Progressive changes in rifting directions in the Campania margin(Italy): New constrains for the Tyrrhenian Sea opening

Alfonsa Milia a,!, Maurizio Maria Torrente b, Bruno Massa b, Pietro Iannace b

a IAMC, CNR, Calata Porta di Massa, Porto di Napoli, I-80100 Naples, Italyb DSBGA, Università del Sannio, Via dei Mulini 59/A, I-82100 Benevento, Italy

a b s t r a c ta r t i c l e i n f o

Article history:Received 14 August 2012Accepted 3 July 2013Available online 9 July 2013

Keywords:Basin analysisSequence stratigraphyBack-arc basinTyrrhenian Sea

Current models for the opening of the Tyrrhenian Sea invoke a unique extension vector throughout the rift todrift process, accommodated by margin parallel faults, but the role of the Campania margin faults in theopening of the Tyrrhenian back-arc basin is still poorly constrained. Gaeta Bay, located on the Campania mar-gin, was investigated through the interpretation of seismic re!ection and borehole data together with a strat-igraphic correlation of dated outcropping units. The interpretation of a seismic grid using seismic andsequence stratigraphy and structural geology approaches in a dedicated GIS environment led to the genera-tion of 2-D models of relevant geological surfaces, isochron maps, a 3-D digital model of the subsurface and tothe reconstruction of the geological evolution of the margin with a resolution of 100 ka. Gaeta Bay is formedby three basins (northern, central and southern) and features a complex stratigraphic architecture: in thenorthern and central basins a syn-rift deposit (unit PP) is buried by the oldest aggradational deposit(unit A) that "lls the accommodation space; a post 0.7 Ma succession (units B and C) "lled the northernbasin with a lateral aggradational geometry; a syn-tectonic wedge (unit B) was deposited in the centralbasin between 0.7 and 0.4 Ma; post 0.4 Ma thick deposits (unit C) are testimony to the collapse of thesouthern basin. A correlation between the geology of the bathyal basin and that of the Campania marginwas established using a CROP seismic section that extended from the Vavilov basin to Gaeta Bay.Based on original and literature data we propose a kinematic evolution of the Tyrrhenian Sea upper plate overthe last 10 Ma. This evolution consists of older extensional events (stages 1–2) off Sardinia and in the Vavilovbasin (leaving the Campania margin unaffected). Younger events (stages 3–5) developed in the eastern (witha Pliocene–Quaternary change of the extension direction along the Campania Margin) and central Tyrrhenianregion.This paper suggests that the Tyrrhenian Sea opening was a polyphase rifting with a migration of activity and achange of style over time (including a period of lithospheric detachment faulting).

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

The Tyrrhenian Sea developed since Tortonian times and is theyoungest basin of the western Mediterranean (e.g. Sartori, 1990).Since the 1960s the Tyrrhenian Sea has been the subject of several geo-physical and geological investigations and surveys (especially DSDP andODP drilling projects in the bathyal basins) that has produced amassiveamount of data. Various geodynamic models of the Tyrrhenian basinand surrounding regions have been suggested by different authors:translational models (e.g. Moussat, 1983; Van Dijk and Okkes, 1991);sphenochasm models (e.g. Patacca et al., 1990); radial drift models(e.g. Wezel, 1981); and plate tectonic models featuring rotation poles(Turco et al., 2006; Martin, 2007). However twomain geodynamic pro-cesses have been used up to now to explain the evolution of theTyrrhenian Sea-Apennine system: a) subduction of the Adriatic-Ionian

lithosphere and formation of the Tyrrhenian back-arc basin; b) upwell-ing of the asthenosphere. Supporters of type (a) models maintain thatthe subduction of the Adriatic-Ionian plate and the consequent slab re-treat are responsible for an asymmetric migration of the extension inthe Tyrrhenian upper plate (e.g. Kastens and Mascle, 1990; Mascleand Rehault, 1990; Sartori, 1990; Doglioni, 1991; Faccenna et al.,1997; Grivtzman and Nur, 1999). By contrast promoters of type (b)models invoke a lithospheric stretching driven bymantle astenosphereexpansion due to the growth of a plume head (e.g. Wezel, 1981;Lavecchia and Stoppa, 1996; Lavecchia and Bell, 2012).

The stratigraphy of the Tyrrhenian basin has been interpreted fol-lowing the classicalmodels of continental break up (rifting immediatelyfollowed by sea!oor spreading) and a single break-up unconformityfollowed by a unique spreading stage in the oceanic area has been doc-umented (e.g. Trincardi and Zitellini, 1987; Sartori et al., 2004). Never-theless recent studies of the rift margins (Whitmarsh et al., 2001;Manatschal, 2004; Péron-Pinvidic et al., 2007) document that the subdi-vision into prerift, sinrift and postrift sediments is hampered by the fact

Global and Planetary Change 109 (2013) 3–17

! Corresponding author. Tel.: +39 081 5423 844; fax: +39 081 5423 888.E-mail address: alfonsa.milia@iamc.cnr.it (A. Milia).

0921-8181/$ – see front matter © 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.gloplacha.2013.07.003

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that rifting is polyphase, rift activity migrates and the mode of riftingchanges through time (including a period of lithospheric detachmentfaulting). These concepts furnish a new key for the interpretation ofthe evolution of the rift regions characterized by exhumed mantle, in-cluding the Tyrrhenian basin.

The Tyrrhenian Sea is a triangular back-arc basin characterized bytwo large bathyal basins (Vavilov and Marsili basins) that are coveredby some hundred meters of sediments, and a number of peri-Tyrrhenian basins "lled by thousands of meters of clastic and/orvolcaniclastic sediments. All these basins feature a down faulted sub-strate at a depth greater than 3 km (Figs. 1-3). The Eastern TyrrhenianSea is characterized by the occurrence of several peri-Tyrrhenian basins(Fig. 1) spanning from Pliocene to Quaternary times (e.g. Savelli andWezel, 1979). The stratigraphic record of these basins offers an oppor-tunity to study the timing and kinematics of the basin-forming faultsthat are relevant for the creation of a model on the opening of theTyrrhenian Sea. Gaeta Bay,which is part of the Campaniamargin, lies be-tween the bathyal Vavilov basin and the Apennines chain (Figs. 1, 3).It represents a key area for the unraveling of the extensional processesthat affect the Tyrrhenian Sea. Even if previous works (e.g. Savelli andWezel, 1979; Selli, 1981; Zitellini et al., 1984; De Alteriis et al., 2006)on Gaeta Bay reported a triangular basin in the northern bay and anE–W lineament around the 41st parallel, a complete knowledge ofbasin "ll and fault patterns, and timing and kinematics is still lacking.

The purpose of this paper is manifold: to reconstruct thethree-dimensional basin architecture of Gaeta Bay; to illustrate thelink between the bathyal Vavilov basin and Campania margin; andto sketch the evolutionary stages of the Tyrrhenian Sea back-arcbasin. The study was conducted using multichannel seismic re!ectionpro"les collected along the continental margin and a CROP seismicpro"le extending from the continental margin to the bathyal basin.The interpretation of these data was performed using seismic andsequence stratigraphy and structural geology in a GIS-dedicatedenvironment.

