Basin Research (2007) 19, 507–527, doi: 10.1111/j.1365-2117.2007.00334.x The Miocene Saint-Florent Basin in northern : stratigraphy, sedimentology, and tectonic implications William Cavazza,n Peter G. DeCelles,w Maria Giuditta Fellin,n 1 and Luigi Paganellin z nDepartment of Earth and Geoenvironmental Sciences, University of Bologna, Bologna, wDepartment of Geosciences, University of Arizona,Tucson, Arizona, USA Department of Geology, Palaeontology and Geophysics, University of Padua, Padua, Italy z ABSTRACT Late early^early middle Miocene (Burdigalian^Langhian) time on the island of Corsica (western Mediterranean) was characterized by a combination of (i) postcollisional structural inversion of the main boundary thrust system between the Alpine orogenic wedge and the foreland, (ii) eustatic sealevel rise and (iii) subsidence related to the development of the Ligurian-Provenc° al basin.These processes created the accommodation for a distinctive continental to shallow-marine sedimentary succession along narrow and elongated basins. Much of these deposits have been eroded and presently only a few scattered outcrop areas remain, most notably at Saint-Florent and Francardo.The Burdigalian^Langhian sedimentary succession at Saint-Florent is composed of three distinguishing detrital components: (i) siliciclastic detritus derived from erosion of the nearby Alpine orogenic wedge, (ii) carbonate intrabasinal detritus (bioclasts of shallow-marine and pelagic organisms), and (iii) siliciclastic detritus derived from Hercynian-age foreland terraines.The basal deposits (Fium Albino Formation) are £uvial and composed of Alpine-derived detritus, with subordinate foreland- derived volcanic detritus. All three detrital components are present in the middle portion of the succession (Torra and Monte Sant’Angelo Formations), which is characterized by thin transitional deposits evolving vertically into fully marine deposits, although the carbonate intrabasinal component is predominant.The Monte Sant’Angelo Formation is characteristically dominated by the deposits of large gravel and sandwaves, possibly the result of current ampli¢cation in narrow seaways that developed between the foreland and the tectonically collapsing Alpine orogenic wedge.The laterally equivalent Saint-Florent conglomerate is composed of clasts derived from the late Permian Cinto volcanic district within the foreland.The uppermost unit ( Formation) is dominated by bioclasts of pelagic organisms.The Saint-Florent succession was deposited during the last phase of the counterclockwise rotation of the Corsica^^Calabria continental block and the resulting development of the Provenc° al oceanic basin.The succession sits at the paleogeographic boundary between the Alpine orogenic wedge (to the east), its foreland (to the west), and the Ligurian-Provenc° al basin (to the northwest). Abrupt compositional changes in the succession resulted from the complex, varying interplay of post-collisional extensional tectonism, eustacy and competing drainage systems.

INTRODUCTION that rifting of Corsica^Sardinia^Calabria from was the result of upper plate extension related to slab The islands of Corsica and Sardinia and the surrounding roll-back along the Ionian subduction zone. Although continental shelves are a fragment of European^Iberian the exact timing is still far from precisely known (see lithosphere, which, together with Calabria, rifted o¡ the Speranza, 1999, for a discussion), rifting started as early southern continental margin of Europe during Oligo- as the early Oligocene (Vially & Tre¤ molie' res, 1996) cene^Miocene time and drifted southeastward by coun- whereas drifting occurred between ca. 22 and 15 Ma terclockwise rotation (Alvarez, 1972, 1976; Alvarez et al., (Ferrandini etal., 2003). Rifting reactivated Pyrenean com- 1974) of about 45 . Malinverno & Ryan (1986) ¢rst proposed 1 pressional structures of the Late Cretaceous^Early Eocene Provenc° al foldbelt (Vially & Tre¤ molie' res, 1996). Subse- Correspondence: William Cavazza, Department of Earth and quent rifting of Calabria from Corsica^Sardinia during Geoenvironmental Sciences, University of Bologna, Piazza di the late Miocene isolated Corsica^Sardinia between the Porta S. Donato 1, 40126 Bologna, Italy. E-mail: william.cavazza @unibo.it Ligurian-Provenc° al basin to the northwest and theTyrrhe- 1 Present address: Geologisches Institut, ETH Zˇrich, Switzer- nian Sea to the east (see Cavazza et al., 2004a, b, for a re- land. view) (Fig.1). r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd 507 W. Cavazza et al.

s lp 45¼N A Francardo

in Ap s en a n B in Alpine l e a s ç Hercynian Corsica n e T v yr Corsica ough o rh Tr r e P n Aleria ia Iberia n Plain 40¼N lencia S a e V a 0 100 200 Km

Neogene Bonifacio 0¼ 10¼E 20¼E sediments

5 km Marine de Farinole Cima di Gratera Gulf 1026 of St. Florent Monte Genova 421 Col de Teghime St-Florent 536 Casta

Nebbio

Tenda Massif Balagne Continental and Metamonzogranite coastal deposits Monte Asto T e of Monte Asto Unit Quaternary 1535 n Metagranodiorite - St. Florent Fm d Metatonalite of L. Langhian a Casta Unit Mt. S.Angelo- and Monzogranite- M Torra Fms Metamonzogranite a Burdigalian- s of Monte Genova Unit s L. Langhian Late Carboniferous - i Fiume Albino Fm f Permian Volcanic Succession Burdigalian

Lower Schistes Neogene fault S Lustrés Autochtonous c L u foreland sediments Balagne Nebbio Nappes h Upper Schistes thrust i s Eocene Mesozoic-Paleogene t Lustrés thrust reactivated as sediments s an extensional fault Hercynian granitoid t r Farinole, and é rock and pre-Hercynian Jurassic Ophiolite- e Serra di Pigno thrust reactivated as s s a strike slip fault crystalline country rock bearing unit orthogneiss

Fig.1. Schematic geologic map of northern Corsica within the framework of the Mediterranean . Modi¢ed after Cavazza et al. (2001) and Fellin et al. (2005).

As the Corsica^Sardinia^Calabria block rifted away components. Remnants of the older portions of this basin from Europe, the progressively widening Ligurian-Pro- ¢ll are preserved in Corsica and are referred to as the venc° al basin was £ooded by marine water. Situated be- Saint-Florent Basin (Fig.1). Most striking are stacked de- tween the extending Provenc° al margin of Europe and a posits of very large-scale gravelly and sandy bedforms and fragment of the collapsing western Alpine orogenic wedge intercalated sediment-gravity £ows. The tectonic setting (Fig. 2), the basin was ¢lled with a diverse assemblage of of the Saint-Florent Basin between the extending orogenic lithofacies that include both carbonate and siliciclastic wedge and the foreland produced a narrow paleostrait

508 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 Miocene Saint-Florent Basin

WSW Balagne Tenda massif St. Florent ENE

s.l.

