Holocene evolution of a Languedocian lagoonal environment controlled by inherited coastal morphology...

Holocene evolution of a Languedocian lagoonal environment controlled byinherited coastal morphology (northern Gulf of Lions, France)

OLIVIER RAYNAL1, FRÉDÉRIC BOUCHETTE1,3, RAPHAËL CERTAIN2, PIERRE SABATIER1, JOHANNA LOFI1,MICHEL SERANNE1, LAURENT DEZILEAU1, LOUIS BRIQUEU1, PIERRE FERRER2 and THIERRY COURP2

Key-words. – Lagoonal environment, Wave-driven littoral, Transgression, Post-glacial deposits, Gulf of Lions, Holocene, Incisedvalley.

Abstract. – The Maguelone shore extends along the northern coast of the Gulf of Lions margin, West of the Rhône deltaand East of some high gradient coastal streams that have been providing most of the clastic sediments to the Gulf ofLions margin since the early Miocene. This 10 km wide area comprises an onshore small coastal watershed (15 kmlong) in low-lying carbonate hills, kilometer wide marshes, sandy beach and shoreface featuring local low sedimenta-tion. Deposit architecture in such a coastal zone records dynamics of incised valley fill under the influence of rivers andwave/current hydrodynamics in a microtidal environment during an eustatic cycle.

A detailed analysis of about 250 km of very high resolution seismic profiles, tens of cores and outcrops data re-vealed the evolution of the Maguelone coastal system from Late-Quaternary to present-day. It highlighted also dominantdenudation processes in the upstream catchments associated to the formation of incised valley seaward during Quater-nary. Combination of this inherited morphology together with hydrodynamics controlled the lagoonal environment evo-lution since the last transgression. In particular, the Maguelone shore is characterized by the formation of built-over-riaslagoonal systems and records an evolution from partially protected lagoon to isolated lagoon environment. These twostages of lagoon evolution correspond to distinct deposit environments. Correlation of fauna contents with deposit ge-ometry improves lagoonal environment models.

Evolution holocène de l’environnement lagunaire languedocien contrôlée par la morphologiecôtière héritée (Nord du golfe du Lion, France)

Mots-clés. – Environnement lagunaire, Littoral microtidal, Transgression, Dépôts post-glaciaires, Golfe du Lion, Holocène, Valléeincisée.

Résumé. – La zone côtière de Maguelone s’étend le long de la partie nord du golfe du Lion, à l’ouest du delta du Rhôned’où provient la quasi-totalité des sédiments détritiques de la marge depuis le Miocène. Cette zone de quelques dizainesde kilomètres de large comprend un petit bassin versant côtier (15 km de long) dans des collines de roches carbonatées,un ensemble d’étangs de taille kilométrique séparé du domaine marin par un cordon sableux étroit et une avant-côte quiprésente une faible sédimentation. L’architecture de dépôt de cette zone côtière enregistre la dynamique de remplissagede vallées incisées sous l’influence des rivières et de l’hydrodynamique microtidale durant un cycle eustatique.

L’analyse détaillée de plus de 250 km de profils sismiques THR, d’une dizaine de carottes et de données de ter-rain a permis de décrire l’évolution du système côtier de Maguelone du Quaternaire à nos jours. On met en évidenced’importants processus de dénudation associés à la formation des vallées incisées en milieu côtier durant le Quaternaire.L’effet combiné de cette morphologie héritée et de l’hydrodynamique contrôle l’évolution de l’environnement lagunairedepuis la dernière transgression. Plus précisément, le système côtier de Maguelone est caractérisé par la formation d’unsystème lagunaire précoce dans les rias (vallées incisées ennoyées) et par son évolution de lagunes partiellement proté-gées vers un environnement lagunaire confiné. D’un point de vue faunistique, ces deux étapes de l’évolution lagunairecorrespondent à des environnements de dépôt distincts. La confrontation des données faunistiques avec l’étude architec-turale apporte une résolution supplémentaire aux modèles d’évolution des environnements lagunaires.

INTRODUCTION

As for most sedimentary environments, climatic cycles con-trol sedimentary architecture and morphology of coastalzones at the geological time scale [Thorne and Swift, 1991;

Cattaneo and Steel, 2003; Vella et al., 2005 and Jouet et al.,2006]. Conversely, detailed stratigraphic analyses of littoraldeposits can reveal sea level changes, history of erosion/de-position and records of other processes under partial clima-tic control. In this general context, many studies deal with

Bull. Soc. géol. Fr., 2010, no 2

Bull. Soc. géol. Fr., 2010, t. 181, no 2, pp. 211-224

1. Geosciences-m, Université Montpellier II/CNRS, cc 60, Place Eugène Bataillon, 34095 Montpellier cedex 5, France. Tel.: +33 4 67 14 42 [email protected]. IMAGES, Université de Perpignan, 52 av. de Villeneuve, 66860 Perpignan cedex, France3. Institut de Mathématiques et de Modélisation de Montpellier, Université Montpellier II/CNRS, cc 51, Place Eugène Bataillon, 34095 Montpellier cedex,FranceManuscrit déposé le 15 octobre 2008; accepté après révision le 15 juin 2009.

the reconstruction of coastal architectures during the lastpost-glacial transgression and highstand to characterize therecent morphological and depositional dynamics [Vellaet al., 2005; Storms et al., 2008]. To meet this objective,some studies focus on coastal incised valleys formed duringprevious lowstand. Such inherited morphologies are privi-leged areas of sedimentation during sea-level rise [e.g.Clauzon et al., 1987; Clauzon, 1990; Boyd et al., 1998;Weber et al., 2004; Duvail et al., 2005 and Chaumillon etal., 2008]. They display high sedimentation rates and goodpreservation of deposits, and record also combined effectsof river-controlled processes and of wave/wind-driven hy-drodynamics.

The littoral of Gulf of Lions (northwestern Mediterra-nean Sea) is characterized by kilometre-wide lagoons sepa-rated from the sea by emerged sandy barriers a few tens ofmetres wide. This peculiar morphology results from awell-known process of shore construction by waves andcurrents in a microtidal environment [Barusseau et al.,1996; Certain et al., 2005b; Short, 1999]. The Magueloneshore extends between the Rhône delta to the East and highgradient coastal streams to the West. One striking feature ofthe Maguelone shore is the fact that a mosaic of numerousoutcrops of rocks ranging from Late Pliocene to Holoceneoccurs onshore [Alabouvette et al., 2003]. This shows thaterosion processes dominated the pre-Holocene landscapeformation, with possible formation of incised valleys; itsuggests that thicknesses of Holocene deposits are small.