2. Geological framework

2.1. Tyrrhenian basin

The Tyrrhenian Sea is a triangular land-locked extensional basinthat spans Tortonian to Quaternary and formed at the rear of the Neo-gene Apennine thrust belt (e.g. Sartori, 1989; Patacca et al., 1990).From Late Tortonian to Pleistocene counter-clockwise rotations inthe Southern Apennines are matched by contemporaneous clockwiserotations in Sicily (Gattacceca and Speranza, 2002; Speranza et al.,2003); these rotations are coeval with the emplacement of thrustsheets in fold-and-thrust belts and rifting and extension in theTyrrhenian back-arc basin.

The development of the Tyrrhenian Sea occurred within the overallcontext of an approximately north–south convergence between theAfrican and the Eurasian plates (e.g. Dewey et al., 1989). Its back-arcevolution has mainly been attributed to the roll-back towards thesouth-east of the subducting Ionian plate that could have provided thebulk of the space required for the backarc extension of the Tyrrhenian

Fig. 1. Index map of the normal faults of the Tyrrhenian Sea, CROP M29A seismic pro"le, ODP and DSDP well sites. V = Vavilov seamount, Ms = Marsili seamount, Ma = Magnaghiseamount, E = Eolie Islands, N = Campania Plain and Naples Bay, P = Paola basin.

Fig. 2. Stratigraphic logs of the ODP sites of the Tyrrhenian Sea. For holes location seeFig. 1. 1) Pleistocene deposits; 2) Pliocene deposits; 3) dolostones; 4) basalts; 5)Messiniandeposits; 6) Tortonian deposits; 7) conglomerates; 8) serpentinized peridotites. FromKastens et al. (1987).

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Sea (e.g. Malinverno and Ryan, 1986; Faccenna et al., 1996; Cavinatoand De Celles, 1999). Based on tomographic images, seismologicaldata, petrology of volcanic rocks and analog models, several authors(e.g. Serri, 1990; Grivtzman and Nur, 1999; Piromallo and Morelli,2002; Faccenna et al., 2003, 2004; Rosenbaum and Lister, 2004;Faccenna et al., 2007) reconstructed a complex geometry of thesubducting slab featuring three segments (Apennines, Calabria andSicily) and proposed a link between the dynamics of the slab and theopening of the Tyrrhenian Sea.

The central plain (depth N3000 m) of the Tyrrhenian Sea can bedivided into two sub-basins, separated by the Issel swell, the westernVavilov basin and south-eastern Marsili basin; both these basins fea-tures large volcanoes standing more than 2500 m above the bathyalplain: the Magnaghi, Vavilov and Marsili seamounts (Fig. 1).

The stratigraphy of the ODP sites (Fig. 2) features different succes-sions from the Sardinia margin to the central plain (Kastens et al.,

1987). The Site 654 presents conglomerates covered by Tortonian–Messinian deposits and a Plio-Pleistocene succession. The Site 653and 652 also displays thick Messinian deposits followed by a Plio-Pleistocene succession. The Site 656 is characterized by a Plio-Pleistocene deposits which base have been dated as Lower Pliocene(biozone NN12) overlying an undated conglomerate, derived from Al-pine type basement. The Site 655, drilled on the crest of the GortaniRidge, encountered 80 m of sediments Pliocene (biozone MPL4/NN15;3.4–3.6 Ma)-Quaternary in age lying above MORB basalts. The Site651, drilled in the Vavilov basin, is characterized by 388 m of a Plio-cene–Pleistocene succession which oldest layers are dated 2.0 Ma(biozone MPL6/NN18); no microfossils occur in the lower 39 m-thickdolostones. The underlying basement is characterized by a 134 m-thick succession of basalts corresponding to several lava !ows and brec-cias that repose above 29 mof highly serpentinized peridotites showinga tectonic fabric. According to Mascle and Rehault (1990) the

Fig. 3. Index map of seismic grid, ship tracks reported in the text and stratigraphic successions of deep wells from the Campania margin. VL = Villa Literno well, CN = Cancello 2well, MO = Mondragone1 well, CA = Cellole Aurunci well, MA = Mara1 well, L = Licola well, I6 = Ischia 6 well. Q = Quaternary; Pl =Pliocene; MI = Miocene; Me =Messinian; TJ = Trias-jura; PE = Paleocene-Eocene. 1) dolomite and dolomitic limestone; 2) limestone; 3) marl and calcareous marl; 4) conglomerate; 5) sandstone; 6) sandyclay; 7) clay; 8) basalt; 9) ignimbrite; 10) thrust fault. The volcanic vents of Naples Bay are from Milia and Torrente (2003), Milia (2010), Torrente et al. (2010). The shaded reliefelevation data from SRTM v.2, 3 arcsec (Farr et al., 2007); bathimetric data from TOPO TOPEX project (Smith and Sandwell, 1997).

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occurrence of these mantle-derived rocks at shallow crustal level re-mainsmysterious, but unroo"ng by shallow-dipping detachment faultsmay have been important. The Site 650, drilled inMarsili basin, displays32 m of vesicular basalts overlain by a 602 m-thick succession of Plio-cene which oldest sediments are 2.0 Ma-old (biozone MPL6/NN18);10 m of the basal nannofossil oozes contain fossil entirely destroyed.

The central plain of the Tyrrhenian Sea is characterized by a thincrust (25 to less than 10 km) and lithosphere (30–50 km) (Nicolich,1981; Panza, 1984), high heat !ow values (Della Vedova et al., 2001)and high positive Bouguer gravity anomalies. These features and the oc-currence of Mid Oceanic Ridge Basalts (MORB) at holes 373 and 655(Fig. 2) led many authors (e.g. Kastens and Mascle, 1990; Mascle andRehault, 1990; Sartori, 1990) to indicate that the Vavilov andMarsili ba-sins are !oored by oceanic crust and correspond to a couple ofdiachronous spreading centers (with associated rifting, spreading andpost rift stages) produced by the eastward migration of extension inthe Tyrrhenian Sea. According to this view Sartori (1990) suggestedthat the Vavilov basin was affected by the rift stage (5.5–4 Ma), follow-ed by the spreading stage (4–2.6 Ma) and post rift stage as the Marsilibasin was characterized by the rifting stage (unknown age), spreadingstage (1.8–1 Ma) and post-rift stage (post 0.78 Ma). FurthermoreSartori (1990) reported that the Marsili episode induced the rejuvena-tion of former faults. It should be noted that while the geology of theVavilov basin is based on several DSDP and OPD data (Figs. 1, 2), thatof theMarsili basin is constrained by only one ODP site (650). In partic-ular the age of the Marsili basin formation has been poorly controlled.Several authors speculated that the crust !ooring the Marsili basin issigni"cantly younger than that of the Vavilov basin. A simple progres-sion of an older stage of extension in the northern part of the bathyalTyrrhenian sea followed by a younger one in the southern one is notin accordance with: the oldest age (7–4.4 Ma) of the oceanic basaltsat DSDP site 373 in the middle of the Tyrrhenian Sea (Savelli andLipparini, 1978); a recent fault activity displacing the break-up uncon-formity and the sea!oor in the Vavilov basin (seismic line TY41 inTrincardi and Zitellini, 1987); extensional faults displacing the Vavilovvolcano active between 2.4 and 0.4 Ma (Robin et al., 1987).

