estuarine, coastal and shelf...

lable at ScienceDirect

Estuarine, Coastal and Shelf Science 79 (2008) 59–70

lable at ScienceDirect
Contents lists avaiContents lists avai
Estuarine, Coastal and Shelf Science

journal homepage: www.elsevier .com/locate/ecss

Estuarine, Coastal and Shelf Science

journal homepage: www.elsevier .com/locate/ecss

Reworked calcareous nannofossils as ocean dynamic tracers:The Guadiana shelf case study (SW Iberia)

J. Ferreira a, M. Cachao b,*, R. Gonzalez c

a Geology Centre, Campo Grande, Edifıcio C6, Piso 3, 1749-016 Lisbon, Portugalb Centre and Department of Geology, Faculty of Science, University of Lisbon, Campo Grande, Edifıcio C6, Piso 4, 1749-016 Lisbon, Portugalc CIACOMAR/CIMA, Universidade do Algarve, Av. 16 de Julho, 8700-311 Olhao, Portugal

a r t i c l e i n f o

Article history:Received 7 September 2007Accepted 7 March 2008Available online 27 March 2008

Keywords:calcareous nannofossilscretaceousGuadiana estuaryPortugal, Gulf of Cadizmud volcanoes

* Corresponding author.E-mail address: [email protected] (M. Cachao).

0272-7714/$ – see front matter � 2008 Elsevier Ltd.doi:10.1016/j.ecss.2008.03.012

a b s t r a c t

For most micropalaeontological studies the presence of reworked specimens is usually considered asa disturbing factor where palaeoenvironmental or biostratigraphic interpretations are to be made.However, reworking of microfossils such as calcareous nannofossils can be used as an additional pa-rameter in routine micropalaeontological work, providing useful information on erosion-transportprocesses acting on silty-clay sized particles deriving from areas surrounding the sedimentary basinunder study. Most of the reworked calcareous nannofossils found in the Guadiana estuary water column(September 2001), adjacent shelf surface sediments, and a slope section of the Gulf of Cadiz were mainlyof Upper Cretaceous age (Campanian to Maastrichtian), being dominated by Biscutum spp.,Cribrosphaerella ehrenbergii, Prediscosphaera cretacea and Watznaueria barnesae. Since there are no UpperCretaceous outcrops in the Guadiana’s hydrographic basin or southern Portugal, the source of this ma-terial must be located elsewhere. Matrix breccias from mud volcanoes discovered in deeper watersouthern Portuguese and western Moroccan margins of the Gulf of Cadiz during the TTR-10 cruise inJuly/August 2000, as well as silty-clay sediments from its slopes, revealed similar calcareous nannofossilassemblages as those found on the Algarve continental shelf and inside the Guadiana’s estuary. This mayindicate that most of the reworked nannofossils have their origin in deepwater areas of the Gulf of Cadiz.The good preservation of most of the reworked Cretaceous nannofossils suggest that, shortly after re-suspension, swift transport occurred from the source area to the coastal region of the Guadiana’s rivermouth, implicating a northward change in the deep Mediterranean water direction within the Gulf ofCadiz, which reaches the upper southwest Iberia slope. The Mediterranean Outflow is, therefore, themajor mechanism accountable for transporting Upper Cretaceous material to the southwest Iberianmargin and the Atlantic inflow, together with longitudinal coastal currents, is the probable responsiblefor carrying and spreading eastward these reworked silty-clay sized particles over the Portuguese andSpanish continental shelf. This case study is a clear example of the potential importance of calcareousnannofossils as ocean dynamic tracers for particles within the silty-clay fraction.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Calcareous nannofossils are a small but heterogeneous size-defined (from 1 to less than 60 mm) micropalaeontological group. Itis mainly composed of past representatives of the calcareous nan-noplankton, which includes present-day coccolithophores as wellas a large variety of other particles (the nannoliths) produced byseveral distinct groups ranging from benthic ascidian spicules tocalcispheres (calcareous dinoflagellates), while some are stillincertae sedis. Their geological record goes back to the Upper

All rights reserved.

Triassic, showing complex evolutionary patterns with moments ofrapid diversification or significant extinction rates (Bown andYoung in Bown, 1999).

Coccolithophores form a major component of the extant marinephytoplankton and are one of the main open ocean primary pro-ducers. Each coccolithophore is surrounded by small calciteplateletsdthe coccolithsdwhich form a discontinuous calcareousshell around the living single cell, representing the most importantcomponent of deep-sea sediments and providing highly significantinformation for the interpretation of global change in the geologicalrecord (Perch-Nielsen, 1989). They are used as a proxy for seasurface temperatures (SST) and productivity in palaeoceanographicstudies, as well as in high-resolution biostratigraphic and evolu-tionary studies (e.g. Herrle, 2003; Herrle and Mutterlose, 2003;Herrle et al., 2003).

mailto:[email protected]

www.sciencedirect.com/science/journal/02727714

http://www.elsevier.com/locate/ecss

www.sciencedirect.com/science/journal/02727714

http://www.elsevier.com/locate/ecss

J. Ferreira et al. / Estuarine, Coastal and Shelf Science 79 (2008) 59–7060

Unexpectedly high amounts of reworked calcareous nanno-fossils (mainly Campanian to Maastrichtian in age), were found inthe Guadiana River estuary water column and in adjacent surfaceshelf sediments during a micropalaeontological survey. Thisprompted us to search for possible explanations for their massiveoccurrence and origin. This study hence focuses on the distributionand source of reworked calcareous nannoplankton, particularlyUpper Cretaceous forms, in order to reconstruct erosion-transportprocesses in the Gulf of Cadiz and the southwestern Iberian shelf, aswell as seasonal changes in the tidal flow pattern within theGuadiana estuary.

2. Mediterranean Outflow Water settings

North Atlantic Surface Water (NASW) and the North AtlanticCentral Water (NACW) flow at the sea surface into the Mediterra-nean Sea. On the other end, the warm and dry climate over theMediterranean Sea causes strong evaporation leading to the pro-duction of dense and saline waters (>38.4&; Baringer and Price,1999) that not only sink into the deep Mediterranean basins butalso escape through the 16 km wide Strait of Gibraltar as theMediterranean Outflow Water (MOW) (Ambar and Howe, 1979;Ambar, 1983). This warm (13 �C) and saline (38&) dense tongue(Bryden and Stommel, 1982) forms a high-velocity bottom currentthat interacts with the southwest Iberian slope sediments at depthsbetween 400 and 1800 m (Nelson et al., 1993). It produces thicksediment drifts and contourite deposits (Kenyon and Belderson,1973), the structures of which are related to changes in the palae-ocirculation of the Mediterranean outflow (Toucanne et al., 2007).

Between 600 and 1400 m water depths at the end of the Strait ofGibraltar, the MOW reaches velocities around 2.5 m s�1 (Boyum,1967). After passing the Strait of Gibraltar, it divides in two mainbranches (Gardner and Kidd, 1987) and, under the influence of theCoriolis force, is deflected northward, making a nearly inertial turnof 90� in less than 20 km to align itself with the local topography(Heenzen and Johnson, 1969; Baringer and Price, 1999). Furtherdownstream, the flow decelerates to less than 0.6 m s�1 (moretypically about 0.3 m s�1) with the deepest, most saline part of theoutflow moving fastest. Eventually, the flow decelerates to speeds ofabout 0.1 to 0.3 m s�1 near Cape St. Vincent where the outflowbegins to completely separate from the bottom. Moreover, a sec-ondary circulation within the outflow which includes a downslopecomponent (southwards) close to the bottom and an upslopecomponent (northwards) located at the interface betweenthe outflow previously mentioned and the water directly above it(approximately 100 m above the floor) has been identified by theseauthors. The strong acceleration due to the steepness of the conti-nental slope appears to be the main reason for the MOW to stronglymix with the North Atlantic Central Water (hereafter called AtlanticInflow) and thereby losing much of its density anomaly, althoughhigh salinities have been logged along the west coast of Portugalwhere the outflow has turned northward after passing the IberianPeninsula at Cape St. Vincent (Maillard, 1986; Zenk and Armi, 1990)with much lower velocities (0.2 m s�1; Johnson et al., 2002).

