The Messinian Var canyon (Provence, southern France) — Paleogeographic implications

Marine Geology, 27 (1978) 231--246 ©

Elsevier Scientific Publishing Company, Amsterdam

231 --

Printed in The Netherlands

THE MESSINIAN VAR CANYON (PROVENCE, SOUTHERN PALEOGEOGRAPHIC IMPLICATIONS*

FRANCE) --

GEORGES CLAUZON

Laboratoire de G~ographie Physique, Universitd d'Aix-Marseille II, Aix-en-Provence (France) (Received July 14, 1977)

ABSTRACT Clauzon, G., 1978. The Messinian Var canyon (Provence, southern France) -- Paleogeographic implications. Mar. Geol., 27: 231--246. From north to south, the lower course of the Var River cuts through three tectonic units: (1) the Nice arc ("arc de Nice"), (2) the oriental part of the Castellane arc ("arc de Castellane"), and (3) the autochthonous Provencal substratum. The Nice and Castellane arcs are sub-Alpine overthrusts, emplaced near the end of the Miocene and reactivated in Plio-Quaternary times. During the Pliocene, the downstream section of the river was invaded by the sea and transformed into aria. The Pliocene sedimentary succession (Tahianian in its oldest levels) fossilizes a deeply incised erosional relief. In order to put together an orderly geographic reconstitution of this pre-Pliocene topography, one has to exclude from the study area the two sub-Alpine units, which were affected by neotectonics, and to limit the observations to the Provencal substratum. Some modest epeirogenic uplift of the substratum and its incision by erosion provide good outcrops of its sedimentary series. The Provencal substratum consists of Mesozoic and Cenozoic sediments, the youngest (Vence succession or "s~rie de Vence") ranging in age from Burdigalian to Tortonian. Chronostratigraphic constraints given by the underlying and overlying sediments respectively, indicate that the erosion surface is younger than Tortonian and older than Tabianian, and can, therefore, be dated as Messinian. Geological observations at the surface and geophysical investigations in the subsurface indicate that at some 40 km from the present abyssal plain of the western Mediterranean, the thalweg of the Messinian paleovalley cuts more than 500 m deep into the Provencal substratum. At 20 km from the abyssal plain, the same thalweg lies some 700 m beneath sea level, or some 1000 m below the former Miocene sea level. Cores and dredges obtained from the continental slope south of the Vat Valley suggest a progressive connection of the Plioeene ria with the abyssal plain. This gigantic incision now fiUed with Pliocene sediments and located along the continental shelf and the emerged land, represents a remarkable example of a Messinian canyon partially exhumed by the Plio-Quaternary epeirogenic movements. This canyon has been eroded subaerially by the paleo-Var River in a setting fairly similar to the modern margin. The subaerial erosion is a product of the endoreic regression that followed the isolation of the Mediterranean during the latest Miocene. The base level coincided with the level of the abyssal plain where evaporites were being deposited.

* Contribution No. 17 of IGCP Project No.96 "Messinian Correlation".

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The presence of Messinian canyons, at present more or less filled by younger sediments, along the continental margins of the Mediterranean basin (the case of the Var River is just one example among others) leads to an independent confirmation of the deep-basin desiccation hypothesis for the genesis of Messinian evaporites.

