I~UTTERWORT H Marine and Petroleum , Vol, 12, No. 8, pp. 809-820, 1995 I~IIE I N E M A N N Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0264-8172/95 $10.00 + 0.00

Structural style and evolution of the Oligo-Miocene rifting: role of the Pyrenean

M. S6ranne*, A. Benedicto and P. Labaum$ Gdofluides-Bassins-Eau, CNRS-Univisitd 2, 34095 Montpellier cedex 05, C. Truffertt and G. Pascal Laboratoire de G@ologie, Ecole Normale Sup@rieure, 24 rue Lhomond, 75231 Paris, France

Received I September 1994; revised lOJanuary 1995; accepted 9 May 1995

The Gulf of Lion margin results from the Oligo-Aquitanian rifting and Burdigalian crustal separation between continental and -. Immediately before the onset of extension, the area of the Gulf of Lion was affected by the Pyrenean orogeny which controlled the structural style of the evolving margin. During extension, the foreland of the Pyrenean orogen was affected by extensional thin-skinned . The d6collement level ramped down into the basement, in areas where the latter was thickened during orogeny. In this intermediate part, the margin was extended by several crustal-scale low-angle faults, which generated small amounts of syn- sedimentation compared with the accumulation of post-rift sediments. However, more than 4 km of syn-rift sediments were deposited in the Camargue basin, which is located at the transition between thin- and thick-skinned extensional systems. Kinematic restorations and stratigraphy suggest a pre-rift surface elevation above -level of at least 1 km in the inter- mediate part of the margin, which is in agreement with reduced syn-rift sedimentation. The slope area extends seaward of the Pyrenean , a boundary inherited from the Pyrenean collision. This part of the margin was stretched by seaward dipping low-angle block tilting of the upper crust, and antithetic lower crustal and sub-crustal detachment. The litho- spheric structures inherited from the Pyrenean orogeny exerted a strong control on the kinematics of the rifting and on the distribution and history of subsidence. Such parameters need to be integrated in the definition of pre-rift initial conditions in future basin-modelling of the Gulf of Lion.

Keywords: Pyrenean orogeny; Gulf of Lion; rifting

Continental studies have been the topic Extension at the expense of an orogenic lithosphere has of numerous studies, in parallel with the development important bearings on the choice of initial conditions of tectonic and subsidence models (McKenzie, 1978; Le for subsidence models: thickness, surface elevation, Pichon and Sibuet, 1981; Lister et al., 1991). It is now thermal regime and theology are strongly dependent on commonly agreed that intra-continental evolve the pre-rift history. The thermal evolution of associated towards passive continental margins, and that the initial sedimentary basins and the maturation of organic stages of subsidence are followed by thermally con- matter are expected to reflect the effects of geotherms trolled subsidence. However, from the late 1980s on- perturbed by the orogenic phase, whereas the in- wards, evidence for extensional collapse and late oro- homogeneous distribution of crustal masses inherited genic extension in general (S6ranne and Malavieille, from the mountain-building process determines the 1994) has drawn attention to a novel type of extension. location and the geometry of the extensional structures. The Gulf of Lion continental passive margin results from the Late Oligocene-Miocene rifting and later -eastward drift of the Corsica-Sardinia block * Correspondence to: Dr M. SEranne (Figure 1). The margin truncates the eastwards continu- tPresent address: BRGM, Service G6ologique National, BP 6009, ation of the Pyrenean range formed during the Palaeo- 45060 Od6ans, France ~: Present address: Laboratoire de Geophysique Interne et Tectono- gene; extensional structures are superimposed onto the physique, CNRS-Universit6 Joseph Fourier, BP 53, 38041 Grenoble, thrusts and folds of the Pyrenean foreland. Exploration France for hydrocarbons triggered the first geological investi-

Marine and Petroleum Geology 1995 Volume 12 Number 8 809 Structural style and evolution of the Gulf of Lion: M. Seranne et al.

' MassifCentra,~b~ ,~ ~ '/ ~ of 11 expanded spread profiles distributed throughout the eastern part of the Gulf of Lion (Le Douaran et al., 1984, reprocessed by Pascal et al., 1993). ~# 41l~*~of| i d rlse i Ietltltltltltltlt~ I ~ '- ...... "' Pre-rift geological setting The major pre-rift structures and stratigraphic features of the study area are now summarized, special attention being paid to those that exerted a strong control on the development of the Oligocene extension.

Late Variscan tectonics The continental basement (Figure 2) consists of Palaeo- zoic rocks deformed during the Variscan orogeny (Devonian to Late Carboniferous). Late Variscan extension activated NE trending and N-S oriented Figure I Location of the Gulf of Lion within the western strike slip faults and E-W extensional faults (Arthaud Mediterranean, with respect to the Pyrenean and thrust and Matte, 1975), which controlled the formation of belt. The pre-rift position of Corsica, Sardinia and the Balearics according to R6hault et al. (1984) is indicated (dotted lines) as Carboniferous and Permian continental basins (Echtler well as the boundaries of accreted oceanic crust (grey lines). The and Malavieille, 1990). deep seismic reflection profiles ECORS- and ECORS- CROP Gulf of Lion are located on this map Mesozoic extensional 'SE Basin' Shales and evaporites of the Mid-Triassic period reflect gations in the Gulf of Lion, with drilling of several a major transgression over the deeply eroded and exploratory wells (Cravatte et al., 1974) and syntheses peneplained Palaeozoic basement. In the Gulf of Lion of existing geological and geophysical data (Arthaud area, the continental to marine facies distribution et al., 1981; Arthaud and S6guret, 1981). Different shows that Triassic sediments were deposited in a subsidence models have been tested against the bore- triangular-shaped open to the , limited to the hole data in an attempt to explain the anomalously high north- by the and to the south by a post-rift subsidence (Steckler and Watts, 1980; Burrus continental elevated area extending into the present and Foucher, 1986; Bessis, 1986; Kooi et al., 1992). day Gulf of Lion. This palaeogeographical setting con- However, these studies assumed a rather 'standard' tinued throughout the Jurassic, allowing deposition of a pre-rift configuration of the lithosphere. Several papers succession of marine carbonates and shale intervals, have suggested a genetic relationship between localized thickening towards the east in the 'Sud-Est Basin' Oligocene rifting and the overall convergence of the (Beaudrimont and Dubois, 1977). The Jurassic African and European plates (e.g. Tapponnier, 1977), sequence deposition was controlled by the Liassic whereas others have proposed that the Gulf of Lion Tethys rifting, which is expressed by syn-sedimentary was a marginal basin above the north-west subduction extensional faults along the NE trending Massif Central of the African plate (e.g. R6hault et al., 1984). The margin (Giot et al., 1991) and E-W trending normal area of the Gulf of Lion was chosen for a ECORS deep faults along the southern margin, from to seismic survey (Burrus et al., 1987; de Voogd et al., (Figure 2). Within this triangular-shaped 1991), the preliminary results of which have been basin, the top of the block-faulted Palaeozoic dips integrated into regional studies (Gorini et al., 1993). In about 10° towards the axis of the synform. The Meso- this paper, we analyse variations in tectonic style across zoic sedimentary cover was thin and discontinuous over the onshore and offshore part of the the southern Corsica-Sardinia continental block. and we investigate the possible role that Pyrenean orogenic structures played in the localization and Cretaceous wrenching and kinematics of extension in the Gulf of Lion margin. During early Late Cretaceous opening of the Bay of The structure of the onshore extensional system was Biscay and North Atlantic, the eastward drift of the assessed by compilation of the published (BRGM) and Iberian block was accompanied by left-lateral unpublished geological maps. Additional detailed along the North Pyrenean Fault Zone (NPFZ, Figures 1 mapping was carried out in specific areas (e.g. Phili- and 2), crustal thinning along the southern European bert, 1992). Data from onshore industrial boreholes margin and development of E-W trending strike-slip and the nine offshore exploratory wells (Cravatte et al., basins and ridges and HT-LP metamorphism 1974; Gorini et al., 1993) were integrated. Industrial (Choukroune and Mattauer, 1978; Golberg et al., multichannel seismic reflection surveys in the H6rault, 1986). This zone of shear, separating Europe and Al~s and Camargue basins (Figure 2) allowed con- Iberia-Corsica-Sardinia extends across the Gulf of straint of the structure at depth. The structural and Lion. It is likely that the metamorphism of Albian age deep crustal configuration of the offshore part of the documented in the basement of the GLP2 well margin is defined by the ECORS-CROP deep seismic (Figure 2) points to the eastwards continuation of the survey shot in 1988 across the north-west Mediterranean NPFZ (Gorini, 1993). The deep and narrow basin from the Gulf of Lion to Sardinia (de Voogd et al., observed north of GLP2 (Figure 2) could therefore be a 1991), which has been reprocessed (Pascal et al., 1994; Late Cretaceous strike-slip basin reactivated during unpublished data) and by a refraction survey consisting Cenozoic rifting. Left-lateral motion of Iberia-

