1997). This tectonic pulse is also recognized in the EEL units

Figure 13. Interpretive section of the subduction zone in the Ligure-Piemontese oceanic basin dur-ing the Palaeocene. In the blow-up, the details of the frontal tectonic erosion of the accretionarywedge slope are shown. The arrows point out the provenance of the two groups of facies deposits ofthe Bocco Shale (hollow arrow: deposits supplied from the Europe plate; solid arrow: deposits sup-plied from accretionary wedge by frontal tectonic erosion). Modified from Marroni and Pandolfi(2001).

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 23

where unconformities within the Cenomanian to Santonian succession have been identi-fied (Vescovi et al. 1999). Thus, this tectonic pulse seems to be recognizable in the wholeEL domain. The geodynamic significance of this tectonic pulse is puzzling. The onlyinterpretation in the frame of plate tectonics is that of Naylor (1982), who proposed afaulted distal passive margin as the source area of the Casanova complex sedimentarymélanges. However, this interpretation is unrealistic, because it cannot explain theoccurrence of normal faults cutting the ocean–continent transition after 80 Ma from theoceanic spreading inception. Some authors (Principi and Treves 1984; Treves 1984)interpreted the sedimentary mélanges from EEL units as lower slope deposits suppliedfrom an accretionary prism. In this picture, the carbonate turbidites, i.e. the HelminthoidFlysch, are interpreted as trench deposits, but their residence time in the basin of about 30Ma, without evidence of deformation, does not fit very well with the proposed scenario.Subsequently, Bertotti et al. (1986) interpreted the mélanges as a sedimentary result ofback-thrusting in the rear of an accretionary prism connected to an east-dipping subduc-tion. In addition, Elter and Marroni (1991) and Marroni and Treves (1998) proposed aninterpretation of these deposits as related to a strike-slip tectonics connected with a majorreorganization of the plates in the Tethys area during the Campanian. However, none of theseinterpretations are completely satisfying, and the geodynamic meaning of this tectonicpulse remains unclear.

Despite this unsolved point, the IL and EL units show features that clearly indicatetheir belonging to two different palaeotectonic domains. The IL units represent theremnants of an accretionary prism, whereas the EL ones can be considered as derived froma supra-subduction basin that, even if affected by tectonics in the Santonian–Campanianboundary, did not suffer any subduction-related deformation and remained undeformedfrom the late Campanian until the middle Eocene. It is important to outline that the ELdomain is deformed only when all the oceanic lithosphere of the Liguria-Piemontese basinwas subducted. In addition, no record of the possible transition between the IL and ELdomains has been identified so far. Similarly, even if both are characterized by the occur-rence of Helminthoid Flysch, the transition between the ophiolite-bearing and ophiolite-free deposits of the WEL and EEL units is not detected in the present-day unit pile of theNorthern Apennines. The evidence of these main gaps have been considered by Marroniand Treves (1998) to support their interpretation of the IL, WEL, and EEL units as ter-ranes separated by strike-slip faults active from the Late Cretaceous up to the Oligocene ina regime of transpression.

Geodynamic history of the Ligure-Piemontese basin: a proposalThe discussed features of the Ligurian successions allow us to propose a possible scenariofor the Late Cretaceous to middle Eocene geodynamic history of the Ligurian Apennines.This reconstruction is depicted step by step in Figure 14. Important key elements from theneighbouring domains, as the Alpine Corsica, have been taken into account in theproposed reconstruction.

Our reconstructed evolution starts in Pre-Santonian time, when the Ligure-Piemontesebasin was dominated by pelagic sedimentation. The architecture of the basin in this timespan was inherited from the rifting history leading to the opening of the Ligure-Piemon-tese oceanic basin (Marroni and Pandolfi 2009 and quoted references). The Early to MiddleJurassic asymmetric stage of the rifting depicted in the reconstruction by Marroni et al.(1998) resulted in profoundly different architecture and lithology of the paired continentalmargins. The Adria plate was characterized by a wide ocean–continent transition floored by

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

24 M. Marroni et al.

Figure 14. Possible scenario for the Late Cretaceous to middle Eocene geodynamic history of theLigurian Apennines. (A) Campanian–Maastrichtian; (B) early Eocene; (C) late Eocene; (D) earlyOligocene. Explanation: IL, internal Ligurian domain; WEL, western external (oceanward) Liguriandomain; EEL, eastern external (continentward) Ligurian domain; SBL, Subligurian domain; ANT,Antola unit; T, Tuscan domain; TPB, Tertiary Piedmont Basin; ELS, Epiligurian Basin.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 25

exhumed subcontinental mantle rocks, intruded by gabbros and covered by extensionalallochthons of upper continental crust, in turn topped by basaltic flows and pelagic sedi-ments. This ocean–continent transition was adjacent to a wide area characterized by thinnedcontinental crust. According to Marroni et al. (2001), the WEL and EEL basins were sep-arated by a ridge consisting of a huge extensional allochton made up of upper continentalcrust, which can be compared with the AlKaPeCa microcontinent identified in thesouthernmost areas of the western Tethys by Michard et al. (2002). In contrast, thetransition from continental to oceanic crust at the Europe/Corsica margin was sharp andcharacterized by escarpments induced by high-angle normal faults (Marroni and Pandolfi2007).

The architecture inherited form the rifting history remained unmodified until theinception of convergence in the Ligure-Piemontese basin, but, as shown below, it played afundamental role during the convergence processes. Convergence possibly started in theSantonian–Campanian boundary, as suggested by the onset of sedimentation of tectonic-controlled deposits as turbidites and mélanges (Marroni et al. 1992). This interpretationfits very well with the 84 ± 5 Ma of the eclogite metamorphism detected in metaophiolitesfrom Corsica by Sm/Nd analyses (Lahondere and Guerrot 1997) and that represents theoldest reliable age for the high pressure (HP), subduction-related metamorphism. Conver-gence led to the onset of intraoceanic subduction that located in close proximity of theocean–continent transition towards the Adria plate.