5 km

St. Florent succession Hercynian basement Schistes Lustrés s.l. Nebbio and Balagne Nappes Eocene foreland sediments Tectonised Hercynian basement Farinole-Oletta orthogneiss

Fig. 2. Schematic cross-section across northern Corsica (see Fig.1for location of trace of section). Solid arrows indicate Alpine-age contractional faulting; open arrows indicate (i) late Oligocene normal faults that reactivated Alpine thrust faults, and (ii) Neogene high- angle normal faults. Modi¢ed after Cavazza et al. (2001). where oceanic (probably tidal) currents were strongly am- Florent, Francardo, the Aleria plain and Bonifacio (Fig. 1) pli¢ed. The purpose of this paper is to document the (e.g. Orszag-Sperber & Pilot, 1976; Alesandri et al., 1977; Saint-Florent Basin ¢ll and to assess its potential signi¢ - Groupe Francais d’Etude du Neogene, 1989; Cubells et al., cance for understanding the history of rifting and orogenic 1994; Ferrandini et al., 1998, 2002, 2003; Loy« e-Pilot et al., collapse in northern Corsica, as well as its implications for 2004; Fellin et al., 2005).The successions at Saint-Florent, the Oligocene^Neogene tectonic evolution of the western Francardo and Bonifacio are thin and cover almost pre- Mediterranean. Our results should be useful for evaluating cisely the same time span (Burdigalian-Langhian).The se- other Neogene basins in the Mediterranean region, where dimentary succession of the Aleria Plain spans Burdigalian upper plate (or back-arc) rifting events in response to sub- to Pliocene time and represents the onland portion of the duction zone retreat (Royden, 1993) are widespread (e.g. 48 km-thick o¡shore Corsica basin to the east (Mau¡ret Jolivet & Faccenna, 2000; Cavazza et al., 2004a). et al., 1999), which developed during rifting of Calabria from the Corsica^Sardinia block. This paper describes and interprets the Miocene succession at Saint-Florent within the framework of the post-collisional evolution of GEOLOGIC SETTING Corsica and the western Mediterranean. Corsica is divided into two distinct geologic terranes (Fig. 1). The western part of the island is characterized by Carboniferous^Permian granitoid rocks and acid volcanic STRUCTURE OF THE BALAGNE ^ rocks related to the Hercynian orogeny, with Precambrian^ BASTIA TRAVERSE middle Palaeozoic metamorphic host rocks and scattered outcrops of Palaeozoic sedimentary rocks.The northeast- The Saint-Florent Basin lies along the Balagne^Bastia tra- ern portion of the island (‘Alpine Corsica’) is a nappe stack verse (Fig. 2), which arguably constitutes the best-studied dominated by Jurassic oceanic crust and its sedimentary part of Corsica. From the west to the east along the tra- cover (Durand-Delga, 1978,1984).These rocks were meta- verse, the major tectonostratigraphic domains include the morphosed at high pressures and low temperatures during following: (i) The autochthonous, relatively undeformed the Alpine orogeny (see Gibbons et al., 1986, and Caron, basement complex of the European^Iberian plate (‘Hercy- 1994, for reviews). Although data pointing to a meta- nian Corsica’), made of Carboniferous to early Permian morphic event older than Late Eocene are scarce and granitoid rocks, their pre-Hercynian metamorphic host questionable (see Brunet et al., 2000, for a discussion), the rocks and Permian volcanic rocks (Mt. Cinto volcanic dis- compressional development of the Alpine orogenic wedge trict); (ii) remnants of the Balagne foreland basin and traditionally has been considered to span Late Cretaceous thrust belt with middle Eocene turbidites, overthrust by to Eocene time. Major thrusting in Corsica occurred dur- W-verging nappes of Jurassic ophiolites and their Cretac- ing the Eocene, producing much of the documented eous^Eocene, unmetamorphosed sedimentary cover; (iii) nappe stacking and metamorphism (Caron, 1994). Local the highly deformed parts of the European continental remnants of an Eocene foreland basin (e.g. the autochtho- margin, including the dome-shaped Tenda massif of Her- nous clastic units of the Balagne region of Fig. 1) are pre- cynian granitoid and Palaeozoic volcanic rocks, and slices sent between the Hercynian crystalline basement of crystalline basement of the Oletta-Serra di Pigno-Fari- complex and Alpine Corsica (Nardi et al., 1978; Jourdan, nole crystalline unit interspersed in the ‘Schistes Lustre¤ s’ 1988). nappe; (iv) the Nebbio nappe, composed of rock units si- From north to south, Miocene rocks are present in milar to those of the Balagne nappe and similarly unmeta- Corsica only in four relatively small areas: Saint- morphosed (Dallan & Puccinelli, 1986, 1995). The Nebbio r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 509 W. Cavazza et al.

Mt. S. Angelo Fm

Foresets N

Axes of CM PS trough x-beds interval 15¼ n = 89 n = 11 Foresets and max 12% trough x-beds St. Florent conglomerate

Gulf of SR St. Florent

Imbrications interval 15¼ n = 85 max 14%

Farinole Fm Alpine contact U. Langhian-Mid. Serravallian Farinole-Oletta orthogneiss St. Florent Fm L. Langhian Alpine contact Mt. S.Angelo- and Torra Fms Tenda orthogneiss Burdigalian-L. Langhian Fiume Albino Fm Neogene fault Burdigalian thrust transgression East Tenda Upper Nebbio Unit shear zone 1 km Lower Nebbio Unit bed attitude

Alpine contact location of stratigraphic SR Strutta Rau PS Punta Saeta CM Campu Maggiore Schistes Lustrés s.l. section

Fig. 3. Geological map of Saint-Florent and its surroundings (after Fellin etal., 2005). Shown are the traces of the stratigraphic sections of Fig. 5. Paleocurrent data (upper left corner) include measurements of (i) foresets plotted as dip directions, (ii) limbs of trough cross- beds plotted as dip directions and (iii) poles of a^b planes of imbricated clasts. All measurements were rotated to horizontal and plotted on the lower hemisphere of a Wul¡ stereonet. Upper rose diagram obtained summing foresets measurements and the trough axes derived using the methods of DeCelles et al. (1984). nappe overlies the previously deformed and metamor- Waters, 1989) during Eocene time (Brunet et al., 2000). phosed ‘Schistes Lustre¤ s’ nappe and is unconformably Westward emplacement of the ‘Schistes Lustre¤ s’ nappe overlain by the Miocene Saint-Florent succession. The onto the Hercynian basement and its Eocene sedimentary Nebbio, Balagne and (NE Corsica; not shown cover ended in late Eocene time (Durand-Delga, 1978). in Figs 1 and 2) nappes are the uppermost, unmetamor- phosed tectonic units of the Alpine orogenic wedge (‘nappe superieure’). The basal thrust faults of these nappes, em- STRUCTURAL SETTING OF THE placed during the Eocene (e.g. Durand-Delga, 1984), were SAINT-FLORENT BASIN tectonically inverted as low-angle detachment faults dur- ing the late Oligocene (Daniel et al., 1996); (v) the ‘Schistes From the structural viewpoint, the Saint-Florent region is Lustre¤ s’ nappe is composed of ophiolitic sequences cov- dominated by the East Tenda shear zone (Figs1^3), a major ered by metamorphosed marine sedimentary rocks. Alpine top-to-the-west thrust fault that was reactivated as It contains eclogitic associations (Caron etal.,1981; Lahon- a detachment fault since the Oligocene (Waters, 1990; de' re, 1988; Fournier et al., 1991) of Late Cretaceous age Fournier et. al., 1991; Brunet et al., 2000) and then cut by (Lahonde' re and Guerrot, 1997) that were retrogressed to high-angle normal faults during late-early to early-middle blueschist facies (Gibbons et al., 1986; Lahonde' re, 1988; Miocene time (Fellin et al., 2005). The dome-shaped

510 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 Miocene Saint-Florent Basin