In the Atlantic the MOW is actually subdivided vertically intotwo main cores identified by temperature and salinity maxima.Horizontal variations in the properties of the MOW at the exit of theGibraltar Strait seem to promote a vertical separation of thenorthern and southern part of this current. Irregularities in bottomtopography may further increase the tendency of the bottom cur-rent to separate by a friction induced mechanism (Borenas et al.,2002).

According to Nelson et al. (1999), the deeper MOW travelsnorthwestward below 300 m as the Mediterranean undercurrentfrom the Gibraltar Strait and accelerates down the Cadiz conti-nental slope due to gravity-driven currents of this denser water.

Maximum undercurrent speeds are 80 cm s�1 in the eastern part ofthe Cadiz continental slope but the flow decreases to 0.7–0.4 m s�1

on the central slope where the undercurrent subdivides intoseveral branches due to interaction with a rugged ridge and valleymorphology. Along the western Cadiz slope the current speeddecreases to 0.1–0.2 m s�1 (Fig. 1).

Above 300 m water depth there is a strong southeastward in-flow of North Atlantic Superficial Water over the Gulf of Cadiz shelfwhich intensifies toward the Strait of Gibraltar (Nelson et al., 1999)(Fig. 1). This southeastward current flowing towards Gibraltar isresponsible for the dispersal patterns of shelf surface sediment,along with the terrigenous input from river sources and the phys-iography of the shelf itself (Lopez-Galindo et al., 1999). In fact, theGuadalquivir muddy sedimentary wedge is deflected southeast-ward due to the east and southeastward advection of suspendedsediments by the Atlantic Inflow (Lobo et al., 2004).

The sediment dispersal of the outer shelf and upper slope, bycontrast, is influenced by the location of sea level lowstand pro-cesses and MOW currents flowing northwestward from Gibraltar(Lopez-Galindo et al., 1999). In addition to these water massmovements throughout the Cadiz Gulf, there is also a countercurrent system controlled by the wind regime (Fiuza, 1983) whichopposes the patterns described earlier. Generally, under a westerlydominant wind regime, cold water upwells along the southernPortuguese coasts. However, the relaxation of these upwelling-favourable winds and/or onset of easterlies, favours the de-velopment of an inshore warm water tongue that stretcheswestwards from the Bay of Cadiz (Lobo et al., 2004). This in-teraction with the opposing Atlantic Inflow current is able tofurther enhance sediment dispersal along the Algarve shelf.

3. Regional setting

The Gulf of Cadiz is located at the front of the Gibraltar arc andMiocene foredeep associated with the tectonic evolution of thewesternmost section of the Betic–Rif belt of the Alpine–Mediterranean compression system (Llave et al., 2001; Hernan-dez-Molina et al., 2002), which has formed in response to theconvergence of the African and Eurasian plates. The emplacementof allochthonous units in the form of an accretionary wedge tookplace in the Gulf of Cadiz during the Tortonian (Maldonado et al.,1999), formed by the interaction of the Alboran Domain with thepassive margins of the Eurasian and African plates (Flynch et al.,1996).

The sedimentary basin in the Algarve region represents anemerged part of the continental margin which formed during thedisplacement of Africa with respect to Eurasia and Iberia. Thestratigraphic record of the Algarve Basin spans from Late Triassic toQuaternary, with a major hiatus from the Cenomanian to theMiocene (Terrinha, 1998).

The Mesozoic units begin with Upper Triassic continental con-glomerates, sandstones and red shales associated with volcano-sedimentary and evaporitic units, which constitute the northernrim directly overlying Carboniferous marine flysch (Palain, 1976).The most prominent units are Jurassic marine formations whichcrop out over a distance of 150 km in the Algarve basin between theCape St. Vincent in the west to Tavira in the east, forming a belt witha maximum width around 30 km (Moreau et al., 1997). There is notyet full agreement concerning the age of the youngest Cretaceoussediments, but Lower Cretaceous (Berriasian to Albian) strata makeup most of the outcrops in the Algarve Basin. These sedimentsmainly consist of shallow-marine to supra-tidal limestones andmarls, alternating with detrital deposits. The Lower Cretaceousthickens towards east, where it reaches its maximum thickness(around 1500 m) and a more marine-like facies, whilst in thecentral and western areas the facies are continental and littoral,

Fig. 1. Study area with sampling locations and continental geological setting.

J. Ferreira et al. / Estuarine, Coastal and Shelf Science 79 (2008) 59–70 61

respectively (Correia, 1989). The most important Cretaceous out-crops are illustrated in Fig. 1. The onshore Cenozoic record of theAlgarve Basin is mainly restricted to the Neogene (Cachao andMarques da Silva, 2000) and Quaternary, and altogether is generallynot thicker than 300 m. It mainly covers the central and easternbasin, featuring shallow water and marine depositional environ-ments (Terrinha, 1998).

In southwestern Spain between the Guadalquivir River mouthand Cape Trafalgar, different geological formations are present onthe neighbouring continent. Thus, to the north and northeast, thePalaeozoic Iberian Massif and Mesozoic sedimentary formationsforming the Betic Mountain range are to be found. Syn- and post-orogenic sedimentary formations form the Upper Neogene fore-deep of the Guadalquivir Basin. The submarine pre-Holocenematerials belong to Mesozoic formations as well as to the UpperMiocene and Plio-Pleistocene deposits (Gutierrez-Mas et al., 2003).

4. The Guadiana River

The Guadiana River is entrenched in a resistant silty quartzitematerial. As a result of the pre-Flandrian period the river was un-able to cut a wide valley and instead, excavated a narrow and deepchannel under strong structural control. Only in the seaward kilo-metres of its course was the river able to cut a slightly wider valley.However, this region was nearly completely submerged after thetransgression, forming a small shallow embayment near its presentmouth where the most active sedimentation took place during theHolocene. Here, its funnel morphology cuts through friable Plio-cene strata. Fluvial sands are transported through the estuarinechannel section, although in the course of individual tidal cycles,marine muds are mixed into the estuarine sediments. This mass ofdetrital material has contributed to the filling of the most southern

portion of this system, causing coastal progradation and the for-mation of a wave-dominated delta (Morales, 1997).

Being mainly composed of more or less sandy deposits(Gonzalez et al., 2004; Mendes et al., 2004), the Guadiana shelf liesin a transition zone between the narrow and relatively steepPortuguese shelf and the northeastern corner of the Gulf of Cadizwhere the shelf is more than 30 km wide off the Guadalquivir rivermouth (Lobo et al., 2001). Detailed work on the sediment dispersalpatterns over the northern shelf of the Gulf of Cadiz was un-dertaken by Lobo et al. (2000, 2004), whereas the stratigraphicframework of the continental shelf has been summarized in a seriesof separate publications (e.g. Nelson et al., 1999; Lobo et al., 2001,2004).