In this paper, we analyse the architecture of Holocenecoastal deposits of the Maguelone shore thanks to very highresolution seismic profiles, together with short cores andoutcrop data. From this reconstruction, we determine theevolution of the Maguelone shore from Late Quaternary topresent-day. This paper highlights the existence of incisedvalleys under the present littoral zone and their role in thepreservation of Holocene deposits. The emphasis of thistopographic inheritance on the Holocene sediment dynam-ics is discussed. It is also highlighted how lagoons can formon the long term time scale.

GENERAL SETTING

Morphological setting

The Maguelone shore is a 10 km long littoral segment lo-cated along the Languedocian coast in the Gulf of Lions,closed to Montpellier city (fig. 1). Basically, the Magueloneshore is a wind/wave-dominated microtidal sandy system,characterized by several km wide lagoons isolated from theopen sea by a narrow beach barrier. Existing inlets betweenlagoons and open sea are artificial. At present time, lagoonsare less than 2 metres deep. At sea, the shoreface is an asso-ciation of unconsolidated sand deposits and rocky plateaus(fig. 1). These plateaus are made of continental, lacustrineor marine Pliocene formations, and continental conglomer-atic Pleistocene series [Alabouvette et al., 2003]. TheMaguelone shore includes also a small coastal watershedonshore, in low-lying carbonate hills made of Mesozoiclimestone, Cenozoic detritic deposits (conglomerate, car-bonate sandstone and clay), partly covered by a patchworkof discontinuous decametre-thick sedimentary formations

ranging from Pliocene to Holocene in age [Alabouvette etal., 2003].

Hydrodynamics and sediment fluxes

The Maguelone shore is microtidal, with a maximal tiderange of about 40 cm. Typical wave climate can be derivedfrom real-time wave measurements at Sète buoy station (lo-cated 6 km seaward Sète harbour, at a water depth of 50 m)since 1988. Major wave incidences are from southeast andsouth, with rare but highly energetic waves from southwest.Fair weather waves occur 88% a year (Hs=0.84 m;Tm=4.2 s) and storm conditions may result in waves of theorder of several metres in height. Wind forcing is extractedfrom Sète harbour and Montpellier airport wind stations.The major wind forcing on the Maguelone shore is Mistral(northeasterly wind) and Tramontane (northwesterly wind).Storm wave conditions are usually associated to southeast-erly or southerly winds. At the continental shelf scale, watercirculation is driven by wind/buoyancy and north-western-most Mediterranean circulation (locally termed NorthernCurrent), well evidenced by measurements and simulations[Millot, 1990; and subsequent litterature]. To the nearshore,wave incidence with respect to coastline orientation definesa mean alongshore drift oriented southwestward, that inverts


212 RAYNAL O. et al.

FIG. 1. – (A) Simplified geological map of the study area. Geological dataare taken from the BRGM geological maps of Sète and Montpellier. M-C.Mesozoic to Cenozoic formations. Pl. Pliocene. Q. Quaternary. (B) Loca-tion map of data showing the location of the VHR seismic profiles and co-res. The heavy lines refer to the illustrations cited in the text. Stars showcore location.FIG. 1. – (A) Carte géologique simplifiée de la zone d'étude d'après lescartes géologiques 1/50 000e du BRGM de Sète et Montpellier. M-C. For-mations mésozoïques à cénozoïques. Pl. Pliocène. Q. Quaternaire. (B)Carte de localisation des données de sismique THR et des carottes sédi-mentaires. Les traits et les étoiles foncés correspondent aux profils sismi-ques et aux carottes cités dans le texte.

during storms from south or southwest. In addition,wave-driven currents and classical wind/buoyancy-drivencirculation interact at the inner shelf scale [Denamiel, 2006]and may generate at the coast alongshore drifts orientedsouthwestward alternately with northeastward ones, de-pending on the wave and wind combined forcing condi-tions. The Maguelone shore shows typical morphologicalsand features (sand deposition and erosion in the lee ofcoastal defence structures) that demonstrate that the netlongshore sediment drift is southwestwards, except in theeastern Maguelone shore where some morphological struc-tures argue for a northeastward drift. The change in orienta-tion of the alongshore drift is not well located.

The river Mosson (15 km long) drains a small catch-ment area (370 km2), and supplies fine sediment (silt andclay) to the Maguelone lagoons during flash flood eventsmainly. Mosson River average flow is 1.2 m3/s but hasreached 258 m3/s during the December 3rd 2003 flash floodevent [DIREN, 2009]. Additionally, a longer coastal rivernamed Lez (~30 km long) supplies sediment to theshoreface, eastern Maguelone shore. The main sedimentflux [Certain, 2002; Pont et al., 2002] comes from theRhône river located 50 km to the East.

Gulf of Lions geological background

In the Gulf of Lions, the Pliocene began with the floodingof the Mediterranean basin at the end of the Messinian sa-linity crisis [Hsü et al., 1973], termed the Zanclean trans-gression. Messinian canyons, formed during fall of sea levelthat started around 5-6 Ma [Gautier et al., 1994; Krijgsmanet al., 1999 and Lofi, 2002], were flooded and formed theEarly Pliocene rias. Several studies show that the sedimen-tary filling of incised valleys correspond to Gilbert delta[Clauzon et al., 1987; Clauzon, 1990 and Duvail et al.,2005]. At the top of these formations Early Pliocene in age,prograding sedimentary wedges quickly migrated seawardand covered the Messinian erosion surface. Thanks to seis-mic profile analysis, Lofi et al. [2003] proposed a model ofthree distinct prograding wedges Early Pliocene, MiddlePliocene and Late Pliocene/Quaternary in age. The most re-cent wedge is more than 1000 m thick in the outer-shelf. Ata higher resolution, the upper part of this wedge containsseveral regional scale prograding units, separated by ero-sion surfaces [Tesson et al., 1990; Tesson and Gensous,1998 and Rabineau et al., 2006]. These units were inter-preted as lowstand prograding wedges that took place dur-ing successive sea-level falls of Pleistocene glacio-eustaticcycles [Posamentier et al., 1992; Jouet et al., 2006]. On-shore, Duvail et al. [2001] and Alabouvette et al. [2003] ob-served imbricated terrace systems along the mainRoussillon and Languedocian rivers. Their formation islinked to Pleistocene glaciation cycles. During the lastdeglacial stage, a Rhône subaqueous delta occurred in themiddle/inner shelf, precisely from 15000 to 10500 cal. yrB.P. These deposits correspond to a major transgressivetract on the shelf [Berné et al., 2007]. The present studyarea corresponds to the coastal zone and links onshore envi-ronments to the continental shelf.

