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Marine Geology 249

Late Pleistocene and Holocene sedimentary facies on the SWGalicia Bank (Atlantic NW Iberian Peninsula)

B. Alonso a,⁎, G. Ercilla a, D. Casas a, F. Estrada a, M. Farrán a,M. García a, D. Rey b, B. Rubio b

.a Instituto de Ciencias del Mar-CSIC, Paseo Marítimo de la Barceloneta, 37-49, 08003 Barcelona, Spainb Universidad de Vigo, Facultad de Ciencias del Mar, 36310 Vigo, Spain

Accepted 20 September 2007

Abstract

Five main Pleistocene–Holocene lithofacies are defined in three different sedimentary environments (fault scarp, sedimentarylobe and inter-lobe channel) of the SW Galicia Bank: (1) turbidites (biogenous and terrigenous), (2) hemipelagites, (3) pelagites, (4)debrites, and (5) Heinrich sediments. In the sedimentary lobe and inter-lobe channel, the stratigraphic record consists mainly ofturbidites interbedded with debrites and Heinrich sediments and hemipelagites that are covered by hemipelagites or pelagites. In thefault scarp, the stratigraphy comprises hemipelagites and turbidites covered by pelagites. Frequency of turbidite events has variedbetween 1/1.2 ka and 1/3.1 ka, since 31.3 ka BP.

At least four turbidite events (1 to 4) between 9.1 and 31.3 ka BP, have been correlated between the different sedimentaryenvironments. The downslope of turbidity flows prevailed until 9.1 ka; after which, vertical settling and slow lateral advection havecontrolled sedimentation. The source area of turbidites and debrites is the fault scarp. Erosion of the slope near-surface pelagites/hemipelagites and ancient outcropping deposits could explain the presence of biogenous turbidites and terrigenous turbiditesrespectively. The rhythmic development of turbidites interrupted by hemipelagites could represent the manifestation of differentpulses of sedimentary instability induced by a combination of oversteepening (up to 29°) and occurrence of earthquakes.© 2007 Elsevier B.V. All rights reserved.

Keywords: Late Quaternary; turbidite; sedimentary processes; sedimentary instability; stratigraphy; Galicia Bank

1. Introduction

The Galicia Bank (Fig. 1A) is a structural high in thewestern Galicia continental margin (Atlantic NWIberian Peninsula). From the 1970 s to the 1990 s this

⁎ Corresponding author.E-mail address: [email protected] (B. Alonso).

0025-3227/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.margeo.2007.09.012

area was the subject of numerous geophysical and geo-logical studies aimed at determining its geodynamicevolution (Montadert et al., 1974; Laughton et al., 1975;Dupeuble et al., 1976; Mauffret et al., 1978; GroupeGalice, 1979; Boillot and Winterer, 1988; Murillas et al.,1990). Most studies of the sedimentary evolution of theGalicia Margin and surrounding areas (Iberian andBiscay Abyssal Plains, Portugal and Galicia continentalmargins) have concentrated on the Upper Cretaceousand Cenozoic, using sedimentology, biostratigraphy and

mailto:[email protected]

http://dx.doi.org/10.1016/j.margeo.2007.09.012

Fig. 1. (A) Map of the NE Atlantic Iberian continental margin showing the study area in the SWof the Galicia Bank (white rectangle). The location ofSites 637, 638, 639, 640 and 641 of ODP-Leg 103, Site 398 of DSDP-Leg 47B and Sites 897, 898, 899, 900, 901 of ODP-Leg 149 is also displayed;(B) 3-D multibeam bathymetry of the study area with the location of cores and sedimentary environments. Location of the Prestige (stern and bow) isalso shown. Bathymetric contours are in metres; and (C) Location of the cores in topographic profiles perpendicular and along-strike to the study area(I′–I, II′–II, III′–III and IV′–IV). Legend: Smt, seamount.

47B. Alonso et al. / Marine Geology 249 (2008) 46–63

magnetometry from ODP-Leg 103 Sites 637 to 641 onthe Deep Galicia Margin of the Galicia Bank (Boillotet al., 1987; Comas and Maldonado, 1988), DSDP-Leg47B Site 398 on the southern margin of the VigoSeamount (Maldonado, 1979), and ODP-Leg 149 Sites897 to 901 on the Iberian Abyssal Plain (Alonso et al.,1996; Milkert et al., 1996) (Fig. 1A). These UpperCretaceous and Cenozoic deposits include turbidites,pelagites/hemipelagites, contourites and debrites. Turbi-dites and pelagites dominate Plio-Pleistocene sequences,whereas contourites and debrites occurred mostly duringthe Late Miocene. However, sedimentary studies of theLate Pleistocene and Holocene history of the GaliciaBank Region do not seem to have attracted significantattention just since the Prestige naufrage.

This paper intends to fill this gap and presents a de-tailed study of the Late Pleistocene to Holocene sedi-mentary history in different sedimentary environments ofthe SW flank of the Galicia Bank based on the analysis ofsediment cores (Fig. 1B). This study was included as part

of the detailed geological studies conducted in the areain which the Prestige oil tanker wreck is located (GrupoPrestige, 2004). The main objectives are to define thelithological facies and stratigraphy that characterize thesedimentary environments as well as the near-surfacesedimentary history. The interest of this study lies in thefact that it provides knowledge about recent sedimenta-tion on the Galicia Bank Region and also, due its geo-structural framework, it will contribute to knowledgeof the type of processes and factors (local/regional) gov-erning Late Pleistocene and Holocene sedimentationassociated to a deepwater structural high, isolated fromhinterland sources (Fig. 1A).