5. Materials and techniques

For the present study 107 samples were collected, from the top5 m of the Guadiana river water column, the Mediterranean Out-flow undercurrent core, the surface sediments of the southwestIberia continental shelf and its upper slope, and from a core re-trieved on the continental slope and used for calcareous nanno-fossil observation.

Of these, four samples were collected from the top 5 m of theGuadiana River water and seven samples from the MOW un-dercurrent between 393 and 630 m water depth during the SIRIAProject (September 18, 2001, Portuguese Hydrographic Institute),27 surface sediment samples along three transects off the Guadianariver mouth and over the Algarve continental shelf between 9 and331 m water depth by means of a Smith-MackIntyre sampler underthe projects SIRIA, EMERGE, ODIANA and CRIDA (September andNovember 2001, Nuclear and Technological Institute), and 44samples from the 3 m long GN6 vibracore taken at 40 m water


depth off the Guadiana river mouth under the CRIDA project (July2002) (Fig. 1). An age model for the GN6 vibracore is in progress andwill be presented when available. The absence of age de-terminations, however, does not affect the main objectives of thepresent study.

To demonstrate an eastward spreading of coccoliths over thesouthwestern Iberian shelf and to document that no reworkedmaterial was being carried by the deep MOW from the Mediter-ranean Sea, an additional 22 surface sediment samples (Portimao–Faro transect) were recovered during the SEPLAT and SISPLATProjects of the Portuguese Hydrographic Institute (from 1977 to1982) between 200 and 300 m water depth (Fig. 1) and threesamples from the upper 20 cm of the gravity core M39008 re-covered during METEOR cruise M39/1 in 1997 at 577 m water depthin the Gulf of Cadiz, 100 km west of Gibraltar. All dry samples arestored at the Department of Geology, University of Lisbon.

All water column samples were filtered directly on board or inthe laboratory through 0.45 mm Millipore cellulose nitrate mem-brane filters after which an approximately 25� sector was perma-nently mounted on a slide with synthetic cement (Entellan).Sediment samples were washed several times using increasingamounts of hydrogen peroxide (10, 30, 80 and 130 vol L�1) in orderto eliminate all organic matter. Coarse sediments (i.e. sands andgravels) were separated from the fine-grained fraction (silt andclay) by wet sieving using a 4 B (63 mm) sieve. The surface sedi-ments were then dried, weighed and filtered through 0.45 mmMillipore cellulose nitrate membrane filters. An approximately 25�

sector was permanently mounted as described above.Samples taken from the GN6 vibracore as well as surface sedi-

ments from the Portimao–Faro transect and from the upper 20 cm ofthe M39008 gravity core, were prepared following the randomsettling method by Flores and Sierro (1997) in order to verify theirabsolute abundances (see Table 1). Dismissing the barren samples,the number of coccoliths counted in each slide ranged from 2 to 8067.

The identification and counting was performed using a polariz-ing optical microscope Ortholux II Pol-BK under 1250� magnifi-cation. The taxonomic frameworks of Perch-Nielsen (1989) andBown (1999 and references therein) have been followed. All coc-coliths with more than half of the structure preserved were in-cluded in the counts.

The complete data row counts are available from the Faculty ofSciences of the University of Lisbon database (http://mcprojectos.fc.ul.pt/papers/Guadiana/) as PDF files Core6; Portimao–Faro;Guadiana; Transect791–895; Transect829–837; Transect875–865;and mow.

6. Results

6.1. Water column

Coccolithophore assemblages retrieved from the Guadiana Riverand its river mouth are well preserved and diverse. Due to thescarcity of calcareous nannoplankton the number of coccoliths

Table 1Samples water depth, sampling year and methodology used

Samples No. ofsamples

Samplingyear

Depth (m) Methodology

MOW plume 7 2001 393–630FilteringGuadiana water

column4 2001 Surface

Surface sediments 27 2001 9–331

Vibracore GN6 44 2002 40Random setting(Flores and Sierro, 1997)

Portimao–Farotransect

22 1977–1982 200–300

Core M39008 3 1997 577

counted in each of the four samples ranged from 27 to 29. In thesesamples 22 taxa were identified, from which 16 were reworkednannofossils. Reworked coccoliths range between 59% (sample E3)and 75% (sample E4) of the total assemblage, with a mean of 69%.The relative abundance between extant and reworked coccoliths isshown in Fig. 1. An upstream increase both in coccoliths diversityand abundance was recorded, with the large majority beingreworked Upper Cretaceous forms. Assemblages expressed in 106

liths L�1 of non-reworked coccolithophores are dominated byEmiliania huxleyi (0.033), Gephyrocapsa oceanica (0.026), Gephyr-ocapsa muellerae (0.025), Gephyrocapsa ericsonii (0.017) andCalcidiscus leptoporus (0.009). Reworked forms are dominated byPrediscosphaera cretacea (0.034), Cribrosphaerella ehrenbergii(0.033), Biscutum ellipticum (0.026), Watznaueria barnesae (0.033),Arkhangelskiella confusa (0.022), Biscutum magnum (0.022), Retic-ulofenestra haqii-minutula (0.017), Retecapsa crenulata (0.011) andEiffellithus eximius (0.006).

6.2. MOW

Coccolithophore assemblages observed in samples taken fromthe salinity anomaly of the undercurrent inner core of the MOW arewell preserved and diverse. The number of coccoliths counted ineach sample ranged from 422 (sample 180B) to 709 (sample 150C).In these samples 56 taxa were identified, of which 41 werereworked coccoliths. Reworked coccoliths range between 3.1%(sample 159A) and 13.3% (sample 164B) of the total assemblage,with a mean of 5.6%. The relative abundance of Cretaceous speciesin the bulk of the reworked forms ranges from 7.1% (sample 93A) to53.2% (sample 164B). It is near the shore and in shallower watersthat an increase in reworked coccoliths is documented. Assem-blages expressed in 106 liths L�1 of non-reworked coccolithophoresare dominated by Gephyrocapsa oceanica (0.144), Gephyrocapsaericsonii (0.083), Emiliania huxleyi (0.095), Gephyrocapsa muellerae(0.028) and Calcidiscus leptoporus (0.024). Reworked forms aredominated by Watznaueria barnesae (0.013), Cyclicargolithusfloridanus (0.006), Reticulofenestra pseudoumbilicus (0.006) andReticulofenestra haqii-minutula (0.003).

6.3. Surface sediments

In shelf surface sediments the calcareous nannoplankton as-semblages are usually abundant and well preserved. The numberof coccoliths counted in each sample ranged from 177 (sample875) to 418 (sample 869). Of 38 identified taxa, 24 were reworkedforms. Reworked coccoliths range between 16.1% (sample 871)and 34% (sample 868) of the total assemblage, with a mean of24.8%. The assemblages expressed in 106 liths g�1 are dominatedby small placoliths of Gephyrocapsa ericsonii (425) and Emilianiahuxleyi (304) followed by Gephyrocapsa oceanica (221) andGephyrocapsa muellerae (156). Common taxa are Syracosphaeraspp. (86), Coccolithus pelagicus (36), Calcidiscus leptoporus (35),Umbilicospaera sibogae (26), Helicosphaera carteri (19) andUmbellosphaera tenuis (15). Additional rare taxa are Rhabdosphaeraclavigera (8), Braarudosphaera bigelowii (5), Pontosphaera discopora(4) and Pontosphaera multipora (4). Reworked nannofossils,Cretaceous to Pliocene in age, are an important component of thenannoplankton assemblages. The dominant species are Dictyo-coccites productus (156), Reticulofenestra minuta (94), Watznaueriabarnesae (43), Cyclicargolithus floridanus (43) and Discoaster spp.(25). Other reworked coccoliths include Reticulofenestra haqii-minutula (23), Tetralithoides simeonidesii (22), Hughesius tasmaniae(19), Cruciplaccolithus asymmetricus (13) and Cribrosphaerellaehrenbergii (11). The relative proportion between living and fossilcoccoliths along the three transects is plotted in Fig. 2, illustratingthe dominance of extant taxa over reworked ones, despite the fact

http://mcprojectos.fc.ul.pt/papers/Guadiana/

http://mcprojectos.fc.ul.pt/papers/Guadiana/

Fig. 2. Difference between living (Extant) and fossil (Reworked) coccoliths in surfacesediments.