Some considerations on the dipping of the subduction are crucial to complete thisscenario, even if this is still a matter of strong debate. Evidence of top-to-the-west shearsense during the underplating of the IL units have been identified during structural analy-ses by several authors (Hoogerduijn Strating E.H. 1994; Marroni and Pandolfi 1996;Marroni et al. 2004). However, the strongest constraints are provided in Corsica Island bythe Tenda Massif, which represents a fragment of the Europe/Corsica continental marginsubjected to HP metamorphism at the middle–late Eocene boundary and associated withtop-to-the-west shear zones (Molli et al. 2006). It is important to outline that HP metamor-phism detected in the Adria continental margin developed only since the late Oligocene–early Miocene, i.e. more than 20 Ma after the HP metamorphism detected in the Europe/Corsica continental margin (Brunet et al. 2000). Thus, all the structural and radiometricdata seem to be coherent with a Late Cretaceous scenario dominated by an east-dipping(‘alpine’) subduction where the role of lower plate was played by the Europe/Corsicamargin. This reconstruction is coherent with the data reported by Peccerillo et al. (2001),which provide evidence for an earliest metasomatic modification of the present-day Tus-can mantle as a result of the ‘alpine’ subduction. Therefore, during the Late Cretaceous–Palae-ocene, the IL basin was progressively shortened and consumed by subduction of oceaniclithosphere, whereas the EL basin was characterized by the continuous, monotonoussedimentation of the carbonate turbidites. In this frame, the EL basin can be coherentlyplaced in a suprasubduction basin, located between the accretionary prism and the Adriacontinental margin. However, a tectonic pulse, testified by the sedimentation of sedimentarymélanges, affected also the margin of this basin at the Santonian–Campanian boundary, pos-sibly representing the inception of oceanic subduction. In our reconstruction, the origin ofthe sedimentary mélanges owing to transpressive tectonics is adopted, according to themodel proposed by Elter and Marroni (1991), Pandolfi (1997) and Marroni and Treves(1998).

A few other considerations help a more detailed timing of the subduction evolution,because they allow estimation of the time of oceanic lithosphere total consumption by subduc-tion and that of the involvement of continental crust into the system. The youngest preserved

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

26 M. Marroni et al.

sedimentary cover of the oceanic lithosphere identified along the whole alpine–apenninebelt is represented by the IL units, where the Gottero unit shows a top of the sedimentarycover of the ophiolite sequence of early Palaeocene age (Marroni and Pandolfi 1996).Thus, the Gottero unit probably represented the last portion of the oceanic lithosphere ofthe Ligure-Piemontese basin subjected to underthrusting in the subduction zone. On theother hand, the continental units affected by HP metamorphism from Corsica Islandprovide valuable insights also for the early–middle Eocene time span. As previouslyreported, the Tenda Massif was affected by HP metamorphism with an 40Ar/39Ar age of34.9 ± 0.4 Ma (middle–late Eocene boundary, Brunet et al. 2000). In addition, an 40Ar/39Arage of 46.7 ± 0.6 Ma (early Eocene boundary, Brunet et al. 2000) has been found on thecontinental slices with eclogite metamorphism enclosed in the metaophiolites of Corsica.Therefore, this east-dipping subduction, probably intraoceanic until the Palaeocene–Eocene boundary, involved subsequently the continental crust of the Europe/Corsicaplate. Thus, in the early Eocene, the underthrusting of the Europe/Corsica continentalcrust below the alpine accretionary prism, represented by the ophiolites showing HP met-amorphism today preserved in Corsica Island and in the Northern Apennines, can beenvisaged. In the same time span, the suprasubduction basin corresponding to the ELdomain was still undeformed. The lack of subduction-related magmatism during the LateCretaceous–middle Eocene time span has been explained by Marroni and Treves (1998)as owing to shallow dip angle and slow rate of subduction.

In the middle Eocene, a major tectonic event occurred in the Ligure-Piemontese basin.The east-dipping subduction stopped, probably as a consequence of the involvement of thethick continental crust of Europe/Corsica plate in the subduction zone. The architecture ofthe Europe/Corsica margin inherited from the rifting process, i.e. a sharp transition fromoceanic crust to thick continental crust, is coherent with this interpretation.

As a consequence of the stop in the ‘alpine’ subduction, the convergence migrated tothe EL basin. In our reconstruction, the first result of the convergence in the EL basin is alarge westward displacement of the EEL units, as testified by the present-day tectonicsetting of the Antola unit over the IL units, i.e. the former alpine accretionary prism. Thewest-verging tectonics was followed by east-verging deformations connected with theunderthrusting of the EL units below the alpine accretionary prism. The resulting structurewas a triangular, crocodile-like zone, where the EL units were thrust either below or overthe alpine accretionary prism, whose upper structural levels are today represented by theIL units. A similar structure is also today recognized along the seismic profiles of thewestern (Biella et al. 1997) and central (Lüschen et al. 2004) Alps.

According to that proposed in the model by Carminati et al. (2004), our modelenvisages, at Eocene time, also the break-off of the alpine slab and the inception of the west-dipping ‘apennine’ subduction. The subduction along the northernmost areas of the Ligure-Piemontese basin was probably driven by the west-dipping subduction active in the south-ernmost areas, where a true, wide oceanic area is hypothesized to have been consumed byseveral geodynamic reconstructions (e.g. Figure 8 of Molli 2008 and quoted references). Inaddition, the subduction in the EL basin was favoured by the characteristics of its crustalstructure inherited by rifting history, i.e. a wide area, very easily subducted because it wascharacterized by subcontinental mantle covered by thinned continental crust.

Thus, in the late Eocene, two different paired structures with different tectonic originswere coupled: (i) the alpine accretionary prism (IL units), where in its western margin thecontractional deformation was substituted by the extensional tectonics in the early Oli-gocene and (ii) the proto-Apennine belt (EL units), derived from the subduction of thethinned Adria continental margin. The structures resulting from this series of events are all

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 27

sealed by the deposits of Epiligurian (middle Eocene to Tortonian) in the E and theTertiary Piemontese (late Eocene to Tortonian) basins in the W.

The proposed model fits well with a sharp occurrence of calcalkaline magmatism inthe Adria plate in the early Oligocene (Mattioli et al. 2002), whose remnants are todaypreserved in the Subligurian units (Elter et al. 1997). This picture is also confirmed by theinterpretation of the early Oligocene Aveto Formation as the first, true foredeep depositrelated to eastward migration of the compressive front related to west-dipping subduction(Elter et al. 1999; Catanzariti et al. 2003).