810 Marine and Petroleum Geology 1995 Volume 12 Number 8 Structural style and evolution of the Gulf of Lion: M. Seranne et al.

Corsica-Sardinia is also responsible for the partial the Iberian part, which is separated by the NPFZ from inversion of the Mesozoic basin in Provence and the narrower, north-verging European counterpart Languedoc. Aerial erosion with westwards increasing lying above a subcrustal lithospheric wedge. Shortening amplitude caused the truncation and karstification of of about 100 km is associated with crustal thickening Early Cretaceous sediments across uplifted blocks and and the development of roots about 50 km below the the deposition of bauxites. In the study area, Early Iberian plate. In contrast, the eastern segment of the Cretaceous series were partly preserved north of E-W Pyrenees is less well constrained, as most of this thrust trending basement faults located between Provence belt is now lying under the Gulf of Lion, with only the and Languedoc. northern foreland being exposed. The asymmetrical structure of the Pyrenees seems to have flipped across Pyrenean orogeny the NE trending transfer zone: wide north-verging, Following left-lateral wrenching, the Late Senonian- deformed areas extend north of the NPFZ, whereas Palaeogene convergence and collision of the Iberia- palinspastic reconstruction of Sardinia (poorly de- Corsica-Sardinia block with the southern margin of the formed during the Pyrenean orogeny) in its pre-rift European plate resulted in the Pyrenean orogeny. The position does not allow for a wide southern domain. belt stretches E-W from the to the Gulf The similarity of the Languedoc-Provence belt to of Lion, and from Languedoc to Provence through the the present day southern Pyrenean foreland has already NE trending Corbi6res transfer zone (Mascle et al., been noted by Arthaud and S6guret (1981). Thin- 1994). The structure of the western segment, i.e. the skinned tectonics above the d6collement level of the present day Pyrenees, is now well constrained by Triassic evaporites involves thrusting or folding, ECORS deep seismic reflection (Choukroune and depending on the thickness of the Mesozoic series. The ECORS-Team, 1989; Roure et al., 1989). This profile direction of thin-skinned thrusting (Figure 2) varies displays a wide, thickened, south-verging thrust belt on from north-westward in the NE trending transfer zone

I + /#~i Main extensional basins ÷ Pre-rift cover deformed during Pyrenean orogeny +

Outcropping Paleozoic + Paleozoic of the Pyrenean Axial Zone lr Oceanic crust "I = Intermediate continental crust IIIII Transfer zone ;: OAv •l'--r Main normal faults Front Pyrenean thrusts (Eocene) +Z "v=v" Alpine thrusts (Miocene) - + \ Pyrenean thrusts reactived + ..~ during Alpine compression~l~ + " Pyreneancompression + ~ / + Oligocene extension

43 °

"-, '"",,:'i \

2 ° . /' 4 ° 5" \ I .-- I I

Figure 2 Structural map of the Gulf of Lion area, showing the superimposition of the Oligo-Aquitanian extensional structures over the Pyrenean (Eocene) compressional structures. Note the nearly perpendicular directions of compressional arid extensional deformations. NFPZ, North Pyrenean Fault Zone; Av., ; Ma, ; Mo, Montpellier; Na, Narbonne; Ni, N~mes; Pe, Perpignan; To, ; AB, Al~s basin; AiB, Aix basin; CB, Camargue basin; GC, Central; GFB, Grand Faraman basin; HB, H~rault basin; and MB, Manosque basin. Offshore boreholes: Ag, Agde marine; Au, Autan 1; Be, Beauduc; Ca, Calmar; Ci, Cicindelle; GLP2, Golfe du Lion Profond 2; Mi, ; Ra, Rascasse; Si, ; and Tr, . Regional sections shown in this paper are located on this map. ESPs 201 to 205 are indicated along the ECORS 'NW' profile. Geometry of the offshore syn-rift structures modified from Gorini (1993). Directions of compression and extension from Arthaud and S6guret (1981), Arthaud et al, (1981), Arthaud and Pistre (1993), Tempier (1987) and Hippolite et al. (1993)

Marine and Petroleum Geology 1995 Volume 12 Number 8 811 Structural style and evolution of the Gulf of Lion: M. S~ranne et al.