2. Geological setting

The study area is located on the SW flank of theGalicia Bank in the Galicia continental margin (NWIberian Peninsula) (Fig. 1A). The Galicia continentalmargin resulted from rifting and final break-up between

Table 1Coordinates, water depth, core length and sedimentary environmentsof the nine gravity cores used in this study

Corenumber

Latitude(N)

Longitude(W)

Depth Corelength

Sedimentaryenvironment(m)

(cm)

TG1 42°10.8′ 12°03.2′ 3766 293 Inter-lobe channelTG2 42°12.6′ 12.02.7′ 3424 62 Fault scarpTG3 42°12.6′ 12°01.9′ 3104 34 Fault scarpTG4bis 42°10.9′ 12°01.4′ 3363 66 Fault scarpTG6bis 42°12.6′ 12°06.4′ 4078 259 Inter-lobe channelTG8 42°10.9′ 12°04.1′ 3822 283 Sedimentary lobeTG9 42°10.5′ 12°03.5′ 3811 275 Inter-lobe channelTG10bis 42°10.5′ 12°04.3′ 4171 277 Inter-lobe channelTG11 41°10.3′ 12.03.7′ 3833 263 Sedimentary lobe

48 B. Alonso et al. / Marine Geology 249 (2008) 46–63

the North American and Iberian Plates during the EarlyCretaceous time (Montadert et al., 1974; Boillot et al.,1979a). The overall tectonic style of the Early Cretac-eous main rifting event is characterised by a series oftilted blocks bounded by listric faults (Olivet et al.,1984). Tectonic movements observed on the GaliciaBank can be correlated with the kinematics of the NorthAtlantic, and these movements can be divided into threedifferent stages: pre-rift, syn-rift, and post-rift (Mauffret

Table 2Sedimentological data (textural data, carbonate content, mean grain size, soPleistocene to Holocene sediments in the SW Galicia Bank

Lithofacies Sand Silt Clay CaC03 Mean grainsize(%) (%) (%) (%)(phi)

TurbiditesTB 2–14 17–50 43–79 35–60 8.5–9.3TB+Q 0.1–10 24–37 62–74 17–35 8.5–9.3TT 2–15 21–37 46–76 17–25 7.4–8.6TAB 50–84 15–24 0–48 47–78 3.2–5.9

HemipelagitesHA 11–19 16–23 59–61 69–73 7.9–8.2HB 2–16 26–32 51–68 23–57 7.8–8.7H/T 10–22 18–26 52–70 35–60 7.4–8.5

PelagitesPm 6–16 24–26 59–61 56–73 7.9–8.4Psm 23–64 14–26 23–51 67–74 5.6–7.3

DebritesD 55–84 8–19 0–31 79–85 2.4–5. 3

Heinrich layersH1, H2, H3 2–13 25–40 46–65 15–26 7.4–9.0

TB, carbonate-rich biogenous turbidite muds; TB+Q, carbonate-poor biogeturbidite sands; HA, carbonate-rich hemipelagite muds; HB, carbonate-pooterrigenous hemipelagites muds; Pm, pelagite muds; Pms, pelagite sandy mu

and Montadert, 1987; Murillas et al., 1990). The topo-graphy was created by faulting, with the crest beingsubaereally eroded while the half-graben was not ex-posed (Boillot et al., 1979b; Mauffret and Montadert,1987). From the structural point of view, the GaliciaBank, together with the Vigo and Porto seamounts,forms a NNW–SSE trending alignment of elevatedhighs (Monatschal and Bernoulli, 1999) (Fig. 1A).

The Galicia Bank is a structural high and is bounded tothe north and the west by the Biscay and Iberian AbyssalPlains respectively and represents an isolated region fromhinterland source. The region of the Galicia Bank isdefined by several morpho-stuctural provinces by Váz-quez et al. (2008-this volume), and the study area is locatedat the half-graben province from 3324 to 4171 m waterdepth. The top of this bank is located at b700 m and thesurrounding region displays a water depth range of about5000 m on the northern and western sides and 3000 m onthe eastern and southern sides (Ercilla et al., 2006).

The Galicia Bank Region displays an irregular andcomplex morphology (Llave et al., 2008-this volume;Vázquez et al., 2008-this volume). In particular, the studyarea shows relatively high slope gradients (up to 29°)(Ercilla et al., 2006; Llave et al., 2008-this volume) (Fig. 1).

rting and compositional sand fraction) that characterised to the Late

Sorting Biogeniccomponents

Brokenplanktonicforaminifer

Terrigenouscomponents

Quartz(phi)

(%)(%)

(%)(%)

2.0–2.3 70–90 30–88 10–33 0–102.0–2.5 57–90 67–80 10–50 0–282.1–2. 8 23–45 20–30 55–77 20–570.5–1.2 99–100 0–13 0–1 0

2.4–2.9 95–100 0–10 0–5 0–21.9–2.6 79–100 2–25 0–21 8–142.4–2.8 43–70 27–41 30–57 1–12

2.2–2.7 100 0 0 02.9–3.2 100 0 0 0

0.8–3.6 80–90 0 0 0

1.8–2.4 51–71 5–22 28–83 20–67

nous turbidite muds; TT, terrigenous turbidite muds; TAB, biogenousr hemipelagite muds; H/T hemiturbidites carbonate-poor biogenous-ds; D, debrites; and HL, Heinrich layers.




Here, the main topographic features are a fault scarp in theeastern area, sedimentary wedges and lobes and inter-lobechannels in the central area, and a Main Channel in thewestern area (Llave et al., 2008-this volume) (Fig. 1).These morpho-sedimentary features are formed by mass-wasting deposits eroded from the scarp and deposited atits base (Ercilla et al., 2006; Llave et al., 2008-thisvolume). The sedimentary lobes have elongate positiverelief of variable length (4300–9500 m long) and width(1300–4000 m) covering areas up to 30 km2 reachingheights of 65 m to 90 m. They are separated by inter-lobechannels that show linear to slightly sinuous erosiverelieves. These valleys display a “V”-shaped cross-sectionin the proximal zones and a “U”-shape cross-section in thedistal parts. Their pathways are slightly sinuous, and alltogether they form a system that drains the SW flank of theGalicia Bank. The head of these channels are located onthe steepest lower zone of the fault scarp. The MainChannel has a NNE–SSWorientation with a “V”-shapedasymmetric cross profile (Llave et al., 2008-this volume).This channel coming down from the Galicia Bank. It goesafter passing the study area toward the Iberian AbyssalPlain. This channel represents a collector of erodedsediment from the scarp fault toward the abyssal plain(Ercilla et al., 2008-this volume; Hernández-Molina et al.,2008-this volume).