The subsequent tectonic history of the Ligurian units is achieved during their thrustingonto the Subligurian and Tuscan units in the Oligocene–Miocene time span and thesubsequent extensional tectonics, related to the eastward progressive migration of thecompressive front, continuous from middle Eocene up to Quaternary time. During thisevolution, the structural setting achieved during the Late Cretaceous–middle Eocene by theLigurian units was only weakly modified and the upper structural levels were still wellpreserved as a consequence of the very low exhumation rate of the Northern Apennines belt.

AcknowledgementsThis research was supported by MIUR (Project PRIN), by CNR (Istituto di Geoscienze e Georisorse,Unità Operativa di Pisa), by funds ATENEO grant by Pisa University and by Galileo Programme2008/2009. All the authors are indebted to Professor Piero Elter, who introduced all the authors tothe mystery of the Northern Apennines geology.

ReferencesAbbate, E., Bortolotti, V., and Passerini, P., 1970, Olistostromes and olistoliths: Sedimentary

Geology, v. 4, no. 3/4, p. 521–528.Abbate, E., Bortolotti, V., and Principi, G., 1980, Apennine ophiolites: A peculiar oceanic crust:

Ofioliti, v. 5, no. 1, p. 1–59.Abbate, E., and Sagri, M., 1967, Suddivisioni litostratigrafiche nei calcari ad Elmintoidi Auctt. della

placca dell’Ebro-Antola e correlazioni con terreni simili affioranti tra Voghera e Castelnuovo nèMonti (Appennino Settentrionale): Memorie della Società Geologica Italiana, v. 6, p. 23–65.

Abbate, E., and Sagri, M., 1982, Le unita’ torbiditiche cretaciche dell’Appennino settentrionale ed imargini continentali della Tetide: Memorie della Società Geologica Italiana, v. 24, p.115–126.

Aiello, E., Bruni, P., and Sagri, M., 1977, Depositi canalizzati nei flysch cretacei dell’Isola d’Elba:Bollettino della Società Geologica Italiana, v. 96, p. 297–329.

Argnani, A., Fontana, D., Stefani, C., and Zuffa, G.G., 2004, Late Cretaceous carbonate turbidites ofthe Northern Apennines: Shaking Adria at the onset of Alpine collision: Journal of Geology, v.112, p. 251–259.

Baldacci, F., Cerrina Feroni, A., Elter, P., Giglia, G., and Patacca, E., 1972, Il margine del paleocon-tiente nord-apenninico dal Cretaceo all’Oligocene: nuovi dati sulla ruga Insubrica: Memoriedella Società Geologica Italiana, v. 11, p. 367–390.

Baldacci, F., Elter, P., Giannini, E., Giglia, G., Lazzarotto, A., Nardi, R., and Tongiorgi, M., 1967,Nuove osservazioni sul problema della Falda Toscana e sull’interpretazione dei flysch arenaceitipo ‘Macigno’ nell’Appennino Settentrionale: Memorie della Società Geologica Italiana, v. 6,p. 199–211.

Balestrieri, M.L., Bigazzi, G., Marroni, M., and Tribuzio, R., 1997, Quartzo-feldspathic granulitesfrom External Liguride Units (northern Apennine): tectono-metamorphic evolution and thermo-chronological constraints from zircon fission-track data: Compte Rendu de l’Académie deSciences, v. 324, p. 87–94.

Beccaluva, L., Piccardo, G.B., and Serri, G., 1980, Petrology of the Northern Apennine ophiolitesand comparaison with other Tethyan ophiolites, in Panayiotou, A., ed., Ophiolites: Proceedingof International ophiolite symposium, Cyprus 1979, p. 314–331.

Bellinzona, G., and Boni, A., 1971, Stratigrafia e tettonica della zona tra il T Scrivia e il T. Sisola:Atti dell’Istuto di Geologia dell’ Università di Pavia, v. 21, no. 1, p. 21–137.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

28 M. Marroni et al.

Bertotti, G., Elter, P, Marroni, M., Meccheri, M., and Santi, R., 1986, Le argilliti a blocchi diM.Veri: Considerazioni sulla evoluzione tettonica del bacino ligure nel Cretaceo superiore:Ofioliti v. 11, no. 3, p. 193–220.

Bettelli, G., Bonazzi, U., and Panini, F., 1989, Schema introduttivo alla geologia delle Ligurididell’Appennino Modenese e delle aree limitrofe: Memorie della Società Geologica Italiana, v.39, p. 91–125.

Bettelli, G., and Vannucchi, P., 2003, Structural style of the offscraped Ligurian oceanic sequencesof the Northern Apennines: New hypothesis concerning the development of mélange block-in-matrix fabric: Journal of Structural Geology, v. 25, p. 371–388.

Bezzi, A., and Piccardo, G.B., 1970, Studio petrografico sulle formazioni ofiolitiche della Liguria.Riflessioni sulla genesi dei complessi ofiolitici in ambiente appenninico alpino: Rendiconti dellaSocietà Italiana di Mineralogia e Petrologia, v. 36, p. 1–42.

Biella, G., Polino, R., de Franco, R., Rossi, P.M., Clari, P., Corsi, A., and Gelati, R., 1997, The crus-tal structure of the western Po plain: Reconstruction from integrated geological and seismicdata: Terra Nova, v. 9, no. 1, p. 28–31.

Boccaletti, M., Coli, M., Decandia, F., Giannini, E., and Lazzarotto, A., 1980, Evoluzionedell’Appennino Settentrionale secondo un nuovo modello strutturale: Memorie della SocietàGeologica Italiana, v. 21, p. 359–374.

Boccaletti, M., Elter, P., and Guazzone, G., 1971, Plate tectonic models for the development of theWestern Alps and Northern Apennines: Nature, v. 234, p. 108–111.

Bortolotti, V., and Passerini, P., 1970, Magmatic activity: Sedimentary Geology, v. 4, p. 599–624.Bracciali, L., Marroni, M., Pandolfi, L., and Rocchi, S., 2007, Petrography and Geochemistry of West-

ern Tethys Mesozoic sedimentary covers (Corsica and Northern Apennines): From source areas tomargins configuration: Geological Society of America Memoirs, Special Paper v.420, p. 73–93.

Brunet, C., Monié, P., Jolivet, L., and Cadet, J.P., 2000, Migration of compression and extension inthe Thyrrenian Sea, insights from 40Ar/39Ar ages on micas along a transect from Corsica toTuscany: Tectonophysics, v. 321, p. 127–155.