INTRODUCTION Even before the discovery of Messinian evaporites beneath the abyssal plains of the Mediterranean (Ryan et al., 1973) the age and process of excavation of the western Mediterranean canyons has been the object of numerous research investigations. The names of the eminent geologists J. Bourcart and L. Glangeaud are associated with these studies. The first Mediterranean deep-sea drilling expedition of the "Glomar Challenger" in 1970 created new interest related to the origin of these wellknown submarine canyons. For differentiating between the two genetic models of evaporite formation, the canyons were considered to be particularly decisive criteria. Essentially, if the present configuration of deep offshore basins and, especially, the development of the considerable depths of the abyssal plains were the unique result of a Plio-Quaternary subsidence, then the existence of older (Messinian) subaerial canyons cut into the margin is inconceivable. On the other hand, if it can be d o c u m e n t e d that such canyons originated at the time of the margin's evaporite formation, the magnitude of their incision is a measure of the extent of evaporite drawdown during deep-basin desiccation (Hsii et al., 1973; see also Hsii, 1973; Ryan, 1973; Cita, 1973) and their very presence refutes the shallow-water, shallowbasin hypothesis (Nesteroff, 1973). Bourcart, on the basis of his study of the Lacaze-Duthiers canyon, postulated a Pontian age for all the major canyons of the western Mediterranean (Bourcart, 1948, 1958a, b, 1959, 1963; Bourcart et al., 1961). Reinvestigation of the reference canyon with different techniques enabled Got (1973) to demonstrate that it had been an active site of erosion during the Pliocene and Quaternary. Based on this demonstration, some authors, including Leenhardt (1973) and Stanley et al. (1974), opted for a Recent age of the Balearic basin: " . . . These results have led us to conclude that the present configuration of the western Mediterranean basin is a geologically recent p h e n o m e n o n , and that the sea floor could not have been deep during Messinian salt deposition." (quoted after Stanley et al., 1974). Without debating the validity of the conclusion drawn by the aforementioned authors on the Catalan margin, one can dispute its extrapolation to the whole western Mediterranean basin, since canyons do exist on its margin, whose incision during the Late Miocene desiccation episode is beyond any doubt. One can list three canyons on the coast of France which do not appear to be Quaternary in age: those of the RhSne, the Durance and the Var (Fig.l). The RhSne and Durance canyons have been the subject of previous studies (Clauzon, 1973, 1975a). The Var canyon, which is the most telling example, will be discussed in the present paper.

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Fig.1. Sketch map showing the location of the study area in southern France. DEMONSTRATIVE I N T E R E S T IN THE VAR CANYON

(1) The Messinian Stage, represented in the abyssal plain by a massive 1-km thick flowing salt layer, is u n k n o w n on the emerged land of southern France (Olivet et al., 1971). On the contrary, a spectacular erosional surface can be traced across the continental shelf, resulting from a very active geodynamic evolution along the periphery of the evaporitic basin. (2) The chronological position of the erosional events can be located with accuracy. This erosion affects all of the so-called Vence succession ("s~rie de Vence") of the Provenqal substratum, which extends from the Burdigalian to the Tortonian (Ginsburg, 1960). The sedimentary cover which fossilized the erosional surface was first deposited in the Tabianian (Irr, 1971a, b, 1975). The interval of cutting is thus Messinian in age. (3) A recent and modest epeirogenic uplift brought the t o p of the Pliocene formations up to 350 m above sea level on the right bank of the Var canyon. This uplift has reactivated the erosion and has caused a partial reexhumation of the Var paleocanyon. (4) Within the s t u d y area, which extends over approx|mately 50 km from north to south, one can use several sources of information from the subsurface, including boreholes and seismic reflection profiles. On land there are the wells of Broc and Saint-Martin-du-Var, as well as a geophysical survey of the lower Var Valley (Horn et al., 1965). At sea there is the bathymetric map of the continental margin (Bourcart, 1956b, 1959, 1960), numerous seismic reflection profiles (Olivet et al., 1971; Rehault et al., 1974a, b) and submarine sampling (Genesseaux et Glaqon, 1972, 1973). These submarine data complete the observational data from the land record, so that the resulting paleogeographic reconstruction appears well founded. TOPOGRAPHIC AND S T R U C T U R A L SITUATION OF THE LOWER VAR VALLEY

The Vat River debouches into the Mediterranean Sea b y means o f an indentation more than 20 km in length which cuts into the foreland of