METHODS AND DATA

Datasets acquired for the present study are presented in fig-ure 1B. They consist of: 1) 250 km of very high resolution(VHR) seismic data acquired from 2003 to 2007 offshoreand in lagoons during CALAMARs and BEACHMED-e Eu-ropean cruises, 2) 1 to 15 m long cores collected in theframework of the projects PROGELAC, ECLICA and AL-LIANCE (2003). Numerous samples were extracted for 14Cdating.

Coastal and lagoonal VHR seismic profiles

At sea and in lagoons, seismic profiles were acquired withan IKB-Seistec boomer (CALAMARs Survey). In addition,a surface tow boomer from applied acoustics was used atsea exclusively (BEACHMED-e, IX-Survey). The IKB-Seistec boomer device is a 2 m long catamaran character-ized by a horizontal offset of 0.5 m between the source(boomer plate) and a line-in-cone receiver. It is welladapted to shallow water environments. It was used withfrequencies ranging from 4 kHz to 9 kHz and a signal en-ergy from 50 to 200 J. Seismic data were acquired with theDelph 2.3 software. The applied acoustic device is com-posed of a 1500 J source mounted on a catamaran and of asingle-channel streamer. Seismic data were acquired withan Octopus 360 signal processor and a Coda DA200 digitalrecording system.

The seismic data were converted in SEG-Y format andprocessed with Bash scripts (www.gladys-littoral.org) onthe basis of Seismic Unix tools [Cohen and Stockwell,2001] together with GMT [Akima, 1979; Wessel and Smith,1998].

Lack of seismic data in Arnel lagoon, north MagueloneCathedrale (fig. 1B) is due to a water depth less than 20 cm.

Identification of seismic units and their boundaries re-lies on the analysis of seismic data following a classicalseismic stratigraphic method (in terms of reflector termina-tion and configurations) [Mitchum and Vail, 1977].

Cores and datations

Numerous cores were acquired in the present-dayMaguelone shore. Six cores were used in this study:MAG-1, TOTH-1, M5-1, M5-2, AR06, PB06 (fig. 1B). Thelongest cores (MAG-1 and TOTH-1) were collected from thebeach barrier and the Mosson delta by a Triplex method.This method requires a steel corer tube including two dis-tinct sleeves. During coring, the rotation of the outer sleeveis dissociated from that of the internal sleeve. This drasti-cally reduces the deformation of the sediment contained inthe inner sleeve and maximizes the amount of retrieved ma-terial (about 97%). Cores AR06 and PB06, about 3 m and7.80 m long respectively, was extracted with the hammercoring platform of University of Savoie (Chambery). Shortcores M5-1 and M5-2 were extracted manually with PVCtubes.

In the laboratory, cores were split, photographed,logged in details (measurement of physical proxies, deter-mination of biogenic sedimentary structures and of verticalfacies succession with a resolution of one centimetre). Incore PB06, macro-fauna content analyses were performedon 2 cm long sections. To study mollusc shells, sampleswere sieved at 1 mm and the number of individuals of all


HOLOCENE EVOLUTION OF A LANGUEDOCIAN LAGOONAL ENVIRONMENT 213

species was counted (every 2 cm). The most representativemolluscs of lagoonal environments are Hydrobia acuta,Abra ovata, Cerastoderma glaucum. Those typical of ma-rine hard substrate environment are Bittium recticulatumand Rissoa ventricosa [Dezileau et al., 2005; Sabatier et al.,2008].

14C analyses in the cores MAG-1, TOTH-1 and AR06(table I) were conducted at the “Laboratoire de Mesure 14C”at Saclay (LM14C) in the framework of the ARTEMIS pro-ject. The dating M5-145 in the core M5-1 was conducted atthe Beta Analytic Radiocarbon Dating Laboratory at Miamiin 2004. 14C age calibrations were computed with the Calib5.0.2 software [Hughen et al., 2004] at two standard devia-tions. Reservoir age in lagoon environments of the Mediter-ranean region is high due to a strong continental carboncontribution [Siani et al., 2000 and Zoppi et al., 2001]. Thereservoir age used in this study has been estimated bySabatier et al. [2009] at about 943 +/– 25 years, by extrapo-lating the reservoir age measured at the seabed and by cor-relation with Pb210 data. In marine facies, reservoir age usedfor calibration is 618 +/– 30 years.

RESULTS

Seismic units

Basement Upl and regional erosional surface

Acoustic basement Upl is the deepest unit that was observedin the study area. The base of this unit is not observed, nei-ther on seismic data (fig. 2 and fig. 3) nor in the deepestcore. Where the seismic signal is good, Upl displays thickseismic facies including continuous and very high-ampli-tude reflections (fig. 4C). These reflections present a south-eastward gentle dip on cross-shore sections and alow-amplitude folding on alongshore sections (fig. 3B). Insome cases, Upl consists of transparent or chaotic reflec-tions, with some undulating sub-parallel discontinuoushigh-amplitude reflections (fig. 3A). These facies character-ize seismic zones where there is no major reflection(fig. 4D) and where seismic signal is blurred (fig. 4E) re-spectively. Upl is separated from overlying formation U1 byan erosional surface, illustrated by significant seismic fa-cies changes and truncated reflections. Where Upl unit isoverlaid by any other units (U2, U3L, U3F), its top corre-sponds to a Regional Erosional Surface (= RES), as testified

by truncated reflections (fig. 3). The RES forms a highlyuneven surface that fits locally with the present-dayseafloor (fig. 3B). To the east, the RES passes to the marinePalavas plateau and to the marine Maguelone plateau(fig. 3A). To the west, it coincides with the Aresquiers ma-rine plateau. The RES displays two major incisions 10 to15 m deep and 200 m long. The main directions of these in-cisions are roughly perpendicular to the present-day coast-line. One of the incisions is located off the city of Palavas,and the other is off the Vic lagoon (fig. 3B).

Unit U1

In this paper, the seismic unit U1 groups all sub-unitsflanked by Upl and the RES (fig. 2 and fig. 3A). Unit U1infills the highly irregular top of Upl (fig. 2A and fig. 3A).It forms hundreds of meters long and meters thick bodies oflimited lateral extension. These deposits display chaoticseismic facies mainly with some low-amplitude reflections.This facies corresponds to disorganized and discontinuousreflections (fig. 4E). Figures 2B and 2C show that, in la-goon area, unit U1 is composed of three distinct sub-unitstermed U1-1, U1-2 and U1-3. These sub-units display dif-ferent seismic facies and are separated by erosional sur-faces. The first sub-unit, U1-1, is characterized bytransparent or chaotic reflections with some irregular anddiscontinuous high-amplitude reflections which formtrough. The top of U1-1 is an uneven erosional surface as il-lustrated by truncated reflections. U1-2 consists of parallelfacies (fig. 4A). It fills depressions and presents some drap-ing reflections at the base. The top of U1-2 corresponds to aplane surface at the seismic profile scale. U1-3 consists ofsigmoïd clinoform seismic facies as illustrated by downlapreflections on the base surface. A 3D detailed analysis ofU1-3 on all seismic profiles gives evidence of a fandelta-like geometry prograding south-westward (fig. 5A).U1-3 is exclusively located in the north of Vic lagoon. Inthe same area, another smaller fan delta progrades south-eastward. The top of unit U1 corresponds to the RES sur-face. The RES surface is diachronic and corresponds to thetop of U1 and Upl.