Fig. 3. Difference between living (Extant) and fossil (Reworked) coccoliths down theGN6 vibracore.

Fig. 4. Abundance of living (Extant) and fossil (Reworked) coccoliths along thePortimao–Faro transect. The trend line crossing the reworked forms shows a slighteastward increase.


that both coccolithophore and nannofossil abundances decliningin numbers towards the coastal environment.

6.4. Core GN6

The down-core nannofossil assemblages of the vibracore arewell preserved and diverse, with a large percentage of calcareousnannofossils again coming from the Upper Cretaceous. The numberof coccoliths counted in each sample ranged from 2 (sample 33) to536 (sample 165). Along the core, 74 taxa were identified of which59 were reworked. Reworked nannofossils range between 9%(sample 297) and 60% (sample 19) of the total assemblage, witha mean of 29.9%. The nannofossil abundance between living andfossil forms are given in Fig. 3. When expressed in 106 liths g�1 it ispossible to recognize that the most persistent extant species alongthe core length were Gephyrocapsa ericsonii (7.3), Gephyrocapsaoceanica (4.4), Emiliania huxleyi (3.5), Coccolithus pelagicus (1.6),Gephyrocapsa muellerae (1.1), Syracosphaera spp. (0.7) andCalcidiscus leptoporus (0.3). The reworked nannofossils are domi-nated by Reticulofenestra minuta (1.4), Dictyococcites productus (1.2),Watznaueria barnesae (1.1) Reticulofenestra haqii-minutula (1.1),Reticulofenestra pseudoumbilicus (0.8) and Cyclicargolithus flori-danus (0.5). As recorded in surface sediments from the continentalshelf, along the core length we find that extant coccolithophoresagain outnumber the fossil ones, with one exception at 19 cm depthwhere the reworked taxa represent 60% of the assemblage. Therelative proportion between extant and reworked taxa is more orless constant along the core, both changing within a similar pattern.The sedimentological analysis of GN6 core (Fig. 3) shows that thesilty-clay fraction remains almost constant down-core, rangingbetween 60% and 100%.

6.5. Portimao–Faro transect

The nannofossil assemblages over the outer shelf, along thePortimao–Faro transect are very diverse and well preserved, with

a large percentage of calcareous nannoplankton belonging to theUpper Cretaceous. The number of coccoliths counted in eachsample ranged from 763 (sample 1185) to 8067 (sample 1217). Inall, 89 taxa were identified of which 72 were reworked forms.Reworked nannofossils range between 8.2% (sample 3355) and25.6% (sample 1185) of the total assemblage, with a mean of 13.4%.The nannofossil abundances between living and fossil forms isgiven in Fig. 4. When expressed in 106 liths g�1 it is possible torecognize that the most persistent extant species were Gephyr-ocapsa ericsonii (105), Gephyrocapsa oceanica (54), Emiliania huxleyi(53), Coccolithus pelagicus (16), Gephyrocapsa muellerae (12),

Fig. 5. Schematic representation of MOW silty-clay advection and the Atlantic Inflow winnowing over the continental shelf.


Syracosphaera spp. (6), Calcidiscus leptoporus (5) and Helicosphaeracarteri (3). The reworked nannofossils are dominated byWatznaueria barnesae (8.2), Reticulofenestra haqii-minutula (5.3),Dictyococcites productus (4.8), Reticulofenestra minuta (2.6),Dictyococcites antarcticus (2.5), Reticulofenestra daviesii-dictyoda(2.1) and Cyclicargolithus floridanus (1.8). In all samples extantcoccolithophores outnumber the fossil ones, following the samepattern seen in the surface sediments sampled over the continentalshelf. The relative abundance between extant and reworked taxa ismaintained along this profile, both changing accordingly.

6.6. Core M39008

Cretaceous nannofossils were scanned from the top threesamples of this core at 1, 16.5 and 20 cm of the core depth. Afterscanning 176 fields of view (4 mm2) in each slide, only seven Cre-taceous coccoliths were recorded in each of them. The overall 21coccoliths belonged to ten different taxa. There were no dominantspecies, although Watznaueria barnesae, W. britannica and W.biporta were represented. When compared to all previous samplesscanned previously, the Cretaceous nannofossils represented in thetop section of this core occur in very low quantities, ranging from0.035 to 0.106 � 106 liths g�1, which argues against the Mediter-ranean coccolith advection hypothesis.

7. Discussion

7.1. Preservation and extant coccolithophores

Dissolution and diagenesis can significantly alter the preser-vation of calcareous nannofossil assemblages. The overall nanno-fossil assemblages in this study, however, were well preserved.Nevertheless all collected samples showed that reworked cocco-liths were only partially and slightly etched and overgrown.

The extant coccolithophore assemblages recovered from thewater column, the continental shelf surface sediments and theGN6 vibracore follow those found by Sierro et al. (1999) in deepterraces located between 400 and 700 m water depth, just belowthe upper continental slope in the Gulf of Cadiz and those foundby Kenyon et al. (2001) and Pinheiro et al. (2003) in the samesector. In these cases Recent or extant coccolith assemblages aremainly composed of Emiliania huxleyi, Gephyrocapsa spp., Cocco-lithus pelagicus, Calcidiscus leptoporus, Rhabdospaera clavigera andSyracosphaera spp.

Calcareous nannoplankton densities in both the shelf surfacesediments and down the GN6 vibracore vary in accordance with thebottom hydrodynamic conditions. This is shown by the similaritybetween the distribution patterns of both extant and fossil cocco-liths in the three transects off the Guadiana river mouth, along thePortimao and Faro transect and also down the GN6 core (Figs. 2–4).This co-variation can only be achieved if factors such as near bot-tom currents influence the sedimentation of both present daycoccoliths derived from neritic productivity and the passivelytransported reworked forms within the oceanic water masses. Be-cause MOW bottom currents produce contourites while washingthe upper slope sediments of the Gulf of Cadiz throughout theQuaternary (Gonthier et al., 1984), the final sedimentary facies canbe considered to be the result of a very delicate balance betweenthe sediment input and loss rates (Sierro et al., 1999). This is con-firmed by surface samples containing less than 10% of silty-clayfraction in water depths above 50 m (Gonzalez et al., 2003) wherethere is a significant decline in the nannoplankton abundance (seeFig. 2).

7.2. Reworked calcareous nannofossils

A considerable percentage (ranging from 3.1% in MOW samplesto 75% in the water column) of reworked coccoliths was recordedin all samples from both the water column and sediments.