Tenda massif (Fig. 2) is the footwall of the detachment northern boundaries of the outcrop area (Fig. 3). Ferrandi- fault and is mostly composed of Hercynian granitoid rocks ni et al. (1998, Fig. 2) and Fellin et al. (2005, Fig. 6) reported and Palaeozoic volcanics. These rocks were recrystallized total thicknesses of 550 and ca. 600 m, respectively. Our in blueschist conditions during west-vergent Alpine measured stratigraphic sections, integrated from observa- thrusting at peak pressures/temperatures of 0.8 GPa/ tions throughout the Saint-Florent Basin, point to a max- 300 1C to 1.1GPa/500 1C (minimum burial depth of 27 km) imum total thickness of about 400 m for the preserved and later overprinted by ductile extension in greenschist basin ¢ll, in agreement with Durand-Delga (1978), Rossi facies along its eastern border during Oligocene time et al. (1994) and Dallan & Puccinelli (1995). (Waters, 1990; Fournier et al., 1991; Brunet et al., 2000; Tri- From the bottom to the top, the succession begins with buzio & Giacomini, 2002). a thin (maximum 60 m), discontinuous unit named the In its presently outcropping extent, the Saint-Florent Fium Albino Formation by Ferrandini et al. (1998) (Fig. 4). Basin is bounded on the east by an N-striking,W-dipping This unit crops out locally in erosional depressions cut normal fault system (Fig. 3) active during Burdigalian^ into the underlying Nebbio nappe (Fellin et al., 2005) and Langhian time (i.e. during deposition of the Saint-Florent is composed of pebble conglomerate and very coarse- to succession), based on the integrated results of structural coarse-grained sandstone thatwere interpreted by Ferran- analysis and apatite^zircon ¢ssion-track analyses (Fellin dini et al. (1998) as the deposits of an alluvial/£uvial envir- et al., 2005). The western boundary of the basin is a onment. Conglomerate clasts were mostly derived from N-to-NW-striking fault partially obscured by Quaternary the Alpine orogenic wedge, whereas sandstone lithic frag- alluvium of the Aliso River. According to Fellin etal. (2005), ments have a more varied provenance (see following sec- this high-angle normal fault displaces the East Tenda tion). No direct age determination exists for this unit. shear zone and juxtaposes terraines exhumed at di¡erent Poor outcrops hinder unambiguous interpretation of ages, thus substantiating the notion that high-angle nor- the contact between the Fium Albino Formation and the mal faulting postdated and was unrelated to detachment overlying Torra Formation (Fig. 4); Ferrandini et al. (1998) faulting along the East Tenda shear. Syndepositional tec- inferred it to be an angular unconformity, whereas Fellin tonism along minor associated normal faults is documen- et al. (2005) interpreted the contact as conformable. Most ted also by widespread soft-sediment deformation and likely, local minor unconformities are the result of synde- growth faults a¡ecting the basin ¢ll, both particularly positional deformation, the e¡ects of which are also visible common along the northern end of the basin. in the overlying calcarenites of the Monte Sant’Angelo Jolivet et al. (1990) and Fournier et al. (1991) interpreted Formation. In most places the Torra Formation directly the Saint-Florent Basin as the result of extension along the East Tenda shear zone, in spite of the rather large time gap between the youngest ages in the exhumed metamorphic Ma Age rocks (33^32 Ma), and the age of the base of the basin ¢ll 11.2 Farinole at about19^18 Ma. Brunet et al. (2000) reported Ar/Ar ages allian Fm v from the Tenda massif as young as 25 Ma, thus reducing a St. Florent the time gap to 6^7 Ma. Serr Structural and ¢ssion-track analyses indicate that dur- conglomerate 14.8 ing the early late Miocene (Tortonian) the Saint-Florent

Basin was uplifted, acquiring its open synclinal shape. Ki- Lang. nematic indicators suggest that uplift occurred through 16.4 right-lateral transpressional reactivation of the boundary faults under a NNE-oriented maximum compressional Mt. S. Angelo axis (Fellin et al., 2005). Partial annealing of apatites from Fm

the basement beneath the basin indicates that signi¢cant Burdigalian biomicrite erosion occurred and that the basin ¢ll was originally much thicker. 20.5 calcarenite Torra Fm siliciclastic Fium conglomerat STRATIGRAPHYAND SEDIMENTOLOGY Albino Fm basement OF THE SAINT-FLORENT SUCCESSION 23.8 Aquitanian The region of Saint-Florent is characterized by a thick Fig.4. Generalized stratigraphic section for the Saint-Florent area.The entire succession is here considered as conformable, succession of Neogene sedimentary rocks unconformably with only minor unconfomities locally present between the overlying the Nebbio tectonic unit (Fig. 3) (Dallan & Puc- £uvial deposits of the Fium Albino Formation and the cinelli, 1986, 1995; Dallan et al., 1988; Rossi et al., 1994).The transitional ones of theTorra Formation Data sources: Orszag- Saint-Florent sedimentary succession delineates a large, Sperber & Pilot, 1976, Loy« e-Pilot & Magne¤ , 1987, Ferrandini et al. open, north-plunging syncline. The lower contact of the (1998), Fellin et al. (2005), and unpublished data.Time scale after Saint-Florent succession is exposed locally along the Berggren et al. (1995). r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 511 W. Cavazza et al.

(a) (b) CAMPU MAGGIORE 70 50 LEGEND

Covered interval Fluid escape structures Wispy horizontal lamination Pecten Reverse ripples Echinoids Unidirectional current ripples Bryozoa 60 Trough cross-stratification Large-scale planar cross- Thalassanoides stratification Macaronichnus Hummocky cross-stratification Skolithos 40 Plane-parallel lamination Diffuse bioturbation Unstratified Molluskan debris Ophiolitic rock fragments Oncolites with ophiolitic cores Quartzo-feldspathic lithic 50 Oncolites with carbonate cores conglomerate

GRAIN SIZE KEY s/c ss cg e

n 30 o t s y a Medium

40 l Siltstone/ c Sandstone Conglomerate

PUNTA DI SAETA 30 100

Monte Sant’ Angelo Fm 20 Monte Sant’ Angelo Fm

20 90

10

10 80 Mt. Sant’ Angelo Fm.

0 70 0 s/c ss cg s/c ss cg s/c ss cg Fig. 5. Measured stratigraphic sections. See Fig. 3 for location.

overlies the rock units of the Nebbio nappe.TheTorra For- glomerate is a local coarse-grained facies that cuts ero- mation is about 50^60 m thick (Fig. 5c) and it is made of sively into and is partly a lateral equivalent of the Monte massive medium- to coarse-grained sandstone and pebble Sant’Angelo Formation.The age of the Monte Sant’Angelo conglomerate with abundant oyster and pectinid shells, Formation is late Burdigalian^early Langhian, based on echinoids, bryozoans and Skolithos burrows. The upper foraminifera and nannoplankton biostratigraphy (Ferran- portion of the unit comprises thick carbonate-dominated dini etal.,1998; Fellin etal., 2005) and on magnetostratigra- beds rich in corallinaceous algae and is transitional to the phy (Vigliotti & Kent, 1990; Ferrandini et al., 2003). overlying Monte Sant’Angelo Formation. The Monte Sant’Angelo Formation is dominated by Reaching ca. 250 m in thickness, the Monte Sant’Angelo bioclastic detritus (corallinacean red algae, bivalves, Formation represents the bulk of the Saint-Florent sedi- bryozoans and foraminifera) although varying amounts of mentary succession (Figs 4 and 5). This unit conformably siliciclastic detritus are present throughout (on average overlies the Torra Formation and is overlain with a sharp 15% of sand-sized grains consist of noncarbonate extra- contact by the Farinole Formation.The Saint-Florent con- basinal detritus).The extrabasinal clasts are dominated by

512 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 Miocene Saint-Florent Basin

(c) 70 140 210 280

60 130 200 270

50 120 190 260

Shw

Sh 40 110 180 250 Shw

Sp

orra Formation 100 T 30 170 240 Monte Sant’Angelo Formation Monte Sant’ Angelo Formation Monte Sant’ Angelo Formation

20 90 160 230 STRUTTA RAU Sm

Sm 10 80 150 220 290 Sm Gmm minor fault Sm Sm Sm St/Sp Sm 0 70 140 210 280 s/c ss cg s/c ss cg s/c ss cg s/c ss cg s/c ss cg Fig. 5. Continued.