Unit U2

The base of unit U2 corresponds to the RES everywhere itwas observed. U2 fills paleo-topographic depressions of theRES. Raynal et al. [2009] show that U2 consists in stackedprograding sets (U2-1, U2-2 and U2-3, fig. 3B) that display



TABLE I. – 14C datations from sediment cores in marine and lagoonaldomain. 14C age calibrations were computed with the Calib 5.0.2software [Hughen et al., 2004] at two standard deviations. In marinefacies, reservoir age (= R) used for calibration is 618 +/- 30 yr. In la-goonal facies, reservoir age used is 943 +/- 25 yr [Sabatier et al.,2008]. Depth WRT present-day s.l = Depth with respect to pre-sent-day mean sea-level.TABL. I. – Datations 14C effectuées sur les carottes en domaine marinet lagunaire. Les âges sont calibrés avec le logiciel Calib 5.0.2 [Hug-hen et al., 2004] avec 2 standards de déviations. Dans les faciès ma-rins, l'âge réservoir (R) utilisé pour la calibration est de 618 +/- 30ans. Dans les faciès lagunaires, l'âge réservoir utilisé est de 943 +/-25 ans [Sabatier et al., 2008]. Depth WRT present-day s.l = profon-deur par rapport au niveau marin actuel.

internal erosion surfaces arguing for alternated episodes oferosion and progradation. The southwestward kilometerlong progradation is roughly consistent with that of thepresent day coastline. The top of U2 corresponds to asmooth erosional surface, which fits to the present dayseafloor.

Unit U3F

The base of this seismic unit corresponds to the RES. U3Fis located exclusively on the main incision in Vic lagoon(fig. 2B). This incision is tens of m wide (up to 200 m) anddisplays meanders (fig. 5). This incised valley presents amean southwestward orientation. To the base, U3F ismainly aggradational with draping parallel facies. The up-per part of U3F displays sigmoïd clinoform reflections inopposite directions (fig. 2B). The top of this seismic unit isglobally flat.

Unit U3L

Unit U3L was observed both at sea and in the present-daylagoons. It occurs on the RES surface and was not observedon U2. However, seismic profiles do not provide data belowthe present-day emerged barred beach where such geometrymay have occurred. The thickness of unit U3L is highlyvariable, as testified by the important vertical shifts of theRES surface. U3L shows draping parallel seismic facies(fig. 4A) characterized by parallel and roughly horizontalhigh-amplitude reflections. Where the underlying RES sur-face is uneven, basal reflections in U3L present onlap ge-ometry (fig. 2A and 2C). In the lagoon, the top of unit U3Lis the water/sediment interface. The centre of Vic lagoonpresents a large area of biogenic gas release that preventsseismic imaging of the lagoon-fill in that place (fig. 2). Atsea, the top of U3L is truncated by a smooth erosion surfacedisplaying a seaward dipping. Locally, this erosion surfacemerges with the seafloor.



FIG. 2. – Interpreted VHR seismic profiles CAIII VIC-07 (A), CAIII VIC-35 (B) and CAIII VIC-36 (C), showing global units architecture in the lagoons.RES (Regional Erosional Surface) corresponds to the top of Upl or U1. Seismic data in the centre of lagoons shows biogenic gas release.FIG. 2. – Profils sismiques THR interprétés, CAIII VIC-07 (A), CAIII VIC-35 (B) et CAIII VIC-36 (C), montrant l'ensemble des unités observées en la-gune. La RES (Regional Erosional Surface) correspond au toit de l'unité Upl ou U1. Le centre des lagunes est caractérisé par la présence de gaz biogé-nique.

Unit U4

The base of unit U4 is observed seaward and correspondseither to a smooth erosion surface on U3L or locally to theRES surface. U4 is characterized by transparent or chaoticfacies with few low-amplitude reflections (fig. 4D and 4E).Cross-shore profiles such as Maguelone-5 (fig. 3A) showthat the seaward extension of U4 is limited to the pres-ent-day shoreface, about one kilometer away from theshoreline. The reflections within U4 show a moderate dip-ping oriented seaward, roughly parallel to the present-daymean nearshore slope. The top of U4 corresponds to thepresent-day seabottom.

Cores

Three main facies successions are distinguished in thecores, corresponding to the main sub-environments that

compose the study area, i.e. from North to South, the la-goon, the beach-barrier and the shoreface (fig. 6).

Back-barrier facies succession

The typical succession observed in back-barrier areas be-gins at the base with a coarse polygenic conglomerate com-posed of rounded elements of carbonate lime mud, quartzand yellow silt (fig. 6). In core TOTH-1, this conglomerateis older than 7665 yr. In core AR06, from 3.32 to 3.40 m,this coarse deposit consists of limestone and quartz clastsand some marine bioclasts like Bittium reticulatum andRissoa sp., dated at 5800 +/– 105 cal yr B.P. This deposit isalso observed at the base of PB06. Above the coarse con-glomerate or marine bioclastic sand, grey uniform lagoonalmud with thin silty and sandy intervals occurs. Thickness ofthe lagoonal mud intervals is variable. Maximum thicknessis observed in core TOTH-1, reaching 17 m (fig. 6).



FIG. 4. – Seismic facies observed in very high resolution seismics in the study area. (A) Draping parallel facies. (B) Sigmoïd clinoform facies. (C) Thickfacies. (D) Transparent sandy facies. (E) Chaotic facies. All these facies can be observed in seismic profiles of figure 2 and figure 3.FIG. 4. – Faciès sismiques observés sur l'ensemble des profils THR de la zone d'étude. (A) faciès drapant parallèle. (B) faciès à sigmoïdes. (C) faciès à ré-flecteurs épais. (D) faciès sableux transparent. (E) faciès chaotique.