Table 3Thickness lithofacies (in cm and %) in the fault escarp, sedimentary lobe an

Location TB TB+Q TT TAB HA+H

Core Length (cm) (%) (cm) (%) (cm) (%) (cm) (%) (cm)

Fault scarpNothern areaTG2 62 cm 0 0 0 0 0 0 0 0 32TG3 34 cm 0 0 0 0 0 0 0 0 24Southern areaTG4bis 66 cm 0 0 0 0 0 0 44 66.7 0

Sedimentary lobeFlankTG11 263 cm 110.6 42 29.8 11.3 0 0 0 0 29.8CrestTG8 283 cm 220.7 78 14.2 5 0 0 8.5 3 19.8

Inter-lobe channelNorthern areaTG6bis 259 cm 13 5 0 0 0 0 0 0 5.2Southern areaTG1 293 cm 192 65.5 0 0 10.6 3.6 0 0 0TG9 275 cm 89.4 32.5 107.3 39 30.5 11.1 0 0 0TG10bis 277 cm 148 53.4 33.2 12 11 4 0 0 26.9

TB, carbonate-rich biogenous turbidite muds; TB+Q, carbonate-poor biogeturbidite sands; HA+HB, carbonate-rich hemipelagite muds and carbonate-pomuds between turbidites units; H/T, hemiturbidites, P, pelagites; D, debrites;

3. Materials and methods

3.1. Location

The study area covers about 200 km2 and was definedto include the Prestige wreck site and the surroundingarea. Nine gravity cores were collected around the sternand bow, divided into four transects, three E–W (I–I′,II–II′, and IV–IV′) and one N–S (III–III′) (Fig. 1Band C).Water depth varies from 3104 to 4171m and corelengths are from 34 to 293 cm (Table 1). Table 1summarises their depth, location, recovered lengths, andsedimentary environment.

3.2. Methods

Continuous, non-destructive high-resolution measure-ments of the whole-round cores were obtained with theGEOTEC Multi-Sensor Core Logger (MSCL). Themeasured parameters include wet-bulk density (byGamma Ray Attenuation), magnetic susceptibility andP-wave velocity (Weber et al., 1997) at 1 cm intervals.Representative lithological samples were taken from thesplit cores at 5–10 cm intervals and in some selectedsections at 1 cm intervals for analysis of grain size, sandcomposition, and carbonate content.

d inter-lobe channel sedimentary environments

B HB HT P D HL

(%) (cm) (%) (cm) (%) (cm) (%) (cm) (%) (cm) (%)

52 0 0 0 0 30 48 0 0 0 070.6 0 0 0 0 10 29.4 0 0 0 0

0 0 0 0 0 22 33.3 0 0 0 0

11.3 63.1 24.11 0 0 0 0 0 0 29.8 11.3

7 0 0 0 0 0 0 0 0 19.8 7

2 207 80 0 0 33.6 13 0 0 0 0

0 11.1 3.8 40.1 13.7 0 0 28.7 9.8 10.5 3.60 0 0 30 11.1 0 0 0 0 17.3 6.39.7 40.2 14.5 0 0 0 0 0 0 17.7 6.4

nous turbidite muds; TT, terrigenous turbidite muds; TAB, biogenousor hemipelagite muds of the core top; HB, carbonate-poor hemipelagiteand HL, Heinrich Layers.





Fig. 2. Selected core photograph (TG10bis) showing the lithofacies types of the SW of the Galicia Bank. Note that the turbidite lithofacies aredominant. Examples of the sand fraction components of the turbidite lithofacies are also shown. Legend: P, pelagite muds; HA, carbonate-richbiogenous hemipelagite muds; HB, carbonate-poor biogenous hemipelagites muds; H/T, carbonate-poor biogenous–terrrigenous hemipelagite muds;D, debrites; TB, carbonate-rich biogenous turbidite muds; TT, terrigenous turbidite muds, TB+Q, carbonate-poor biogenous turbidite muds, TAB,biogenous turbidites sands; and HL, Heinrich layers (H1, H2, H3). Numbers 1 to 3 correspond to location of samples at core.


Sedimentological logs were made of all cores. Specialattention was paid to colour, grain size, sand composition,bed thickness variations, primary physical sedimentary

structures and physical properties. Textural analysis wasperformed using settling-tube techniques for the coarse-grained fraction (b4 phi) and the Sedigraph-X ray


technique for fine fraction (N4 phi) (Micromeritics 5100)(Giró and Maldonado, 1985). The standard deviationadopted for the classification of sediments refers to sortingclasses (Friedman and Sanders, 1978; Swan et al., 1979;Alonso and Maldonado, 1990; Alonso et al., 1999).They are the following: 0.50 phi to 0.80 phi for wellsorted sediments; 0.80 phi to 1.40 phi for moderatelysorted sediments; 1.40 phi to 2.00 phi for poorly sortedsediments; and 2.00 phi to 2.60 phi for very poorly sortedsediments. The sand fraction composition was studiedusing a binocular microscope counting about 300 grainsper sample. The following components were identifiedand counted: light minerals (quartz, mica, feldspar, andothers), heavy minerals, rock fragments, neoformationminerals (pyrite), bioclasts (planktonic foraminifera,benthic foraminifera, pteropods and others that includeundifferentiated remains). Core chronology was based onthe relative positions of the lithofacies in all nine coresexamined and physical properties. Age control is based on14C dating. The chronology of sediments refers to thecalibrated BP ages which have been determined by Reyet al. (2008-this volume).

4. Lithofacies

Five main lithofacies are identified based on texture,colour, carbonate content, sand composition, planktonicforaminifera preservation, and physical properties: (1)turbidites, (2) hemipelagites, (3) pelagites, (4) debrites,and (5) Heinrich sediments. Each type of lithofacies isinterpreted in terms of a specific sedimentary process.The main sedimentological data (textural and composi-tional sand fraction) of these lithofacies are illustrated inthe Table 2. Brief descriptions of each of the lithofaciesfollow.

4.1. Turbidites

Four subtypes of turbidite lithofacies were identified:(TB) carbonate-rich biogenous muds, (TB+Q) carbo-nate-poor biogenous muds, (TT) terrigenous muds, and(TAB) carbonate-rich biogenous sands. The dominantturbidites are carbonate-rich biogenous (TB, up to 74%in thickness) and carbonate-poor biogenous turbiditesmuds (TB+Q, up to 35% in thickness) (Table 3, Fig. 2).The turbidite muds belong to the E turbidite division ofPiper (1978) and correspond to fine-grained turbidites,which are described and well documented in theliterature (Piper, 1978; Stow and Shanmugam, 1980;Stow, 1985). We identified graded basal units (e.g. mean8.0 to 9.0 phi) passing up to ungraded muds (mean about8.6 phi), which are characterised by moderate to poor

sorting (2.0–2.8 phi). These fine-grained muds displayintervals of laminated colour bands, finely laminatedsilts and black lenses of silt and homogenous structure-less sediment (Figs. 2 and 3).