The occurrence of oceanic crust has stimulated some researchers(Faggioni et al., 1995; Nicolosi et al., 2006; Florio et al., 2011) tostudy the magnetic anomalies in this area, looking for a stripedpattern (similar to those characterizing ocean environments) thatcould constrain the temporal evolution of the Tyrrhenian Sea open-ing. Nicolosi et al. (2006) identi"ed seven magnetic anomaly stripesin the Marsili basin, produced by alternate normal and reversed po-larity of the crust magnetization, similar to those observed in matureoceanic environments and postulated an age of 2.1–1.6 Ma for theMarsili basin spreading. To "nd such a regular magnetic anomaly pat-tern, otherwise invisible, a composite high-pass and strike-sensitive"lter was applied. Unfortunately, this "ltering process is very subjec-tive and in this case its application is not appropriate (Florio et al.,2011). Florio et al. (2011) indicate that the resulting pattern of nor-mal and reverse magnetized bodies does not "t with an ocean-likecentral expansion model. Alternatively, the distribution of magneticsources may suggest that the crustal tearing induced by extensionalprocesses is not concentrated solely beneath the seamounts, but in-volved different areas in different times.

Many researchers suggest a constant extension direction in theTyrrhenian Sea in the last 10 Ma: NW–SE (Rehault et al., 1987;Faccenna et al., 1997, 2004; Rosenbaum and Lister, 2004) or E–W(Trincardi and Zitellini, 1987; Doglioni, 1991; Gueguen et al., 1997;Faccenna et al., 2007). Other workers propose a change of extensiondirection in the Tyrrhenian basin from E–W to NW–SE in the Quater-nary (Sartori, 2003). An extension of 390 km in the Tyrrhenian regionwas obtained after restoring a NW–SE crustal section extending fromCalabria to the Gulf of Lyon (Faccenna et al., 2003); this was done bysubtracting the ocean !oored area (Vavilov and Marsili basins) andthen restoring the continental crust to the thickness of the surrounding

undeformed domain. However this assessment of the amount of ex-tension suffers from simpli"cation: it assumes a single orientation(NW–SE) of the strain axis and two-dimensional extensional processesin the Tyrrhenian basin. The Tyrrhenian Sea back arc basin is affected bya complex pattern of normal faults (Fig. 1) that cannot be linked to aunique extension direction.

2.2. Campania margin

The Campania margin of the Tyrrhenian Sea includes three basins(Gaeta Bay, Naples Bay, Salerno Bay) "lled by thousands of meters(from 3 to 5 km) of Neogene–Quaternary clastics and volcanics(Sacchi et al., 1994; Milia et al., 2003, 2009; Milia and Torrente, 2011).

The physiography of Gaeta Bay consists of a wide shelf areaextending from Zannone and the Circeo Promontory to Ischia andProcida (Fig. 3). The volcanic products of Zannone Island coverboth thrust sheets made up of Mesozoic–Cenozoic sedimentary rocksand quartz-sericite phyllites (Paleozoic basement?); the lattermetamorphic unit is tectonically overlain by black clays, dolomiticlimestones and dolomites of late Triassic age (De Rita et al., 1986). TheApennine fold-and-thrust belt formed during Miocene and LowerPliocene times whereas extensional tectonics started in Pliocene time(Zitellini et al., 1984; Mostardini and Merlini, 1986; Cascello et al.,2004). Deep-seated normal faults, that displaced the Apennine thrustbelt, are responsible for the down throwof theMesozoic–Cenozoic sub-stratum toward the sea and the formation of Lower Pliocene structuraldepressions in Gaeta Bay and westwards of Gaeta Bay (Zitellini et al.,1984) and Quaternary deep sedimentary basins in the Campania Plainand Naples Bay (Ippolito et al., 1973; Milia, 1999; Milia and Torrente,1999). According to previous studies the tectonic evolution of thisarea played a signi"cant role during the development of the SouthernApennine thrust belt-Tyrrhenian Sea back-arc basin system (e.g. Pataccaand Scandone, 1989; Turco et al., 2006). It is well established that thegeologic evolution of the Campania Margin is controlled by NW–SEand NE–SW faults (Gars and Lippman, 1984; Mariani and Prato, 1988;De Rita and Giordano, 1996; Milia and Torrente, 1997; Milia et al.,2003; Acocella and Funiciello, 2006). On the basis of the age of thefault-bounding basins, Torrente et al. (2010) and Milia and Torrente(2011) proposed a chronology and kinematics of the Campania marginstructures: Lower Pleistocene activity of the NW-trending normalfaults; Middle Pleistocene activity of the NE-trending normal faults;and late Pleistocene–Recent reactivation of both fault systems due toan E–W directed extension.

An impressive volcanic activity on the Campania margin spannedfrom Pliocene to the Present and produced the volcanic Pontine Islands(Palmarola, Ponza, Zannone and Ventotene), the Roccamon"na volcanoand the volcanoes of Campi Flegrei, Ischia, Procida and Vesuvius (Fig. 3).Volcanic products were emplaced, respectively, from 4.2 Ma to 1.0 Maat Ponza, Zannone and Palmarola (De Rita et al., 1986; Cadoux et al.,2005), from 0.8 to 0.13 Ma at Ventotene and from 0.63 to 0.13 Ma atRoccamon"na volcano (Radicati di Brozolo et al., 1988). Within theCampanian Plain an up to 2000 m-thick volcano characterized by basal-tic and andesitic lavas (buried by about 800 m of clastics) was drilled atParete and Villa Literno (Fig. 3; Ortolani and Aprile, 1978; Barbieri et al.,1979; Albini et al., 1980). Over the last 0.3 Ma a voluminous ignimbriteactivity started in the Campanian Plain and Naples Bay (Milia, 1998; DeVivo et al., 2001; Rolandi et al., 2003; Bellucci et al., 2006; Milia andTorrente, 2007) that culminated 39 ka with the cataclysmic CampaniaIgnimbrite eruption.

3. Data set and methodologies

Gaeta Bay was investigated using a seismic grid formed by multi-channel seismic pro"les from the Western Geophysical Company(Western Co.) and some additional multi-channel pro"les off CampiFlegrei (Fig. 2).