(Gorini et al., 1991; Mascle et al., 1994), to northwards zone (Figure 2). in Montpellier area (Arthaud and S6guret, 1981) and in .The Al~s basin (Figure 2) shows a rollover and a Provence (Tempier, 1987). In Languedoc and in syn-tectonic diverging basin-fill, indicating the control Provence, Pyrenean foreland structures account for by an extensional listric fault that is superimposed onto, about 25-30 km of shortening (Tempier, 1987). This and partly reactivates, the C6vennes Fault. Recon- value is derived from the deformed Mesozoic strata and struction of the Oligocene fault shows that it detaches does not take into account most of the shortening in the in the Triassic level, whereas earlier studies suggest the Palaeozoic basement of the hinterland (which lacks existence of a structurally lower detachement in the Mesozoic cover) nor the south-verging, southern part Carboniferous (Roure et al., 1992). Syn-rift sedimenta- of the belt. Thus it may be assumed that shortening tion unconformably overlies the syn-tectonic com- across the Languedoc-Provence segment was of the pressional Middle Eocene sediments. Extension started same order of magnitude as in the Pyrenees, resulting earlier (latest Eocene) than in the rest of Languedoc in similar values of crustal thickening. and extended into the Late Oligocene (Alabouvette E-W faults inherited from the Late Cretaceous and Cavelier, 1984). The exclusively continental basin- inversion were reactivated as north-verging thrusts fill consists of alluvial fans along the NW margin that (Arthaud and S6guret, 1981; Tempier, 1987). Base- pass to silt and lacustrine limestones in the axis of the ment frontal ramps are found close to the present day basin. The maturity of organic matter within pre-rift coastline. The Cap Sici6 thrust (Figure 2, near Toulon), late Cretaceous shales located in the hanging wall which displays a minimum shortening of 8 km, is the suggests a late uplift of several hundred metres only exposed basement thrust, but basement thrusts are (A. Mascle, pers. comm.) that is related to Alpine also present in wells (e.g. Cicindelle) and inferred in inversion, and which is not detailed here (see Roure the construction of seismically controlled sections of et al., 1992). To the SW, the basin is associated with a southern Carmargue. The ECORS profile also displays NNW trending transfer fault zone, which is identified in a set of SE dipping reflectors that cannot be related to the Palaeozoic footwall and whose structural and strati- the extensional system, which we interpret as the trace graphic effects can be recognized across the whole of north-verging thrusts or lateral ramps. Basement margin (Figure 2). It corresponds to the Arl6sienne ramps are associated with a network of NE trending transfer fault zone (Gorini, 1993). North-east of this lateral ramps accommodating left-lateral strike-slip transform zone, the only significant syn-rift basins are movement (Mauffret and Gennessaux, 1989). Thrust- located along the C6vennes fault (Al6s basin) and close ing and folding in Provence and Languedoc is to the fault (Manosque and Aix basins, commonly dated as Lutecian-Bartonian. However, Figure 2). Seismic reflection data clearly indicate that thrusting may have started earlier, when the syn- these basins have been formed on listric faults that tectonic breccia of Cuisian age (Early Eocene) were detach above the Hercynian basement (Biondi et al., deposited in front of the Montpellier thrust. 1992; Roure et al., 1992) and there is no Oligocene basin overlying the thick and tabular Mesozoic cover which could indicate basement ramps located between Structure of the landward part of the margin the C6vennes and Durance faults. The mechanism by The landwardmost part of the margin extends south- which the continental crust is extended north-east of east of the C6vennes fault which controlled the forma- the Arlesienne transfer fault zone remains an open tion of the Oligocene H6rault and Al~s half-graben question. basins (Figure 2). They are the larger basins active during the post-Pyrenean rifling phase, the other Les Matelles basin example extensional structures being very small half-graben. Les Matelles basin (Figure 4, location on Figure 3) is an The H6rault basin (Maerten, 1994; Maerten and asymmetrical NE-trending . The SE limb S6ranne, in press) (Figures 2 and 3) displays a NW displays the complete regional stratigraphic series from dipping monoclinal series unconformably overlying the Mesozoic marine carbonate up to the latest Eocene north-verging Eocene Montpellier thrust. The onset of alluvial deposits ('Ludian', previously dated Early syn-rift sedimentation occurred during the Stampian in Oligocene (Alabouvette and Cavelier, 1984)). The NW small fault-bounded basins now deeply buried below steep limb corresponds to a hanging wall flat resting later syn-rift Aquitanian alluvial plain deposits. Syn-rift against the footwall ramp of the Les Matelles fault. The basin-fill gives evidence for an overall north-westward NW limb displays a thin interval of lower Cretaceous migration of depocentres. Burdigalian marine sedi- marly limestones and lower Eocene marls, and the ments unconformably overlie the previous deposits and complete middle Eocene limestone. The uppermost onlap pre-rift basement to the SE. Extensional faulting Eocene interval onlaps toward the NW and is not affects the pre-rift Mesozoic cover detached above the exposed in the NW limb. This gives evidence for pre- Palaeozoic basement, which remained undeformed Oligocene downthrow of the SE block of Les Matelles during rifting. Faulting propagated north-westwards fault (Figure 4), due to previous Pyrenean left-lateral from the Triassic d6collement level, which passed strike-slip (Arthaud and S6guret, 1981). The syncline is downdip into -- and reactivated in an extensional cored by coarse breccia, which locally unconformably regime -- the basement ramp of the Montpellier thrust overlie the NW steep limb in a typical syn-tectonic (Figure 3). Depocentres distribution in the H6rault progressive unconformity pattern. These coarse and basin provides evidence for a NNW-trending transfer angular breccia were generated along the NW active fault across the basin (Maerten and S6ranne, in press), margin of the basin at the expense of Lower Cretaceous which can also be traced in the Gulf of Lion (Gorini, or Middle Eocene limestones; there is no significant 1993) and that we informally name the S6toise transfer input from the presently exposed Upper Jurassic lime-

812 Marine and Petroleum Geology 1995 Volume 12 Number 8 -- Cross-section A Cross-section B Thin-skinned Low-anglethick-skinned -- 4 I , Fig.4 i CamargueBasin SE NW HSraultBasin La BoissiereB. MontarnaudBasin ~ Vistrenquegraben ~ Petit Rh6negraben ~ Off-shoredomain CO CSvennesfault zone ~ If/~.,,~~ • ~ • Lee MateltesSasin AssesBasin Castries MontpellierThrust Marette Aigues Mortes Stes Maries 102 Beauduc

.I1 (1)

7~ NE-SWstr ke-sl 7 o_ 8~ Mesozoicsedim 8 •io 9 ~ne~ ~ 9 to V=H ,,,~ ~o =0 POST-RIFT i~ I I Plio-Queternary ~ Miocenepost-Aquitanian 8 SYN-RIFT ~ ~ Aquitanian ~ Oligocene PRE-RIFT ill, ~ Eocene I Lower Cret...... ~ Upper Jurassic I I Middle-LowerJ..... ic I Triassic ~ Paleozoic ¢3 E-