The subtype TB is composed of dark brown (greyisholive-10Y4/2, pale olive-10Y6/2; light olive brown-5Y5/6) muds (mean 8.5 to 9.3 phi) with a high carbonatecontent (35–60%) (Table 2). These turbidite muds havelow sand content (2–14%) which is composed mainly ofpoorly preserved planktonic foraminifera (up to 88%)(Table 2, Fig. 4). The average compressional-wavevelocity is 1438 m/s and the average density is 1.54 g/cm3. The magnetic susceptibility values are relativelylow (6.23×10−5 SI average) with minimums of 1.92×10−5 SI (Figs. 5 and 6).

The subtype TB+Q consists of moderate olive brown(5Y4/4) and light olive grey (5Y5/2) muds (mean 8.5–9.3 phi) with a lower carbonate content (17–35%) thanthe type TB (Table 2, Fig. 4). These turbidite muds havelow sand content (0.1–10%) and their compositionconsists predominantly of poorly preserved planktonicforaminifera (67–80%) (Table 2); in addition, there is ahigh presence of some terrigenous components, such asquartz which reaches 28% and other light minerals(mica, feldspar) (15%). The average compressional-wave velocity is 1429 m/s and the average density is1.48 g/cm3. The average magnetic susceptibility is low(5.81 SI), with a peak at 15.28×10−5 SI at the base ofsome units (Figs. 5 and 6).

The subtype TT consists of muds (mean 7.4–8.6 phi)that aremoderate olive brown (5Y4/4) and light olive grey(5Y5/2) in colour, with a low carbonate content (17–25%)(Table 2, Figs. 2 and 4). These turbidite muds have lowsand content (2–15%) and their composition is formedpredominantly by quartz (20–57%) (Fig. 4), other lightminerals (mica, feldspar) and other terrigenous constitu-ents (rock fragments and iron oxide); the biogenic grains(b45 %) include poorly preserved planktonic foramini-fera (20–30%) (Table 2, Fig. 4). The average compres-sional-wave velocity is 1,392 m/s and the average densityis 1.54 g/cm3. The average magnetic susceptibility isrelatively high (11×10−5 SI) (Fig. 6).

The subtype TAB comprises silty sands (mean 3.2–3.9 phi) and muddy sands (mean 3.5–5.9 phi) (Table 2),both pale yellow brown (10YR6/2) in colour (Fig. 3).The carbonate content is high (47–78%) (Table 2). Themean grain size shows two types of texture: coarse sands(b3.5 phi) and finer sands (N3.5 phi). These sands aremoderately well sorted (0.50 to 0.80 phi) and moder-ately sorted sediments (0.8 to 1.20 phi) (Table 2). Thesand fraction is composed predominantly of well pre-served planktonic foraminifera (Table 2). These coarse-



Fig. 3. Core photographs showing the sedimentary features (structures and colours) of the lithofacies in the SW Galicia Bank. For legend, see Fig. 2.


grained turbidite display intervals of colour banded,finely laminated with moderately yellowish brown incolour (Fig. 3). The average compressional-wave ve-locity is 1435 m/s and the average density is 1.56 g/cm3.The average magnetic susceptibility is low (3.75×10−5

SI) (Fig. 7).We note that these calcareous biogenic turbidites

show similitudes to “pelagic turbidites” described byKelt and Arthur (1981) from the sedimentological andphysiographic setting point of views. They are generallyinferred to be the result of injection of low-concentra-tion, sluggish turbidity currents from spreading flanks(Kelt and Arthur, 1981).

4.2. Hemipelagites

Hemipelagites are defined as “deep-sea sedimentscontaining a small amount of terrigenousmaterial as wellas remains of pelagic organisms” (Bates and Jackson,1987). The hemipelagic sediments include structureless,homogenous and highly bioturbated muds (mean 7.4 to8.7 phi) (Table 2, Fig. 3). They consist of biogenic muds(planktonic foraminifera) with a presence (b57%) of

terrigenous components (quartz, mica, light minerals).They are poorly and very poorly sorted sediments (1.9 to2.9 phi). Three subtypes of hemipelagites were identi-fied: (HA) carbonate-rich biogenous muds, (HB)carbonate-poor biogenous muds and (H/T) carbonate-poor biogenous-terrigenous muds (Table 2).

Subtype HA occurs at the top of most of the cores(Figs. 5 and 6). It consists of light-brown colour (10YR7/4) mud with high carbonate content (69–73%) andintact planktonic foraminifera (Table 2, Fig. 2). SubtypeHB occurs below subtype HA and between turbiditeunits (Figs. 2, 5 and 6). It comprises dark brown (5Y6/4and 10YR6/6) and light-grey colours (5Y5/6, 5Y6/4)mud (Fig. 2) with low carbonate content (23–57%), andintact planktonic foraminifera (Table 2). Subtype H/T hasa local presence, occurring only at the top of two cores(Figs. 4 and 6). It consists of light-grey colours (5Y5/6)mud with low carbonate content (b60 %) (Table 2,Fig. 4). Mixed terrigenous–biogenous componentshighly fragmented planktonic foraminifera (27–41%)and a decrease in the clay/silt ratio are observed in theseunits (Fig. 4). These characteristics allow these beds to beinterpreted as hemiturbidites (Stow and Wetzel, 1990).

Fig. 4. Analytical data from a selected core (TG 9): sand, silt and clay (%); mean grain size (phi); carbonate content (%); sand composition (%)(biogenous and terrigenous components); intact planktonic foraminifer (Plank. Foram.) tests (%); broken planktonic foraminifers tests (Plank. Foram)(%) in the sand fraction; and quartz content (%) of the turbidites, hemiturbidites and Heinrich layers. For legend, see Fig. 2.


For subtype HA, the average compressional-wavevelocity is 1457 m/s, the average density is 1.50 g/cm3,and the average magnetic susceptibility is 4.59×10−5 SI(Figs. 5 and 6). For subtype HB, the average compres-sional-wave velocity is 1475 m/s, the average density is1.62 g/cm3, and the average magnetic susceptibility isthe lowest (1.64×10−5 SI) (Figs. 5 and 6). For H/T theaverage compressional-wave velocity is 1426 m/s, theaverage density is 1.59 g/cm3, and the average magneticsusceptibility is 2.02×10−5 SI (Fig. 6).