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The Western Co. seismic grid was acquired in 1968 after the com-mitment of Italy's Minister of Industry to carry out a regional surveyof the entire Eastern Tyrrhenian continental shelf (ViDEPI, 2009).These seismic data were acquired using: an acquapulse energysource, 24-trace and 1600 m-long streamer, 2 ms sample rate, 68 mshot and group interval, 10–80 Hz "lter, and recorded length of 4 s.The processing sequence was: deconvolution before stack, normalmove out stack of 1200%, time variant "lter, and playback un"ltered.Additional multi-channel pro"les were acquired off Campi Flegreiin 1988. These data were recorded using a double water gun, a24-trace and 575 m-long streamer, 2 ms sample rate, and recordedlength of 4.5 s. The data processing sequence included deconvolution,velocity analysis, normal move out stack of 1200% or 2400%, and timemigration. These multi-channel pro"les are characterized by a highsignal–noise ratio with the best vertical resolution being 10 m.

Raster image of the overall seismic pro"les were converted to SEGY format and then collected in a dedicated geographic informationsystem (GIS) environment. Line drawing, interpretation of pro"lesand modeling of geological surfaces were performed using Kingdom®software (copyright IHS); gridding and contouring were performedon geologic horizons in order to generate 2-D models and isochronmaps of the succession. An iterative testing was done to select thebest algorithm and processing parameters. Finally a 3-D digitalmodel of the Gaeta Bay was produced.

The seismic units were calibrated using the lithostratigraphic dataof deep offshore and onshore boreholes (Ippolito et al., 1973; Rosi andSbrana, 1987; ViDEPI, 2009). The seismic interpretation was madeusing seismic stratigraphy and sequence stratigraphy methods: seis-mic units are groups of seismic re!ections, the parameters of which(con"guration, amplitude, continuity and frequency) differ fromthose of adjacent groups. Volcanic and sedimentary units were delin-eated on the basis of contact relations and internal and external con-"gurations (e.g. Mitchum et al., 1977). The sequence stratigraphyapproach (e.g. Posamentier and Vail, 1988) allows the identi"cationof 4th-order depositional sequences (100 ka), forecast depositionalsettings, and lithologies. The used chronostratigraphic framework istaken from the International Commission on Stratigraphy (2010).

The Tyrrhenian Sea was studied using the data acquired within theframe of the CROP Project (performed by a pool composed of theConsiglio Nazionale delle Ricerche of Italy, CNR, the national oil com-pany, Agip, and the national electric company, Enel) a comprehensiveattempt to study the crust of Italy and surrounding seas. The CROPseismic pro"les were acquired and processed in the 1980s and1990s and an atlas of these seismic pro"les was successively pub-lished by CNR (Scrocca et al., 2003). The CROP data differ fromcommercial multichannel pro"les because they are Near VerticalRe!ection seismic pro"les characterized by deep penetration (17 sof twtt) and low resolution. Offshore sections are the most readableseismic lines, and in this paper we present one CROP seismic sectionthat crosses the Eastern Tyrhenian Sea (Fig. 1). The seismic pro"leinterpretation has been calibrated by analyzing and compiling theavailable geological and geophysical constrains.

4. Gaeta Bay seismic stratigraphy

This study of Gaeta Bay reveals the occurrence of three deep ma-rine sedimentary basins: Northern Gaeta Bay (hereinafter NGB), Cen-tral Gaeta Bay (hereinafter CGB) and Southern Gaeta Bay (hereinafterSGB) (Fig. 3).

The seismo-stratigraphic interpretation permitted us to recognizefour seismic unconformity-bounded units (PP, A, B, C) overlying theacoustic substrate. The boundaries of these units are marked byre!ectors that represent major unconformities. We calibrated theseismic re!ection pro"les based on the stratigraphic succession ofthe 2910 m-deep Mara1 well, located in Gaeta Bay, displaying aMesozoic–Cenozoic tectonic unit over thrusting a Cenozoic carbonate

tectonic unit (Fig. 4). In detail the upper tectonic unit (from older toyounger) is made up of thick Triassic–Giurassic limestone and Mio-cene dolostones, sandstones and clays, a thick regressive successionof neritic environment made up of conglomerates (undated), andsands and clays Pleistocene in age. We maintain that the conglomer-ates of the Mara1 well can be dated to the Pliocene age because theycan be stratigraphically correlated to a deposit made up of conglom-erates–sands and clays containing Pliocene fossils occurring onshorenear Gaeta (Bergomi et al., 1969). The seismic section across Mara 1well and offshoreMount Massico (Fig. 4) shows: Mesozoic carbonatesdipping northwestwards, Miocene clastic deposits characterized byan oblique prograding wedge with an erosional toplap surface,Pliocene conglomerates–sands and clays deposited on the baselap ofthe older prograding unit, and the Pleistocene sands and clays uncon-formably covering the older units affected by a high angle fault.

The succession of the Gaeta Bay basin is thicker than 3.0 s (twtt)and the sequence stratigraphic approach permitted us to identifythirteen depositional sequences above an older unconformity-bounded unit (Pliocene-early Pleistocene in age, see the followingparagraphs) overlying the Meso-Cenozoic substrate. We assume aQuaternary age for these depositional sequences because more than3300 m of Quaternary deposits were drilled adjacent to Gaeta Bay(for example the Cancello well close to the coast) in the CampaniaPlain (Ippolito et al., 1973). In this case the depositional sequencesof Gaeta Bay must be necessarily of 4th order (100 ka). Thirteensequences of 3rd order (1 Ma) or 5th order (10 ka) would implyrespectively, either a too-old (13 My) or too-young (0.13 My) age.Furthermore the occurrence of 4th order sequences has alreadybeen reported in the Eastern Tyrrhenian margin (Chiocci, 1993;Milia, 1999; Milia et al., 2009).

4.1. Acoustic substrate

The acoustic substrate of Gaeta Bay, disrupted by faults, ismarked byre!ection-free high-amplitude and moderate continuity at the top(Fig. 5). Based onwell and outcrop data it is possible to correlate it to Pa-leozoic phyllites outcropping at Zannone and to Mesozoic carbonatesand Miocene clastics that outcrop at Zannone, Circeo Promontory,Gaeta mountains and Mount Massico (Fig. 3). In the SGB basin the oc-currence of a Quaternary thick volcanic unit (see unconformity-bounded unit C) makes it dif"cult to detect the acoustic substrate thatwas postulated at a depth of N3 s (twtt) on the basis of the seismicand well data of adjacent areas.

The contour map and the 3-D model of the substrate (Figs. 6A, 7)clearly show a complex architecture of the study area featuring thetriangular NGB basin, the roughly east–west CGB basin and the SGBbasin.

4.2. Unconformity-bounded unit PP (Pliocene–Lower Pleistocene)

The unconformity-bounded unit PP is wedge-shaped and separat-ed into two subunits by the unconformity Ux. It is characterized inthe lower part (subunit 1) by chaotic facies, re!ectors with low-amplitude, low-frequency and poor to moderate continuity andsome re!ectors with high-amplitude, low-frequency and good conti-nuity; in its upper part (subunit 2) it is made up of divergent re!ec-tors with low to high amplitude, low to high frequency and goodcontinuity (Fig. 5). The lower boundary of the unconformity boundedunit PP corresponds to a non-conformity (where it covers the Meso-zoic carbonatic substrate) that laterally passes to an angular uncon-formity (where it overlies the Miocene clastic deposits). Its upperboundary corresponds to an onlap surface laterally passing to a cor-relative conformity; several angular unconformities are present with-in this stratigraphic unit.