material derived from the Alpine orogenic wedge. Rhodo- are composed primarily of siliciclastic clasts. In either liths (i.e. nodules of red corallinacean algae concentrically case, the siliciclastic clasts are usually normally graded encrusted) are very common (Orszag-Sperber et al., 1977), (Fig. 8f); in a few cases we observed inverse grading (Fig. often concentrated in 1.0^2.5-m-thick beds intercalated 8e) and inverse to normal grading (Fig. 8g) among the with large-scale cross-bedded calcarenites virtually de- siliciclastic clasts. Out-sized clasts are present in many void of rhodoliths (Figs 6, 7 and 8a). Amalgamated beds of these beds, £oating in an unsorted and unstrati¢ed are common in both the rhodolitic and calcarenitic facies. matrix. Rhodoliths reach a maximum diameter of 12 cm (average Large-scale sets of cross-bedded calcarenite are up to 4^5 cm) and have either bioclastic or siliciclastic nuclei 5 m thick (Figs 5, 6 and 8a, c) and are made of well-sorted, (Fig.8b).The rhodolitic beds are tabular, laterally continu- very coarse- to coarse-grained intrabasinal bioclastic ous and their bases are £at and not obviously erosional sandstone (biosparite and biomicrosparite) with a subordi- (Fig. 8c). Although some of these beds contain weakly de- nate siliciclastic extrabasinal detrital component. Rhodo- veloped horizontal strati¢cation, most are not internally liths are scarce in cross-bedded calcarenites and are always strati¢ed (Fig. 8c, d).These beds exhibit distinctive grain- concentrated at the base of the foresets. At the outcrop size and grain-compositional variations. In beds with scale the bounding surfaces of the cross-sets are mostly abundant rhodoliths, the denser siliciclastic clasts, either planar; only in a few cases were curved bounding surfaces free or as cores within rhodoliths, are concentrated in the visible (Fig.8a). Reactivation surfaces are common. Foreset lower part of the bed, whereas densely packed rhodoliths dips are commonly greater than 201.The internal geome- are concentrated in the upper part (Fig. 8e). Other beds try of the large-scale sets of cross-bedded calcarenite is r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 513 W. Cavazza et al.

foresets. Foresets are commonly burrowed, particularly near the bottom, withThalassinoides, Ophiomorpha and Ma- caronichnus as the most common ichnogenera (Fig. 8h). Spreiten structures are also present. Cosets commonly are bounded by laterally extensive, sheet-like erosional sur- faces. No mud drapes were detected. Well-rounded, well-organized pebble-to-cobble con- glomerate made of rhyolitic ignimbrite clasts is inter- bedded with the Monte Sant’Angelo Formation along the coast north of the town of Saint-Florent (Fig. 3) and also crops out just east of the town in the core of the syncline. These conglomerates have been referred to as poudingues de Fortino (Hollande,1917), poudingues deSaint-Florent (Maury, 1909), Formation de Saint-Florent (Ferrandini et al., 1998) Fig. 6. Massive, inversely graded rhodolith bed (rh) erosively and St Florent conglomerate (Fellin et al., 2005). The rhyolite overlying large-scale cross-beds (sandwave deposits) (sw) in the (ash- £ow tu¡) clasts are distinctive in colour, texture and Monte Sant’Angelo Formation near the Campu Maggiore section composition, and were derived from the Permian volcanic (see Fig. 3 for location). Jacob’s sta¡ is1.5 m long. complex of , located about 30 km to the southwest of the study area.This rock type is so distinctive that derivation of the conglomerate clasts from the Monte Cinto complex was ¢rst proposed by Reynaud in1833. Pos- sibly because of its siliciclastic nature ^ markedly di¡erent from the carbonate-dominated majority of the Saint-Flor- ent succession ^ this conglomerate has long been consid- ered to postdate the deposition of the carbonate succession, in spite of several outcrops along the coast north of Saint-Florent where the conglomerate is inter- bedded with the carbonates. In addition, in the coastal outcrops just east of the town of Saint-Florent, these con- glomerates have the same structural orientation as the Monte Sant’Angelo Formation (Durand-Delga, 1978, p. 158; Dallan et al., 1988; Dallan & Puccinelli, 1995, p. 51), suggesting that the two units are laterally equivalent to each other. Therefore, based on our observations and those of Fellin et al. (2005), we propose to discontinue the use of the terms poudingues de Fortino, poudingues de Saint-Florent, and Formation de Saint-Florent for these characteristically well-rounded conglomerates. Because they are intimately associated with and laterally equivalent to the thick carbonate layers of the uppermost Monte San- t’Angelo Formation, we consider this distinctive unit as an informal member of the Monte Sant’Angelo Formation with the name ‘Saint-Florent conglomerate’. In spite of the lack of direct age control, we agree with Fellin et al. (2005) that the inter¢ngering with the upper Monte Sant’Angelo Formation points to an early Langhian age Fig.7. Interbedded large-scale cross-beds (sandwave deposits for this conglomerate. with subordinate smaller scale cross-beds produced by The Saint-Florent succession is capped by foramini- migrating megaripples) and massive rhodolith beds (Monte fera-rich marls and calcarenites of the Farinole Formation Sant’Angelo Formation; middle portion of the Strutta Rau (Fig. 4).This unit is about 80 m thick and crops out only in stratigraphic section ^ approximately170^205 m above base of the northeastern part of the study area (Fig. 3). Its age is section; Fig. 5c).These deposits indicate the alternation of late Langhian-middle Serravallian, based on nannoplank- traction and sediment-gravity-driven currents in a current- ton and foraminifera biostratigraphy (Loy« e-Pilot & swept marine environment. Magne¤ , 1987; Ferrandini et al., 1998; Fellin et al., 2005) and magnetostratigraphy (Ferrandini et al., 2003). Compared fairly straightforward, with simple, tabular (or slightly tan- with the underlying Monte Sant’Angelo Formation, the gential) avalanche sets and minor occurrences of megarip- Farinole Formation was deposited in a deeper marine ple cross-lamination limited to the bottom portion of the environment, as indicated by the presence of a pelagic

514 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 Miocene Saint-Florent Basin

(a) (b)

(c) on (d)

sw

on

on

sw

(e) (f)

(g) (h)

Fig. 8. Field photographs of sedimentary facies within the Monte Sant’Angelo Formation of the Saint-Florent sedimentary succession. (a) Large-scale cross-bedding in sandwave deposits (base of Campu Maggiore stratigraphic section). (b) Detail of a massive rhodolith bed with ophiolitic clasts at the core of several rhodoliths (Strutta Rau stratigraphic section). (c) Alternating massive rhodolith beds (on) and cross-bedded sandwave deposits (sw); cross-beds dip away from observer. Note the nonerosive contacts between depositional units (Strutta Rau stratigraphic section). (d) Structureless, 3-m-thick bed of rhodoliths. (Campu Maggiore stratigraphic section). (e) Bed containing both siliciclastic and rhodolitic grains, with siliciclastic grains concentrated in lower part and showing subtle inverse grading (Punta di Saeta). Scale bar is10 cm long. (f) Bed of mixed rhodoliths and siliciclastic grains, with inverse to normal grading (Campu Maggiore). Scale bar is10 cm long. (g) Bed containing a mixture of rhodoliths and siliciclastic clasts. Note the absence of strati¢cation, and the upward ¢ning size of the siliciclastic components (Strutta Rau). (h) Ichnofacies (Spreiten structures,Thalassinoides and Macaronichnus) of the Monte Sant’Angelo Formation (Campu Maggiore). r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 515 W. Cavazza et al.