Capponi, G., Crispini, L., Federico, L., Piazza, M., and Fabbri, B., 2009, Late Alpine tectonics in theLigurian Alps: Constraints from the Tertiary Piedmont Basin conglomerates: GeologicalJournal, v. 44, no. 2, p. 211–224.

Carminati, E., Doglioni, C., and Scrocca, D., 2004, Alps vs Apennine, in Crescenti, U., D’offizi, S.,Merlino, S., and Sacchi, L., eds. Geology of Italy. Special volume of the Italian GeologicalSociety for the IGC 32 Florence-2004, p. 141–152.

Casnedi, R., 1982, Sedimentazione e tettonica delle Unità Liguridi dell’Appennino Nord-Occidentale:Atti dell’Istituto di Geologia dell’Università di Pavia, v. 30, p. 42–66.

Castellarin, A., 1992, Strutturazione eo-e mesoalpina dell’Appennino Settentrionale attorno al nodoligure: Studi Geologici Camerti, v. 2, p. 99–108.

Catanzariti, R., Cerrina Feroni, A., Marroni, M., Ottria, G., and Pandolfi, L., 2003, Ophiolites debrisin the Aveto unit (Trebbia Valley, Northern Apennines, Italy): A record of the Early Oligoceneapenninic foredeep?: Ofioliti, v. 28, p. 71.

Catanzariti, R., Ellero, A., Levi, N., Ottria, G., and Pandolfi, L., 2007, Calcareous nannofossil bios-tratigraphy of the Antola Unit succession (Northern Apennines, Italy): New age constraints forthe Late Cretaceous Helminthoid Flysch: Cretaceous Research, v. 28, p. 841–860.

Cavazza, W., Roure, F., Spakman, W., Stampfli, G.M, and Ziegler, P.A., eds., 2004, The TRANSMEDAtlas: The Mediterranean Region from Crust to Mantle: Heidelberg, Springer-Verlag, 141 p.

Cerrina Feroni, A., Fontanesi, G., and Martinelli, P., 1989, La struttura a sinclinale coricata delFlysch di M.Caio tra la Val Cedra e la Val Parma nell’Appennino Settentrionale: Memorie dell’Accademia di Scienze Lunigianense, v. 57/58, p. 43–44.

Cerrina Feroni, A., Martinelli, P., and Ottria, G., 1994, L’edificio strutturale della media Val Nure(Appennino settentrionale): Nuovi dati strutturali e biostratigrafici: Atti Ticinensi di Scienzedella Terra, v. 1, p. 105–115.

CNR, 1992, Structural Model of Italy: Progetto Finalizzato Geodinamica: Florence, Italy, SELCA.Cobianchi, M., Piccin, A., and Vercesi, P.L., 1994, La Formazione di Val Luretta (Appennino

Piacentino): Nuovi dati litostratigrafici e biostratigrafici: Atti Ticinensi di Scienze della Terra,v. 37, p. 235–262.

Cobianchi, M., and Villa, G., 1992, Biostratigrafia del Calcare a Calpionelle e delle Argille aPalombini nella sezione di Statale (Val Graveglia, Appennino ligure): Atti Ticinensi di Scienzedella Terra, v. 35, p. 199–211.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 29

Conti, M., Marcucci, M., and Passerini, P., 1985, Radiolarian cherts and ophiolites in the NorthernApennines and Corsica: age correlations and tectonic frame of siliceous deposition: Ofioliti,v. 10, p. 201–225.

Corsi, B., Elter, F.M., and Giammarino, S., 2001, Structural fabric of the Antola unit (Riviera diLevante, Italy) and implications for its Alpine versus Apennine origin: Ofioliti, v. 26, p. 1–9.

Cortesogno, L., Galbiati, B., and Principi, G., 1987, Note alla ‘carta geologica delle ofioliti del Bracco’e ricostruzione della paleogeografia giurassico-cretacica: Ofioliti, v. 12, no. 2, p. 261–342.

Costa, E., De Nardo, E.T., Mattioli, A., and Ronchi, P., 1991, Evoluzione tettonica delle Liguridi: lestrutture di Monte Carameto e M.Dosso (Val Ceno, Provincia di Parma): Memorie Descrittivedella Carta Geologica d’Italia, v. 44, p. 375–386.

Costa, E., Frati, G., and Villa, G., 1995, Note illustrative della Carta Geologico-Strutturale delleLiguridi Esterne nell’area tra la media Val Ceno e la Val d’Arda (Provv. di Parma e Piacenza):Atti Ticinensi di Scienze della Terra, v. 3, p. 3–29.

Daniele, G., and Plesi, G., 2000, The Ligurian Helminthoid Flysch Units of the EmilianApennines:stratigraphic and petrographic features, paleogeographic restoration and structuralevolution: Geodinamica Acta, v. 13, no. 5, p. 313–334.

Decandia, F.A., and Elter, P., 1969, Riflessioni sul problema delle ofiditi nell’ Appennino Settentri-onale (Nota preliminare): Atti Società Toscana Scienze Natturali, Memorie, v. A76, p. 1–9.

Decandia, F.A., and Elter, P., 1972, La ‘zona’ ofiolitifera del Bracco, nel settore compreso traLevanto e la Val Graveglia: Memorie della Società Geologica Italiana, v. 11, p. 503–530.

Del Castello, M., McClay, K.R., and Pini, G.A., 2005, Role of preexisting topography and overbur-den on strain partitioning of oblique doubly vergent convergent wedges: Tectonics, v. 24, p.TC6004, doi:10.1029/2005TC001816.

Dellisanti, F., Pini, G.A., Tateo, F., and Baudin, F., 2008, The role of tectonic shear strain on theillitization mechanism of mixed-layers illite-smectite. A case study from a fault zone in theNorthern Apennines, Italy: International Journal of Earth Sciences, v. 97, p. 601–616.

Di Biase, D., Marroni, M., and Pandolfi, L., 1997, Age of the deformation phases in the InternalLiguride Units: Evidences from Early Oligocene conglomerates of Tertiary Piemontese Basin(Northern Apennine, Italy): Ofioliti, v. 22, no. 2, p. 231–238.