The unconformity-bounded unit PP is the "rst sedimentary depos-it that was laid down in the Gaeta Bay basin. Subunit 1 was calibrated

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to conglomerates, sands and some clays drilled in the Mara 1 well andis physically correlated (by means of the seismic line 188 perpendic-ular to the coast) with coarse-grained clastic sediments inter-layeredwith marine clays cropping out east of Gaeta and dated Pliocene(younger than 4 Ma due to the presence of Globorotalia puncticulata;Bergomi et al., 1969). In the western part of the NGB basin subunit 1of the unconformity-bounded unit PP was encountered in two coresby Zitellini et al. (1984) and Marani et al. (1987) who reportedclays and silts of Pliocene age. We attribute a Lower Pleistocene ageto subunit 2.

The isochron map of the unconformity-bounded unit PP (Fig. 6B)features two thickness maxima: the "rst one reaching N1.5 s (twtt) inthe area of the CGB-Mara1 well and the second one reaching 1.3 s(twtt) in the NGB basin. The seismic facies calibrated with cores, welldata and outcrops indicates that subunit 1 deposited in a coastal-shallow water environment, whereas subunit 2 corresponds to a ma-rine environment; the presence of the angular unconformity (Ux),dividing subunits 1 and 2, indicates a rapid deepening of the basin.

4.3. Unconformity-bounded unit A (Lower Pleistocene)

Theunconformity-boundedUnit A is characterized byparallel re!ec-tors with variable amplitude and frequency and very good continuity;its lower boundary corresponds to an onlap surface whereas its upperboundary is an erosional one; in detail the unconformity-boundedunit A is characterized by an aggradational stacking pattern and severalunconformities corresponding to onlap or erosional surfaces (Fig. 5).The isochron map of the unconformity-bounded unit A shows(Fig. 6C) two clear thickness maxima in the NGB basin and CGB basin.

Characterized, respectively, by thicknesses of 1.5 s and 1.0 s (twtt);the aggrading pattern of the parallel re!ectors is in accordance withthe fact that Unit A "lls previously formed grabens (Figs. 6, 8).

A sequence stratigraphy approach in the interpretation of the seis-mic unit "lling the basin allowed the de"nition of twelve depositionalsequences overlying unit PP. Assuming that these twelve stratigraph-ic units correspond to fourth order (100 ka) depositional sequences,the deposition of unconformity-bounded Unit A occurred between1.3 Ma and 0.7 Ma.

4.4. Unconformity-bounded unit B (0.7–0.4 Ma)

In the NGB and CGB basins unconformity-bounded Unit B corre-sponds to a thick prograding complex characterized by severalprogradational unitswith a sigmoidal external form that indicate aggra-dation/progradation of the sediments from the coast toward the sea(Fig. 5). The seismic re!ectors of this complex are characterized by var-iable amplitude and frequency and very good continuity. The occur-rence of several onlaps and erosional surfaces, including incisedvalleys, permitted us to recognize three unconformities in the strati-graphic succession. Unconformity-bounded unit B consists of fourthorder (100 ka) cycles arranged into an overall regressive succession de-posited in the initial part of theMiddle Pleistocene. The isochronmap ofunconformity-bounded unit B displays (Fig. 6D) two depocenters in theCGB and NGB basins characterized by respective thicknesses of 0.9 sand 0.8 s (twtt). The architecture of unit B differs in the NGB and CGBbasins. Sigmoid-progradational units occur in the NGB basin whereaswedge-shaped units are present in the CGB basin that was affected bysyn-depositional fault activity.

Fig. 4. Interpreted seismic section through the eastern part of Gaeta Bay and the Mara1 well. PE = Paleocene-Eocene; MZ = Mesozoic; MI = Miocene; PP = Pliocene; Q = Qua-ternary (for section location see Fig. 3).

Fig. 5. Interpreted seismic section that shows the stratigraphic in"ll of the NGB basin, formed by unconformity-bounded units PP, A, B, C, overlying the acoustic substrate (for sec-tion location see Fig. 3).

8 A. Milia et al. / Global and Planetary Change 109 (2013) 3–17

4.5. Unconformity-bounded unit C (post !0.4 Ma)

The unconformity-bounded unit C in the NGB and CGB basins showsthree progradational unitswith an oblique con"guration correspondingto fourth-order depositional sequences and featuring a rapid shift to-ward the sea (Fig. 5). In the SGB basin, by contrast, the unconformity-bounded unit C shows an architectural changemoving southeastwards:from a progradational seismic con"guration, characterized by high am-plitude continuous re!ectors, (northwestern part of Fig. 9) to a wedgeshaped unit thickening toward the southeast close to Campi Flegreiand Ischia (southeastern part of Fig. 9), characterized by a unit with achaotic seismic facies inter-layered with some re!ectors with high am-plitude and good continuity. Thesewedge-shaped chaotic units (!, ", #)inter layered within the unconformity-bounded Unit C are interpretedas a post 0.4 Ma volcanic "eld off Campi. Torrente and Milia (2013)correlated these wedge-shaped units to the thousands of m-thick bur-ied lava volcanoes interlayered with volcanoclastic deposits drilled atCampi Flegrei (Licola, Mofete, Ischia wells; Fig. 3).

The isochron map of unconformity-bounded unit C (Fig. 6D) fea-tures two striking depocenters in the SGB basin reaching a thicknessof 2.35 s (twtt) that can be explained with the emplacement of volumi-nous volcanic units in the strongly subsiding area close to Campi Flegrei.By contrast the NGB and CGB basins feature low-value thickness maxi-ma (0.8 s twtt) roughly parallel to the coast re!ecting the coastalprogradation of the unconformity-bounded unit C.

5. Gaeta Bay Plio-Quaternary tectonics

The stratigraphic and structural interpretation of the multichannelseismic data calibrated by wells, the generation of 2-D and 3-Dmodels of stratigraphic surfaces and isochron maps of the strati-graphic units of Gaeta Bay supply "rst-order constraints for amulti-stage tectonic model of the Campania continental margin. Inparticular the Plio-Quaternary structural evolution of the Gaeta Baysector of the Eastern Tyrrhenian Margin is seen to be controlled bymajor faults. These structures bound three main tectonic domains(Figs. 6A, 7): 1) the NGB Basin; 2) the CGB Basin; 3) the SGB Basin.