Plate 1. All figures at the same magnification (2000�) and taken under cross nicols except when mentioned. 1, Arkhangelskiella confusa; sample E6 (water sample, Guadianaestuary). 2, Arkhangelskiella maastrichtiana; sample E4 (water sample, Guadiana estuary). 3, Biscutum ellipticum; sample E4 (water sample, Guadiana estuary). 4, Biscutum ellipticum;sample E4, transmitted light (water sample, Guadiana estuary). 5, Chiasmolithus sp.; sample E4 (water sample, Guadiana estuary). 6, Chiastozygus amphipons; sample 112 cm (coreGN6). 7, Chiastozygus bifarius; sample 112 cm (core GN6). 8, Chiastozygus sp.; sample 112 cm (core GN6). 9, Cretarhabdus striatus; sample 1030 (PT transect). 10, Cribrosphaerellaehrenbergii; sample 1030 (PT transect). 11, Cruciellipsis cuvillieri; sample 1030, transmitted light (PT transect). 12, Cruciellipsis cuvillieri; sample 1030 (PT transect). 13, Cyclagelos-phaera tubulata; sample 1034 (PT transect). 14, Dictyococites antarcticus; sample 1034 (PT transect). 15, Eiffellithus eximius; sample E4 (water sample, Guadiana estuary). 16, Eif-fellithus paralellus; sample 0 cm (core GN6). 17, Eiffellithus turriseiffelii; sample 1433 (PT transect). 18, Microrhabdulus undosus; sample 3306 (PT transect). 19, Micula staurophora;sample 1138 (PT transect). 20, Micula staurophora; sample 1138 (PT transect). 21, Percivalia fenestrata; sample 3377 (PT transect). 22, Petrarhabdus copulatus; sample 110 cm (coreGN6). 23, Petrarhabdus copulatus; sample 110 cm, transmitted light (core GN6). 24, Prediscosphaera sp.; sample E6 (water column, Guadiana estuary).


Unexpected high densities of Cretaceous and Palaeogene reworkedcalcareous nannofossils within present-day coccolithophore tha-natocoenoses in the water column of the Portuguese and Spanishshelf offshore and within the Guadiana estuary prompted us tosearch for possible sources of this resuspended silty-clay material.The abundance and diversity of reworked calcareous nannofossilswithin the Guadiana estuary cannot be explained by the runofffrom adjacent emergent outcrops since the catchment mainlycomprises Palaeozoic metamorphic units, Triassic continental

sediments and subvolcanic rocks (Mapa Geologico de la PeninsulaIberica, 1981) devoid of any nannoliths. On the other hand, thecoastal drift should only supply Neogene reworked forms from thenearby eroding coastal cliffs cut out of the Cacela Formation, whichcontains rich Upper Tortonian marine calcareous nannofossils in itslower member (Cachao, 1995). Possible sources of the reworkedforms are thus Lower Cretaceous outcrops, although the nearestones located 30 km to the west at Olhao are not exposed along thecoast (Correia, 1989).

Plate 2. All figures at the same magnification (2000�) and taken under cross nicols except when mentioned. 1, Prediscosphaera sp.; sample E6, transmitted light (water sample,Guadiana estuary). 2, Prediscosphaera sp.; sample E6 (water sample, Guadiana estuary). 3, Quadrum gartneri; sample 1022 (PT transect). 4, Quadrum gartneri; sample 1022 (PTtransect). 5, Quadrum gartneri; sample 1022, transmitted light (PT transect). 6, Quadrum giganteum; sample 1138 (PT transect). 7, Retecapsa ficula; sample E6 (water sample,Guadiana estuary). 8, Retecapsa ficula; sample 15 cm (core GN6). 9, Retecapsa surirella; sample 1138 (PT transect). 10, Retecapsa surirella; sample 1138 (PT transect). 11, Retic-ulofenestra asanoi; sample 3285 (PT transect). 12, Reticulofenestra bisecta; sample 1138 (PT transect). 13, Reticulofenestra umbilica; sample 1160 (PT transect). 14, Staurolithites dorfii;sample 1138 (PT transect). 15, Watznaueria barnesae; sample E3, transmitted light (water sample, Guadiana estuary). 16, Watznaueria barnesae; sample E3 (water sample, Guadianaestuary). 17, Watznaueria biporta; sample 1217 (PT transect). 18, Watznaueria biporta; sample 1217, transmitted light (PT transect). 19, Watznaueria biporta; sample 1217 (PT transect).20, Zeugrhabdotus bicrescenticus; sample 3285 (PT transect). 21, Zeugrhabdotus bicrescenticus; sample 3285 (PT transect). 22, Zeugrhabdotus embergeri; sample 3285, transmittedlight (PT transect). 23, Zeugrhabdotus embergeri; sample 3285 (PT transect). 24, Zeugrhabdotus embergeri; sample 1098 (PT transect).


Cachao (1993) already recognized a strong difference in thequantities of reworked coccoliths between the southern Portu-guese continental shelf (up to 21%) and the Occidental Atlantic shelf(1–3.5%). The present study shows that, on the Algarve shelf, thereworking pattern along the Portimao–Faro transect (PF transect)increases slightly and irregularly eastwards after the PortimaoCanyon. In the absence of a northward flowing ocean current nor-mal to the Algarve shoreline directly from the Cadiz mud volcano

region and the presence of the eastward current activity by theAtlantic Inflow, the earlier evidence suggests that the Palaeogeneand Upper Cretaceous (at least) nannofossils are being activelytransported towards the shelf by the MOW from the Gulf of Cadizdeep basin through the Portimao Canyon. Recently, Marches et al.(2007) demonstrated the capture of the MOW deep-sea current bythe Portimao submarine canyon, which displays a clear asymmetricstructure of its contourites.


Nannofossils are subsequently scattered through the entireAlgarve shelf in such quantities that they can be recognized inpresent day water column samples inside river estuaries such asthe Guadiana. Previously, Ruiz et al. (2003) have suggested thatcoastal drift currents were derived from North Atlantic circulationand that these had the greatest effects on the sediment re-distribution of this littoral area. Since seasonal changes in thereworking forms have been recorded within the Guadiana estuary,this transport may in fact be seasonal. Water samples recoveredduring winter actually show a distinct pattern in the ratiobetween extant and reworked coccoliths (Ferreira and Cachao,2005).

Thus, at present the MOW is probably actively transportingCretaceous and Palaeogene material from the offshore mud volcanofields, while rivers runoff and coastal weathering are mainly sup-plying Neogene material from the widespread Middle MioceneLagos–Portimao and Upper Miocene Cacela formation outcroppingalong the Algarve margin.

There is a significant qualitative difference between thereworked nannofossils found in the water column and those oc-curring in the continental shelf surface sediments. Whereas in thewater column the main reworked coccoliths belong to the UpperCretaceous, those in the sediments are dominated by Tertiaryforms. However, in the recent past this pattern may have changedsince the percentage of rework coccoliths down the GN6 corechange considerably and is also dominated by Upper Cretaceousnannofossil taxa, despite the relative abundance of Tertiary forms.It is thus reasonable to assume that, over time, there were periodswhen the reworked silty-clay particles transported by the MOW

Table 2Stratigraphic range of selected nannofossil taxa recorded on water column

from the Gulf of Cadiz deep ocean basin were particularly plentifuland thereby overprinted the Neogene assemblages supplied bylocal shoreline erosion. On the other hand, the almost constantsilty-clay ratio (between 60% and 100%) down the GN6 core sug-gests that the significant shifts in coccolith and nannolith abun-dances might be attributed to changes in sedimentation rates and,consequently, dilution of the nannofossil assemblages (e.g. be-tween 20 and 40 cm) and/or increase in the nannofloral pro-ductivity and preservation (e.g. between 240 and 290 cm) ratherthan intensity variations in bottom currents.