FIG. 3. – Interpreted VHR seismic profiles Maguelone-5 (A) and IX-Survey-39 (B), showing global units architecture in the shoreface. RES is a RegionalErosional Surface, which corresponds to the top of Upl or U1. Localization of cores M5-1 and M5-2 is reported on Maguelone-5 profile.FIG. 3. – Profils sismiques THR interprétés, Maguelone-5 (A) et IX-Survey-39 (B), montrant l'ensemble des unités observées à l'avant-côte. La RES (Re-gional Erosional Surface) correspond au toit de l'unité Upl ou U1. La localisation des carottes M5-1 et M5-2 est reportée sur le profil Maguelone-5.

Radiocarbon data testify that lagoonal deposits are Holo-cene in age. The base of those deposits was dated at 7665+/– 110 cal yr B.P. at 20 m of depth in TOTH-1 and at 5695+/– 145 cal yr B.P. at 3.32 m of depth in AR06. Conse-quently, the base of lagoonal deposits is not isochron. Thetop of lagoonal deposits corresponds to the present lagoonfloor. In core TOTH-1, located in the Mosson delta (fig.1B), lagoonal deposits are overlain by deltaic deposits(from 1.20 to 3 m of depth). The top of this core corre-sponds to an embankment.

Present beach barrier facies succession

The typical facies succession observed in the present beachbarrier area is described in core MAG-1. This core is locatedon the sandy beach barrier close to Maguelone Cathedrale(fig. 1A). From the base to 12.20 m, the core displays sandmixed with coarse polygenic conglomerate. This conglom-erate is the same as that observed at the base of coresTOTH-1, AR06 and PB06. According to radiocarbon data,these deposits are older than 45600 years (fig. 6). From12.20 to 9 m of depth, green, grey or yellow ochre mud andsilt, with carbonate concretion occur. All these layers arepoor in organic matter. The top of the carbonate level corre-sponds to an erosional surface. A bioclastic marine sandbed, dated at 5520 +/– 115 cal yr B.P., takes place on thissurface. At 8.50 m, the first lagoonal deposits appear. From8.50 to 5 m, lagoonal facies are intercalated with marinesands. At 7.30 m, this deposit is dated at 5590 +/– 110 calyr B.P. At 5 m, lagoonal muds are topped by an erosionalsurface covered by sands. This sand is composed of quartz,chlorite, biotite and includes up to 15% of bioclastic con-tent. At the base of this uppermost sandy interval, sedi-ments are dated at 1745 +/– 120 cal yr B.P.

Shoreface

The shoreface area is limited by the present sandy barrier tothe North and by marine plateaus to the South (fig. 1A). Atthe base, short cores M5-1 and M5-2 display a grey homo-geneous mud rich in organic matter. Presence of 5 to 10% ofbioclastic content argues for lagoonal deposits with marineinfluence. Most of these sediments consist of mud, mixedwith silt or fine sand, and present marine bioclasts such asBittium reticulatum, Rissoa sp. and Cerastoderma glaucum.Usually, these deposits are interbedded with marine sand in-cluding open sea bioclasts like Turritella, Pecten sp. andBittium reticulatum (e.g. from 116 to 118 cm, and from 129to 136 cm in core M5-1). In core M5-1, lagoonal depos-its were dated at 9450 +/– 460 cal yr B.P. This 14C datingof lagoon deposits with marine influence shows contamina-tion, according to the depth of the dated level and the globaleustatic curve. Contamination is in agreement with marinesilt and sand supply in the lagoon. This dating gives a maxi-mal age but indicates that these lagoonal deposits, locatedoff the present-day sandy barrier, are older. A layer offine-grained detritic sand covers the top of the lagoonalmuds. Locally, this layer is mixed (M5-1) or interbedded(M5-2) with cm-long rolled pebbles. This sandy materialoriginates from the present-day barrier.

Fauna contents

Lithostratigraphy and macropaleontology are powerful ap-proaches to highlight the complexity of wetland environ-ments [Mazzini et al., 1999; Amorosi et al., 2005; RicciLucchi et al., 2006]. By this way, paleoenvironmental evo-lution of lagoons in relation to their closure by sandy bar-rier can be determined.

From a sedimentological point of view, the study ofcore PB06 (fig. 6) suggests a relative homogeneous la-goonal depositional environement from 744 cm of depth tothe top. This deposit is characterized by grey clays and siltswith intercalated sand layers (less than 10% of the total sed-iment) interpreted as paleostorm events [Sabatier et al.,2008]. However, the high-resolution analysis performed onfauna indicates a significant change (fig. 7), marked by aclear shift in mollusc population at around 190-170 cm (i.e.about 731 +/– 87 cal yr B.P.). This shift corresponds to anincrease of typical lagoonal species (Hydrobia acuta)whereas the number of marine species (Bittiumrecticulatum) decreases. This argues that a change in envi-ronmental conditions (salinity, temperature, nutriments, andoxygenation) occurred at about 700 cal yr B.P.: thedepositional environment evolved from a lagoonal with ma-rine influences to an isolated lagoon. This change dates theclosure of the lagoon by the sandy barrier.

Sedimentary units

Substrate of Holocene deposits

In this paper, the substrate of Holocene deposits groups theseismic units located below the RES (Upl and U1; fig. 8).To the west of Vic lagoon, the top of Upl is directly corre-lated with Pliocene onshore outcrops, as testified byAlabouvette et al. [2003] (fig. 1A). These Pliocene outcropsare represented by lacustrine white chalky limestone or al-tered white chalky limestone nodules in an ocher to red silty



Fig. 5. – (A) Isopach map of the U1-3 sub-unit. This map shows two fandeltas in the northern area of Vic lagoon. The main fan delta, km-long andwith a maximal thickness of 4 m, displays southwestward progradation (ar-row). To the east, the smaller delta progrades southeastward. (B) Isopachmap of the U3F unit, showing partially 200 m-wide channel meander. Seis-mic profiles CAIII VIC-35 and CAIII VIC-36 presented in the figure 2 arelocated on these maps with the hard lines.Fig. 5. – (A) Carte isopaque de la sous-unité U1-3. Cette carte montredeux lobes deltaïques dans la partie nord de l'étang de Vic. Le principal,de longueur kilométrique et de 4 mètres d'épaisseur maximale, progradevers le sud-ouest (flèche). A l'est, le delta secondaire prograde vers lesud-est. (B) Carte isopaque de l'unité U3F, montrant une partie d'un che-nal méandriforme de 200 mètres de large. Les profils sismiques CAIIIVIC-35 et CAIII VIC-36 illustrés sur la figure 2 sont localisés sur ces car-tes en traits foncés.

matrix. The gentle southeastward dip of Upl (fig. 3A) isconsistent with the Pliocene strata dip in outcrops. Adifferencial subsidence induced by the sedimentary and hy-drostatic loading of the shelf [Tesson and Allen, 1995] canexplain this regional dip. Where unit U1 can be extendedonshore, to the north of Vic lagoon, a comparison with theoutcrops demonstrates that U1 is made of terrigenous siltsand conglomerates with clasts of Mesozoic and Cenozoiclimestones as well as quartz and biotites. This facies is inagreement with observation of the marine Maguelone pla-teau, where U1 is composed of conglomerates and sand-stones. Unit U1 is interpreted as Pleistocene continentaldeposits. Core MAG-1 is correlated with the offshore seis-mic by geometrical projection. The interval dated at morethan 45600 yr B.P. in cores MAG-1 (fig. 6) may correspondto U1 or Upl. In Vic lagoon, U1 is composed by threesub-units (U1-1, U1-2 and U1-3), which correspond to de-posits of coastal alluvial plain, as testified by the chan-nel-levee system in U1-1 and the southwestward progradingbodies in U1-3.