The triangular NGB Basin covers an area of approximately 500 km2

(Fig. 6A); it is bounded to the West by NNE-trending faults and to theEast by NW-trending faults. The NW-trending faults bound large blocksand display listric geometry (Fig. 10); the south eastern fault features athrow of the substrate of 1.4 s (twtt). By contrast the NNE trendingfaults, also affecting unit PP, display high angles (Fig. 8). These normalfaults form a triangular basin with the apex located in the southernPontina Plain, bounded to the South by an approximately E–W faultzone (Fig. 6A). The unconformity-bounded unit PP shows a wedge-shaped geometry linked to the activity of a normal fault (Fig. 5). It ischaracterized by two subunits (separated by the tectonic-enhanced un-conformity Ux) and a thickness increasing towards the boundary fault.Unit PP (Fig. 6B) was deposited between 4 and 1.3 Ma during two tec-tonic stages: in the Lower Pliocene normal faults controlled the

Fig. 6. (A) Structure contour map of the acoustic substrate. NGB = Northern Gaeta Bay, CGB = Central Gaeta Bay, SGB = Southern Gaeta Bay. Contour interval is 0.20 s (B) Iso-chron map of the unconformity-bounded units PP. Contour interval is 0.12 s. (C) Isochron map of the unconformity-bounded units A. Contour interval is 0.15 s. (D) Isochronmap of the unconformity-bounded units B. Contour interval is 0.10 s. E) Isochron map of the unconformity-bounded units C. Contour interval is 0.25 s. F) Isochron map of theunconformity-bounded units PP and A. Contour interval is 0.20 s. Map coordinate system: UTM, WGS84.

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deposition of subunits 1 in a coastal-shallowwater environment; in thePliocene–Lower Pleistocene the basin deepened and subunit 2 formedin a marine environment. We correlated the Gaeta Bay structures ofthe "rst stage to Lower Pliocene faults (Zitellini et al., 1984) formedwestwards of Gaeta Bay (unconformably covered by Pleistoceneprogradational units, Marani et al., 1987) and south of Ventotene, onthe Campania margin slope (offsetting Lower Pliocene marls, DredgeT71-7, Zitellini et al., 1984). By contrast the structures of the secondstage can be linked to Lower Pleistocene normal faults of the Campaniamargin (Gars and Lippman, 1984; Mariani and Prato, 1988; Milia andTorrente, 1997).

The triangular NGB basin is bounded toward the south-west by anarched relief (Fig. 6A). The seismic line E178 (Fig. 5) displays unit PPcontemporaneously affected by normal faults to the North anduplifted, tilted and wedge-shaped to the South, suggesting a concom-itant activity of these structures. Thus the arched southern boundaryof the NGB basin corresponds to an approximately E–W steep faultzone (Fig. 6A) that can be interpreted as a positive !ower structure(sensu Harding, 1985) that causes a nearly 1 s (twtt) structural upliftof the substrate in the faulted anticline (Fig. 5).

The CGB basin is rhomboidal in shape due to boundary faultstrending approximately E–W and NE–SW (Fig. 6A), a substrate at adepth of 3.0 s (twtt) in the hanging wall blocks (Fig. 11) and coversan area of approximately 150 km2. The analysis of the interplay be-tween stratigraphic in"ll and faulting permitted us to unravel theCGB basin complex structural evolution due to the superposition ofa younger ENE-trending depression (Fig. 6D) over an older ellipticalone that trends NW–SE (Fig. 6F). An older tectonic event producedan elliptical basin characterized by an up to 2.0 s-thick synkinematicdeposit corresponding to the wedge-shaped unconformity-boundedunits PP and A and steep faults (Figs. 6F, 11) characterized by a max-imum throw, respectively, of 2.5 s (twtt) in the substrate and 1.2 s(twtt) in the top of unit PP. By contrast a younger stage producedan asymmetric 1 s-thick basin (Fig. 6D) bounded by NE-trending nor-mal faults, dipping towards the southeast and characterized by amaximum throw of 0.4 s (twtt) in the top of unit A (Fig. 10); theage of this tectonic event is 0.7–0.4 Ma due to the divergent seismiccon"guration of unconformity-bounded unit B.

The SGB basin covers an area of approximately 500 km2 and wasproduced by the interaction of several fault systems (NE–SW, NW–

Fig. 7. The 3-D digital model inserted into the spatial-oriented grid of the acoustic substrate in Gaeta Bay; view from south, vertical scale in seconds.

Fig. 8. Interpreted seismic section through the western boundary of NGB basin (for section location see Fig. 3).

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SE and NNE–SSW; Fig. 6D). It corresponds to a strongly subsiding areaof Gaeta Bay where the acoustic substrate was postulated at a depthof N3 s (twtt) on the basis of seismic and well data of adjacent areas(Figs. 6D,E, 9). The northern boundary of the SGB basin correspondsto a NE-trending fault swarm located at south of Volturno river thatdownthrows the top of the unconformity-bounded unit A (Fig. 9)south-eastwards; these faults display listric geometry and dipsouth-eastward. We recognized faults of different ages: older NE–SW and NW–SE structures (0.7 Ma and 0.4 Ma) were active through-out the deposition of the 0.6 s-thick unconformity-bounded unit Bclose to the Campi Flegrei coast (Fig. 6D); a couple of NNE–SSWsteep normal faults and NE–SW and NW–SE faults (Fig. 6E) formedduring a strong post 0.4 Ma subsidence event (horizon 0.4 at depthof N2 s in the hanging wall blocks; Fig. 9), coeval with the emplace-ment of a thick volcano-clastic wedge off Campi Flegrei–Ischia.

On the basis of the reconstructed structural pattern and age of thesyn-kinematic strata we distinguished a poly-phased structure inGaeta Bay. The oldest structures were active during the Pliocene–Lower Pleistocene and produced two main depocenters (2 s-thick) inthe NGB, and CGB basins (Fig. 6F); they correspond to NW–SE andNE–SW faults that developed throughout the whole bay. Intermediateage structures controlled the depocenters of GCB (0.9 s-thick) andSGB (0.6 s-thick) basins but were buried in the NGB basin by theunconformity-bounded unit B (Fig. 6D). The youngest structures areNNE–SSW normal faults and NW–SE and NE–SW faults located in theSGB basin (6E); they controlled a large thickness maximum (2.3 s) inthe SGB basin (coeval with the post 0.4 Ma emplacement of the volca-nics of unconformity-bounded unit C), while the deposition of the lateQuaternary progradational units gave rise to a small thickness maxi-mum (0.8 s) elongated parallel to the coast of the NGB and CGB.

6. Crop M29B seismic pro!le

Although several studies of the Tyrrhenian Sea have already point-ed out the stratigraphy and the main structural features of this basin,a new picture of the structural setting of the Tyrrhenian Sea is provid-ed by the interpretation of seismic data acquired within the frame-work of the CROP project. To link the geologic evolution of theCampania continental margin with the Tyrrhenian Sea central plainour study considered the CROP section M29B, that runs from GaetaBay to the Vavilov basin (Figs. 1, 13).