0 Figure 3 Cross-sectionof the upper structures in the onshore Gulf of Lion. The landward part of the margin is characterizedby thin-skinned tectonics, whereas SE of the Nimes Fault, the 0 margin was extended by thick-skinned low angle faulting. Note the discontinuity between sections A and B. Location in Figure 2

¢b

< o e-

o,

Z e- CO

¢b Structural style and evolution of the Gulf of Lion: M. Seranne et al.

stone of the footwall. The small (500 m radius) alluvial model of the Les Matelles hanging wall syncline basin fans interfinger with marly shales and conglomerate applies to most small-scale Oligocene basins of channel-fill belonging to an axial south-westward flow- Languedoc. ing braided 'fluvial system, or with lacustrine carbonate deposits in the NE end of the basin (Crochet, 1984). Structure of the intermediate part of the margin These sediments are biostratigraphically well dated as latest Stampian and span a time interval less than one The intermediate part of the margin extends over million years (Grambast, 1962; Rey, 1962; Crochet, 100 km from the Nimes Fault to the trace of the NPFZ 1984) The structure of the basin is complicated by the in the Gulf of Lion (Figure 2). The thin-skinned occurrence of slivers of Lutecian limestone -- some extensional system of the NW end of the margin, ramps tens of metres thick and several kilometres along-strike down into the Nimes Fault. This NE trending fault -- within the syn-rift sediments (Figure 4a). The strikes normal to the extensional direction and acts as a Lutecian imbricate thrusts overlie and deform the frontal ramp. On this transect, three major normal lower part of the Oligocene breccia and they are sealed faults involve the Palaeozoic basement and formed by the same formation. Clast composition and distri- several syn-rift graben. The pre-rift surface corre- bution within the breccia suggests that a significant part sponds to the Pyrenean erosional unconformity that of the clasts are derived from the Lutecian thrusts. The exhumes allochthonous Mesozoic cover beneath deformation pattern at the front of the thrusts indicates Camargue and Palaeozoic basement beneath the gulf. a SE and shows that they have been emplaced This intermediate zone is characterized by a large thick- in the basin during sedimentation of the syn-rift ness of post-rift series that is not proportional to the Oligocene (Philibert, 1992). The structure of the basin thin and discontinuous syn-rift series nor to the amount can be accounted for by thin-skinned extensional of crustal thinning. However, due to its structural tectonics, characterized by a ramp in the massive position on the margin, the 4000 m deep Carmargue Upper Jurassic limestones, a fiat in the Lower basin (Figure 2) stands out as an exception in the group Cretaceous marly limestones and an emerging ramp in of syn-rift basins. the Middle Eocene limestones (Figure 4b). Seismic reflection and rollover geometry indicate that the ramp Camargue basin across the Upper Jurassic (Les Matelles Fault) is a The Camargue basin is subdivided into the NE trending listric fault that detaches in the Triassic series at a depth Vistrenque graben and the associated Petit Rh6ne of 4000 m. During extension along the Les Matelles graben (or Petite Camargue in the offshore along strike Fault, the Lutecian hanging wall flat was transported continuation) (Figures 2 and 3). The over 4000 m thick towards the ramp and formed the hanging wall syn- Stampian to Aquitanian syn-rift series unconformably cline, where detritus was trapped. Part of the hanging overlies Mesozoic carbonates. Stampian sequences wall flat became detached from the ramp/flat system comprise thick continental to iagoonal shales and silts and was gravitationally emplaced into the basin as an overlain by evaporitic sediments characterizing playa olistolithe, and subsequently eroded and overlain by environments. The structural repetition of evaporites syn-tectonic syn-rift sedimentation. The imbricate results from basinward gravity thrusting above the roll- thrusts represent successive reactivations of the surface over during syn-rift sedimentation (Valette, 1991; of gravitational slide, following successive increases of Valette and Benedicto, 1995). Overlying Aquitanian accommodation in the basin due to the activity of the shales and silts were deposited in littoral to very Les Matelles Fault. The structural and stratigraphic shallow marine environments. The entire syn-rift series was thus deposited close to sea level, indicating that sedimentation always balanced accommodation. It further indicates that surface elevation in the Vistrenque (~ Presentday cross-section NW SE basin was close to sea level from Early Oligocene times 500 - Presenttapography onwards. A Burdigalian marine sequence onlaps an

250- -'i-7 -----7-~----~---;---T---r-'~3:~;.~,, erosional unconformity developed under subaerial conditions (Valette, 1991), which is interpreted as the ~_ .... .--7~7=, 0m- ,-= T _~T • r-! : : - l'IkT"~, break-up unconformity. The upper part of the basin-fill Middle Oligocene ' J 250 - [~] Ludian ~ is truncated by the erosional surface corresponding to Lutetlan ~ Eocene / 500 - the Messinian lowstand of the Mediterranean; this ~ Cuisian ~ 1 unconformity is onlapped by the transgressive Pliocene 1000 - II Valanginlan Upper Jurassic to Present series.

1500- The structure of the Vistrenque graben is controlled (~ Restoredcross-section by the NE trending, SE dipping Nimes Fault. Sections 500 - across the south-western part of the graben display a 250 - typical rollover due to the concave-upward profile of 0m- the bounding fault in the upper 3 km of the crust (Figure 3), whereas sections across the north-eastern 250 - part of the graben display compensation graben due to 500 - a planar attitude of the fault (Valette and Benedicto, 1995). Syn-rift series of the Vistrenque basin extend Figure 4 Detailed section of Les Matelles basin and restoration of the section before Oligocene extension. Note the Lutecian over the entire down-faulted block, beyond the hanging lacustrine limestones slivers emplaced during sedimentation wall crest. This indicates subsidence due to the low within Oligocene. Location on Figure 3 angle (25 °) Nimes Fault, which is planar from 3 km

814 Marine and Petroleum Geology 1995 Volume 12 Number 8 Structural style and evolution of the Gulf of Lion." M. S~ranne et al.