Fig.9. Synsedimentary extensional features within the Monte Sant’Angelo Formation along coast between Campu Maggiore and Punta di Saeta. micro£ora and microfauna. A few channelized conglomer- reworking and redeposition of shallow marine biogenic ate bodies composed of rhyolite clasts are present. detritus into a deeper environment were common in the One hundred eighty-six paleocurrent indicators were Saint-Florent Basin. measured throughout the stratigraphic thickness of the The Monte Sant’Angelo Formation has been inter- Saint-Florent Basin ¢ll over its entire outcropping area. In preted as beach deposits (e.g. Durand-Delga, 1978; Ors- order of decreasing abundance, measured paleocurrent in- zag-Sperber, 1980), with the large-scale cross-bedded dicators include (i) sandwave foresets, (ii) imbricated clasts deposits representing beach ridges. However, more recent and (iii) axes of trough cross-beds. Outcrops of the Fium sedimentological analyses led to the interpretation of the Albino Formation are too poor for measuring unequivocal cross-bedded facies as the deposits of large sandwaves paleocurrent indicators. Despite some scatter, paleocurrent (Cavazza & DeCelles, 1995, 1996; Ferrandini et al., 1998). indicators of the Monte Sant’Angelo Formation yield an The common interbedding of sandwave deposits and rho- average paleo£ow direction towards the NNE (Fig. 3). Fore- dolith beds is interpreted here as the result of sediment- sets dipping in opposite directions at any one location are gravity £ows reworking the rhodoliths and other bioclastic rare. The Saint-Florent conglomerate also shows well- detritus from a shallow nearshore environment into a dee- de¢ned paleocurrent directions toward the NNE. Paleocur- per marine realm swept by intense, mostly unidirectional rent indicators are absent in the Farinole Formation. currents. Periodic deposition of thick rhodolith beds can be viewed within the framework of the intense syndeposi- PALAEOENVIRONMENTAL tional tectonism documented by growth faults and soft- INTERPRETATION OF THE sediment deformation (Fig.9). SAINT-FLORENT SUCCESSION A key component of our environmental reconstruction is the sediment-gravity £ow interpretation of the rhodo- Overall, the sedimentological and palaeontological char- lith and mixed rhodolith^siliciclastic beds. We interpret acteristics of the Saint-Florent Basin ¢ll point to a pro- these beds as the deposits of concentrated and hypercon- gressive deepening, from the £uvial^alluvial deposits of centrated density £ows (sensu Mulder & Alexander, 2001). the Fium Albino Formation, through the transitional Several aspects of these beds require this interpretation: deposits of theTorra Formation, to the shallow marine de- (1) The general absence of internal traction-current stra- posits of the Monte Sant’Angelo Formation and the pela- ti¢cation (Fig. 8d) indicates deposition from turbulent gic sediments of the Farinole Formation. high-density/high-concentration £ows in which typical The macropalaeontological association of the Monte traction-current bedforms were suppressed, probably be- Sant’Angelo Formation, which constitutes the bulk of the cause of a high rate of suspended-load fall-out (Lowe, Saint-Florent sedimentary succession, comprises coralli- 1982, 1988; Arnott & Hand, 1989; DeCelles & Cavazza, nacean red algae, bivalves, bryozoans, foraminifera and 1992) and extreme unsteadiness of the £ows (Allen, 1991). echinoderms, and suggests a shallow-water warm-temperate (2) The common presence of normal grading, particularly association (Flˇgel, 2004), in agreement with the approxi- among the denser siliciclastic clasts (Fig. 8g), is consistent mate palaeolatitude of Corsica of 37^381N during Burdi- with rapid suspension fall-out. Similarly, the density stra- galian^Langhian time (e.g. Dercourt et al., 1993). The ti¢cation within these beds (Fig 8e), with the siliciclastic micropaleontological association (£ora and fauna) points clasts concentrated in the lower parts of beds (dense-grain to an outer shelf depth range; yet the coarser-grained bio- tail normal grading, Mulder & Alexander, 2001), indicates clastic detritus was derived from a littoral environment that rapid suspension fall-out, rather than traction £ow, (Ferrandini et al., 1998). Along with the broken and was the dominant depositional process. (3) Inverse and in- abraded nature of the larger bioclasts, this indicates that verse-to-normal grading (Fig. 8e,f) are common attributes

516 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 r 20 0 7 The A u t h o rs. J o Table1. Framework composition of sandstone samples u r nal Torra and Monte Sant’Angelo formations Farinole Fm c Formations Fium Albino Fm St. Florent Fm o mp Samples TE59/1 CO98-1 CO98-2 CO98-3 CO98-4 CO98-5 CO98-8 CO98-9 CO98-11 CO94-10 CO98-12 CO98-15 CO98-26 SP14 SP15 i l a t i o Quartz 14.5 15.2 17.8 12.0 23.0 9.6 2.0 3.1 13.1 13.5 12.6 8.6 25.0 5.5 5.3 n r K-feldspar 4.8 2.8 1.8 2.8 3.2 1.0 0.4 0.2 1.7 1.7 2.1 2.9 9.0 0.6 0.5

20 Plagioclase 12.5 4.2 4.4 5.0 5.2 2.6 0.4 1.7 4.9 2.9 1.6 3.3 9.0 1.2 0.7 0 7 Felsitic Lv 1 Aplite 12.3 4.8 3.4 0.6 3.0 0.8 0.4 1.4 4.0 2.7 3.1 3.1 30.5 0.9 0.5 B l a Basic Lv 5.3 0.2 0.4 0.2 ^ 0.6 0.4 0.9 1.0 ^ 3.1 0.5 4.0 ^ ^ c k well Ab-Ep semischist 10.0 0.6 1.0 2.4 3.0 3.2 ^ 0.2 1.0 ^ ^ 0.2 ^ ^ ^

Pu Phyllite 16.8 6.0 3.2 4.0 7.0 3.0 1.2 0.9 1.7 1.7 0.8 2.4 5.8 0.6 0.7

bl Chlorite schist ^ 0.2 0.2 0.6 0.2 1.2 0.2 ^ ^ ^ ^ ^ ^ ^ ^ i s hi Serpentinite schist 2.8 0.2 ^ ^ 1.0 3.2 ^ ^ ^ ^ ^ ^ ^ ^ ^ ng Serpentinite 1.8 ^ ^ ^ ^ 0.6 0.2 ^ ^ ^ ^ ^ ^ ^ ^ Ltd Mudstone ^ ^ ^ ^ ^ 0.8 0.2 ^ ^ 0.2 0.8 ^ ^ ^ ^ , B Siltstone 1.0 ^ ^ ^ ^ ^ 0.2 0.2 0.5 0.2 0.5 ^ 3.8 ^ ^ a si n Chert 0.3 ^ ^ 0.2 ^ ^ 0.2 ^ ^ ^ ^ ^ ^ ^ ^ R e

s Mica 1 chlorite 12.0 0.8 1.0 0.8 1.2 1.2 ^ ^ ^ ^ ^ 1.2 11.3 0.3 ^ e a r c Others 5.8 0.6 1.8 1.4 1.6 1.8 0.4 0.2 1.2 ^ ^ 0.2 1.8 ^ ^ h ,

1 CE 0.3 ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 9 , 5

0 CI ^ 64.4 65.0 70.0 51.6 70.4 93.8 91.0 70.9 77.1 75.3 77.7 ^ 91.0 92.3 7 ^ 5 2

7 %NCE 99.7 35.6 35.0 30.0 48.4 29.6 6.2 9.0 29.1 22.9 24.7 22.3 100.0 9.0 7.7 %CE 0.3 ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ %CI ^ 64.4 65.0 70.0 51.6 70.4 93.8 91.0 70.9 77.1 75.3 77.7 ^ 91.0 92.3 M i %Q 18.0 44.4 55.3 43.9 50.4 36.1 37.9 35.1 46.9 58.9 51.1 40.9 28.7 63.3 68.8 o c