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southern France, including overthrusting sub-Alpine units. This incision was already existent in Pliocene times. It was drowned by a major marine transgression, transforming the indentation into a protected ria, within which a submarine delta was created, consisting of submarine conglomerates. This coastal embayment in the front of the Alpine edifice was aligned along the socalled Var fault, recognizable in seismic profiles as the boundary between two tectonic units: the Castellane arc ("arc de Castellane") to the west and the Nice arc ("arc de Nice") to the east. Upstream of Saint-Martin
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the Maures and Esterel external massifs. The basement has been detected by geophysical exploration at a depth of 4 km beneath the Vat (Rehault et al., 1974b). Its sedimentary cover, which consists essentially of Mesozoic and Cenozoic limestones, outcrops from the shoreline to the confluence of the Var and Esteron rivers. The youngest sediments of the autochthonous cover (Vence succession, see Goguel, 1936; De Lapparent, 1938; Ginsburg, 1960 ) are Tortonian in age. (2) A large slice of sub-Alpine material unconformably overlies the northern edge of the Provenqal substratum. The disjunction is at the level of the Triassic, which is a gypsiferous facies. The so-called Baous overthrust ("chevauchement des Baous"; Goguel, 1936), which represents the southeastern termination of the Castellane arc, has a radius of approximately 5 km. (3) The autochthonous unit and its overlying sub-Alpine tectonic slice, as well as the covering delta of the Var, are limited in exposure and occasionally also overthrusted by the Nice arc (Bertrand, 1905; G6ze, 1963; Vernet, 1968; Bulard et al., 1975). This arc, as well as the Castellane arc, belong to the sub-Alpine sedimentary domain. R E T R O T E C T O N I C ANALYSIS

I have demonstrated that, contrary to previous thinking (Glangeaud, 1967), the emplacement of these three structural units (the Provenqal unit, the Baous overthrust, and the Nice arc) was later than the pre-Pliocene cutting of the Var canyon (Clauzon, 1975a, 1976). Since the latest tectogenetic episodes of the Castellane and Nice arcs were diachronous, the geodynamic evolution of this area from the Miocene onwards is fairly complex. In order to precisely reconstruct the original configuration of the Var paleovalley, it is essential to make a retrotectonic analysis. On the right bank of the Var, the Baous overthrust did not undergo a Quaternary reactivation, with the exception of the epeirogenic uplift, which also involved its substratum. On the left bank, instead, there is evidence of a Villafranchian (Late Pliocene to Early Quaternary) orogenic phase on the front of the Nice arc. The retrotectonic analysis will therefore start from this latter unit, which was recently deformed. Quaternary neotectonics o f the "arc de Nice" At the foot of the Baous overthrust, the Pliocene marine conglomerate keeps its original sedimentary setting and does not rise above a height of 350 m. On the left bank of the river, these same formations have a vertical dip in contact with the "arc de Nice" (Maury, 1923; LIGUS, 1955; Perriaux, 1957; Vernet, 1962, 1968; G~ze, 1963), reaching a height of 500 m above sea level. In between Aspremont and Saint-Blaise, one can see a real overthrust, not a simple straightening as described by the aforementioned authors. The deformation dates back to the Quaternary or to the terminal Pliocene. The Pliocene conglomerates have been uplifted to more

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Fig.3. The l o w e r Var Valley in its s t r u c t u r a l frame. 1 = T e c t o n i c c o n t a c t (Nice arc over. t h r u s t ) ; 2 = Baous o v e r t h r u s t ; 3 = Provencal a u t o c h t h o n o u s u n i t ; 4 = Baous s u b - A l p i n e slice; 5 = Nice arc ( " a r c de N i c e " ) ; 6 = Pliocene erosional d i s c o r d a n c e ; 7 = Messinian erosional d i s c o r d a n c e ; 8 = infra-Miocene u n c o n f o r m i t y ; 9 = V a t alluvial plain; 1 0 = Pliocene delta o f t h e Var ( " d e l t a plioc~ne du V a r " ) ; 11 = Messinian breccia o f Carros; 1 2 = M i o c e n e V e n c e succession ("s~rie de V e n c e " ) .