Present-day situation cover. Such a high in the hanging wall of the N~mes NW SE Fault may (i) be the result of the flattening of the fault Messinian erosion profile at depth or (ii) pre-date the extensional structure (Figure 5). The Messinian erosion prevents Syn-rift fillin~ Pyrenean Thrust observing the geometry of the syn-rift sequences NTmes Fault ~ ~ ?~ ~ [ O~,~:~5km against this high. Restoration of the extensional fault in the case of a planar low angle fault (as suggested by seismic reflection) indicates a pre-rift relief south-east Ramp-flat fault No ore-rift relief of the Vistrenque basin, in excess of 1000 m, that would be inherited from northwards Pyrenean thrust- ing. Thrusting and erosional denudation of the Palaeo- zoic basement becomes prominent south of the Pre-rift relief =1250m Ramp fault Camargue basin. Pre-rift sedimentary cover is extremely reduced in the nearshore boreholes and Palaeozoic rocks subcrop beneath syn- or post-rift sequences in the offshore wells. Restoration of the extensional motion on the three major basement faults in Camargue (Figure 6) points to a pre-rift topography having an Figure 5 Sketch of a simplified present day section in the elevation of about 2000 m. These estimates possibly Camargue basin, showing the geometrical relationships include errors due to (i) the lack of isostatic compen- between extensional fault, previous thrust and partially preserved syn-rift infill (sediments deposited close to sea level). sation and (ii) the lack of a precise pre-rift topographic The two possible fault profiles imply two pre-rift hanging wall reference datum as the area has been later truncated by topographies the Messinian erosion; however, they provide a valu- able indication of the location and order of magnitude of the pre-rift relief. downwards and that penetrates the basement to at least 10-km depth (Figure 3). In contrast, the Petit-RhOne basin that developed in the hanging wall of the Nimes Crustal sections Fault is characterized by a lack of syn-rift sedimentation From the shoreline to an area between ESP201 and beyond the rollover crest. The bounding fault is a listric ESP202, the ECORS profile (Figure 7A) displays a flat ramp which flattens in the Triassic dOcollement and it is Moho reflection, at about 20 km depth, and a 5 km associated further to the SE with a ramp in the base- thick reflective lower crust. The reflections correspond- ment. ing to the major faults that affect the upper crust either disappear above or merge with the reflective crust Pre-rift restoration (Figure 714). Major faults dip basinward, with the An E-W structural high extending along the shoreline exception of the steep fault bounding the Vistrenque corresponds to a Pyrenean thrust in the Mesozoic basin, at the NW end of ECORS. This landward dip-

.... Camargue Basin Off-shore domain NW 0krn 1 2 3 4 5 6 7 8 9 10

I--

Restored cross-section to Oligocene 3 Messinian erosion 2 .,ooo --2 1 Datum surface 0k~ .0 1 .1 2 2 3 -3 4 .4 5 5 6 6 ~ ~ ~ --'~ ~ ~ ~ Extension = 9km 7 -7 9 -8 9 H=V ~9 10 10

Figure 6 Section across the Camargue basin (SE part of section B, Figure 3) and restoration in a pre-rift position (bottom panel) using the method (surface conservation, 60 ° shearing). Same caption as in Figure 3. Such a simple kinematic restoration (no isostatic effect) shows (i) a horizontal extension of about 10 km and (ii) that the area SE of Camargue was elevated above sea level before rifting. The approximate location of the cartoon in Figure 5 is given on the top panel

Marine and Petroleum Geology 1995 Volume 12 Number 8 815 0o CO ¢b t ¢3 .... Cross-section C ~ , ECORS NW-SE ~0 2. ..~ I Thin-skinned I Low-anglethick-skinned Low-angleblock tilting I A) ¢n r~k

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Intermediatecontinental crust "~-~ North-verging Pyreneanthrust

Figure7 Crustal-scalesections of the Gulf of Lion area (locationon Figure 2) showing the variationof structuralstyle acrossthe margin. (A) Section constrainedby ECORS NW profile (pre-stackdepth migratedin the lower part of the margin). (B) Camarguesection constrainedby seismicreflection and by data from Gorini (1993) in the lower margin Foldout 1 Slope section of the ECORS NW profile (see Figure 7A) showing the tilted blocks reflector. Me, Messinian erosion; t-B, top-Burdigalian; prU, post-rift unconformity; and sr, s seismically defined Moho, at ESP 203. Vertical = horizontal scale. Pre-stack depth migration

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. ~- • .~ .~__ :-= IbKm __~- ~ .... _ _- ~_~_ Structural style and evolution of the Gulf of Lion: IV/. S~ranne et al. ping fault could be interpreted as an antithetic fault of the Camargue basin can be accounted for by the com- the Nimes Fault (Guennoc et al., 1994). However, the bined effects of (i) preservation of syn-rift sedimenta- available data do not suggest the existence of a major tion north of the elevated area of the Pyrenean range SE dipping normal fault between the NW end of and (ii) control by a crustal-scale low-angle extensional ECORS and onshore outcrops. The Nimes Fault seems fault which allowed a large amount of accommodation. to die out south-eastwards before it reaches the S6toise The Central Graben (Figure 2), the large syn-rift depo- transfer zone and deformation is taken up by the land- centre in the SW of the Gulf of Lion (Gorini et al., ward-dipping normal fault. According to the ECORS 1993; Guennoc et al., 1994) lies in a similar structural section, the fault bounding the Petite Camargue basin position. has a listric profile rooted in a mid-crustal level, which is in agreement with the rollover of the pre-rift. This Structure of the basinward part of the margin Petite Camargue Fault correlates north-eastwards with the fault bounding the Petit Rh6ne basin (Figure 7B). The basinward part of the continental margin, imaged Transition from a listric basement ramp profile in the on the ECORS profile (Figure 7A), is limited by a deep SW (Figure 7A) to a listric-flat-basement ramp in the and narrow basin probably controlled by a SE dipping NE (Figure 7B) is achieved through the reactivation of steep fault. This narrow basin is located in the east- the Pyrenean thrust as lateral ramp, north of Cicindelle ward, along-strike continuation of the North Pyrenean well. In addition, a major NE trending, low-angle Fault (see Figure 2). Newly reprocessed pre-stack (25°), intra-crustal planar reflector has been mapped migration of the ECORS profile (Pascal et al., 1994; offshore (Gorini et al., 1993) bounding the Grand unpublished data) displays the structures of this part of Faraman basin (Figure 7A), and which correlates with the margin (Foldout 1). It is characterized by tilted the major extensional fault beneath Beauduc well blocks bounded by low-angle normal faults. Half- (Figure 7B). graben contain tilted and diverging reflectors, inter- A number of reflectors which are apparently un- preted as syn-rift sediments. The basal unconformity is related to Cenozoic graben (below ESP201) and are unclear. Depending on the interpretations, there is at observed at middle crustal levels (SE of Sirocco) are least 1000 m and a maximum of 2000 m of syn-rift in interpreted as Pyrenean north-verging thrusts. In the deepest depocentre. Syn-rift series are truncated by addition, the tectonic contact which accommodates the a prominent post-rift unconformity. Syn-rift sedimenta- thin-skinned extension in the H6rault basin corre- tion did not keep up with faulting as the crest of the sponds to the basement ramp of the previous Pyrenean tilted blocks stand above the post-rift unconformity, Montpellier thrust (motion oblique to the section in resulting in elevation of the tilted block crests above the Figure 7A). Major low-angle extensional faults bound syn-rift basins. The post-rift unconformity is overlain half-graben, the sedimentary fill of which displays by a post-rift sequence onlapping to the NW onto the divergent and partly onlapping reflectors interpreted as basement highs. The GLP2 borehole located on the syn-tectonic sediments. They are truncated by a break- side of a structural high drilled the upper part of this up unconformity attributed to the earliest Burdigalian transgressive sequence. It indicates that the first sedi- (Valette and Benedicto, 1995) or the latest Aquitanian ments onlapping the basement at this point (late (Gorini et al., 1993). Depth conversion of the profile Burdigalian) are continental and that they very rapidly using the velocity stacks indicates syn-rift sediments pass upwards into open marine series (Gorini, 1993). with a maximum thickness of 1000 m in the offshore This implies that: (i) the diachronous lower boundary Vistrenque and Petite Camargue basins, and less in the of the transgressive post-rift sequence corresponds to a more seaward syn-rift depocentres. This is far less than coastal onlap on the flank of an emergent land present- what is measured in the onshore Camargue basin. On ing high topographies; (ii) the syn-rift Oligo-Aqui- the parallel section (Figure 7B) the thin-skinned tanian sediments were deposited in continental tectonics zone displays only one large syn-rift basin in environment; and (iii) the rate of post-rift subsidence the Camargue. This section is characterized by the was very fast. three major SE dipping basement faults described This 60 km wide zone coincides with a sharp rise of earlier, in the hanging wall of which a structurally high the Moho discontinuity from 20 km (beneath GLP2) to Palaeozoic basement is directly overlain by post-rift 15 km (at ESP 203) and a decrease in crustal thickness sediments. In spite of SE dipping extensional faults, the from 15 to 5 km. In this area, the lower crust does not top of the basement is located at a higher structural display the typical laminated seismic facies as in the level in the hanging wall than in the footwall. This is in intermediate zone. The upper crust is affected by tilted agreement with pre-extension basement culmination blocks controlled by low-angle normal faults dipping and erosion of the Mesozoic cover in the offshore 30-35 ° towards the basin (Foldout 1). These faults domain of the Gulf of Lion. Pre-rift surface elevation seem to detach in a group of very shallow dipping can easily account for the lack or very small amount of reflectors located about 2-3 km beneath the top of the syn-rift sediments in this part of the margin. If conti- fault blocks, which could correlate landwards with the nental basins were formed on the collapsing mountain R reflector that cuts the top of the basement near GLP2 belt, they were rapidly cannibalized. There is thus no well (de Voogd et al., 1991). At variance with the S stratigraphic record of the early stages of rifting reflector which is imaged on the northern Bay of Biscay (Oligocene) in the areas of surface pre-rift elevation. In Margin (Le Pichon and Barbier, 1987), the R reflector contrast, where surface elevation was close to sea level cuts down-section towards the basin, synthetically to from the onset of extension as in Camargue, the com- the normal faults bounding the tilted blocks. It lies plete syn-rift sequence has been preserved. The within a domain of typical crustal velocities (6.2 km/s), presence of the deepest syn-rift depocentre localized in differing in this respect from the S reflector observed on