%F 21.1 20.5 19.3 28.1 18.4 13.5 13.8 21.6 23.9 20.0 14.9 29.5 20.7 20.0 15.6 e n

%L 60.9 35.1 25.5 28.1 31.1 50.4 48.3 43.2 29.2 21.1 34.0 29.5 50.6 16.7 15.6 e S a i Notes: Lv, volcanic lithic fragments; Ab, albite; Ep, epidote; CE, extrabasinal carbonate clasts; CI, intrabas. carb. clasts; NCE, noncarb. extrabasinal clasts; Q , total quartz grains; F, feldspars; L, aphanitic lithic grains. n t - F l o r e n t B a 5 s 1 i n 7 W. Cavazza et al. of hyperconcentrated density £ows, and result from inertial nance was also qualitatively assessed on 14 conglomerate grain-to-grain collisions (Lowe, 1982; Mulder & Alexander, outcrops covering the entire Saint-Florent sedimentary 2001). Analogous high-concentration turbidites are widely succession.The following is a synthesis of all quantitative documented in the literature (Surlyk, 1978, 1984; Postma, and qualitative observations. 1986; Ghibaudo, 1992; Cavazza & DeCelles, 1993; Mulder & The detrital modes of the Fium Albino Formation are Alexander, 2001; Naruse & Masuda, 2006; Eyles & Januszc- characterized by abundant siliciclastic lithic fragments: zak, 2007; Payros et al., 2007). Although the water depth in phyllite, felsitic volcanics, albite^epidote semischist, basic which these deposits accumulated is not known,we can con- volcanics, serpentinite and serpentine schists (Table 1). A ¢dently state that they must have been below storm wave few aplite grains are also present. The relative proportions base because of the general absence of typical storm-related of these lithic grains vary locally, suggesting control by the coarse-grained lithofacies such as hummocky and swaley local drainage network of the small £uvial systems repre- cross-strati¢cation, storm- and poststorm lags and strongly sented by this lithostratigraphic unit. These rock types erosional basal surfaces (e.g. Clifton, 1981; DeCelles, 1987; match those presently exposed in the Alpine orogenic Duke,1987; Dumas & Arnott, 2006). wedge nearby to the east, except for the felsitic volcanics, Using the terminology proposed by Ashley (1990) the which do not have a counterpart within the orogenic wedge Saint-Florent sandwaves can be classi¢ed as large subaqu- and were derived from the Permian Mt. Cinto volcanic dis- eous dunes, mostly two-dimensional (i.e. straight-crested). trictwithin the foreland. Sandstones of theTorra and Monte Altogether, the sedimentological features described above Sant’Angelo Formations have a predominant carbonato- indicate that the sandwave deposits of the Saint-Florent clastic intrabasinal component (Table 1, Figs 11 and 12). succession formed in response to e¡ectively unidirectional Most common bioclasts are calcareous algae, bryozoans, currents, perhaps because the reversing tidal £ow benthic foraminifera and mollusks. Siliciclastic rock frag- remained below the critical threshold for sediment trans- ments are identical to those in the Fium Albino Formation. port, resulting in bedforms with unidirectional, angle- Averaging 2.5%, felsitic volcanic grains are less abundant in of-repose foresets.The simple internal structure indicates these units than in the underlying Fium Albino Formation. that temporal and spatial variability of processes produ- TheSaint-Florent conglomerate is composed almost exclu- cing the bedforms was low. sively (498%) of felsitic volcanic clasts (ash- £ow tu¡s). The predominance of corallinaceous red algal detritus Suchvolcanic clasts are identical to those present in the un- at Saint-Florent ¢ts well with global chronolithostrati- derlying lithostratigraphic units. The ¢ne-grained sand- graphic patterns. In fact, late-early to early-late Miocene stones of the Farinole Formation are dominated by neritic carbonate settings are characterized by a worldwide carbonate intraclasts (planktic foraminifera) with subordi- bloom of coralline red-algal (rhodalgal; Carannante et al., nate quartz and feldspars grains (Fig. 10); minor amounts 1988) facies. Coralline red algae are commonly known as of phyllite and felsitic volcanic clasts also are present. encrusters in shallow coral reefs and on rocky substrates On a carbonate lithic grains plot (Fig.12), all sandstone or, in the absence of hard substrates, can also occur as samples of the Saint-Florent succession lack extrabasinal rhodolith nodules inhabiting sandy substrates. Rhodalgal carbonate grains.The litharenites of the Fium Albino and facies are known to develop extensively in areas of nutri- Saint-Florent Formations are devoid of intrabasinal car- ent-rich upwelling and under reduced-light conditions. bonate detritus; the detrital modes of all other samples Halfar & Mutti (2005) attributed the global shift from are dominated (52^94% of the total framework grains) by coral- to rhodolith-dominated carbonate communities intrabasinal carbonate grains. during the Burdigalian to early Tortonian to Miocene On a standard QFL plot (Fig.12), most sandstone sam- global changes. According to these authors, a combination ples of the Saint-Florent succession fall within the ‘re- of a global enhancement of trophic resources and declin- cycled orogen’ ¢eld of Dickinson et al. (1983), i.e. ing temperatures led to oceanographic conditions that fa- compositions resulting from the orogenic uplift and ero- voured the expansion of rhodalgal communities. sion of fold belts and thrust sheets. The only exceptions are the litharenites of the basal Fium Albino Formation (Alpine metamorphic rock fragments) and Saint-Florent DETRITAL COMPOSITION conglomerate (late Hercynian volcanic rock fragments). The abundance of serpentinitic silicliclastic grains ^ typi- In order to determine sandstone detrital modes and prove- cal of sandstones derived from collisional orogenic ter- nance of the Saint-Florent Basin ¢ll 25 samples were col- ranes (Suczek & Ingersoll, 1985) ^ indicates that ophiolitic lected, thin-sectioned and examined petrographically. Of units of the Alpine orogenic wedge were available as sedi- these, ¢fteen samples were point-counted following the ment source rocks. Gazzi^Dickinson method (Gazzi, 1966; Dickinson, 1970), Based on the qualitative observation of conglomerate a procedure that minimizes the variation of composition composition, Fellin et al. (2005) concluded that the extra- with grain size. Three hundred points per thin section basinal provenance of the Saint-Florent succession is were counted and assigned to one of seventeen categories. dominated by the Alpine units, which still form the east- Sandstone point-count data were then recalculated to ern margin of the basin, with a subordinate detrital input produce the grain parameters indicated in Table 1. Prove- from the Tenda gneissic dome to the west. In their inter-

518 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 Miocene Saint-Florent Basin