The tectonic evolution of the Vavilov basin was investigated byKastens et al. (1987) and Mascle and Rehault (1990) who reported aLower Pliocene detachment fault responsible for the exhumation ofman-tle rocks underlying extensional allochthons made up of Alpine rocks. Inaddition Robin et al. (1987) documented Pleistocene normal faults thatproduced the tilting of the Vavilov volcano substrate (2.4 My in age)that, in turn, was covered by 0.4 Ma-old lavas. The relevance of detach-ment faults in the Vavilov basin leads us to interpret the Tyrrhenian Searifting by use of lithospheric scale models, developed for riftedmagma-poor margins, that treat tectonism and magmatism together,describing a sequential mode of extension from pure shear to simpleshear (detachment faulting and exhumation of continental mantle) tosea!oor-spreading (e.g. Whitmarsh et al., 2001; Manatschal, 2004).

The CROP M29B seismic section (Fig. 13) displays a complex struc-ture that can be associated to a polyphased rifting; we will discussthese faults according to their chronology. The oldest structure (LowerPliocene in age according to Kastens et al., 1987 and Mascle andRehault, 1990) is a detachment fault in the subsurface of the Vavilovbasin, that separates footwall mantle rocks (serpentinized peridotites,drilled at Gortani Ridge, ODP Site 651, 655) by hanging wall Alpine

Fig. 9. Interpreted seismic section through the SGB basin showing extensional structures and a seismic facies change of unconformity-bounded unit C (for section location seeFig. 3).

Fig. 10. Interpreted seismic section through the eastern part of the NGB basin (for section location see Fig. 3).

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ophiolites (ODP Site 656); footwall and hanging wall blocks arestratigraphically covered byMid-Oceanic Ridge basalts. Coeval structuresoccur in the lower part of the Campania margin (at water depths of be-tween 3500 m and 500 m) corresponding to tilted blocks and intraslopebasins bounded by listric normal faults that merge into a low-angle de-tachment fault; one of such structures bounds the crest of a faultedblock where Lower Pliocene marls were dredged south of Ventotene(Dredge T71-7), thus implying a Pliocene age for this fault. We suggestthat these faults located on the margin correspond to the crustal part ofthe detachment fault system that developed in the Vavilov basin. Youn-ger structures are Plio-Pleistocene high-angle faults diffused in both theMarsili basin and Campania margin that were active during the onset ofsea!oor spreading at Vavilov basin (Fig. 13). Conjugate normal faultsdisrupt the detachment fault: an east-dipping normal fault, bounded inthe east by the D'Ancona ridge, displaces the basal conglomerates andthe lower part of the Plio-Pleistocene succession; a west-dipping normalfault, located at the eastern boundary of the Vavilov basin, featuresa sin-kinematic growth of the Plio-Pleistocene succession. Plio-Pleistocene high angle normal faults also controlled the deposition ofthick asymmetric wedges in the upper part of the Campania margin(Fig. 13; see Gaeta Bay Plio-Quaternary tectonics).

7. Tyrrhenian Sea kinematic evolution

Martin (2006) developed a general tectonic model where duringsubduction rollback, two arc-parallel rifts propagate in the opposite

directions, from an initial central location, causing pairs of terranesto simultaneously rotate clockwise and anticlockwise. As the move-ment continues a gap begins to extend between them, and a thirdrift initiates in the opposite direction to the subduction rollback. Suc-cessively the same author (Martin, 2007), using the triangular mapgeometry of the Tyrrhenian basin and coeval anticlockwise and clock-wise rotations, respectively, of Southern Apennines and Sicily, sug-gested that double-saloon-door tectonics occurred in the TyrrhenianSea back-arc basin during subduction rollback.

Due to the young age of the Tyrrhenian Sea, tectonic and volcanicprocesses exert a strong in!uence on the sea!oor physiography. Con-sequently the analysis of the Tyrrhenian Sea sea!oor map offers theopportunity to reveal the complex fault pattern affecting the basin.The map of the Tyrrhenian Sea normal faults (Fig. 1) features an inho-mogeneous pattern, lacking simple sets of parallel faults anddisplaying crossing–converging structures that suggest different tec-tonic stages. In order to discriminate homogenous sets of normalfaults a two-fold approach was used: the sets were grouped in faultsystems according to their age (obtained by the stratigraphic dataavailable in the Tyrrhenian Sea) and, following the work of Turco etal. (2006) and Martin (2007), their convergence in an instantaneouspole rotation. In this way we distinguish "ve systems of normal faultsin the upper plate and propose a kinematic model for the Tyrrhenianback-arc basin that links extension and volcanism (Fig. 14). Furtherwe discuss, in detail, the stages of the tectonic evolution of the Cam-pania margin (Fig. 15) by integrating the results of this study on

Fig. 11. Interpreted seismic section through the CGB basin (for section location see Fig. 3).

Fig. 12. Interpreted seismic section through the CGB basin displaying a Middle Pleistocene half-graben (for section location see Fig. 3).

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Gaeta Bay with those published for the adjacent Bay of Naples, Cam-pania Plain and Sele Plain (Gars and Lippman, 1984; Mariani andPrato, 1988; Milia and Torrente, 1997, 2003; Milia et al., 2003).

7.1. Tortonian–Messinian p.p. (Fig. 14A)

During the Tortonian–Messinian p.p. the extensional process de-veloped in the Sardina margin, the Cornaglia basin and the Vavilovbasin (DSDP Sites 132, 373 and ODP Site 654; Sartori et al., 2004);these normal faults converge towards Tunisia. During this stage theoldest basalts (7.0–5.5 Ma) of the Tyrrhenian Sea were emplaced inthe Vavilov basin area.

7.2. Messinian p.p.–Pliocene p.p (Fig. 14B)

The extension migrated eastwards within the Vavilov basin and atthe border of the Eastern Tyrrhenian margin. This fault system con-verges toward Latium and its age was calibrated in the bathyalbasin at ODP sites 655 and 652 and in the Campania margin slope.Throughout this stage detachment faulting exhumed footwall mantlerocks in the Vavilov basin that were successively covered byMid-Oceanic Ridge basalts (4.4–2.6 Ma). Volcanism started at PonzaI. (4.0–1.0 Ma).

7.3. Pliocene p.p–Lower Pleistocene (Fig. 14C)

This fault system spread over a wide area of the Tyrrhenian basin.Indeed we recognized three extension directions: NE–SW in the Cam-pania margin and Vavilov basin (sub-fault system convergent towardthe Pontina Plain), NW–SE in Marsili basin and N–S in Paola basin.These three contemporaneous extension directions match Martin'sdouble-saloon-door model (2006): the Campania margin and Marsilibasin approximately correspond to the two arc-parallel rifts and thePaola basin to the rift orthogonal to the subduction zone. Volcanic ac-tivity developed in the Marsili basin (ODP site 650), continued atPonza (4.0–1.0 Ma) and the Campania Plain (Parete volcano). Onthe Campania margin (Fig. 15A) this stage of rifting was characterizedby NNE–SSW and NW–SE normal faults in the NGB and CGB basins("lled by the N1.5 sec-thick PP unit), and NW–SE normal faults inthe Campania Plain and Naples Bay (Campi Flegrei, Sorrento Peninsula,SarnoMountains, Vesuvius) "lled by thousands ofmeters of Quaternaryclastic deposits.