Dickinson, W.R., 1985, Interpreting provenance relations from detrital modes of sandstones, inZuffa, G.G., ed., Provenance of arenites: NATO ASI Series, p. 333–362.

Di Giulio, A., and Geddo, G., 1990, Studio petrografico delle Arenarie di Casanova (alta ValTrebbia, Appennino settentrionale): Atti Ticinensi di Scienze della Terra, v. 33, p. 243–254.

Ducci, M., Lazzaroni, F., Marroni, M., Pandolfi, L., and Taini, A., 1997, Tectonic framework of thenorthern Ligurian Apennine, Italy: Compte Rendu de l’Académie de Sciences, v. 324, p. 317–324.

Ellero, A., Leoni, L., Marroni, M., and Sartori, F., 2001, Internal Liguride Units from CentralLiguria, Italy: New constraints to the tectonic setting from white mica and chlorite studies:Swiss Bulletin of Mineralogy and Petrology, v. 81, p. 39–54.

Elter, G., Elter, P., Sturani, P., and Weidmann, M., 1966, Sur la prolungation du domaine ligure del’Apennin dans le Monferrat e les Alpes et sur l’origine de la Nappe de la Simme s.l. desPrealpes romandes et chaiblaisiennes: Archives des Sciences, v. 176, p. 279–377.

Elter, P., 1960, I lineamenti tettonici dell’Appennino a NE delle Apuane: Bollettino della SocietàGeologica Italiana, v. 79, no. 2, p. 273–312.

Elter, P., 1975, L’ensemble ligure: Bullettin dé la Société Géologique de France, v. 17, p. 984–997.Elter, P., Catanzariti, R., Ghiselli, F., Marroni, M., Molli, G., Ottria, G., and Pandolfi, L., 1999,

L’unità Aveto (Appennino Settentrionale): caratteristiche litostratigrafiche, biostratigrafia,petrografia delle areniti ed assetto strutturale: Bollettino della Società Geologica Italiana, v. 118,p. 41–64.

Elter, P., Ghiselli, F., Marroni, M., and Ottria, G., 1997, Note illustrative del Foglio 197 ‘Bobbio’ dellaCarta Geologica d’Italia in scala 1:50.000: Istituto Poligrafico e Zecca dello Stato, Roma, p. 1–106.

Elter, P., Haccard, D., Lanteaume, M., and Raggi, G., 1961, Osservazioni sui rapporti tra Flysch adElmintoidi ed Arenaria Superiore nell’Appennino Ligure e nelle Alpi Marittime: Bollettinodella Società Geologica Italiana, v. 80, no. 3, p. 115–120.

Elter, P., Lasagna, S., Marroni, M., Pandolfi L., Vescovi, P., and Zanzucchi, G., 2005, Note illustra-tive del Foglio 196 “Bedonia” della Carta Geologica d’Itdic in scala 1:50,000: Istituto Poli-grafico e Zecca della Stato, Roma, 117 p.

Elter, P., and Marroni, M., 1991, Le Unità Liguri dell’Appennino Settentrionale: sintesi dei dati enuove interpretazioni: Memorie Descrittive della Carta Geologica d’Italia, v. 44, p. 121–138.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

30 M. Marroni et al.

Elter, P., Marroni, M., Molli, G., and Pandolfi, L., 1991, Le caratteristiche stratigrafiche delComplesso di M.Penna/Casanova: Atti Ticinensi di Scienze della Terra, v. 34, p. 97–106.

Elter, P., and Pertusati, P.C., 1973, Considerazioni sul limite Alpi-Appennino e sulle relazioni conl’arco delle Alpi Occidentali: Memorie della Società Geologica Italiana, v. 12, p. 359–375.

Elter, P., and Trevisan, L., 1973, Olistostromes in the tectonic evolution of the Northern Apennines, in DeJong, K.A., and Scholten, R., eds., Gravity and tectonics: New York, John Wiley & Sons, p. 175–188.

Federico, L., Spagnolo, C., Crispini, L., and Capponi, G., 2009, Fault-slip analysis in the metaophio-lites of the Voltri Massif: Constraints for the tectonic evolution at the Alps/Apennine boundary:Geological Journal, v. 44, no. 2, p. 225–240.

Ferrara, G., and Tonarini, S., 1985, Radiometric geochronology in Tuscany: Results and problems:Rendiconti della Società Italiana di Mineralogia e Petrologia, v. 40, p. 111–124.

Fontana, D., Spadafora, E., Stefani, C., Stocchi, S., Tateo, F., Villa, G., and Zuffa, G.G., 1994, TheUpper Cretaceous Helminthoid Flysch of the Northern Apennines: Provenance and sedimenta-tion: Memorie della Società Geologica Italiana, v. 48, p. 237–250.

Galbiati, B., 1976, Le litofacies ‘Liguridi’ della zona di Tavarone: Atti dell’Istuto di Geologiadell’Università di Pavia, v. 26, p. 1–14.

Gardin, S., Marino, M., Monechi, S., and, Principi, G., 1994, Biostratigraphy and sedimentology ofcretaceous Ligurid Flysch: Paleogeographical implication: Memorie della Società GeologicaItaliana, v. 48, p. 219–235.

Gianelli, G., and Principi, G., 1974, Studies on mafic and ultramafics rocks. 4.- Breccias of theophiolitic suite in the M. Bocco area (Ligurian Apennine): Bollettino della Società GeologicaItaliana, v. 93, p. 277–308.

Giannini, E., Nardi, R., and Tongiorgi, M., 1962, Osservazioni sul problema della Falda Toscana:Bollettino della Società Geologica Italiana, v. 81, p. 17–98.

Grandjacquet, C., and Haccard, D., 1977, Position structurale et role paleogeographique de l’unitédu Bracco au sein du contexte ophiolitique liguro-pièmontais (Apennin, Italie): Bullettin dé laSociété Géologique de France, v. 19, no. 4, p. 901–908.

Haccard, D., Lorenz, C., and Grandjacquet, C., 1972, Essai sur la liaison Alpes-Apennins (de la Lig-urie à la Calabrie): Memorie della Società Geologica Italiana, v. 11, p. 309–341.

Hoogerduijn Strating, E.H., 1994, Extensional faulting in an intraoceanic subduction complex-workinghypothesis for the Palaeogene of the Alps-Apennine system: Tectonophysics, v. 238, p. 255–273.