deposits and high-density turbidity current deposits composed of reworked shallow-marine carbonate biodetritus, raises the prospect that this assemblage may have paleotectonic/paleoenvironmental signi¢cance. In particular, we propose that this blend of lithofacies should be characteristic of relatively deep marine environ- ments that are swept by both powerful bottom currents and sporadic turbidity currents. O¡shore marine gravel and sandwave deposits have been documented in a number of turbidite fan systems (e.g. McHugh & Ryan, 2000), but these deposits ty- pically exhibit very low-angle cross-strati¢cation. High-angle gravel and sandwave deposits are known from a range of water depths (100^1000 m) in the Messina Strait and its approaches (e.g. Ryan & Heezen, 1965; Santoro et al., 2002, 2004), and in shallower (30^106 m) shelf environments near the Golden Gate of San Francisco, USA (Barnard etal., 2005, 2006). Both these set- tings are characterized by powerful bottom currents (1.2 m/s at ^300 m in the Messina Strait) produced mostly by bathymetric focussing of tidal currents. How- ever, only deeper environments such as the Messina Strait are also sites of deposition by means of gravity £ows. At this location, at depths in excess of 400 m, Selli et al. (1975) documented the presence of turbidite layers (aver- age recurrence time ca. 60 years) interbedded with sand- wave deposits and derived from the rugged and tectonically unstable basin margins. The MonteTorre pa- leostrait of ^ which linked the Tyrrhenian and Ionian seas during Plio-Pleistocene time (Colella & D’Alessandro, 1988) ^ provides a well-documented fossil Fig.10. Photomicrographs (uncrossed nicols) of Monte analogue of the Messina Strait. Sedimentation along the Sant’Angelo (sample CO98-12, top) and Farinole (SP-14, bottom) axis of the paleostrait was characterized by gravel or very Formations Monte Sant’Angelo Formation samples are typically coarse sandwave deposits composed mostly of carbonate coarser grained, hybrid (mixed siliciclastic-carbonatoclastic) biodetritus. Such large carbonate sandwaves required arenites with abundant bioclasts of calcareous algae, benthic foraminifera and bryozoans. Farinole Formation samples are strong currents and high biological productivity, which ¢ner grained biomicrites-biomicrosparite with abundant were induced by current ampli¢cation along the paleos- planktic foraminifera and a limited siliciclastic component. trait and the corresponding upwelling of nutrients, re- spectively. The Monte Torre sandwave deposits are pretation, the distinctive Permian rhyolitic volcanics of interbedded with thick turbidites ^ the result of intermit- central Corsica (Monte Cinto) would have reached the ba- tent high-density turbidity currents mobilizing mixed sin with the deposition of the Saint-Florent conglomerate bioclastic^siliciclastic detritus from the tectonically active (early Langhian). This was interpreted to be the result of basin margins. Based on ichnofacies, stratigraphic rela- the integration of a paleoriver (Fellin et al., 2005, tionships and sedimentary facies analyses, Colella & Fig. 6b). Sandstone petrographic results of this study chal- D’Alessandro (1988) concluded that deposition in the lenge this notion, however, as silicic volcanics are present MonteTorre paleostrait occurred at water depths in excess as lithic fragments throughout the succession, thus indi- of 350 m. cating that the Monte Cinto district was already tapped Combined with the structural-tectonic setting, the by the drainage system of the Saint-Florent Basin during Saint-Florent Basin lithofacies assemblage may be the Burdigalian. interpreted as a type of tectofacies, characteristic of narrow, relatively deep-water (upper bathyal?) basins subject to bathymetric focussing of (tidal) currents and derivation DISCUSSION of coarse-grained turbidites from nearby rugged Paleoenvironmental significance of the topographic highlands, a physiographic situation charac- Saint-Florent Basin teristic of the early stages of microplate fragmentation and drifting. In support of this hypothesis, similar The peculiar assemblage of lithofacies in the Saint- biocalcarenitic sandwave deposits of Tortonian age Florent Basin, characterized by intercalation of sandwave occur along the Tyrrhenian coast of southern Italy r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 519 W. Cavazza et al.

(a) (b)

(c) (d)

(e) (f)

(g) (h)

Fig.11. Photomicrographs of lithic fragments within the arenites of the Saint-Florent succession. (a) Diabase with arborescent texture (uncrossed nicols; sampleTE59-1, Fium Albino Formation). (b) Acid volcanic rockwith porphyritic texture and rounded quartz phenocryst (crossed nicols; sample CO98-8, Monte Sant’Angelo Formation). (c) Albite^epidote schist (crossed nicols; sample CO98-5, Monte Sant’Angelo Formation). (d) Basic volcanic rockwith microlitic texture (crossed nicols; sampleTE59/1, Fium Albino Formation). (e) Serpentine schist (crossed nicols; sampleTE59/1, Fium Albino Formation). (f) Albite^epidote semischist (crossed nicols; sample CO98-5, Monte Sant’Angelo Formation). (g) Folded slate/phyllite (crossed nicols; sampleTE59/1, Fium Albino Formation). (h) Phyllite (crossed nicols; sample CO98-1,Torra Formation).

(Longhitano & Nemec, 2005) and mark the early Tectonic significance of the stages of rifting of the Tyrrhenian back-arc basin Saint-Florent Basin (Bonardi etal., 2001), when the Calabria^Peloritani terrane drifted o¡ the Corsica^Sardinia microplate (see following The Saint-Florent sedimentary succession was deposited section). in a tectonic context of regional extension that character-

520 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 Miocene Saint-Florent Basin

NCE Rifting in the Ligurian-Provenc° al basin area occurred CO98-26 at least from the Oligocene (34 Ma) to the middle Aquita- TE59/1 nian (21Ma), according to the age of the sediments drilled in the Gulf of Lions beneath the break-up unconformity (Gorini etal.,1993). A number of grabens have been seismi- cally imaged and drilled in , both on land and o¡- shore, in order to test their hydrocarbon potential (Vially & Tre¤ molie' res,1996).The development of the Provenc° al rifts traditionally has been interpreted as the result of the col- CO98-4 lapse of the ^Provence thrust belt, an eastward CO98-1 CO98-3 extension of the Pyrenees. From a wider perspective, the CO98-2 CO98-5 Q CO98-11 Provenc° al rifts are part of a regional extensional area cross- CO98-12 CO94-10 cutting the Pyrenees^Languedoc^Provenc° al orogen and CO98-15 CO98-9 ultimately driven by incipient roll-back of the Ionian SP14 SP15 subduction zone. CO98-8 Drifting and the creation of the central, oceanic portion CE SP15 CI SP14 of the Provenc° al basin took place during the Burdigalian, CO94-10 as indicated by paleomagnetic data (Vigliotti & Langen- CO98-2 CO98-4 CO98-12 heim, 1995) and by the transition from syn-rift to postrift CO98-11 CO98-3 CO98-1 subsidence of its margins (Vially & Tre¤ molie' res, 1996; CO98-15 CO98-8 CO98-9 CO98-5 Roca, 2001). Although still somewhat controversial, CO98-26 paleomagnetic studies (Alvarez etal.,1974;Vigliotti & Lan- Farinole Fm genheim, 1995; Speranza et al., 2002) indicate counter- St Florent Fm TE59/1 clockwise rotation of the Corsica^Sardinia block between Mt. S. Angelo e Torra Fms Fium Albino Fm ca. 19 and 16 Ma (Burdigalian), synchronous with the for- mation of oceanic crust in the Provenc° al basin (Fig. 13). F L The rifted margins of Provence and western Corsica dis- Fig.12. NCE-CE-CI (Zu¡a, 1980) and QFL ternary plots of play the same Oligocene^Aquitanian synrift sequences, composition of sandstone samples of the Saint-Florent being the conjugate margins of the same Neogene Proven- sedimentary succession. NCE, CE and CI indicate noncarbonate c° al oceanic domain. Postrift thermal subsidence com- extrabasinal grains, carbonate extrabasinal grains and carbonate menced during the middle Miocene in the adjacent intrabasinal grains, respectively. Q , Fand L indicate total quartz, Provenc° al and Algerian basins (Roca, 2001; Carminati total feldspars and total aphanitic lithic fragments, respectively. et al., 2004; Roca et al., 2004). SeeTable1for modal analyses of samples. Despite its small size, the Saint-Florent Basin has played a signi¢cant role in tectonic interpretations of the western Mediterranean region. Traditionally, the accre- ized the late Oligocene^Neogene postcollisional evolution tionary prisms of northern Corsica and the northern of the western Mediterranean region, from the Alboran Apennines have been considered as separate entities.The Sea to Calabria (see Cavazza et al., 2004a, b, for a review). west-vergent orogenic wedge of Corsica is considered the A number of microplates (Kabylides, Balearic block, Cor- continuation of the western (see Dal Piaz et al., 2003, sica^Sardinia block, Calabria^Peloritani terrane) were and Lacombe & Jolivet, 2005, for reviews). Similarly, the sundered from the southern margin of the European^ crystalline rocks of Calabria in southernmost peninsular Iberian plate leaving in their wake areas of thinned conti- Italy have been long considered a fragment of the Alpine nental lithosphere (e.g.Valencia trough) and small oceanic orogen separated from the Corsica^Sardinia block by the basins (Algerian, Provenc° al, central Tyrrhenian basins) development of the since the Tortonian (Fig.13) (Carminati etal., 2004; Roca etal., 2004).This tec- (see Bonardi et al., 2001, for a review). The correlation be- tonic regime has been ascribed to the prolonged Adriatic tween Corsica and the western Alps is based on a wealth indentation and collisional coupling, and the ensuing pas- of structural and stratigraphic similarities, both in the sive sinking (roll-back) of the subducting Adria-African orogenic wedges and in the foreland basins. Such similari- plate, which, in turn, induced crustal extension in the ties point to the existence of an east-dipping subduction upper plate (e.g. Malinverno & Ryan, 1986). Before rifting, zone (present-day coordinates) beneath the Corsican Al- Corsica sat in a very complex structural setting between pine orogenic wedge. The northeast-vergent northern the intracontinental, strike-slip-dominated Pyrenean^ Apennines are considered to have been produced by lim- Languedoc orogen to the west and the Alpine orogenic ited, possibly passive, subduction of the Adriatic sub-plate wedge to the east. Corsica su¡ered deformation related towards the west (see Vai & Martini, 2001, and Elter et al., to both orogens, and thus its subsequent geological evolu- 2003, for reviews) in a di¡erent tectonic regime that mostly tion was strongly governed by preexisting structural postdated Alpine compression and thus was not related to discontinuities. the genesis of the Corsican orogenic wedge. r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 521 W. Cavazza et al.

