es a,c, J. Noiva a, M. Cacho d, J. Ferreira d,
a LNEG, Laboratrio Nacional de Energia e Geologia, Unidb EMAM, Estrutura de Misso para os Assuntos do Mar, Poc IDL, Instituto D. Luz, Portugald Universidade de Lisboa, Centro e Dep. Geologia Fac. Cine CICEGe, DCT, Faculdade de Cincias e Tecnologia, Univerf ISMAR, Istituto di Scienze Marine, Bologna, Italy
seismostratigraphy ning of the Middle-Pleistocene Transition at about 1.31.0 Ma, accounting for the deposition of mounded
Marine Geology 303306 (2012) 4262
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j ourna l homepage: www.e lstectonicsdrifts and formation of the lvares Cabral moat. Seismostratigraphic interpretation and isochron mapsallowed for the establishment of the main oceanographic, climatic, morphologic and tectonic factors thatcontrolled the drifts deposition: i) the Pliocene and Quaternary MOW circulation forced by climate changes;ii) the sea bottom topography inherited from the Late Miocene, mainly shaped by the Portimo, Lagos andBartolomeu Dias canyons system; iii) the interaction between along-slope and down-slope processes sincethe Pliocene; and iv) PlioceneQuaternary fault-activity and diapirism.
2011 Elsevier B.V. All rights reserved.
The contourite drifts of the Algarve margin are located on thenorthern Gulf of Cadiz, between 500 and 700 m water depth andare formed as a consequence of the interaction of the MediterraneanOutow Water (MOW) with the middle continental slope of south-
most of them dedicated to the Faro and Albufeira drifts (e.g. Vanneyand Mougenot, 1981; Faugres et al., 1985a, 1985b; Stow et al.,1986; Nelson et al., 1993; Sierro et al., 1999; Llave et al., 2001;Hernndez-Molina et al., 2003, 2006; Llave et al., 2006, 2007, 2011).Conversely, a small number of works investigated the Lagos and Por-timo drifts (Marchs et al., 2007, 2010) and the Sagres drift (Llavewest Iberia. The existence of the contourite dgin was rstly described by Siedler (1968) fo
Corresponding author at: LNEG, Laboratrio NacUnidade de Geologia Marinha. Apartado 7586, 2720-866210 924 600; fax: +351 2147919018.
E-mail address: email@example.com (C. Roque).
0025-3227/$ see front matter 2011 Elsevier B.V. Alldoi:10.1016/j.margeo.2011.11.001of Early Pleistocene age is related to a strengthening of the MOW close to the onset of the Northern Hemi-sphere glaciations at about 2.6 Ma during which were deposited low-mounded drifts. Thirdly, the growingphase from Middle-Pleistocene through Holocene suggests the presence of a stronger MOW since the begin-Mediterranean Outow WaterPlioceneQuaternarya r t i c l e i n f o
Article history:Received 1 July 2011Received in revised form 2 November 2011Accepted 3 November 2011Available online 12 November 2011
Communicated by D.J.W. Piper
Keywords:contourite driftsAlgarve marginade de Geologia Marinha. Apartado 7586, 2720-866 Amadora, Portugalrtugal
cias, Portugalsidade Nova de Lisboa, Portugal
a b s t r a c t
The contourite drifts off southwest Iberia that formed as a result of the interaction of the Mediterranean Out-ow Water (MOW) with the continental middle slope were studied in the Algarve margin using multichan-nel reection seismic lines, oil-wells, piston cores, and a bathymetric compilation of four datasets. Theseismostratigraphic interpretation of a dense array of oil industry seismic and stratigraphic correlationallowed the identication of ve seismic units of Early Pliocene through Holocene in the Faro and Albufeiradrifts and four correlative seismic units in the Lagos and Sagres drifts and three in the Portimo drift. Athree-phased evolutionary model for the contourite formation is proposed. Firstly, a precursory phase of Pli-ocene age made up of sheeted drifts represents an initial phase of deposition under bottom-current activitythat is correlated with the rst stages of an enhanced MOW at about 3.5 Ma. Secondly, the building up phaseP. Legoinha e, N. Zitellini f
C. Roque a,b,c,, H. Duarte a, P. Terrinha a,c, V. ValadarPliocene and Quaternary depositional mo(Gulf of Cadiz, SW Iberia): Seismic architepaleoceanographic insightsrifts in the Algarve mar-llowed by several works,
ional de Energia e Geologia,Amadora, Portugal. Tel.: +351
rights reserved.l of the Algarve margin contourite driftsture, tectonic control and
ev ie r .com/ locate /margeoet al., 2007). These works rely on the interpretation of gravity cores,high-resolution seismic lines, multibeam bathymetry and backscatter,focusing on the relationships between the depositional architectureand morphology of the drifts, the Quaternary climatic/eustaticchanges and consequent modications in the MOW circulation pat-tern (e.g. Faugres et al., 1985b; Llave et al., 2001; Hernndez-Molina et al., 2006; Llave et al., 2006; Hanquiez et al., 2007;Toucanne et al., 2007).