Marine sand deposits

On the RES, at the base of the Holocene lagoonal deposits(fig. 8), a 10 cm thick sand interval was described in cores,but not observed as a seismic unit (cores AR06 and MAG-1,

fig. 6). This discontinuous interval corresponds to bioclasticsand including Pecten sp., Bittium reticulatum, Cerastodermaglaucum, Rissoa sp., Loripes sp. and Hydrobia acuta. Thesemarine deposits are dated at 5520 +/– 115 cal yr B.P. in coreMAG-1 and 5800 +/– 105 cal yr B.P. in core AR06.

Prograding sand bodies

Detailed study of geometries and facies in Unit U2 (fig. 3)shows that this unit consists in several stacked bodies ofmarine sandy deposits [Raynal et al., 2009]. In addition,U2-1, U2-2 and U2-3 bodies reveal the existence of 10 mhigh sets that fill up former depressions and prograde to-ward the southwest over several kilometres. U2 consists ofstacked prograding sets that display internal erosional sur-faces, arguing for alternated episodes of erosion andprogradation. Raynal et al. [2009] interpret this formation aspaleo-sand spit prograding alongshore (i.e. southwestwards).To explain the sand spit formation, the authors refer to a sedi-ment transfer from the Rhône delta by alongshore hydrody-namics during the last stage of Holocene transgression.

Alluvial meander filling

Unit U3F, observed in the northern Vic lagoon, correspondsto the filling of an incised valley (fig. 8). Two kinds of



FIG. 6. – North-South transect of sedimentary successions and 14C dating established from cores [modified after Raynal et al., 2009]. The cores are locatedin land (TOTH-1), in the present day lagoon (AR06 and PB06), in the present day sand barrier (MAG-1) and in the shoreface (M5-1 and Core M5-2), andallow highlighting: 1) the uneven inherited morphology and 2) the Holocene littoral retrogradation on lagoonal deposits.FIG. 6. – Transect Nord-Sud des logs et des datations 14C réalisés sur les carottes sédimentaires [modifiée d'après Raynal et al., 2009]. L'ensemble de ceslogs localisés à terre (TOTH-1), dans la lagune (AR06 et PB06), sur la barrière sableuse actuelle (MAG-1) et en mer (M5-1 et Core M5-2), met en évi-dence : 1) la forte irrégularité de la morphologie holocène héritée ; 2) la rétrogradation du système littoral au cours de l'Holocène.

filling were distinguished. At the base, the filling is charac-terized by a regular aggradation. Where the incision en-larges, in the upper part, the filling consists of lateralaccretion, perpendicular to the main direction of the inci-sion (fig. 2B). The isopach map of U3F (fig. 5B) shows me-ander geometry in this unit interpreted as the filling of analluvial incised valley. The incision is located southward adepression oriented South-North between Vic lagoon andthe Mosson river.

Lagoonal deposits

Correlations of seismic profiles and cores show that U3Lunit consists of clays accumulated in a low energy environ-ment and interpreted as lagoonal deposits. These lagoonaldeposits display a highly variable thickness (fig. 8). Theoldest lagoonal muds were dated at 7500 yr B.P. (table I).Two types of lagoonal deposits are distinguished, (1) la-goonal deposits formed of grey uniform muds with thinsilty and sandy intervals (cores TOTH-1, AR06, PB06 andMAG-1, fig. 6). They correspond to a lagoonal environmentwith intermittent connexion to marine environment duringpaleostorms events [Sabatier et al., 2008]; (2) lagoonal sed-iments made of mud mixed with silt or fine grained sandand including some marine bioclasts such as Bittiumreticulatum, Cerastoderma glaucum and Rissoa sp. (M5-1and M5-2, fig. 6). These deposits reflect a lagoon environ-ment with important marine influence. At the edge of pres-ent-day lagoons, deposits are characterized by mixed faciescomposed of lagoonal muds, lithoclasts from the local sub-strate facies, bioclasts and vegetal fragments.

Sand barrier

Seismic unit U4, characterized by transparent or chaotic fa-cies with few low-amplitude reflections, is correlated withthe last littoral sand prism. These deposits show an externalmeter high and 10 m wide sand bar that forms one of themain morphological features of the present-day nearshorezone.

DISCUSSION

Sand barrier retrogradation

The geometrical study of the Maguelone shore highlightsthe evolution of the barrier, which closes the lagoonal envi-ronment. During an early stage, the barrier corresponds tosand spits evolving as a narrow sandy beach retrogradingbarrier. This change and more specifically the retrograda-tion are the result of balance between sea-level rise, hydro-dynamics and sediment supply. The destabilization of thesand spit system and the retrogradation of the sandy barrierwere controlled by accommodation space during sea-levelrise [Cattaneo and Steel, 2003]. This accommodation de-pends on sediment supply and sea-level rising rate (with notectonic and subsidence). From about 7500 to 5500 yr B.P.,the rate of eustatic rise is considered as constant, with avalue of 3.3 mm/yr in average. During this period, creationof accommodation is counterbalanced by the formation andgrowth of sand spits, as testified by the deposition of la-goonal facies (fig. 9). From 5500 yr B.P., the rate ofsea-level rise has decreased to 2.4 mm/yr. Accommodation

becoming lower, alongshore-transported sediments mi-grated to the spit head preferentially. As a result, the sandspit, except at its head, corresponds since that moment to aby-pass or erosional zone [Ollerhead and Davidson-Arnott,1995]. The low to non-existent direct sediment supply fromlocal rivers, combined with important wave erosion, inducethe retrogradation of the sand barrier. This retrogradationoccurs on previously lagoonal deposits and the subsequentconstruction of unit U4 (fig. 8), as testified by the base ofthe sandy barrier, which corresponds to a wave ravinementsurface (fig. 9) [Cattaneo and Steel, 2003]. The sandy bar-rier retrogradation has been facilitated by the presence offlat and smooth lagoonal deposits. With such conditions,the sandy barrier retrogradation is enhanced, in spite oflower sea-level rising rate [Roy et al., 1994]. This processof sandy barrier retrogradation during a low rate ofsea-level rise is in agreement with other regional studiessuch as in the Thau lagoon [Barusseau et al., 1996; Ferrer etal., 2010].