4.3. Pelagites

Pelagites are defined as “deep-sea sediments withoutterrigenous material” (Bates and Jackson, 1987). Thesesediments consist of light-coloured moderately yellow-ish brown-10YR5/4 (Fig. 3); very pale orange (10 YR 8/2) calcareous biogenic muds and sandy muds with intactplanktonic foraminifera (Table 2). The carbonate

content is high (56–73%) and texturally are very poorlysorted sediments (2.2–2.6 phi) (Table 2). The meangrain size shows two types of textures: muds (N7.9 phi)and sandy muds (b7.3 phi) (Table 2). The averagecompressional-wave velocity is 1372 m/s, the averagedensity is 1.81 g/cm3, and the average magneticsusceptibility is 9.1×10−5 SI (Fig. 7).

4.4. Debrites

Debrites consist of pteropods gravel size (millimetres insize)within amatrix-supported bioclasts of also pteropods.The matrix is composed of sands (mean 2.4–3.5 phi),muddy sands (mean 5.6–5.6 phi) and sandy muds (mean7.1–7.4 phi) (Table 2) that are light olive grey (5Y5/2) incolour (Fig. 8). The carbonate content is high (up to 85%)(Table 2). The sand fraction is composed predominantly offragmented pteropods shells (80–90%) (Fig. 8). Thissediment is poorly stratified, with an upward coarsening

Fig. 5. Lithofacies logs and physical properties of cores in the sedimentary lobe environment. The location of the cores is shown in Fig. 1B, and C.Vp, compressional-wave velocity (m/s); D, density (g/cm3); and MS, magnetic susceptibility (x10–5 SI). For legend, see Fig. 2.


grain size trend of the matrix, and a major presence ofmillimetre-sized pteropod fragments (Fig. 8). The averagecompressional-wave velocity is 1476 m/s, the averagedensity is 1.48 g/cm3, and the average magneticsusceptibility is relatively high (8.69×10−5 SI) (Fig. 6).

4.5. Heinrich sediments

Three Heinrich Layers (H1, H2, H3) have beenrecognised and characterised base on their magneticproperties assemblages by Rey et al. (2008-this volume).These layers were found within specific turbidite mudunits and between hemipelagites. They display lowcarbonate content (17–26%) (Table 2). These levels

contain in most beds abundant terrigenous components(up to 83%) in the sand fraction, mainly transparentquartz (up to 67%). They display an increase magneticsusceptibility and density in most beds (Figs. 5 and 6).The average compressional-wave velocity is 1370 m/s,the average density is 1.6 g/cm3, and the averagemagnetic susceptibility is 20.75×10−5 SI (Figs. 5 and 6).

5. Chronostratigraphy

5.1. Sedimentary environments

Here we refer to the sedimentary stratigraphy of thethree modern sedimentary environments previously


Fig. 6. Lithofacies logs and physical properties of cores in the inter-lobe channel environment. The location of the cores is shown in Fig. 1B and C.Vp, compressional-wave velocity (m/s); D, density (g/cm3); and MS, magnetic susceptibility (x10–5 SI). For legend, see Fig. 2.


defined by morpho-seismic study by Ercilla et al. (2006)and Llave et al. (2008-this volume) of the SW GaliciaBank. They are: (a) a fault scarp, (b) sedimentary lobes,and (c) inter-lobe channels (Figs. 5 to 7). The differentvertical arrangements of the five types of lithofacies(turbidites, pelagites, hemipelagites, debrites and HeinrichLayers) within these sedimentary environments aredescribed in detail. The age of the Heinrich Layer H3top has been dated at 31.3 ka by Rey et al., while the agesof the otherHeinrich Layers H1 (16.6 ka) andH2 (24.7 ka)are taken from Thouveny et al. (2000) (Rey et al., 2008-this volume).

(a) The stratigraphy of the fault scarp environment(2790 and 3600 m water depth) displays differ-ences from the northern to southern areas (Fig. 7).In the northern area, it is represented bycarbonate-rich hemipelagites muds (HA, average

core thickness 61%) that change to pelagites(average core thickness 39%) toward the top(Table 3, Fig. 7). In the southern area, thestratigraphy is defined by biogenous turbiditesands (TAB, core thickness 66.7%) that arecovered by pelagites (P, core thickness 33.3%)(Table 3, Fig. 7). The boundary between theselithofacies is diffuse. Three units of pelagites andone unit of carbonate-rich hemipelagites muds aredated respectively at 22.4 ka, 22.2 ka, 5.9 ka and25.9 ka (Table 4, Fig. 9).

(b) The stratigraphy of the sedimentary lobe environ-ment (3500 to 4400 m water depth) showsdifferences in thickness and lithofacies betweenthe flank and crest (Fig. 5). The flank displayshighly variable lithofacies with carbonate-richbiogenous turbidite muds (TB, core thickness42%), which alternate with carbonate-poor




Fig. 7. Lithofacies logs and physical properties of cores in the fault scarp environment. The location of the cores is shown in Fig. 1B and C. Vp,compressional-wave velocity (m/s); D, density (g/cm3); and MS, magnetic susceptibility (x10–5 SI). For legend, see Fig. 2.


biogenous turbidite muds (TB+Q, core thickness11%), carbonate-poor hemipelagite muds (HB, corethickness 24%) and Heinrich Layers (HL, corethickness 11%), (Table 3). Toward the top, thelithofacies change to hemipelagite muds (HA+HB)

Fig. 8. (A) Photographs showing an example of a debrite unit composedof pteropods sand size within a matrix-supported bioclast of alsopteropods overlying turbidite muds. Note the negative grading and theerosive basal boundary. (B) Photograph showing broken pteropod tests.

(core thickness 11%). Three units of hemipelagicmuds yielded calibrated ages of 10.2 ka, 19.5 ka and19.7 ka (Table 4, Fig. 9). In contrast, the crest of thesedimentary lobe is stratigraphically much morehomogeneous, being characterised by abundantcarbonate-rich biogenous turbidite muds (TB, corethickness 74%), alternating with a few thin units(b5 cm) of carbonate-rich biogenous turbidite sands(TAB, average core thickness 3%), carbonate-poorbiogenous turbidite muds (TB+Q, core thickness5%) and Heinrich Layers (HL, core thickness 11%)(Table 4, Fig. 5). Hemipelagites prevail at the top of

Table 4Calibrated BP ages (14C dated) of the lithofacies and sediment rates

Sedimentaryenvironment

Corenumber

Level Lithofaciestype

Age(cm) (ka)

Fault scarp TG2 29 P 22.4⁎

53 HA 25.9⁎

Fault scarp TG3 4 P 22.2⁎

Fault scarp TG4bis 11 P 5.9Sedimentarylobe (crest)

TG8 33 HB 13

Sedimentarylobe (flank)

TG11 29 HB 10.294 HB 19.5140 HB 19.7

Inter-lobechannel

TG1 30 H/T 8.643 H/T 11.1104 D 20.2120 HB 17.6158 D 18.6

Inter-lobechannel

TG9 24 H/T 7.230 H/T 9.1

Inter-lobechannel

TG10bis 29 HA 10.796 HB 16.9

⁎Refers to datings below the precision limit of the 14C method(N21.7 ka) (for details see Rey et al., 2008-this volume).