than 700 m on the flanks of Mount Cima (Figs.3 and 4). Along the paleochannel of the Vat, they rise from 600 m above sea level near Levens to 1000 m at Collet de Huesti (Maury, 1916). However, this eastern part of the valley of the Var does not play an

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essential role in our reconstruction. The paleogeographic evidence has been mostly buried, or it is inaccessible due to subsequent deformation. Moreover, we have no observational data from the subsurface so that we cannot make a realistic estimate of the total thickness of the Pliocene deposits under the "arc de Nice". From the outcrops of the Pliocene conglomerates, the visible thickness is some 300 m. The uplift resulting from the Quaternary neotectonics along the longitudinal profile of the pre-Pliocene thalweg is up to 200 m. The Pliocene paleovalley upstream of this breaking off is considerably uplifted and it underwent a strong erosion: only a few scattered fragments can be observed (see Figs.3 and 4).

The emplacement of the Baous sub-Alpine overthrust The emplacement of the Baous overthrust postdates the youngest element of the Miocene sedimentary succession of Vence, which is referred to the Tortonian (Ginsburg, 1960). The precise age o f the tectonic event is controversial (Zfircher, 1900, 1905; Gu~bhard, 1903, 1905); the debate concerns in particular the chronologic attribution of the Carros breccia. This synorogenic unit (Clauzon, 1975a, 1976) seals the overthrust at Chapelle SaintSebastien; consequently, its age determination also involves the age of the overthrust. A fossil fauna was recovered in the breccia (Gu~bhard, 1903, 1905) and has been assigned to the Astian b y Dep~ret and Caziot (1903) and to the Early Pliocene b y De Lapparent (1938). These biostratigraphic determinations led several authors to infer either a Pliocene, or a Miocene to Pliocene age for b o t h the breccia and the overthrust (De Lapparent, op. cit.; Ginsburg, 1960). However, a recent reexamination of the fossiliferous beds has shown that t h e y are marls which consistently overlie the coarse breccia and that they are in a situation o f a reworked beach deposit within the erosional cleft (Clauzon, 1976). According to the micropaleontological evidence provided b y Irr (1971b), the episode of resedimentation involving some of the underlying breccia occurred in the Pliocene.

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The Early Pliocene age attributed to the Carros breccia involved the existence of a lateral facies change from the coarse breccia to the fossiliferous marls of Saint-Martin-du-Var. An imbrication of these t w o facies is never observed at the surface; it should, however, occur at depth. The Broc borehole, located in the thalweg of the Vat River right where such a lateral facies change might occur (see Fig.3) revealed a normal superposition of the t w o facies (breccias below, marls above) instead of the postulated interfingering. It follows from the above observations that the Carros breccia stratigraphically underlies the oldest Pliocene deposits known from this area, or in other words, it is older than the Tabianian identified at Saint-Martin-du-Var (Irr, 1971a, b, 1975), and it is younger than the Tortonian of the Vence succession. Consequently, b o t h the breccia and the emplacement of the sub-Alpine unit of Baous have to be referred to the Messinian. Apparently, ever since Messinian times, the overthrust did not undergo neotectonic deformations other than an epirogenic uplift which affected the entire region.

The Provencal autochthonous unit The Provenqai unit, the lowest both topographically and structurally among those discussed here, underwent a synclinal deformation before the arrival of the sub-Alpine nappe. The synclinal fold had a medium bending radius and is d o c u m e n t e d in the sedimentary basin of Vence by olistoliths which crown the succession (Goguel, 1936; Ginsburg, 1960). These precursory movements of the Messinian tectonic episode are the youngest recorded by the Provenqal substratum before the overthrust of the subAlpine allochthonous unit. The retrotectonic analysis permits one to reconstruct the topographic and structural setting predating all the deformations. In addition to the geometric placement of the various tectonic units, however, we have to consider carefully the stratigraphic, sedimentary and paleogeographic information provided by the only a u t o c h t h o n o u s unit. THE PRE-PLIOCENE E R O S I O N A L GAP