Iaccarino, S., and Rio, D., 1972, Nannoplancton calcareo e Foraminiferi della serie di Viano (Val Tres-inaro Appennino settentrionale: Revista Italiana di Paleontologia e Stratigrafia, v. 78, p. 641–678.

Lahondere, D., and Guerrot, C., 1997, Datation Sm-Nd du métamorphisme éclogitique en Corsicaalpine: un argument pour l’existence au Crétacé supérieur d’une zone de subduction activelocalisée sous le bloc corso-sarde: Géologie de France, v. 3, p. 3–11.

Laubscher, H., 1988, The arcs of the Western Alps and the Northern Apennines; An updated view:Tectonophysics, v. 146, p. 67–78.

Laubscher, H., 1991, The arc of western Alps today: Eclogae Geologicae Helvetiae, v. 84, p. 631–659.Leoni, L., Marroni, M., Sartori, F., and Tamponi, M., 1996, The grade of metamorphism in the

metapelites of the Internal Liguride Units (Northern Apennines, Italy): European Journal ofMineralogy, v. 8, p. 35–50.

Levi, N., Ellero, A., Ottria, G., and Pandolfi, L., 2006, Polyorogenic deformation history at veryshallow structural levels: The case of the Antola Unit (Northern Apennine, Italy): Journal ofStructural Geology, v. 28, no. 1, p. 694–1709.

Lüschen, E., Lammerer, B., Gebrande, H., Millahn, K., Nicolich, R., and TRANSALP WorkingGroup, 2004, Orogenic structure of the Eastern Alps, Europe, from TRANSALP deep seismicreflection profiling: Tectonophysics, v. 388, p. 85–102.

Marroni, M., 1991, Deformation history of the Mt. Gottero Unit (northern Apennines, Italy):Bollettino della Società Geologica Italiana, v. 110, p. 727–736.

Marroni, M., Della Croce, G., and Meccheri, M., 1988, Structural evolution of the Mt.Gottero Unitin the Mt. Zatta–Mt. Ghiffi sector (Ligurian–Emilian Apennines): Ofioliti, v. 13, p. 29–42.

Marroni, M., Molli, G., Montanini, A., Ottria, G., Pandolfi, L., and Tribuzio, R., 2002, The ExternalLiguride units (Northern Apennine, Italy): From rifting to convergence history of a fossilocean–continent transition zone: Ofioliti, v. 27, no. 2, p. 119–132.

Marroni, M., Molli, G., Montanini, A., and Tribuzio, R., 1998, The association of continental crustrocks with ophiolites (northern Apennines, Italy): Implications for the continent–oceantransition: Tectonophysics, v. 292, p. 43–66.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 31

Marroni, M., Molli, G., Ottria, G., and Pandolfi, L., 2001, Tectono-sedimentary evolution of theExternal Liguride units (Northern Apennine, Italy): insights in the pre-collisional history of afossil ocean–continent transition zone: Geodinamica Acta, v. 14, p. 307–320.

Marroni, M., Molli, G., Pandolfi, L., and Taini, A., 1999, Foliated cataclasites at the base of theAntola unit: structural features and geological implications: Compte Rendu de l’Académie deSciences, v. 329, p. 135–141.

Marroni, M., Monechi, S., Perilli, N., Principi, G., and Treves, B., 1992, Late Cretaceous flyschdeposits of the northern Apennines, Italy: age of inception of orogenisis-controlled sedimenta-tion: Cretaceous Research, v. 13, p. 487–504.

Marroni, M., and Pandolfi, L., 1996, The deformation history of an accreted ophiolite sequence: TheInternal Liguride units (Northern Apennines, Italy): Geodinamica Acta, v. 9, no. 1, p. 13–29.

Marroni, M., and Pandolfi, L., 2001, Debris flow and slide deposits at the top of the Internal Ligu-ride ophiolitic sequence (Northern Apennine, Italy): A record of frontal tectonic erosion in afossil accretionary wedge: The Island Arc, v. 10, p. 9–21.

Marroni, M., and Pandolfi, L., 2007, The architecture of the Jurassic Ligure-Piemontese oceanicbasin: Tentative reconstruction along the Northern Apennine–Alpine Corsica transect: Interna-tional Journal of Earth Science, v. 96, p. 1059–1078.

Marroni, M., Pandolfi, L., and Meneghini, F., 2004, From accretion to exhumation in a fossil accre-tionary wedge: a case history from Gottero Unit (Northern Apennines, Italy): GeodinamicaActa, v. 17, p. 41–53.

Marroni, M., and Perilli, N., 1988, L’età della successione del flysch ad Elmintoidi nell’area diCaranza (Appennino Settentrionale): nuovi dati sulla base del nannoplancton: Memoriedell’Accademia di Scienze Lunigianense, v. 42/43, p. 27–41.

Marroni, M., and Perilli, N., 1990, The age of the ophiolite sedimentary cover from the Mt. GotteroUnit (Internal Liguride Units, northern Apennines): New data from calcareous nannofossilsvOfioliti, v. 15, no. 2, p. 251–267.

Marroni, M., and Treves, B., 1998, Hidden Terranes in the northern Apennines, Italy: A record ofLate Cretaceous-Oligocene transpressional tectonics: Journal of Geology, v. 106, p. 149–162.

Marroni, M., and Tribuzio, R., 1996, Gabbro-derived granulites from External Liguride units (north-ern Apennine, Italy): Implications for the rifting processes in the western Tethys: GeologischeRundschau, v. 85, p. 239–249.

Martini, P.I., Sagri, M., and Doveton, J.H., 1978, Lithologic transition and bed thickness periodicitesin turbidite succession of the M. Antola Formation, Northern Apennines, Italy: Sedimentology,v. 25, p. 605–623.

Mattioli, M., Di Battistini, G., and Zanzucchi, G., 2002, Petrology, geochemistry and age of thevolcanic clasts from the Canetolo Unit (Northern Apennines, Italy): Bollettino della SocietàGeologica Italiana, v. 1, p. 399–416.

Meccheri, M., Clerici, A., and Costa, E., 1982, Analisi mesostrutturale delle deformazioni plicativein alcuni affioramenti delle Arenarie di Ostia (Appennino Parmense): Bollettino della SocietàGeologica Italiana, v. 101, p. 3–16.