Moreover, the upper 20 cm of the M39008 core show an al-most total absence of Cretaceous nannofossils. Due to the AtlanticInflow circulation pattern and the fact that this core is locatedoutside the Gibraltar Strait and therefore directly influenced bythe upper and strong MOW (Lowemark et al., 2004), renders theprobability that the Guadiana reworked nannoliths are directlyderived from the Mediterranean Sea as quite low, despite theoccurrence of mud volcanoes recently described in the southernsector of the mud diapir province of the west Alboran Basin whichshow a similar Cretaceous nannofossil assemblage (Sautkin et al.,2003). The stratigraphic distribution of reworked nannofossils inthe water column, in shelf surface sediments and in vibracore GN6is shown in Tables 2 and 3. It demonstrates that the stratigraphicrange of the main reworked assemblages are Upper Cretaceous.The generalized zonation scheme follows Perch-Nielsen (1989)and Bown (1999).

Data obtained from the MOW samples off the Gibraltar Straitand along the Cadiz slope show that reworked forms, and partic-ularly the Mesozoic ones originating from the Alboran Sea, are by

Table 3Stratigraphic range of selected nannofossil taxa recorded on sediments



no means sufficient to explain the densities recorded either in theGuadiana estuary and on the Algarve continental shelf.

Resuspension and resedimentation of coccoliths eroded fromNeogene formations, either in southern Portugal or southwestSpain, and particularly in the Guadalquivir basin, is a feasible ex-planation for the Cretaceous coccoliths found over the continentalshelf. However, Cachao (1995) already recognized the absence ofMesozoic coccoliths in the Algarve Neogene formations, whileFlores (1985), when studying the Guadalquivir Basin, found around1% of reworked forms (Mesozoic and Tertiary in age) in marls, andaround 10% in coastal sandy units. When comparing the abundanceof Upper Cretaceous coccoliths found in present day surface sedi-ments on the southwest Iberian shelf and in the water column ofthe Guadiana estuary with the overall reworked taxa in each of thesamples, it is easily recognized that Mesozoic reworked nannoflorarepresents an important fraction, both in percentage and in di-versity, of the total assemblage, ranging from around 7.1% in MOWsamples (excluding sample 164B which is under the Guadiana’sterrigenous input) and from 21.5% to 55.2% in the PF transect (seeFig. 5). There is an eastward decreasing abundance in Cretaceoustaxa in the reworked associations from the Portimao Canyon toGibraltar and the Guadiana or Guadalquivir watershed outcrops arehence not a probable terrigenous source.

7.3. Mud volcanism

In July 2000 the Russian research vessel Professor Logachev,operating under the UNESCO TTR-10 (Training Through Research,UNESCO/IOC) Program, studied the Gulf of Cadiz mud volcanismoccurring at 1000–3000 m water depth along the southern Portu-guese, western Moroccan and Spanish margins. Being geologicalstructures formed as a result of the emission of argillaceousmaterial on the Earth’s surface or the sea floor, they are (besides thecontinuous active hydrocarbon generation) strongly controlledby the existence of thick, fine-grained, soft, plastic sedimentsdeep in the sedimentary succession (Dimitrov, 2002). Micro-palaeontological studies made by Sautkin’s group (Sautkin, 2001;Pinheiro et al., 2003) on the breccia matrix (up to 99% of the vol-cano breccia total volume (Dimitrov, 2002)) of 10 cores taken fromfive mud volcanoes, recorded a surprisingly identical Mesozoicnannofossil assemblages as those found on the southwestern Ibe-rian shelf and in water column within the Guadiana river mouth.The most abundant species found were Micula staurophora (syn. M.decussata) and Watznaueria barnesae. Other taxa were Arkhangel-skiella spp., Calculites obscurus, Cribrosphaerella ehrenbergii, Eiffel-lithus turriseiffelii, Lithraphidites carniolensis, Microrhabdulusdecoratus, Prediscosphaera spp., Stradneria crenulata and Tranolithusphacelosus. These authors suggested that Upper Cretaceous de-posits were located near the roots of the mud volcanoes on thePortuguese margin (Kenyon et al., 2001; Pinheiro et al., 2003). ThePalaeogene coccoliths found in our samples and those found inthe mud volcanoes breccia matrix, also show some resemblance.The great similarity of these assemblages and the fact that nomarine formation of this age outcrop on the Algarve onshore sug-gests a common origin for these forms. In mud volcanoes, Palae-ocene species occur very sporadically and the Eocene taxa aremainly characterized by the genera Reticulofenestra, Discoaster andEricsonia. The Oligocene assemblages are characterized by thegenera Discoaster, Cyclicargolithus and Dictyococcites. The Mio-Pli-ocene assemblages are characterized by the genera Discoaster,Reticulofenestra and Dictyococcites, and by the species Sphenolithusheteromorphus, Calcidiscus macintyrei among others coccoliths(Kenyon et al., 2001; Pinheiro et al., 2003).

Although some of the reworked coccoliths found in this study,particularly the Upper Cretaceous forms, may come from the samemud volcanoes in the Gulf of Cadiz, a significant number

presumably has its origin in the widespread Neogene formationsspanning the Algarve onshore.

Also the Guadalquivir Diapiric Ridge (GDR) and the TASYO mudvolcano fields located on the Spanish margin described by Somozaet al. (2003) are a potential source for the resuspension of deepburied calcareous nannofossils. However, to date there are nonannofossil data to support this hypothesis.

8. Conclusions

Continental terrigenous fluxes cannot account for the reworkednannofossil accumulations of the southwestern Iberia continentalshelf and in the water column within the Guadiana River becausethere are no Upper Cretaceous outcrops in either southern Portugalnor in the Guadiana catchment.

The advection of Mesozoic nannofossils from the MediterraneanSea into the Gulf of Cadiz by the MOW is too insignificant to explainthe densities observed on the Algarve shelf. The source of Mesozoicassemblages must therefore be located within the Gulf of Cadizitself since there are no continental outcrops in southwest Iberiathat could produce such quantities documented here.

Through deep sea water circulation, Gulf of Cadiz mud volca-noes are actively transporting large numbers of Mesozoic andPalaeogene nannofossils to the sea bed, which are then scatteredalong the Iberian shelf by the MOW and most probably as far asthe Portimao Canyon. The data suggest that the Atlantic Inflowthen transports them eastward across the continental shelfproducing an eastward gradient of reworked nannofossils. Whilestill over the shelf, coastal currents and the Atlantic Inflow con-tinue to actively transport large quantities (103 per litre) of thesecoccoliths towards the shore, while coastal tidal oscillationsseasonally carry the reworked material into the Guadiana estuary.A significant proportion of the reworked silty-clay particles thatcover the southern Iberian continental shelf thus have theirdepositional settings closely dependent on the MOW and theAtlantic Inflow.

Using calcareous nannofossils as ocean dynamic tracers wepropose the MOW to be a crucial factor in ocean floor erosion/weathering due to its ability to scrape and transport materialupslope over several miles. By following the reworked Upper Cre-taceous calcareous nannofossil pathway in the Gulf of Cadiz, it ispossible to clarify the main track of the MOW in this sector in greaterdetail (Fig. 5), as well as its relationship with the Algarve continentalshelf currents which, despite showing changes in the recent past, arestill active today, although with a seasonal periodicity.

The presence of Upper Cretaceous formations under the roots ofat least some of the Gulf of Cadiz mud volcanoes and their nan-noliths exhumation allows their use as potential tracers for oceandynamic processes such as those which today may be connectingthe deep ocean basin of the Gulf of Cadiz with the Algarve conti-nental shelf and paralic shallower present-day environments.