Two series of the Neogene of the lower Var Valley are recognized: (1) the Miocene series of Vence, of Burdigalian to Tortonian age, and (2) the Var series of Messinian to Middle--Late Pliocene age. From a structural point o f view, the former predates the sub-Alpine overthrust, whereas the latter postdates it. The depressions in which these successions have been deposited had a spacial configuration as well as a t o p o g r a p h y which were entirely different one from the other. The Vence succession originated in an epicontinental basin striking east to west. The younger Messinian and Pliocene sediments filled a deep channel of a north to south orientation. A major discordance is recorded between these t w o sedimentary epochs. It is n o t an angular unconformity, b u t an erosional discordance, for b o t h overlying and underlying beds are entirely horizontal.

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The erosional surface between the Vence and Var successions deserves a detailed discussion. The tectonic contact on t o p of the Vence succession consistently lies between 450 and 500 m above sea level on the western bank of the Var, in b e t w e e n St. Jeannet and Le Broc (Fig.4). To the east o f the village of Carros, in the axis o f the Vence syncline, the thickness of the horizontal Miocene strata is approximately 400 m. Since the base of the thrust is more or less at the Tortonian pre-regression sea level, the depth of the infra-Pliocene succession can be measured at 500--600 m below Tortonian sea level prior to the retreat of the sea during the Messinian. The calculations are as follows: (1) the top of the Miocene succession is approximately 500 m above sea level, (2) the exposed base of the Miocene is at +90 m, and (3) in a well at Le Broc, the base of the sedimentary fill of the Var was encountered at 200 m below the riverbed, or at approximately 100 m beneath sea level. Consequently, the relative difference between the youngest Miocene (pre-erosion Tortonian) and the oldest Pliocene (post-erosion Tabianian) is 400 + 200 = 600 m. These data are supported b y the geophysical study o f the lower Var Valley (Horn et al., 1965). The exceptionally high value of the relative relief at this point, as well as the considerable thickness of the Pliocene formations in the ria of the Var, are puzzling. H o w was the general configuration of the erosional surface? What was its genesis? The Messinian e v e n t

The gigantic erosion predated the emplacement of the sub-Alpine overthrust. Indeed, the Carros breccia (derived from the overthrust) has infilled and then preserved the erosional surface. The classical conception which claimed that the cutting was derived from orogenic uplift (i.e., tectonically controlled) is refuted b y the breccia sedimentary contact. The examination of the basal contact of the breccia on the right bank shows a paleoexpression of a thalweg oriented WNW--ESE, dipping downslope towards the present Mediterranean (Fig.5). All these parallel thalwegs are tributaries of the Var, which was then probably oriented NNE--SSW. This general collector tributary of a southern base level was located eastwards of the present-day river, along the axis of the Pliocene ria. In b e t w e e n the paleovaUeys with steep longitudinal slopes (Fig.5, profile C--D), Miocene marls and Nummulitic marls were sculptured into giant badlands. The essentially transient character of such a topography involves a rapid fossilization of a juvenile relief, which halted before it could evolve into anything more mature. The pre-Tabianian paleotopography which postdates the retreat of the Miocene sea down into the abyssal plain and which predates the formation of breccias from the overthrust sheet, would appropriately seem to correlate with the time of evaporitic drawdown.

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Fig.5. The outcrop of the Saint-S~bastien--Bau Rous Chapel. The Cazros breccia, unconformably overlying the Miocene marine section of Vence by means of an erosional surface, fossilizesa paleovalley tributary of the Var and seals the sub-Alpine overthrust of Baous. A bore: transverse profile (A--B) and longitudinal profile (C--D) of the Messinian paleovalley of Bau Rous. Below: the erosional discordance of Bau Rous. 1 = Pre-Miocene Provenqal substratum; 2 = Vence succession, basal part. 3 = Vence succession (Middle and Late Miocene): a as shown in sketch m a p and b as shown in the sections; 4 = Baous sub-Alpine slice;5 = Carros breccia; 6 = alluvial Plain of the Var; 7 = Infra-Miocene unconformity; 8 = Messinian e r o s i o n a l d i s c o r d a n c e ; 9 = B a o u s o v e r t h r u s t : a as s h o w n in t h e s e c t i o n s a n d b as s h o w n in sketch map.