3) identify and characterize the main build-up phases; and 4) proposea model for the evolution of the contourite drifts that aims to under-
43C. Roque et al. / Marine Geology 303306 (2012) 4262stand the relationships between the seismostratigraphic architectureand the general depositional, tectonic and oceanographic processes ofthe study area from Early Pliocene to the present.
2. Geological and oceanographic settings
2.1. Geological setting
The continental slope of the Algarve margin (SW Iberia) is lo-cated in the northern part the Gulf of Cadiz near the northwestAfrica (Nubia)Eurasia plate boundary (Zitellini et al., 2009). Thekinematics and relative trajectory changes between these twomajor plates since early Mesozoic times until the present governedthe geodynamic evolution of this margin. During the Mesozoic arift basin formed in a sinistral transtensive regime, and is relatedto the opening of the Neo-Tethys and the North Atlantic fromTriassic through Cenomanian times (Terrinha et al., 2002). Tecton-ic inversion of the Algarve rift basin occurred from the LateCretaceous through the Paleogene (Terrinha, 1998; Roque, 2007),related to the Alpine compression as a consequence of theEurasiaAfrica collision and subduction of the Tethyan oceaniccrust between Iberia and Africa. As a consequence of this, a seriesof southwards directed imbricate thrusts formed (Terrinha, 1998;Lopes et al., 2006; Terrinha et al., 2006, 2009), some of whichwere reactivated in the Miocene.
In Miocene times, the subduction of the Tethyan oceanic crust inthe westernmost Mediterranean and the collision between Iberiaand Africa led to the formation of the BeticRif orogenic arc, the sub-marine accretionary wedge of the Gulf of Cadiz (Maldonado et al.,1999; Gutscher et al., 2002; Grcia et al., 2003; Medialdea et al.,2004) and the closure of the oceanic communication between the Te-thys and the Atlantic. At the same time the Algarve basin wentthrough exural subsidence that lasted until the QuaternaryAn integrated vision of the contourite drifts formation as part of abroader and more complex depositional system controlled bychanges in the MOW circulation pattern was rstly proposed byKenyon and Belderson (1973), and reappraised by Hernndez-Molina et al. (2003, 2006).
This work presents an attempt to reconstruct the temporal andspatial evolution of a contourite depositional system (CDS) duringglobal climate changes from Early Pliocene through Quaternary. Thedetail of this study allows the understanding of the inuence of exter-nal factors, such as tectonics, paleogeography and climate changes ona CDS from its very beginning, conrming the degree of responsive-ness of this system to environmental changes and how it can beassessed using seismic reection methods.
The forthcoming IODP 339 Expedition (November, 2011,Mediterranean Outow http://publications.iodp.org/scientic_prospectus/339/339sp_5.htm) will allow: i) accurate timing of the eventsdescribed in this paper, ii) their sedimentological and climatic charac-terization and iii) depth conversion of two way time maps andquantitative sedimentary and erosive modeling associated with theMOW.
The novelty of this work is threefold, consisting of: i) the use of afull multichannel reection seismic dataset that images the sedimen-tary record of the Algarve basin from the Mesozoic through theHolocene; ii) the re-appraisal of the Pliocene faunal data of the oil-industry reports of the offshore wells and iii) the dating of recentlyacquired seaoor samples. The interpretation of these data allowedto: 1) better constrain the age of the contourite drift formation; 2) de-termine the development of the depositional architecture of the driftsthrough space and time since their formation through present;(Terrinha, 1998; Lopes et al., 2006; Roque, 2007).2.2. Oceanographic setting
The oceanic circulation dynamics in the Gulf of Cadiz is driven bydensity contrast between the water masses of Atlantic andMediterra-nean origin that ow on either side of the Gibraltar Straits (Fig. 1a)(Armi and Farmer, 1988; Bryden and Kinder, 1991; Baringer andPrice, 1999). This water exchange denes an inverse estuarine circu-lation pattern that involves an eastwards upper layer of Atlanticwater into the Mediterranean Sea and a westwards bottom layer ofoutowing Mediterranean water, the MOW (Ambar et al., 2002;Serra et al., 2005).
The Atlantic InowWater (AIW) is a 0500 m layer formed by theNorth Atlantic Surface Water (NASW) and North Atlantic CentralWater (NACW) (Criado-Aldeanueva et al., 2006). The NASW origi-nates from shallow NACW that has been modied by the seaatmo-sphere interactions and ows at depths shallower than 100 m, withtemperatures above 16 C and salinity around 36.40. The NACWows between 100 and 700 m, has temperature of 11 C to 17 Cand salinity of 35.636.5 (Criado-Aldeanueva et al., 2006).
The MediterraneanWater originates in the Mediterranean Sea as aconsequence of excess of evaporation over precipitation and runoffand consists mainly of the mixture of two types of water masses,the Levantine Intermediate Water and the Western MediterraneanDeep Water (Pinardi and Masetti, 2000).