FIG. 7. – Evolution of species amounts of Hydrobia acuta (lagoonal specie)and Bittium recticulatum (marine specie) in lagoonal deposits (core PB06).This evolution is characterized by a clear increase of Hydrobia acuta anddecrease of Bittium recticulatum around 731 +/- 87 cal yr B.P. This shift isinterpreted to be the result of environmental condition change (salinity,temperature, nutriments, and oxygenation).FIG. 7. – Evolution de la quantité des espèces Hydrobia acuta (espèce lagu-naire) et Bittium recticulatum (espèce marine) dans les dépôts lagunaires(carotte PB06). Cette évolution est caractérisée par une forte augmenta-tion de l'espèce Hydrobia acuta et une forte diminution de l'espèce Bittiumrecticulatum autour de 731 +/- 87 cal B.P. Cette variation brutale est in-terprétée comme le résultat d’un changement des conditions environne-mentales (salinité, température, nutriments, oxygénation).

At present, a landward displacement of the sand barrieris observed, induced by wave erosion of the beach barrierand sediment transport by overwash processes toward thelagoon [Honeycutt and Krantz, 2002; Buynevich et al.,2004; Certain et al., 2005a; Certain et al., 2005b;Buynevich et al., 2007 and Sabatier et al., 2008].

Holocene systems tract

The Holocene sedimentary succession is differently pre-served into the incised valleys and outside of the valleys(fig. 10), highlighting the influence of incised valleys on thegeometry and chronology of coastal systems tracts.

The RES (Regional Erosional Surface) topography isinherited from sea-level fall during successive glacial

periods when the coastal rivers of Maguelone shore(Mosson and Lez rivers) formed coastal incised valleys (fig.3B and fig. 8B). The RES corresponds as well to the base ofthe Holocene coastal system tracts, and thus is the Holocenetransgressive surface. Therefore the RES is a polygenic ero-sional surface, the last stage of erosion corresponding towave action during the Holocene transgression.

Transgressive System Tract (TST)

The TST is composed of deposits that give evidence for var-ious environments.

The first transgressive deposit corresponds to a 10 cmthick discontinuous marine sand interval onto the RES(cores TOTH-1, AR06, PB06 and MAG-1, fig. 6). The



FIG. 8. – (A) Compilation of sea-level changes data showing the last glacial cycle (left) and the last deglacial evolution (right). The three dashed-lines cor-respond to Mediterranean sea-level studies. Others correspond to studies of global sea-level changes. (B) Interpreted cross-shore and alongshore sectionsin lagoons and Maguelone area. These north-south and west-east sections displays correlation of cores TOTH-1, AR06, MAG-1 and M5-1 (fig. 6), seismicprofiles CAIII VIC-35, Maguelone-5, IX-Survey-07 and IX-Survey-39 (fig. 2 and fig. 3), reported to the present sea-level. Location of cores is indicated byvertical arrows on the section. 14C dating of each core are drawn on this section. Depth WRT present-day s.l = Depth with respect to present-day meansea-level.FIG. 8. – (A) Compilation de données des variations du niveau marin au cours du dernier cycle glaciaire (gauche) et au cours de la dernière déglaciation(droite). Les trois courbes en pointillés correspondent aux études du niveau marin en Méditerranée. Les autres courbes correspondent aux études du ni-veau marin à l'échelle mondiale. (B) Coupes interprétatives cross-shore et longshore en lagune et dans la zone de Maguelone. Ces coupes correspondent àla corrélation des carottes TOTH-1, AR06, MAG-1 et M5-1 (fig. 6), des profils sismiques CAIII VIC-35, Maguelone-5, IX-Survey-07 et IX-Survey-39(fig. 2 et fig. 3), par rapport au niveau marin actuel. La localisation des carottes sur les coupes, est indiquée par les flèches verticales. Les datations 14Csont reportées sur chaque carotte. Depth WRT present-day s.l = profondeur par rapport au niveau marin moyen actuel.

northernmost places where such marine deposits are ob-served, on the RES, at the base of unit U3L, are locatedalong the northern edge of the present-day lagoons, belowthe Mosson delta (core TOTH-1). Comparison betweensea-level curves (fig. 8A) and 14C dating of bioclastic ma-rine sand (table I) is in agreement with this interpretation.The dating fits with Mediterranean [Labeyrie et al., 1976;Aloïsi et al., 1978; Dubar and Anthony, 1995] and globalsea-level curves [Fairbanks, 1989; Bard et al., 1990;Chappell and Polach, 1991; Edwards et al., 1993; Bard etal., 1996; Hanebuth et al., 2000 and Cutler et al., 2003].Sabatier et al. [2008] described as well in anotherpalavasian lagoon, at 8 m depth below present sea-level,this transgressive sand interval dated it at 7850 +/– 125 calyr B.P.. This age demonstrates that sea-level was at this mo-ment at 8 m maximum below the present level. Due to thetopography of the RES, the sea invaded the studied zone,reaching the location of the present Mosson delta. Duringthe Holocene transgression, the Mosson and Lez incisedvalleys formed rias, and the coastline was very irregular,with successive gulfs and rocky headlands made of Plioceneor Pleistocene material.

The next transgressive deposits consist of a tract of syn-chronous deposits observed in incised valley filling (fig. 10).They are composed of marine sand spit (unit U2), lagoonaldeposits (unit U3L) and retrograding fluvial deposits (unitU3F). This incised valley fill is in agreement with the modelof Zaitlin et al. [1994]. The progradation toward the south-west of sand spits induces the infill of depressions, includingthe incised valleys, and the closure of the coastal environ-ment that transformed progressively as a lagoon. The earlylagoon muds were observed in the valleys. They are dated at7665 +/– 110 cal yr B.P. (core TOTH-1). The alluvial chan-nel filling (unit U3F) was observed exclusively in theMosson incised valley (fig. 2B and fig. 8).