P

S B C C K K

46-40 Ma (Lutetian) 21 Ma (late Aquitanian)

AP

PB

TB

C

16 Ma (late Burdigalian) 4 Ma (early Pliocene)

Fig.13. Schematic maps showing the paleotectonic evolution of the W Mediterranean during Oligocene-Neogene time (modi¢ed after Bonardi et al., 2001; Roca, 2001; Cavazza & Wezel, 2003; Cavazza et al., 2004b). Only active tectonic elements are shown.White, exposed land; light grey, epicontinental sea; darker grey, oceanic and quasi-oceanic crust. Black arrows indicate the direction of ’s motion with respect to Europe (after Mazzoli & Helman,1994, for the Neogene, and Dercourt etal.,1993, for the Lutetian).White arrows indicate the upper-plate direction of extension. Stars indicate subduction-related magmatism. AP, Apennines; B, Balearic block; C, Calabria- Peloritani terrane; K, Kabilies; P, Pyrenean deformation; PB, Provenc° al basin, S, Sardinia;TB,Tyrrhenian basin.

Brunet et al. (2000) proposed an alternative interpreta- tween the youngest metamorphic ages and the age of the tion envisioning a continuous time^space migration of de- oldest sedimentary unit in the Saint-Florent Basin ¢ll. Ac- formation from Corsica to the Apenninic frontal thrust cording to Brunet et al. (2000), two generations of white from at least 35 Ma to the present in a context of continued micas coexist in the basement rocks of the Tenda massif. W-dipping subduction. From this viewpoint, ductile A ¢rst generation is the relict of blueschist-facies contrac- structural inversion of Alpine thrusts in Corsica (Jolivet tional metamorphism around 45^35 Ma (i.e. the e¡ect of et al., 1990; Fournier et al., 1991) and the development of late Eocene Alpine thrusting), whereas the second formed the Saint-Florent extensional basin (Burdigalian^Lan- around 25 Ma during lower grade metamorphism asso- ghian) would represent a bridge between the opening of ciated with the structural inversion of Alpine top-to-the- the Provenc° al basin (early Miocene) and of theTyrrhenian west thrust faults.The mid-Burdigalian (ca. 19^18 Ma) age Sea (latest Miocene^Pliocene), thus supporting the notion of the base of the Saint-Florent Basin ¢ll would seem to of an extensional wave moving towards the east. preclude a direct tectonic relationship between the basin In contrast with this hypothesis, available isotopic ages and low-angle normal faulting, although it is not excluded from Alpine Corsica point to a substantial time gap be- that signi¢cant increments of displacement along the East

522 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 Miocene Saint-Florent Basin

1. LATE OLIGOCENE: beginning of orogenic collapse, inversion of Alpine boundary fault

West East foreland basin deposits

Alpine European orogenic wedge basement complex

brittle-ductile Schistes transition Lustrés

Moho

10 km 10 km

2. EARLY MIOCENE (Burdigalian): deposition of St Florent calcarenites (Mt. S. Angelo Fm)

Tenda Balagne St Florent Corsica massif basin basin

new brittle-ductile transition Moho

Fig.14. Schematic cross-section across northern Corsica showing (1) inversion of Alpine boundary thrust and orogenic collapse of the Alpine tectonic wedge during the late Oligocene, and (2) early Neogene block faulting and deposition of Saint-Florent calcarenites within supradetachment graben.This reconstruction subscribes to the notion by Fellin et al. (2005) that high-angle normal faulting providing accommodation for the Saint-Florent Basin postdates and is unrelated to detachment faulting along the east Tenda shear zone. Modi¢ed after Jolivet et al. (1991).

Tenda shear zone might have occurred later in the brittle middle Miocene time with a cluster of ages at 22^15 Ma. ¢eld. The data show that before exhumation most of Corsica The exact crosscutting relationships between the E was covered by at least 2 km of Alpine thrust sheets and Tenda shear zone and the high-angle normal faults are far foreland deposits.There are no systematic age di¡erences from being completely understood. Fellin etal. (2005) have across the main boundary fault system separating the Al- interpreted the high-angle normal faults as cutting the de- pine orogenic wedge and the foreland, indicating that tachment, an interpretation we have incorporated in Fig. large-scale inversion of this structure was no longer active 14. On the other hand, the supradetachment location of during the early Miocene. the basin suggests that the high-angle faults might sole Following this line of reasoning, the late Oligocene^ out into the main detachment, and that isostatic uplift ow- early Miocene structural evolution of northern Corsica ing to tectonic unroo¢ng of theTenda core complex could can be summarized as shown in Fig. 14. During the late have delayed subsidence and at least temporarily pre- Oligocene, following maximum thickening of the Alpine vented the development of large amounts of sediment orogenic wedge, the boundary fault system between the accommodation. Alpine wedge and its foreland was tensionally reactivated The apatite and/or zircon ¢ssion-track studies of Ca- as a low-angle detachment fault. This ¢rst phase corre- vazza et al. (2001), Jakni et al. (2000), Zarki-Jakni et al. sponds to the development of the marginal grabens along (2004) and Fellin et al. (2005) indicate that Corsica under- the Provenc° al conjugate margin. During early Miocene went a widespread episode of rapid exhumation in early- time, Corsica was uplifted wholesale although high-angle r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 523 W. Cavazza et al. brittle normal faults locally created accommodation space REFERENCES for basin development both on land (Saint-Florent) and o¡shore (Corsica basin). This interpretation is also sup- Alesandri, J.A., Magne¤ , J., Pilot, M.D. & Samuel, E. (1977) Le Mioce' ne de la re¤ gion de Corte-Francardo. Bull. Soc. Hist. ported by geomorphological data pointing to the existence Nat. Corse, 622, 51^54. of a piedmont-type planation surface, which formed dur- Allen, J.R.L. (1991) The Bouma division A and the possible ing a phase of tectonic quiescence in the middle Miocene duration of turbidity currents. J. Sed. 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