The MOW exits the Gibraltar Straits (Fig. 1a) as a warm (13 C)and dense (37.00) water mass that sinks and ows westwardsinto the Gulf of Cadiz as a bottom current, with eroding capability ofbottom structures such as mud volcanoes (Ferreira et al., 2008),being deected northwards due to the Coriolis force (Madelain,1970; Zenk, 1970; Ambar and Howe, 1979a, 1979b; Baringer andPrice, 1997; Ambar et al., 2002; Serra et al., 2005). The MOW showsa westwards velocity decrease from 250 to 180 cm s1 near the Gi-braltar Straits gateway to values between 80 and 40 cm s1 alongthe northern continental slope of the Gulf of Cadiz where it is con-strained to ow along valleys bounded by diapiric ridges (Nelsonet al., 1993). The lowest velocity (about 10 cm s1) is reached alongthe South Portuguese continental slope although locally it can reachvalues up to 50 cm s1 as in the Diogo Co Deep (Ambar and Howe,1979b). As the MOW spreads westwards its density progressively de-creases by turbulent entrainment of overlying less-salty NACW atdepths between 500 and 1500 m, until it approaches neutral buoyan-cy near 8 W at about 1000 m depth (Ambar and Howe, 1979a;Ambar et al., 2002; Bower et al., 2002; Serra et al., 2005; Ambaret al., 2008).
Westwards of 6207 W, the main core of the MOW separatesinto two major cores and two minor ones with distinct densitiesand owing at different depths (Fig. 1a) (Zenk, 1970; Ambar andHowe, 1979a, 1979b; Ambar et al., 2002, 2008). The two majorcores are the Mediterranean Upper Water (MU) and the Mediterra-nean Lower Water (ML) and the minor cores are the Shallow Core(SC) and Deep Core (DC) (Madelain, 1970; Zenk, 1970; Ambar andHowe, 1979a; Ambar et al., 2002; 2008). The MU is warmer andless saline (1314 C and 35.737) and ows at depths between600 and 1000 m depth, centered at 700800 m depth close to thecontinental slope of southwest Iberia. The ML is colder and more sa-line (10.511.5 C and 36.537.5) and ows at depths between1000 and 1300 m depth, stabilizing at around 12001300 m depth.After turning the Cape St. Vincent, the ML splits into a major branchowing westwards and northwestwards and a minor branch thatprogresses northwards along the continental slope of the West Por-tuguese margin, reaching the North Atlantic (Bower et al., 2002).The SC is found at around 400600 m depth along the continentalslope off southwest Iberia, being characterized by comparativelyhigher temperatures (Ambar et al., 2002, 2008). The DC is traceablefrom the Portimo Canyon to the Cape St. Vincent at depths be-
tween 1300 and 1600 m (Ambar et al., 2002; Bower et al., 2002;
44 C. Roque et al. / Marine Geology 303306 (2012) 4262Ambar et al., 2008) and it is characterized by salinities of 36.4236.53. This core seems to be a structure detached from the ML as-sociated with pulses of denser water forced to descent to greaterdepths by interaction with the canyon topography (Bower et al.,2002; Ambar et al., 2008).
The Portimo Canyon acts also as a source of meddies detachedfrom the DC, which are found farther downstream from the canyon(Ambar et al., 2002; Serra et al., 2005; Ambar et al., 2008). The CapeSt. Vincent is another area for meddies formation detached from theML (Ambar et al., 2008).
The North Atlantic Deep Water (NADW) that originates in theNordic and Labrador Seas ows southwards underneath the MOW isa cold (38 C) and low salinity (34.9535.20) water (Reid,1979; Via and Thomas, 2006).
2.3. The PlioceneQuaternary paleoceanography of the MOW
The knowledge of the Quaternary MOW oceanographic variabilityimproved over the past decades due to the use of multiple proxies an-alyses applied to the last 9015 ka sedimentary record: measurementof molecular biomarkers (Cacho et al., 2000, 2006); planktonic andbenthic foraminifers 13C and 18O records (e.g. Schnfeld andZahn, 2000; Rogerson et al., 2005, 2006; Cacho et al., 2006; Voelkeret al., 2006; Schmiedl et al., 2010); measurement of Mg/Ca ratios inbenthic foraminifera (Cacho et al., 2006); total organic carbon(Cacho et al., 2000); magnetic susceptibility (Llave et al., 2006;Voelker et al., 2006); high-resolution grain-size analysis (e.g.
Fig. 1. (A) General oceanographic circulation pattern in the Gulf of Cadiz (modied from G(MOW), the North Atlantic Supercial Water (NASW) and the North Atlantic DeepWater (Nof datasets used in this work: (1) oil-wells (I, Imperador; R, Ruivo; C, Corvina; A, Algarve-(Chevron74, Esso81, GSI84, BIGSETS). Thick lines indicate the location of the seismic line seFaugres et al., 1985b; Nelson et al., 1993; Rogerson et al., 2005;Llave et al., 2006; Toucanne et al., 2007; Hanquiez et al., 2010); radio-carbon dating (Schnfeld and Zahn, 2000; Llave et al., 2006; Voelkeret al., 2006); Nd and Pb isotope record of past ambient seawaterfrom authigenic ferromanganese coatings of sediments (Stumpfet al., 2010).
Reconstruction models based on such proxies and on modelingstudies (e.g. Myers, 2002; Xu et al., 2007) indicate a distinct behaviorof the MOW under different climatic...