Meccheri, M., Marroni, M., Casella, A, Della Croce, G., and Sergiampietri, L., 1986, L’Unità diColli/Tavarone nel quadro dell’evoluzione stratigrafica e strutturale del Dominio Ligure (AltaVal di Vara, Appennino Settentrionale): Ofioliti, v. 11, no. 3, p. 275–292.

Meli, S., Montanini, A., Thoni, M., and Frank, W., 1996, Age of mafic granulite blocks from theExternal Liguride Units (northern Apennine, Italy): Memorie di Scienze Geologiche, v. 48, p.65–72.

Meneghini, F., Marroni, M., and Pandolfi, L., 2007, Fluid flow during accretion in sediment-domi-nated margins: Evidences of a high-permeability fossil fault zone from the Internal Ligurianaccretionary units of the northern Apennines, Italy: Journal of Structural Geology, v. 29, no. 3,p. 515–529.

Mezzadri, G., 1964, Petrografia delle ‘Arenarie di Ostia’: Rendiconti della Società Italiana diMineralogia e Petrologia, v. 20, p. 193–228.

Michard, A., Chalouan, A., Feinberg, H., Goffé, B., and Montigny, R., 2002, How does the Alpine beltend between Spain and Morocco?: Bulletin de la Société Géologique de France, v. 173, p. 3–15.

Migliorini, C.I., 1933, Considerazioni su di un particolare effetto dell’orogenesi: Bollettino dellaSocietà Geologica Italiana, v. 52, no. 2, p. 293–304.

Molli, G., 1996, Pre-orogenic tectonic framework of the northern Apennine ophiolites: EclogaeGeologicae Helvetiae, v. 89, p. 163–180.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

32 M. Marroni et al.

Molli, G., 2008, Northern Apennine–Corsica orogenic system: an updated overview, in Siegesmund,S., Fuhrgenschuh, B., and Froitzheim, N., eds., Tectonic aspects of the Alpine-Dinaride-Car-pathian System: London, Geological Society, Special Publications, v. 298, p. 413–442.

Molli, G., Tribuzio, R., and Marquer, D., 2006, Deformation and metamorphism at the easternborder of the Tenda Massif (NE Corsica): a record of subduction and exhumation of continentalcrust: Journal of Structural Geology, v. 28, no. 10, p. 1748–1766.

Montanini, A., 1997, Mafic granulites in the Cretaceous sedimentary mèlanges from the northernApennine (Italy): petrology and tectonic implications: Schweizerische Mineralogische undPetrographische Mitteilungen, v. 77, p. 43–64.

Montanini, A., and Tribuzio, R., 2001, Gabbro-derived granulites from the Northern Apennine(Italy); Evidence for lower-crustal emplacement of tholeiitic liquids in post-Variscan times:Journal of Petrology, v. 42, p. 2259–2277.

Montanini, A., Tribuzio, R., and Vernia, L., 2008, Petrogenesis of basalts and gabbros transition(External Liguride from an ancient continent–ocean ophiolites, Northern Italy): Lithos, v. 101,no. 3–4, p. 453–479.

Mutti, E., Papani, L., Di Biase, D., Davoli, G., Mora, S., Segadelli, S., and Tinterri, R., 1995, IlBacino Terziario Epimesoalpino e le sue implicazioni sui rapporti tra Alpi ed Appennino:Memorie della Società Geologica di Padova, v. 47, p. 217–244.

Mutti, E., and Ricci Lucchi, F., 1972, Le torbiditi dell’Appennino Settentrionale: Introduzioneall’analisi di facies: Memorie della Società Geologica Italiana, v. 11, p. 161–199.

Naylor, A.M., 1982, The Casanova Complex of the Northern Apennines: A mèlange formed on adistal passive continental margin: Journal of Structural Geology, v. 4, p. 1–18.

Nilsen, T.H., and Abbate, E., 1983–1984, Submarine-fan facies associations of the UpperCretaceous and Paleocene Gottero Sandstone, Ligurian Apennines, Italy: Geo-Marine Letters, v.3, p. 193–197

Nirta, G., Principi, G., and Vannucchi, P., 2007, The Ligurian Units of Western Tuscany (NorthernApennine): Insight on the influence of pre-existing weakness during oceanic closure:Geodinamica Acta, v. 20, p. 71–97.

Ohnenstetter, D., Ohnenstetter, M., and Rocci, G., 1976, Etude des métamorphisme successifsdes cumulates ophiolitiques en Corse: Bullettin de la Société Géologique de France, v. 18,p. 115–134.

Pandolfi, L., 1997, Stratigrafia ed evoluzione strutturale delle successioni torbiditiche cretacee dellaLiguria orientale (Appennino Settentrionale). Tesi di Dottorato, Università di Pisa, 175 p.

Passerini, P., 1965, Rapporti tra le ofioliti e le formazioni sedimentarie fra Piacenza e il MareTirreno: Bollettino della Società Geologica Italiana, v. 84, p. 92–176.

Peccerillo, A., Poli, G., and Donati, C., 2001, The plio-quaternary magmatism of Southern Tuscanyand Northern Latium: Compositional characteristics, genesis and geodynamic significance: Ofi-oliti, v. 26, p. 229–237.

Pertusati, P.C., and Horremberger, J.C., 1975, Studio strutturale degli Scisti della Val Lavagna (Unitàdel Gottero, Appennino ligure): Bollettino della Società Geologica Italiana, v. 94, p. 1375–1436.

Piccardo, G.B., Müntener, O., and Zanetti, A., 2004, Alpine-Apennine peridotite: New concepts ontheir composition and evolution: Ofioliti, v. 29, p. 63–74.

Piccardo, G.B., 1976, Petrologia del massiccio lherzolitico di Suvero (La Spezia): Ofioliti, v. 1, p.243–279.

Piccardo, G.B., Rampone, E., and Romairone, A., 2002, Formation and composition of the oceanic litho-sphere of the Ligurian Tethys: Inferences from the Ligurian ophiolites: Ofioliti, v. 27, p. 134–145.

Piccardo, G.B., Rampone, E., and Vannucci, R., 1990, Upper mantle evolution during continentalrifting and ocean formation: Evidences from peridotite bodies of the western Alpine-northernApennine system: Memoire dé la Societé Geologique de France, v. 156, p. 323–333.