Acknowledgements

The authors wish to express thanks to Luis Pinheiro (Fac. Sci-ences, Univ. Aveiro) and Ludvig Lowemark (Earth Sciences, KielUniversity) for their contributions and generosity; to Jens O. Herrle(Dept. Earth and Atmospheric Sciences, Alberta University, Canada)for his valuable suggestions and critical comments on this study.Two referees’ comments and three English revisions are also ac-knowledged. The Portuguese Foundation for Science and Technol-ogy funded this work through CRIDA (FCT-PLE/8/00) and CANAL(FCT-POCTI/32724/99) projects.


References

Ambar, I., 1983. A shallow core of Mediterranean water off western Portugal. Deep-Sea Research 30, 677–680.

Ambar, I., Howe, M.R., 1979. Observations of the Mediterranean outflow: II. Thedeep circulation in the vicinity of the Gulf of Cadiz. Deep-Sea Research. Part A.Oceanographic Research Papers 26 (5), 555–568.

Baringer, M.O., Price, J.F., 1999. A review of the physical oceanography of theMediterranean outflow. Marine Geology 155, 63–82.

Borenas, K.M., Wåhlin, A.K., Ambar, I., Serra, N., 2002. The Mediterranean outflowsplittingda comparison between theoretical models and CANIGO data. Deep-Sea Research II 49, 4195–4205.

Bown, P.R. (Ed.), 1999. Calcareous Nannofossil Biostratigraphy. British Micro-palaeontological Society Series. Kluwer Academic Publishers, Cambridge, p. 315.

Boyum, G., 1967. Hydrological observations of the M.S-1 Helland-Hansen and cur-rent measurements in the area west of Gibraltar. May 1965 NATO Sub-Com-mission Oceanogr. Research Tech. Rep. 34, 35–36.

Bryden, H.L., Stommel, H.M., 1982. Origins of the Mediterranean outflow. Journal ofMarine Research 40, 55–71.

Cachao, M., 1993. Distribuiçao de nanoplancton calcario em sedimentos superficiaisda plataforma continental portuguesa (dados preliminares). Gaia 6, 1–9.

Cachao, M., 1995. Utilizaçao de nanofosseis calcarios em biostratigrafia, paleo-ceanografia e paleoecologia: aplicaçoes ao Neogenico do Algarve (Portugal) e doMediterraneo ocidental (ODP 653) e a problematica de Coccolithus pelagicus.PhD Thesis, University of Lisbon, 356 pp.

Cachao, M., Marques da Silva, C., 2000. The three main marine depositional cycles ofthe Neogene of Portugal. Ciencias da Terra (UNL) 14, 303–312.

Correia, F.M.C., 1989. Estudo biostratigrafico e microfacies do Cretacico carbonatadoda Bacia Sedimentar Meriodional Portuguesa (Algarve). PhD Thesis, Universityof Lisbon, 377 pp.

Dimitrov, L.I., 2002. Mud volcanoesdthe most important pathway for degassingdeeply buried sediments. Earth-Science Reviews 59, 49–76.

Ferreira, J., Cachao, M., 2005. Calcareous nannoplankton from the Guadiana estuaryand Algarve continental shelf (Southern Portugal): an ecological model.Thalassas: An International Journal of Marine Sciences 21, 35–44.

Fiuza, A.F., 1983. Upwelling patterns off Portugal. In: Suess, Pt. A.E., Thiede, J. (Eds.),Coastal Upwelling. Plenum, New York.

Flores, J.-A., 1985. Nanoplancton calcareo en el Neogeno del borde noroccidental dela Cuenca del Guadalquivir (SO de Espana). PhD Thesis, University of Salamanca,715 pp.

Flores, J.-A., Sierro, F.J., 1997. Revised techniques for calculation of calcareous nan-nofossil accumulation rates. Micropaleontology 43, 321–324.

Flynch, J.A., Bally, A.W., Wu, S., 1996. Emplacement of a passive margin evaporiticallochton in the Betic Cordillera of Spain. Geology 24, 67–70.

Garcia-Loygorri, A., Olaverri, T., Rey, R. (Eds.) (1981). Mapa Geologico de la PeninsulaIberica, Baleares y Canarias, 1:1.000.000. Instituto Geologico y Minero de Es-pana, Madrid.

Gardner, J.V., Kidd, R.B., 1987. Sedimentary processes on the Iberian continentalmargin viewed by long-range side-sonar and seismic data. Journal of Sedi-mentary Petrology 57 (3), 397–407.

Gonthier, E.G., Faugeres, J.C., Stow, D.A.V., 1984. Contourite facies of the Faro Drift,Gulf of Cadiz. In: Stow, D.A.V., Piper, D.J.W. (Eds.), Fine Grained Sediments: DeepWater Processes and Facies. Blackwell, Oxford, pp. 275–292.

Gonzalez, R., Dias, J.M.A., Lobo, F., Mendes, I., Plaza, F., 2003. The sedimentary shelfcover between the Ria Formosa and the mouth of the Guadalquivir Estuary(northern Gulf of Cadiz, SW Iberia). In: Vilas, F., Rubio, B., Diez, J.B., Frances, G.,Bernabeu, A.M., Fernandez, E., Rey, D., Roson, G. (Eds.), Special Volume on the 4thSymposium on the Atlantic Iberian Continental Margin. Thalassas 19 (2a), 50–51.

Gonzalez, R., Dias, J.M.A., Lobo, F., Mendes, I., 2004. Sedimentological and paleo-environmental characterisation of transgressive sediments on the GuadianaShelf (Northern Gulf of Cadiz, SW Iberia). Quaternary International 120,133–144.

Gutierrez-Mas, J.M., Moral, J.P., Sanchez, A., Dominguez, S., Munoz-Perez, J.J., 2003.Multicycle sediments on the continental shelf of Cadiz (SW Spain). Estuarine,Coastal and Shelf Sciences 57, 667–677.

Heenzen, B.C., Johnson, G.L., 1969. Mediterranean under-current and micro-physiography West of Gibraltar. Bulletin of the Institute of OceanographyMonaco 67, 1–97.

Hernandez-Molina, F.J., Somoza, L., Vasquez, J.T., Lobo, F., Fernandez-Puga, M.C.,Llave, E., Dias-de-Rio, V., 2002. Quaternary stratigraphic staking patterns on thecontinental shelves on the Southern Iberian Peninsula: their relationshipwith global climate and paleoceanographic changes. Quaternary International92, 5–23.

Herrle, J.O., 2003. Reconstructing nutricline dynamics of mid-Cretaceous oceans:evidence from calcareous nannofossils from the Niveau Paquier black shale (SEFrance). Marine Micropaleontology 47, 307–321.

Herrle, J.O., Mutterlose, J., 2003. Calcareous nannofossils from the Aptian-LowerAlbian of southeast France: palaeoecological and biostratigraphic implications.Cretaceous Research 24, 1–22.

Herrle, J.O., Pross, J., Friedrich, O., Koßler, P., Hemleben, C., 2003. Forcing mecha-nisms for mid-Cretaceous black shale formation: evidence from the UpperAptian and Lower Albian of the Vocontian Basin (SE France). Palaeogeography,Palaeoclimatology, Palaeoecology 190, 399–426.

Johnson, J., Ambar, I., Serra, N., Stevens, I., 2002. Comparative studies of thespreading of the Mediterranean water through the Gulf of Cadiz. Deep-SeaResearch 49, 4179–4193.