Fig. 9. Correlation of turbidite events in the SWof the Galicia Bank. The summarised lithological logs and the core location are also shown. Numbers 1 to 4 refer to the turbidite events from younger toolder from 9.1 ka to 31.3 ka respectively. For legend, see Fig. 2.

57B.Alonso

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the section (HA+HB, core thickness 7%) andhemipelagites bases have been dated at 13 ka and31.3 ka (Table 4, Fig. 9). In both sectors, flank andcrest, Heinrich Layers (H1, H2, H3) are present.

The inter-lobe channel environment (3600 toN4600 mwater depth) has different stratigraphies in the northern tosouthern areas (Fig. 6). In the north, it consists mainly ofcarbonate-poor hemipelagite muds (HB, core thickness80%) alternating with a few thin (b3 cm) carbonate-richbiogenous turbidite mud units (TB, core thickness 5%)(Fig. 6); toward the top this association of lithofacieschanges to pelagites (average core thickness 13%)interrupted by two thin (b3 cm) units of carbonate-poorhemipelagite muds (HB, core thickness 2%) (Fig. 6). Bycontrast, the southern area stratigraphy is more hetero-geneous (Fig. 6). Here, there are alternations of carbonate-rich biogenous turbidite muds (TB, average core thickness50%), carbonate-poor biogenous turbidite muds (TB+Q,average core thickness 17%), terrigenous turbidite muds(TT, average core thickness 6%), debrites (D, average corethickness 3%), carbonate-poor hemipelagite muds (HB,average core thickness 3%) and Heinrich Layers (HL,average core thickness 7%) (Table 3, Fig. 6). Toward thetop these alternating lithofacies, mixed terrigenous–biogenous hemipelagites (H/T, average core thickness8%) and hemipelagites (HA+HB, average core thickness3%) prevail (Table 3). The debrites have been dated around18.6 ka and 20.2 ka, which are similar to Portuguesecontinental margin pteropods muds (17.8 and 24.6 ka)(Bass et al., 1997). Dating of hemiturbidites yieldedcalibrated ages of 8.6 ka and 7.2 ka. The ages ofhemipelagite mud units are: 17.6 ka, 16.9 ka, 10.7 kaand 9.1 ka (Table 4, Fig. 9).

5.2. Correlation: turbidite distribution

The correlation of turbidites through basins has beendescribed many times and various criteria have beenused to perform it (Weaver et al., 1986; Weaver andRothwell, 1987; Davies et al., 1997). However, in thiswork, it was not possible to correlate all the identifiedturbidites. Nevertheless, we were able to correlate fourindividual turbidite events, named 4 to 1 from older toyounger, and dated between 31.3 ka and 9.1 ka (Fig. 9).These events have been defined in the lobe and inter-lobechannel environments. They were correlated accordingto several criteria, including texture, mean grain size,carbonate content, composition of sand fraction, relativestratigraphic position, thickness, age of the underlyinghemipelagites and vertical distribution pattern of thephysical properties.

Event 4 comprises mainly carbonate-rich, biogenousturbidite muds (TB) and carbonate-poor biogenousturbidite muds (TB+Q) that overlies the Heinrich LayerH3 (31 ka) and underlying the Heinrich Layer H2(24.7 ka); this event has been defined in those cores atrelatively shallow sites (Fig. 9). Both types of sedimentbelong to the same event, because we consider thatcarbonate-poor biogenous turbidite muds may haveevolved downslope to rich-carbonate biogenous turbiditemuds. The explanation offered is the turbidity flow chargedmostly with biogenous and some of terrigenous (quartz),moves depositing the quartz particles at a shallowestposition whereas the tail of skeletal particles of extremelylow effective densities incorporate in the upper part of thecarbonate-poor biogenous turbidite muds; downslope,once lost most of the terrigenous, the turbidity flowwould deposit the biogenous ones forming the carbonate-rich biogenous muds. Event 4 is an important unit takinginto account its maximum thickness (up to 110 cm) andextent (Fig. 9). This event affects two sedimentaryenvironments: the inter-lobe channel and the sedimentarylobe (Fig. 9). Vertical mean grain size variation fairlygraded muds at the turbidite base (mean 8.3 to 8.8 phi) andungraded muds at the top (mean 8.9 phi). The lateraldistribution of the mean grain size from core to core showsno variation across the different sedimentary environments.Based on Heinrich Layer H2 chronostratigraphy and theresults of calibrated ages at base of this event, an agebetween 31.3 ka and 24.7 ka is assigned for theemplacement of the turbidite event 4 (Fig. 9).

Event 3 is defined by terrigenous turbidite muds (mean7.4 to 8.4 phi) and affects the inter-lobe channelenvironment (Fig. 9). This turbidite event forms a thin(average thickness 8 cm) fining-upward succession thatoverlies the Heinrich Layer H1 (16.6 ka). The mean grainsize from core to core does not vary. 14C dating of theoverlying carbonate-poor hemipelagite muds and theHeinrich Layer H1 chronostratigraphy suggest this eventoccurred at some time between 11.1 ka and 16.6 ka (Fig. 9).

Event 2 consists of carbonate-poor, biogenous tur-bidite muds and affects inter-lobe channel and sedi-mentary lobe environments. This pattern of distributionis quite similar to those observed for Event 4 (Fig. 9).Event 2 always underlies the carbonate-poor hemipela-gite muds and overlies the Heinrich Layer H1 (16.6 ka).This turbidite event forms a thin unit (average thickness20 cm) displaying graded muds (mean 7.6 to 8.3 phi).Mean grain size does not vary across the differentsedimentary environments. This event occurred between13 ka and 16.6 ka (Fig. 9).