Pini, G., 1999, Tectonosomes and olistostromes in the argille scagliose, northern Apennines, Italy:Geological Society of America Special Paper, v. 335, 70 p.

Principi, G., and Treves, B., 1984, Il sistema corso-appenninico come prisma d’accrezione. Riflessisul problema generale del limite Alpi-Appennini: Memorie della Società Geologica Italiana,v. 28, p. 549–576.

Rio, D., and Villa, G., 1983, I nannofossili calcarei del Cretaceo superiore del flysch di Solignano,media Val di Taro, Appennino Settentrionale: Memorie di Scienze Geologiche, v. 36, p. 239–282.

Rio, D., and Villa, G., 1987, On the age of the ‘Salti del Diavolo’ conglomerates and the M. Cassio ‘Basalcomplex’ (Northern Apennines, Parma province): Giornale di Geologia, v. 49, no. 1, p. 63–73.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010

International Geology Review 33

Rio, D., Villa, G., and Cantadori, M., 1983, Nannofossils dating of the Helminthoid flysch Units inthe Northern Apennines: Giornale di Geologia, v. 45, p. 57–86.

Rovereto, G., 1939, Liguria geologica: Memorie della Società Geologica Italiana, v. 2, p. 1–743.Rowan, M.G., 1990, The Upper Cretaceous Helminthoid Flysch of the Northern Apennines and

Maritime Alps: correlation and provenance: Ofioliti, v. 15, p. 305–326.Sagri, M., 1979, Upper cretaceous trench wedge turbidites in the Northern Apennines (Italy): Rendi-

conti della Società Geologica Italiana, v. 2, p. 27–28.Sagri, M., 1980, Le Arenarie di Bordighera: una conoide sottomarina nel bacino di sedimentazione

del flysch ad Elmintoidi di San Remo (Cretaceo superiore, Liguria occidentale): Bollettino dellaSocietà Geologica Italiana, v. 88, p. 205–226.

Scholle, P.A., 1971, Sedimentology of fine-grained deep-water carbonate turbidites. Monte Antolaflysch (Upper cretaceous, Northern Apennines, Italy): Geological Society of America Bulletin,v. 82, p. 629–658.

Sestini, G., 1970, Development of the Northern Apennines geosyncline: Sedimentary Geology, v. 4,no. 3/4, p. 1–645.

Teichmüller, R., 1932, Uber das Vorland des Apennin. Nachricten von der Gesellschaft der Wissen-schaften zu Gottingen, v. 4, no. 17, p. 8–52.

Tillmann, N., 1926, Tektonishe studien in der Catena Metallifera Toskanas: GeologischeRundschau, v. 17, p. 631–660.

Treves, B., 1984, Orogenic belts as accretionary prism: the example of the northern Apennines:Ofioliti, v. 9, p. 577–618.

Treves, B.A., and Harper, G.D., 1994, Exposure of serpentinites on the ocean floor: Sequence offaulting and hydrofracturing in the Northern Apennine ophicalcites: Ofioliti, v. 19, p. 435–466.

Valloni, R., and Zuffa, G.G., 1984, Provenance changes for arenaceous formations of the NorthernApennines (Italy): Geological Society of American Bulletin, v. 95, p. 1035–1039.

Van de Kamp, P.C., and Leake, B.E., 1995, Petrology and geochemistry of siliciclastic rocks ofmixed feldspatic and ophiolitic provenance in the Northern Apennines, Italy: Chemical Geol-ogy, v. 122, p. 1–20.

Van Wamel, W.A., Bons, A.J., Franssen, R.C.M.W., Van Lingen, W., Postuma, W., and VanZupthen, A.C.A., 1985, A structural geologic traverse through the Northern Apennines fromRapallo to Bettola (N.Italy): Geologie en Mijnbouw, v. 64, p. 119–187.

Van Zutphen, A.C.A., Van Wamel, W.A., and Bons, A.J., 1985, The structure of the Lavagna nappein the region of Monte Ramaceto and Val Graveglia (Ligurian Apennines, Italy): Geologie enMijnbouw, v. 64, p. 373–384.

Vannucci, R., Rampone, F., Piccardo, G.B., Ottolini, L., and Bottazzi, P., 1993, Ophiolitic magma-tism in the Ligurian Tethys: An ion microprobe study of basaltic clinopyroxenes: Contributionsof Mineralogy and Petrology, v. 115, p. 123–137.

Vercesi, P.L., and Cobianchi, M., 1998, Stratigrafia di un frammento di margine continentalegiurassico: la successione di C.se Caldarola (Appennino Piacentino): Bollettino della SocietàGeologica Italiana, v. 117, p. 537–554.

Vescovi, P., Fornaciari, E., Rio, D., and Valloni, R., 1999, The Basal complex stratigraphy of theHelminthoid Monte Cassio Flysch: A key to the Eoalpine tectonics of the Northern Apennines:Rivista Italiana Paleontologia e Stratigrafia, v. 105, p. 101–128.

Vignaroli, G., Faccenna, C., Jolivet, L., Piromallo, C., and Rossetti, F., 2008, Subduction polarityreversal at the junction between the Western Alps and the Northern Apennines, Italy:Tectonophysics, v. 450, p. 35–40.

Villa, G., 1991, Biostratigrafia a nannofossili calcarei delle Arenarie di Ostia nella località tipo enella zona di Berceto (Prov. di Parma): Memorie Descrittive della Carta Geologica d’Italia, v.46, p. 433–443.

Wildi, W., 1985, Heavy mineral distribution and dispersal pattern in penninic and ligurian flyschbasins (Alps, Northern Apennines): Giornale di Geologia, v. 47, no. 1–2, p. 77–99.

Zaccagna, D., 1932, Descrizione geologica delle Alpi Apuane: Memorie Descrittive della CartaGeologica d’Italia, v. 25, p. 1–440.

Zuffa, G.G., Fontana, D., Morlotti, E., Premoli Silva, I., Sighinolfi, G.P., Stefani, C., and Fontani,L., 2002, Anatomy of carbonate turbidite mega-beds (M. Cassio Formation, Upper Cretaceous,northern Apennines, Italy), in Valloni, R., and Basu, A., eds., Qualitative provenance studies inItaly: Memorie Descrittive della Carta Geologica d’Italia, v. 61, p. 129–144.

Downloaded By: [University of Stellenbosch] At: 12:13 26 April 2010