Kenyon, N.H., Belderson, R.H., 1973. Bed forms of the Mediterranean undercurrentobserved with side-sonar. Sedimentary Geology 9 (2), 77–99.

Kenyon, N.H., Ivanov, M.K., Akhmetzhanov, A.M., Akhmanov, G.G. (Eds.), 2001. In-terdisciplinary Approaches to Geoscience on the North East Atlantic Margin andMid-Atlantic Ridge. IOC Technical Series, 60. UNESCO.

Llave, E., Hernandez-Molina, F.J., Somoza, L., Diaz-del-Rio, V., Stow, D.A.V.,Maestro, A., Dias, J.M.A., 2001. Seismic stacking pattern of the Faro-Albufeiracontourite system (Gulf of Cadiz): a Quaternary record of paleoceanographicand tectonic influences. Marine Geophysical Researches 22, 487–508.

Lobo, F.J., Hernandez-Molina, F.J., Somoza, L., Rodero, J., Maldonado, A., Barnolas, A.,2000. Patterns of bottom current flow deduced from dune asymmetries overthe Gulf of Cadiz shelf (southwest Spain). Marine Geology 164, 91–117.

Lobo, F.J., Hernandez-Molina, F.J., Somoza, L., Dıaz del Rıo, V., 2001. The sedimentaryrecord of pot-glacial transgression on the gulf of Cadiz continental shelf(Southwest Spain). Marine Geology 178, 171–195.

Lobo, F.J., Sanchez, R., Gonzalez, R., Dias, J.M.A., Hernandez-Molina, F.J., Fernandez-Salas, L.M., Dıaz del Rıo, V., Mendes, I., 2004. Contrasting styles of the Holocenehighstand sedimentation and sediment dispersal systems in the northern shelfof the Gulf of Cadiz. Continental Shelf Research 24, 461–482.

Lopez-Galindo, A., Rodero, J., Maldonado, A., 1999. Surface facies and sedimentdispersal patterns. Southeastern Gulf of Cadiz Spanish margin. Marine Geology155, 83–97.

Lowemark, L., Schonfeld, J., Werner, F., Schafer, P., 2004. Trace fossils as paleo-ceanographic tool: evidence from Late Quaternary sediments of the south-western Iberian margin. Marine Geology 204, 27–41.

Maillard, C., 1986. Atlas of Hydrologique de l’Atlantique Nord-est. IFREMER, Brest,France.

Maldonado, A., Somoza, L., Pallares, L., 1999. The Betic orogen and the Iberian-African boundary in the Gulf of Cadiz: geological evolution (Central NorthAtlantic). Marine Geology 155, 9–43.

Marches, E., Mulder, T., Cremer, M., Bonnel, C., Hanquiez, V., Gontier, E., Lecroart, P.,2007. Contourite drift construction influenced by capture of MediterraneanOutflow Water deep-sea current by the Portimao submarine canyon (Gulf ofCadiz, South Portugal). Marine Geology 242, 247–260.

Mendes, I., Gonzalez, R., Dias, J.M.A., Lobo, F., Martins, V., 2004. Factors influencingrecent benthic foraminifera distribution on the Guadiana shelf (SouthwesternIberia). Marine Micropaleontology 51, 171–192.

Morales, J.A., 1997. Evolution and facies architecture of the mesotidal GuadianaRiver delta (S.W. Spain-Portugal). Marine Geology 138, 127–148.

Moreau, M.G., Berthou, J.Y., Malod, J.-A., 1997. New paleomagnetic Mesozoic datafrom the Algarve (Portugal): fast rotation of Iberia between the Hauterivian andthe Aptian. Earth and Planetary Science Letters 146, 689–701.

Nelson, C.H., Baraza, J., Maldonado, A., 1993. Mediterranean undercurrent sandycontourites, Gulf of Cadiz, Spain. Sedimentary Geology 82, 103–131.

Nelson, C.H., Baraza, J., Maldonado, A., Rodero, J., Escutıa, C., Barber Jr., J.H., 1999.Influence of the Atlantic inflow and Mediterranean outflow currents on LateQuaternary sedimentary facies of the Gulf of Cadiz continental margin. MarineGeology 155, 99–129.

Palain, C., 1976. Une serie detritique terrigene. Les ‘‘gres de Silves’’: Trias et Liasinferieur du Portugal. Memorias dos Serviços Geologicos de Portugal 25, 377.

Perch-Nielsen, K., 1989. Mesozoic and Cenozoic calcareous nannofossils. In: Boli, H.M., Saunders, J.B., Perch-Nielsen, K. (Eds.), Plankton Stratigraphy, Vol. 1. Cam-bridge University Press, pp. 329–554.

Pinheiro, L.M., Ivanov, M.K., Sautkin, A., Akhmanov, G., Magalhaes, V.H.,Volkonskaya, A., Monteiro, J.H., Somoza, L., Gardner, J., Hamouni, N., Cunha, M.R.,2003. Mud volcanism in the Gulf of Cadiz: results from the TTR-10 cruise. MarineGeology 195, 131–151.

Ruiz, F., Gonzalez-Regalado, M.L., Munoz, J.M., Pendon, J.G., Rodrıguez-Ramırez, A.,Caceres, L., Rodrıguez Vidal, J., 2003. Population age structure techniques andostracods: Applications in coastal hydrodynamics and paleoenvironmentalanalysis. Palaeogeography, Palaeoclimatology, Palaeoecology 199, 51–69.

Sautkin, A., 2001. Micropalaeontological investigation of matrix from mud volcanicdeposits. In: Kenyon, N.H., Ivanov, M.K., Akhmetzhanov, A.M., Akhmanov, G.G.(Eds.), Interdisciplinary Approaches to Geoscience on the North East AtlanticMargin and Mid-Atlantic Ridge. IOC Technical Series, 60. UNESCO.

Sautkin, A., Talukder, A.R., Comas, M.C., Soto, J.I., Alekseev, A., 2003. Mud volcanoesin the Alboran Sea: evidence from micropaleontological and geophysical data.Marine Geology 196, 237–261.

Sierro, F.J., Flores, J.A., Baraza, J., 1999. Late glacial to recent paleoenvironmentalchanges in the Gulf of Cadiz and formation of sandy contourite layers. MarineGeology 155, 157–172.

Somoza, L., Dıaz-del-Rıo, V., Leon, R., Ivanov, M., Fernandez-Puga, M.C., Gardner, J.M.,Hernandez-Molina, F.J., Pinheiro, L.M., Rodero, J., Lobato, A., Maestro, A.,Vazquez, J.T., Medialdea, T., Fernandez-Salas, L.M., 2003. Seabed morphology andhydrocarbon seepage in the Gulf of Cadiz volcano area: Acoustic imagery, mul-tibeam and ultra-high resolution seismic data. Marine Geology 195, 153–176.

Terrinha, P., 1998. Structural Geology and Tectonic Evolution of the Algarve Basin,South Portugal. PhD Thesis, Department of Geology, Royal School of Mines,Imperial Colleague. University of London, 430 pp.

Toucanne, S., Mulder, T., Schonfeld,Hanquiez, V., Gonthier, E., Duprat, J., Cremer, M.,Zaragosi, S., 2007. Contourites of the Gulf of Cadiz: a high-resolution record ofthe paleocirculation of the Mediterranean outflow water during the last 50,000years. Paleogeography, Paleoclimatology, Paleoecology 246, 354–366.

Zenk, W., Armi, L., 1990. The complex spreading pattern of Mediterranean water offthe Portuguese continental slope. Deep-Sea Research 37, 1805–1823.

estuarine, coastal and shelf...

Documents