Highstand System Tract (HST)

As previously explained, during the highstand the combina-tion between high-energy hydrodynamics and low sedimentsupply, causes the retrogradation of the sandy barrier (unitU4). During the retrogradation, lagoonal deposits continuedto fill the back-barrier area. The retrogradation surface ofthe sandy barrier corresponds to a wave ravinement surface

(wRs) after Cattaneo and Steel [2003]. During this stage,wave action erodes the sand spits so that rocky plateau(Pliocene and Pleistocene) and previously deposited la-goonal muds outcrop off the present-day barrier (fig. 3Aand fig. 10). In the landward edges of the lagoon, fluvial de-posits prograde on lagoonal mud (fig. 6 and fig. 10). As aconsequence of the barrier retrogradation and deltaicprogradation, the size of the lagoon has decreased continu-ously from the early highstand.

Because the transition between the TST and the HSTappears to be very progressive, no maximum flooding sur-face (MFS) was identified.

Isolated and protected lagoon

This study questions the basic definition of a lagoonal envi-ronment. The mechanisms for the formation of a lagoonalenvironment have long been discussed, on the basis of con-ceptual studies mainly [De Beaumont, 1845; Gilbert, 1885;McGee, 1890; Johnson, 1919; Hoyt, 1967; Fisher, 1968;Davis and Fitzgerald, 2003]. All these theories hinge on abasic idea: a lagoon occurs as soon as a topographic troughis filled of water with some connections with the open sea.This results in a brackish environment.

This study has revealed the existence of a Holocene la-goon thanks to geometrical and sedimentological criteria,the lagoon fill being characterized by typical seismic faciesand units (e.g. U3L) and the presence of sediment distinctfrom that of open sea (e.g. that found in TOTH-1). It wasdemonstrated that the lagoon exists as soon as a topographichigh occurs. In the Maguelone lagoon case, this high wasformed by the sand spits that migrated alongshore around7500 yr B.P. [Raynal et al., 2009]. On the lee-side of thesand spit, wave and wind energy became very low, and la-goonal conditions could start to develop. Indeed, a lagoon isdefined as a protected environment with respect to thehydrodynamical action of the open sea. However, in thisstudy, macrofauna analysis shows the complexity of la-goonal environment (fig. 7). Lagoonal species developmentdepends on water temperature, salinity, water chemicalcomposition. All these parameters are controlled partly bythe existence of connections with the open sea. The drasticchange that is observed in mollusc population probably re-flects the construction of a continuous sandy barrier with no



FIG. 9. – (A) Sketch (cross-shore section) of sand bar-rier evolution since 7500 years B.P., controlled by sedi-ment supply and sea-level rising rate. r: approximatesea-level rising rate (m/year).FIG. 9. – (A) Modèle en coupe cross-shore de l'évolu-tion de la barrière sableuse depuis 7 500 ans B.P., con-trolée par les apports sédimentaires et le tauxd'élévation du niveau marin. R : taux approximatifd'élévation du niveau marin.

permanent inlet and thus no continuous inflow of marinewater into the Palavasian lagoon system. The sediment fillmainly records temporary connections during storms thatprovoke the deposition of over-wash sands into the lagoon[Sabatier et al., 2008]. We assume that the final closure ofenvironment, leading to an isolated lagoon, occurred atabout 731 +/– 87 cal yr B.P. when lagoonal species becamesignificantly dominant and simultaneously the number ofmarine species decreased drastically.

CONCLUSION

This study based on very high resolution seismic profiles,cores and field observations, has revealed the three-dimen-sional architecture of the Maguelone coastal system tract.The sedimentary dynamics evolution from the Late Quater-nary to present-day has been determined. Before the Holo-cene deglacial eustatic rise (fig. 8A), the Maguelone shoreis characterized by an uneven topography (RES in this pa-per; fig. 10), inherited from the Pleistocene glacio-eustaticcycles. In this context, rivers like the Mosson and Lez haveincised valleys. During the Holocene, while sea-level rises,the sea invades this topography and delineates successiveuneven shorelines that migrates northward. Inherited in-cised valleys form rias. The trangression is recorded by thedeposition of thin and discontinuous marine sand intervals.At the end of the transgression (around 7500 yr B.P.),alongshore sand supplied from the Rhône delta nourishesnearshore spits, which protect back-barrier domain. At thesame time, lagoonal sedimentation occurs in the deeper partinherited topography formed by the Lez River. At around5500 yr B.P., the decrease in rate of sea-level rise

destabilizes the sand spit depositional system, allowing ero-sion and reworking of sands. The combination between thelow rate of sea-level rise, relatively high energy hydrody-namics and low sediment supply induces the retrogradationof the sandy barrier [Barusseau et al., 1996]. Dating of sandon the present-day barrier demonstrates that it almostreached its present-day position around 1800 yr B.P.

The presence of incised valleys plays a decisive role inthe depositional evolution. In the Maguelone shore,cross-shore section in the Holocene fill of the incised valleysshows a succession from marine to continental deposits.

Comparison of geometrical contents and fauna analysisof lagoonal deposits highlights the difference between aprotected lagoon and an isolated lagoon. In the Magueloneshore, sedimentary geometries indicate that lagoonal sedi-mentation began around 7500 yr B.P. However, the large in-crease of lagoonal species, simultaneous with a significantdecrease of marine species at 731 +/– 87 cal yr B.P., demon-strate that the lagoons became isolated since that period.Between 7500 yr B.P. and about 700 yr B.P., the lagoons ofthe Maguelone shore have kept an important marine con-nection, due to the instability of beach barriers.

Acknowledgements. – This work has been funded by GDR MARGES, Eu-ropean project BEACHMED-E NAUSICAA (BMe-3S0155R-2.2) andPROGELAC (ATIP CNRS). We are grateful to DRE Languedoc-Roussillonand Région Languedoc-Roussillon to have funded GLADYS (www.gla-dys-littoral.org), as well as to EID-Méditerranée and CG34 for providingtopobathymetric data and technical support. 14C analyses were performedby the Laboratoire de Mesure 14C (LMC14, CEA, Saclay, France) in theframework of ARTEMIS and ARMILIT proposals, as well as the ANR pro-ject ECLICA. The authors wish to thank IFREMER Palavas for allowingthe storage of the cores in their cold room. The authors are grateful to Ber-nadette Tessier (UMR CNRS M2C, Caen University) for providing theIKB-Seistec Boomer.



FIG. 10. – Stratigraphic model of coastal systems tract onthe Maguelone shore in incised valleys (A) and outside ofvalleys (B). The interpretation of sedimentary architectureshows the effect of inherited morphology on Holocene de-posits.FIG. 10. – Modèle stratigraphique des cortèges de dépôt dusystème côtier de Maguelone dans les vallées incisées (A)et au niveau des interfluves (B). L'interprétation des archi-tectures sédimentaires montre le rôle important que joue lamorphologie héritée sur l'enregistrement des dépôts holo-cènes.

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Holocene evolution of a Languedocian lagoonal environment controlled by inherited coastal morphology...

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