Marine and Petroleum Geology 1995 Volume 12 Number 8 817 Structural style and evolution of the Gulf of Lion: M. Seranne et al. the Galicia margin, where it is interpreted as the tectonic boundary between crustal material in the hanging wall and serpentinized peridotites in the footwall (Boillot et al., 1988). We interpret the R reflector as an extensional intra-crustal into which the low angle normal faults are rooted, and which allows stretching of the upper crustal level. Estimates of the extension across the low-angle faults indicate horizontal extension of about 60% above the R reflector, which cannot account alone for the whole crustal thinning observed on this part of the ECORS profile. Near the base of the crustal section a 5-20 ° landward dipping reflector T is visible on the prestack migration as well as on the initial processing (e.g. Gorini et al., 1993). It links the 20 km deep Moho beneath ESP202 to a 12 km deep level below ESP203, where, according to the ESP203 velocity determinations, it lies within crustal material (Foldout 1). The T reflector therefore offsets the Moho discontinuity by 5 km between the GLP2 and ESP203 locations. Mapping of this reflector shows that it is parallel to the margin and that it is con- sistently located above the seismic Moho (Pascal et al., 1993). We interpret T as a shallow dipping extensional fault that truncates the upper lithospheric mantle and the lower crust. Blockfaulting and seaward dipping shear zones in the upper crust, together with antithetic Thin-skinned extensional detachment in the lower crust, may account Low-angle thick-skinned extensional tectonics for the extreme thinning of this zone. Consequently, Low-angle block tilting this interpretation requires that the crust located sea- I I Zone undeformed during extension ' ' ' Extensional cover fault wards of the T reflector is composed of lower crust and Extensional basement fault upper lithospheric mantle, exhumed in a fashion similar IIIll~ Transfer zone to that proposed for the Galicia margin (Boillot et al., ==.~u Pyrenean basement ramp reactivated during extension 1988). Alternatively, the T reflector may be compared - ~. Direction of extension with the lower crustal and subcrustal reflectors observed on BIRPS profiles which are interpreted as Figure8 Kinematic map of the rifting in the Gulf of Lion shear zones transfering the bulk strain from upper showing the tectonic styles distribution and the position of the basement ramps. Note that some basement oblique ramps crustal faults to mantle faults (Reston, 1990). oriented E-W are reactivated previous Pyrenean thrusts. Also Basinwards of the emergence of the T reflector, the note the transfer fault zones which segment the margin. See text crust is characterized by a constant thickness (4 km). for discussion According to Pascal et al. (1993), velocities from expanded spread profiles suggest the existence of a crust with intermediate characters. It could be either a to deep extensional ramps. The intermediate zone, lower continental crust, stretched and intruded by corresponding to thick-skinned faulting, developed in mafic volcanics, or serpentinized peridotites at the top the area of previous Pyrenean crustal thickening, where of the mantle, denuded by a landward dipping the Mesozoic cover was removed by erosion. The extensional detachment (T reflector). Typical oceanic evidence for surface elevation in that area accounts for crust is found in the basin beyond ESP207. the rather thin syn-rift series. Stretching resulted firstly in the collapse of the elevated relief without syn-rift sediment preservation. At the periphery of the topo- Discussion and conclusion graphic high where surface elevation was close to sea The extensional structural style of the Gulf of Lion level (e.g. Camargue), stretching was associated with passive continental margin changes considerably from sedimentation from the onset of rifting, allowing for the the landward end to the - transition formation of the thickest syn-rift series. Note that the (Figure 8). The zoning of the Oligo-Miocene ex- extensional faults in this area are trending NE, there- tensional province reflects the zoning of the Pyrenean fore they are not reactivated Pyrenean thrusts. They structures: the extensional thin-skinned system over- are either neoformed faults or inherited lateral ramps prints the external thin-skinned thrust system which of the contractional system. The zone of low-angle characterizes the northern foreland of the Pyrenees. block faulting characterized by extreme continental South-west of the Arlesienne transfer fault the thin- stretching and very thick post-rift series is located south skinned extensional system ramps down into the base- of the NPFZ, e.g. the Iberia-Sardinia-Corsica plate. ment at the Nimes fault. Figure 8 also shows that the The structural style and the subsidence pattern change Pyrenean inherited frontal ramps were reactivated as across the terrane boundary between the European oblique extensional ramps along a restricted E-W (north of the NPFZ) and the Iberia-Sardinia-Corsica segment near the S6toise transform and linking shallow plate. The present day structure of the Pyrenees

818 Marine and Petroleum Geology 1995 Volume 12 Number 8 Structural style and evolution of the Gulf of Lion: M. S#ranne et al.