7.4. Middle Pleistocene (0.7–0.4 Ma; Fig. 14D)

The new fault system features a SW-directed extension directionand consists of approximately NE-trending normal faults developedcontemporaneously on the Campania Margin and Marsili basinbetween 0.7 Ma and 0.4 Ma. The associated volcanism occurred atMarsili seamount (post 0.780 Ma), Roccamon"na volcano (0.63 to

0.13 Ma) and Ventotene (0.8 to 0.13 Ma). The present morphologiccon"guration of the Campania margin (Fig. 15B), consisting of alter-nating NE–SW structural highs (Mount Massico, Sorrento Peninsula)and lows (CGB and SGB basins) transversal to the Apennine chain(Mariani and Prato, 1988; De Rita and Giordano, 1996; Milia andTorrente, 1997; Milia et al., 2003; Milia and Torrente, 2011) was ac-quired during this tectonic stage. These NE-trending normal faults,mainly dipping to the SE, produced half grabens and are responsiblefor the rapid deepening of Naples Bay basin (Milia and Torrente, 1999)and CGB basin (Fig. 12) that occurred between 0.7 Ma and 0.4 Ma.

7.5. Middle Pleistocene (post 0.4 Ma; Fig. 14E)

The youngest fault system developed over the last 0.4 Ma from theCampania Margin (E–W extension direction) to the Eolie I. (NW–SEextension direction) and was accompanied by the emplacement ofhuge volumes of volcanic rocks on the Campania margin (SGB basin,post 0.3 Ma ignimbrites of the Campania Plain, Campi Flegrei,Ischia I.,Ventotene I., Roccamon"na volcano), at Vavilov volcano(0.4–0.1 Ma) and Eolie I. (post!0.22 Ma, De Rosa et al., 2003). This ex-tension stage was characterized on the Campania Plain and SGB basinby NNE–SSW normal faults, E–W transfer faults and the reactivationof older NW–SE and NE–SW faults (Fig. 15C). It gave rise to a rapiddeepening of the SGB basin and a tectonically-enhanced unconformitythat underlies the wedge-shaped, up to 2.3 s-thick, unit C.

8. Conclusions

A detailed basin analysis of the sedimentary basins off the Campaniamargin and the study of the Eastern Tyrrhenian continental margindown to the bathyal Tyrrhenian basin (CROP 29B seismic line) permit-ted us to reconstruct a complex opening of the Tyrrhenian back-arcbasin drawing attention to the role of the pery-Tyrrhenian basins.

Our tectono-stratigraphic study of Gaeta Bay adds to previousones dedicated to Naples Bay (e.g. Milia, 1999; Milia and Torrente,1999) and Paola Basin (Milia et al., 2009) and provides a furtherstep in the reconstruction of the geological evolution of the EasternTyrrhenian Sea margin with a resolution of 100 ka.

Gaeta Bay is formed by three basins (northern, central and south-ern basins) and features a complex stratigraphic architecture: in theNGB and CGB basins a syn-rift deposit (unit PP) is buried by the oldestaggradational deposit (unit A) "lling the accommodation space; apost 0.7 Ma succession (units B and C) "lled the NGB basin with alateral aggradational geometry; a syn-tectonic wedge (unit B) wasdeposited in the CGB basin between 0.7 and 0.4 Ma; post 0.4 Mathick deposits (unit C) are testament to the collapse of the SGB basin.

A geologic link between the Campania continental margin and theVavilov bathyal basin was reconstructed. Indeed to our knowledge,this paper contains the "rst published cross section describing theVavilov detachment fault system, although this structure has been

Fig. 13. M29A CROP seismic pro"le and interpretation. For pro"le location see Fig. 1.

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already inserted into crustal sketches describing the Tyrrhenian Seaevolution by Mascle and Rehault (1990). The interpretation of theCROP 29B section, extending from the Vavilov basin to the Campaniamargin, "rst documents a tectonic evolution of the Tyrrhenian basincommon to other extensional margins (e.g. Whitmarsh et al., 2001;Manatschal, 2004) and shows that rifting was seen to be polyphase,

with rift activity migrating and the mode of rifting changing throughtime (including a period of lithospheric detachment faulting).

Taking into account the published geological data, we propose akinematic evolution of the Tyrrhenian basin over the last 10 Ma thatconsists of older extensional events (stages 1–2) off Sardinia and inthe Vavilov basin (leaving the Eastern Tyrrhenia margin unaffected)

Fig. 14. Kinematic sketch of the Tyrrhenian back-arc basin over the last 10 Ma. Yellow arrows are extension directions and red spots volcanism. Only the faults associated with everytectonic stage are shown. (A) stage 1; CB = Cornaglia basin; VB = Vavilov basin. (B) stage 2; VB = Vavilov basin, Po = Ponza. (C) stage 3; VB = Vavilov basin, MB = Marsilibasin, GB = Gaeta Bay, P = Paola basin, Po = Ponza, Pa = Parete volcano. (D) stage 4; MB = Marsili basin, Ve = Ventotene, R = Roccamon"na. (E) stage 5; MB = Marsilibasin, E = Eolian volcanoes, V = Vavilov volcano, Ve = Ventotene; R = Roccamon"na; SGB = Southern Gaeta Bay volcanoes, Ca = ignimbrites of the Campania Plain.

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and younger ones (stages 3–5) developed in the whole Tyrrhenian re-gion. In particular we document a Pliocene–Quaternary change of theextension direction along the Campania continental margin. It isworth mentioning that a similar progressive change in rifting direc-tion has also been proposed in the NE Atlantic during continentalrifting and break-up (Walker et al., 2011).

Acknowledgments

This manuscript bene"ted from the stimulating and constructivecriticisms of F. Roure and two anonymous reviewers; we acknowl-edge the editorial work of S. Cloeting. We thank E. Roberts for the En-glish revision. This research was funded by the University of Sannioand MIUR (PRIN 2008, Prot.2008YWPCWB_002) grants. A.M. andM.M.T. wrote the paper. A.M. performed the stratigraphic interpreta-tion. A.M., B.M., and M.M.T. made the structural interpretation of theGaeta Bay. All the authors created and managed the GIS database.

Appendix A. Supplementary data

Supplementary data associated with this article can be found inthe online version, at http://dx.doi.org/10.1016/j.gloplacha.2013.07.003. These data include Google maps of the most important areas de-scribed in this article.

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Fig. 15. Tectonic evolution of the Campania margin. Only the faults associated withevery tectonic stage are shown; solid lines are normal faults and dashed linesstrike-slip transfer faults; the "lled red circle is the apex of the NGB triangular basinand the rotation pole. NGB = Northern Gaeta Bay; CGB = Central Gaeta Bay;SGB = Southern Gaeta Bay; CP = Campania Plain, Naples Bay; Po = Ponza; V =Ventotene, R = Roccamon"na; I = Ischia; CF = Campi Flegrei; V = Vesuvius, S =Sorrento; Sa = Sarno Mts, Ma = Massico Mt. Map coordinate system: UTM, WGS84.

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