Event 1 is characterised by carbonate-rich biogenousturbidite muds and appears along the inter-lobe channel


environment. It represents a thin unit (average thickness20 cm). The vertical distribution of the mean grain sizeshows graded muds (mean 8.5 to 9.3 phi). The spatialdistribution of mean grain size does not vary along theinter-lobe channel environment. This event alwaysunderlies the carbonate-poor hemipelagite muds andmixed terrigenous–biogenous hemipelagite muds. Thestratigraphic control suggests that this event occurredbefore 9.1 ka (Fig. 9).

6. Discussion and conclusions

6.1. Sediment source

The literature indicates that deep water turbidites aremostly introduced into the marine environment fromfluvial and glacial discharges, coastal erosion and eoliantransport (Stow, 1985). However, these sources do notseem to have played a relevant role in the study area dueto the Galicia Bank represents an isolated region fromhinterland sources. Here, the source area of turbiditesand debrites is represented by the fault scarp environ-ment (Ercilla et al., 2006; Hernández-Molina et al.,2008-this volume; Llave et al., 2008-this volume).Ancient deposits outcrop in this faulted scarp and itsexhumation has triggered mass-movements on the faultscarp, building the major depositional lobes and inter-lobes channels. Hernández-Molina et al. (2008-thisvolume) based on the analysis of acoustic facies alsosuggest that depositional lobes are make up mud/debrisflow deposits and inter-lobe channels are formed byturbidity flows. Mass-movements could be triggered by(a) the tectonism responsible for the formation of thefault scarp and (b) the steep slopes (up to 29°). Thesefacts would give an unstable scarp, favouring a deposi-tional/erosive downslope transport that contributes to thedevelopment of a rill and gully topography and theaccumulation of biogenous turbidite sands on the faultscarp, and of carbonate-rich biogenous turbidite muds,carbonate-poor biogenous turbidite muds and terrigenousmuds on the depositional lobes and inter-lobe channels.

The source area affects the nature and texture of theturbidites. With respect to the nature of the turbidites,changes in the sand components are observed establishing2 types: biogenous and terrigenous. The nature ofturbidites indicates that sediment supplied by the faultscarp comes from the erosion of the near-surfacepelagites/hemipelagites which is supported by the majorhiatus at the top of TG3 (the fault scarp), where sedimentat 4 cm core depth is dated at 22.2 ka (Fig. 7). In addition,the ancient outcropping deposits (Middle Eocene toValanginian in age) contribute to the presence of

terrigenous turbidites. We thus interpreted three periodsof high terrigenous input: after and before of HeinrichLayer H1 (16.6 ka) and before of Heinrich Layer H3(31 ka) (Fig. 9). Most of the turbidites are fine-grainedsediments. They occur in all sedimentary environmentsexcept on the fault scarp environment (southern sector)where coarse-grained turbidites (biogenous turbiditesands) have been deposited. These, which are also calledpelagic turbidites (Kelt and Arthur, 1981) representsediments redeposited in the same source area.

6.2. Sediment transport and deposition during LatePleistocene–Holocene

The last few decades have been times of majorreorientation in the sedimentologist's view of deep-seasediment transport and deposition, and the mechanismsthat operate on continental margins and the deep-seaocean (Evans et al., 1998; Stow and Myall, 2000; Wynnet al., 2002). The sedimentary processes have beendivided into three categories taking into account thedirection of movement: predominately downslope,alongslope, and vertical flux (Evans et al., 1998). Onthe SW flank of the Galicia Bank, our sedimentologicalstudy indicates that downslope processes predominatemainly in the form of turbidity flows, although thepresence of debris flows are also detected. These flowswould result from slope failures in the fault scarp. Lesscommon are vertical settling (synonymous to pelagicsettling) and slow lateral advection (hemipelagic settling).

With respect to the turbidity flows, according to theresults of the ODP Site 637 (Fig. 1 A) (Comas andMaldonado, 1988), they began in the upper Pliocene andcontinued into the Pleistocene. In addition, the Pleisto-cene and Holocene stratigraphy of this study confirmsthat turbidite sedimentation predominated during theLate Pleistocene on the SW flank of the Galicia Bank.Here, the 14C dating suggests that the oldest datedturbidite event has occurred about 31.3 ka (Fig. 9).

Assuming that each unit corresponds to a singleevent, we observe that the number of turbidite eventsvaries between different sedimentary environments aswell as through the geographic areas (northern andsouthern). The maximum number (at least 9) wasregistered in the inter-lobe channel of the southern area.This suggests that here the channelised flows were morefrequent and only some of them (at least 3) affected theinter-lobe channel of the northern area (Fig. 9). Therelative low presence of turbidite events in the northernarea could be related to the predominance of shortdistance turbidity currents that do not reach the distalmost positions of the inter-lobe channels. In fact, the




analysed core in the northern sector is located in a distalmost position. Nevertheless, a relative minor occurrenceof turbidity currents with respect to the southern areacould be also considered as another explanation.

Furthermore, those turbidity currents that travelledshort distances are responsible for the formation ofbiogenic turbidite sands (or “pelagic turbidites”) in thesouthern area of the fault scarp (Fig. 9). Their lowerosive capability could explain the redeposition ofplanktonic sediment with good preservation of theshells. The erosive mass-movements processes thatoccur on the fault scarp would favour the redeposition ofcarbonate-rich biogenous turbidite sands (TAB) accu-mulated only at areas close to the scarp (b3363 m waterdepth). The occurrence of these mass-movements hasbeen also evidenced by seismic facies and stratigraphi-cal analyses (Ercilla et al., 2008-this volume; Hernán-dez-Molina et al., 2008-this volume).

The great variability of the turbidite events displayedby the cores in spite of the short distance between them(60–100 m), and the differences in thickness (8 to110 cm) and extension of the four correlated eventscould be the result of interplay between the upliftmovements of the fault scarp, rill and gully topography,gradients, occurrence of channelised and unchannelisedflows, and lateral adding of sediment from erosion of theadjacent depositional lobe walls. The combination ofthese elements in a small size area (b200 km2) favoureda complex turbidite deposition that contrasts withsimilar studies in larger areas (hundreds of kilometres),where turbidity flows have travelled long distancesbefore their deposition, forming turbidites with a spatialevolution of grain size, e.g. on the Madeira, Agadir,Iberian, and Horeshoe Abyssal Plains (Weaver et al.,1986; Lebreiro et al., 1998, Wynn et al., 2002).