Thin-skinned Thick-skinned • X- . NPFZ References Alabouvette, B. and Cavelier, C. (1984) Languedoc oriental, in Chapitre Pal~og~ne. In: Synth~se G~ologique du Sud-Est de • ' ;.' . --,'.i:-: '(.,~. -: ~.'/~2/~-.-~ .,'i:.:". la France -- Stratigraphie et Pal~og~ographie (Eds S. Debrand-Passard and S. Courbouleix), BRGM, Orleans, France, M~m. No. 125, 434-438 Arthaud, F. and Matte, P. (1975) Les d~crochements tardi- 50 ~ 50 hercyniens du SW de I'Europe. G~om~trie et assai de re- Thin-skinned Thick-skinned constitution des conditions de la d~formation Tectono- NW • ~_ ~ • SE NPFZ physics 25, 139-171 0kin- ~ ~ 0 Arthaud, F. and Pistre, S. (1993) Les fractures et les pal~o- contraintes du granite hercynien de Millas (zone axiale des Pyrenees): un cas d'~tude de la tectonique cassante d'un aquif~re de socle Geodin. Acta 6, 187-201 i b): Arthaud, F. and S6guret, M. (1981) Les structures pyr~n~ennes 50 , l 50 du Languedoc et du Golfe du Lion (Sud de la France) Bull. Soc. G~oL Fr. XXlII, 51-63 Figure g Cartoon representing the possible crustal pre-rift and Arthaud, F., Ogler, M. and Seguret, M. (1981) Geologie et g6o- present day configuration across the Gulf of Lion. The upper physique du Golfe du Lion et de sa bordure nord Bull. BRGM panel is inspired from the ECORS-Pyrenees section (Roure et {2),1, 175-193 al., 1989,"location in Figure 1), which has been inverted to Beaudrimont, A. F. and Dubois, P. (1977) Un bassin m~sogeen account for the flip of the asymmetrical structures across the NE du domaine peri-Alpin: le sud-est de la France Bull. Cent. trending transfer fault zone in the Cobi~res: in this instance, the Rech. Explor.-Prod. Elf Aquitaine 1,261-308 foreland and the wide area of thickened crust extends in the Bessis, F. (1986) Some remarks on the study of subsidence of European plate. The lower panel is based on the present sedimentary basins. Application to the Gulf of Lions margin interpretation of the ECORS-Gulf of Lion profile. Thin-skinned (Western Mediterranean) Mar. PetroL GeoL 3, 37-63 extensional tectonics developed in the foreland zone of the Biondi, P., Lerat, O. and Phillips, J. (1992) Syntb~se structurale, orogen. The intermediate zone of the margin corresponds to the sedimentologique, et g~ochimique du bassin Eoc~ne- thickened and elevated part of the orogen, almost devoid of Oligoc6ne de Manosque-Forcalquier (Alpes de Haute- syn-rift deposits and which was extended by thick-skinned Provence), Institut Fran¢ais du P#trole, Report 40 151 tectonics. The seaward part of the margin correlates with a Boillot, G., Girardeau, J. and Kornprobst, J. (1988) Rifting of the narrow deformed zone which was moderately thickened during Galicia Margin: crustal thinning and emplacement of mantle orogeny, located south of the NPFZ (Corsica-Sardinia) rocks on the seafloor. In: Proc. ODP, Sci. Res. (Eds G. Boillot and E. L. Winterer) 103, 741-756 Burrus, J. and Foucher, J. P. (1986) Contribution to the thermal regime of the Proven£al Basin based on flumed heat flow surveys and previous investigations Tectonophysics 128, 303- 334 (Roure et al., 1989) could be taken as a model for the Burrus, J., Olivet, J. L., Auzende, J. M., Cazes, M., Curnelle, R., pre-rift configuration of the Gulf of Lion (Figure 9). We Galdeano, .A., Labaume, P., Mauffret, A., Patriat, P. and Pinet, suggest that the pre-rift crustal and lithospheric con- B. (1987) Profil ECORS Golfe du Lion: rapport d'implantation, Institut Fran~ais du Petrole, Report 35 941-1 figuration were different on each side of the NPFZ. For Choukroune, P. and ECORS-Team (1989) The ECORS Pyrenean the same value of 13, extension of the thickened and deep seismic profile reflection data and the overall structure elevated European continental crust led to a moderately of an Tectonics 8, 23-39 thinned crust (intermediate part of the margin), whereas Choukroune, P. and Mattauer, M. (1978) Tectonique des plaques extension of the Sardinia-Corsica continental block, et Pyr6n~es: sur le fonctionnement de la faille transformante nord-pyr~n6enne; comparaison avec des modules actuels little thickened during Pyrenean orogeny, led to an Bull. Soc. GeoL Fr. 20, 689-700 extremely thinned continental crust (basinward part of Cravatte, J., Dufaure, P., Prim, M. and Rouaix, S. (1974) Les the crust). forages du Golfe du Lion. Stratigraphie, sedimentologie The existence of an orogenically destabilized litho- Notes et Memoires, Compagnie Fran~aise des P$troles 11, sphere at the onset of extension has considerable 209-274 Crochet, J. Y. (1984) Geologie et paleontologie de la partie bearing on the mode of crustal extension and, conse- septentrionale du fosse oligoc6ne des Matelles (H~rault, sud quently, on the choice of pre-rift initial conditions. de la France) Geol. Fr. 1-2, 91-104 Future basin modelling of the Gulf of Lion must de Voogd, B., Nicolich, R., Olivet, J. L., Fanucci, F., Burrus, J., integrate the presence of an elevated and thickened Mauffret, A., Pascal, G., Argnani, A., Auzende, J. M., Bernabini, M., Bois, C., Carmignani, L., Fabbri, A., Finetti, I., continental crust before rifting, as well as crustal in- Galdeano, A., Gorini, C. Y., Labaume, P, Lajat, D., Patriat, P., homogeneities inherited from the Pyrenean orogeny. Pinet, B., Ravat, J., Ricci Luchi, F. and Vernassa, S. (1991) First deep seismic reflection transect from the Gulf of Lions to Sardinia (ECORS-CROP profiles in Western Mediter- Acknowledgements ranean). In: Continental Lithosphere: Deep Seismic Reflec- tion. AGU Geodyn. 22, 265-274 This work is supported by the European Community Echtler, H. and Malavieille, J. (1990) Extensional tectonics, DGXII (contract JOULE II - CEC Project n ° PL basement uplift and Stephano-Permian collapse basin in a 920287 Integrated Basin Studies). Elf Aquitaine, Esso- late Variscan metamorphic core complex (Montagne Noire, Rep, Total, Coparex and Elf-Atochem have provided Southern Massif Central) Tectonophysics 177, 125-138 Giot, D., Roure, F., Elmi, S., Lajat, D. and Steinberg, M. (1991) data for this study. The ideas contained in this contri- Decouverte d'accidents distensifs majeurs d'&ge jurassique bution benefited from discussions with N. Chamot- sur la marge continentale du bassin du sud-est, Ard~che, Rooke, J. M. Gaulier, A. Mascle, M. S~guret and R. France, (programme GPF) C. R. Adad. Sci. Paris 312, 747-754 Vially. We are grateful to H. Kooi, P. A. Ziegler, A. Golberg, J. M., Maluski, H. and Leyreloup, A. (1986) Petrological and age relationship between emplacement of magmatic Perez-Estaun and an anonymous reviewer for their in- breccia, alkaline magmatism, and static metamorphism in sightful and detailed comments which improved the the North Pyrenean zone Tectonophysics 129, 275-290 paper, and to S. Cloetingh for his editorial work. Gorini, C. (1993) Geodynamique d'une marge passive: le Golfe