Finally, we can tentatively estimate the frequency ofemplacement of turbidites based on the number of unitsand chronological framework. This estimation has beencalculated for those cores located on the southern area.In general, the frequency ranges from about 1 turbiditeevent every 1 ka to 3 ka. The general distribution of thisfrequency is similar for each sedimentary environment.Thus, the inter-lobe channel environment displaysfrequencies of about 1/1.2 ka to 1/3.1 ka and thesedimentary lobe crest frequencies of about 1/1.2 ka.The rhythmic development of the turbidites interrupted byhemipelagites could represent the manifestation ofdifferent pulses of sedimentary instability. These pulsesmay be induced by a combination of oversteepening andoccurrence of earthquakes at the Galicia Bank (Engdahl&Villaseñor, 2002; Díaz et al., 2008-this volume). Withrespect to seismicity, the results from the OBS experiment

at the Galicia Bank Region detected seismic events withmagnitudes varying between 2.5 and 3 (Ercilla et al.,2006; Díaz et al., 2008-this volume). All the data togetherallow the authors to state that although the Galiciacontinental margin displays a moderate level in the globalcatalogue of seismicity, it can be considered to have a lowto moderate level of local seismicity (5NMagN1.5).

With respect to the debris flows, this process isresponsible for the deposition of two layers of debritesmostly composed of pteropod fragments in the inter-lobe channel environment (Fig. 6). In order to explainthe genesis of these deposits, it is important to considertwo general aspects: (a) the pteropod sediments arerestricted to only 2.4 % in the deep ocean of the Atlanticdue to rapid dissolution of aragonite; and (b) similarpteropod-rich layers have been identified throughout theregion from Portugal to Senegal (Diester-Hass and VanDer Spoel, 1978; Sarnthein et al., 1982; Bass et al.,1997; Kalberer et al., 1993) and also on topographicallyhigh areas in the Atlantic, Pacific and Indican Oceans(Berger, 1978).

The formation of these layers not yet fully under-stood. In this sense, several pre- and post-depositionalprocesses which are yet fully understood may lead to theformation of these sporadic occurrences of pteropods-rich layers. Detailed sedimentological studies bySarntheim et al. (1982) and Melker et al. (1992) inAtlantic Ocean reveal that theses layers are correlatedwith warming pulses combined with reduced coastalupwelling in the surface waters. In our study area wehave to take into account that these layers appear only inone core (TG1), being absent in the rest of the cores,event in the nearest ones, and that the pteropods shellsare very poor preserved. Because of that we cantentatively consider an increased in pteropods sedimen-tation due to a mass mortality deposition on shallowerareas of the Galicia Bank Region (b700 m water depth),and subsequent redeposition by mass-movements toform debrites far away at 3766 water depth, on the inter-lobe channel environment (TG1 in Fig. 6).

Hemipelagic settling of marine microskeletons andterrigenous particles, and pelagic settling with absenceof terrigenous particle input, are responsible for thedeposition of hemipelagites and pelagites respectively.Likewise, hemiturbiditic flows resulted in the depositionof hemiturbidites defined in those core sites close to thefault scarp (TG1 and TG9) (Fig. 7). These have beendefined previously as a fine, muddy sediment withpartially turbiditic and partly hemipelagic characteris-tics. We therefore infer that such beds were depositedclose to the source area from an essentially stationarysuspension cloud that is formed directly from, but




beyond and above, the dying stages of a low-concentration turbidity current (Stow and Wetzel,1990). The deposition of pelagites and hemipelagitescorresponding to the core tops occurred mostly duringthe Holocene (7.2 ka). While deposition of pelagites andhemipelagites in the sedimentary lobe and inter-lobechannel environments occurred during late glacialperiod (13 ka). In contrast, in the fault scarp, thedeposition of the pelagite and hemipalagite lithofacies isolder (25.9 ka) in the northern area (Fig. 9). TheHeinrich Layers were formed during distinct periods ofinstability of the Laurentian Ice Sheet leading debris-carrying icebergs into the North Atlantic during the LatePleistocene (Heinrich, 1988; Broecker et al., 1992).

Finally, the change of sediment transport mechanismfrom Late Pleistocene to Holocene (from predominantlydownslope to pelagic/hemipelagic settling) could berelated to the lack of sedimentary instability pulsesduring this period; in this situation, sedimentation ismainly controlled by vertical settling. This interpretationis also supported by other geological works done in thisarea. For example, the seismic facies study byHernández-Molina et al. (2008-this volume) and thestratigraphy study by Ercilla et al. (2008-this volume)reveal that mass-gravitational processes should be moreactive during fault scarp reactivation periods, throughthe relief rejuvenation, new exposed deposits, andearthquake activity. In addition, taking into accountthat (a) the sediment source is a fault scarp, (b) thesedimentary lobes and inter-lobe channels result fromexhumation of this scarp, (c) the Galicia Bank is anisolated seamount in the continental rise, and (d) thehinterland sources are at a great distance and it isunlikely to consider sea-level fluctuations as a control-ling factor in the sedimentary evolution of the SWGalicia Bank. This would be so, only when the tectonicpulse is dominant and obliterates any signal of sea-levelfluctuations. Nevertheless, taking into account that theGalicia Bank is b700 m, this control could be possible.In this sense, Rey et al. (2008-this volume) haverecognised the oceanographic changes occurred duringthe deposition of our recent most pelagites andhemiplagites based on magnetochemical proxies. Also,paleontological studies on hemipelagites and pelagiteswould be of great interest in order to paleoclimaticapproach.

Acknowledgements

The authors wish to thank the Commander Officerand crew of the BIO Hespérides for their help incollecting the data and the UTM-CSIC technicians for

their assistance during the cruise. This work wassupported by the Comisión de Coordinación Científica(MEC) Special Action, CICYT (MEC) ERGAP project(Ref. VEM 2003-20093-CO3) titled Identificación deriesgos geoambientales potenciales y su valoración enla zona de hundimiento del buque Prestige (Identifica-tion of Potential Geoenvironmental Risks in the SinkingZone of the Prestige, and their Assessment), and CICYT(MEC) SAGAS project (Ref. CTM2005-08071-C03-02/MAR-C03) titled The Gibraltar arc system: activegeodynamic processes in the south Iberian margins ofthe Spanish. Likewise, we would like to thank E.Gonthier and L. Carter for corrections and beneficialcomments on the manuscript.

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