Marine and Petroleum Geology 1995 Volume 12 Number 8 819 Structural style and evolution of the Gulf of Lion: M. Seranne et al.

du Lion (M~diterran6e Occidentale), Th~se de Doctorat, nord-occidental C. R. Acad. Sci. Paris 308, 9601-9607 Univ. Paul Sabatier - Toulouse 3, 256 pp McKenzie, D. (1978) Some remarks on the development of Gorini, C., Viallard, P. and Deramond, J. (1991) ModUle sedimentary basins Planet. Sci. Lett. 40, 25-32 d'inversion n6gative: la tectonique extensive post- du Pascal, G., Mauffret, A. and Patriat, P. (1993) The ocean- foss~ de Narbonne-Sigean (Corbi~res, sud de la France) C, R, continent boundary in the Gulf of Lion from analysis of Acad. Sci. Paris 312, 1013-1019 expanding spread profiles and gravity modelling Geophys. J. Gorini, C., Le Marrec, A. and Mauffret, A. (1993) Contribution to Int. 113, 701-726 the structural and sedimentary history of the Gulf of Lion Pascal, G., Truffert, C., Marquis, G. and Labaume, P. (1994) (western Mediterranean), from the ECORS profiles, industrial ECORS-Gulf of Lion deep seismic reflection profiles re- seismic profiles and well data Bull. Soc. G~oL Fr. 164, 353- visited: geodynamical implications [abstract]. In: 6th 363 Conference, European Association of Petroleum Gee- Grambast, L. (1962) Aper~;u des charophytes tertiaries du scientists & Engineers, Vienna, P803 Languedoc et leur signification stratigraphique C. R. Somm. Phi,libert, S. (1992) G~om~trie et cin~matique de I'extension Soc. G~oL Fr. 10, 313-314 oligoc~ne en Languedoc. Exemple du synclinal des Matelles Guennoc, P., Debeglia, N., Gorini, C., Le Marrec, A. and Mauffret, (H~rault), Dipl6me d'Etudes Approfondies, Univ. Montpellier A. (1994) Anatomie d'une marge passive jeune (Golfe du 2, 43 pp Lion - Sud France); apports des donn~es g~ophysiques Bull. R~hault, J. P., Boillot, G. and Mauffret, A. (1984) The western Cent. Rech. Explor.-Prod. Elf Aquitaine 18, 33-57 geological evolution Mar. GeoL 55, Hippolite, J. C., Angelier, J., Bergerat, F., Nury, D. and Guieu, G. 447-477 (1993) Tectonic-stratigraphic record of time Reston, T. J. 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(1989) ECORS deep seismic data and balanced Le Pichon, X. and Barbier, F. (1987) Passive margin formation by cross sections: geometric constraints on the evolution of the low-angle faulting within the upper-crust: the northern Bay Pyrenees Tectonics 8, 41-50 of Biscaye margin Tectonics 6, 133-150 Roure, F., Brun, J. P., Colletta, B. and Van den Driessche, J. Le Pichon, X. and Sibuet, J. C. (1981) Passive margins: a model (1992) Geometry and kinematics of extensional structures in of formation J. Geophys. Res. 86, 3708-3720 the Alpine of southeastern France J. Struct, Lister, G. S., Etheridge, M. A. and Symonds, P. A. (1991) Detach- GeoL 14, 503-519 ment models for the formation of passive continental S~ranne, M. and Malavieille, J. (Ed) (1994) Late orogenic margins Tectonics 10, 1038-1064 extension Tectonophysics Spec. Issue, 238, 484 pp Maerten, L. (1994) Stratigraphie s~quentielle et structure du Steckler, M. S. and Watts, A. B. (1980) The Gulf of Lion: sub- bassin de I'H~rault, Dipl6me d'Etudes Approfondies, Univ. sidence of a young continental margin Nature 287, 425-429 Montpellier 2, 52 pp Tapponnier, P. (1977) Evolution tectonique du syst~me alpin en Maerten, L. and S6ranne, M. Extensional tectonics of the Oligo- M~diterranee: poin~onnement et ~crasement rigide- Miocene H~rault Basin (S. France), Gulf of Lion Margin. Bull. plastique Bull. Soc. G~oL Fr. XIX, 437-460 Soc. G~oL Fr. in press Tempier, C. (1987) ModUle nouveau de mise en place des Mascle, A., Jacquart, G. and Deville, E. (1994) The Corbi~res structures proven(;ales Bull. Soc. G~oL Fr. 8, 409-628 transverse zone of the Pyrenees-Provence thrust belt (South Valette, M. (1991) Etude structurale du gisement salif~re France)- tectonic history and petroleum [abstract]. In: 6th oligoc~ne de Vauvert (), Th#se de Doctorat, Univ. Conference, European Association of Petroleum Geo- Montpellier II, 229 pp scientists & Engineers Vienna, P556 Valette, M. and Benedicto (1995) Chevauchements gravitaires Mauffret, A. and Gennesseaux, M. (1989) Compression, halotectoniques dans les bassin distensif de Camargue d~crochements et distension sur le pourtour m6diterran~en (Marge du Golfe du Lion, SE de la France) Bull. Soc. G6oL Fr.

820 Marine and Petroleum Geology 1995 Volume 12 Number 8