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The fragments of this paleo-drainage system are faithfully preserved only in the Provenqal a u t o c h t h o n o u s substratum. The Baous overthrust does n o t show any trace of it. The outcrops of Pliocene conglomerates existing within the Nice arc permit a reconstruction that is only broadly approximate and discontinuous. If one restores the nappes to their pre-tectonic setting, or in other words if one displaces the Baous structural unit some kilometers to the north and the Nice arc several hundred meters to the northeast, t w o paleogeographic domains appear. Southwards, the Provenqal domain would have occupied a shallow epicontinental basin in a regressive phase. Northwards there would have been an emerged continental domain (the sub-Alpine domain) without a strong relief. The continental areas were the site o f the Alps before its orogenic crisis. If the erosional event was caused by tectonic uplift of the Alpine chain during the so-called terminal Miocene phase, then one would expect the geomorphic expression o f downcutting to be greater in the hinterland. If the erosional event is b y a lowering of the sea, the resulting relief would be greater at the shoreline and would migrate landward (see Clauzon, 1975a, 1976). The amplitude of the necessary change in base level (shown on land b y the incision o f over 500 m as discussed above) requires a drop in sea level well b e y o n d the emerged Late Miocene continental shelf and it could very well have extended to the abyssal plain.

Arguments for a subaerial cutting Between Saint-Martin-du-Var upstream and the abyssal plains downstream, we have enough observational data to reconstruct a longitudinal profile of the buried Var canyon beneath Plio-Quaternary sediments. This setting with an incision of 500 m below sea level is 40 km from the edge of the modern abyssal plain and 45 km from the salt pinchout (W.B.F. Ryan, personal communication). Jurassic limestones have been detected b y reflection profiles at - 7 0 0 m to the east of the river m o u t h (Horn et al., 1965) and at the edge of the sea (Olivet et al., 1971). Pliocene marls and conglomerates infill the canyon. If we add to this the approximately 200 m of Pliocene conglomerates which the Vat had to accumulate in order to build its present river bed, we obtain 700 + 200 = 900 m for the cutting of the pre-Pliocene thalweg. The downslope course of the Messinian canyon extrapolates at the coast to a depth of --1000 m at a distance of only 20--25 km from the abyssal plain. Beneath the sea the Pliocene marls which infill the canyon of Bale des Anges (Bourcart, 1960; Olivet et al., 1971) correspond to the downstream filling of the Var ria. The upstream clays of Saint-Martin-du-Var of Tabianian and Piacenzian age (Irr, 1971a, b, 1976) are also found at the m o u t h of the ancient canyons.

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Indeed, they have been cored and dredged some 15 km landward of the abyssal plain at --1000 m (Piacenzian in age) and at --1700 m (Tabianian in age) where the canyon exits onto the abyssal plain (Genesseaux and Glaqon, 1972, 1973). All these data allow one to represent in a fairly precise manner the configuration of the Messinian canyon. The cutting into the Provenqal substratum is developed with progressive deepening, in a N--S direction, of approximately 50 km, gradually passing from a depth of--500 m beneath Tortonian strata upstream to a depth of --2000 m downstream. We must recall however that the upstream limit is hidden by a tectonic overthrust and certainly this artificial termination is not the head of the Messinian paleocanyon. The incision, whose bottom is covered throughout by Tabianian sediments, results from the endoreic Messinian regression (Clauzon, 1975a). It shows that the regression extended to the level of the abyssal plain. This conclusion also requires that the Messinian evaporites which are present a few tens of kilometers basinwards of the abyssal plain edge (Olivet et al., 1971) have been deposited in a relatively deep basin from which the water was removed by desiccation (Hsfi et al., 1973; Cita, 1974). The Var canyon has been cut subaerially. It cuts through the continental margin exposed by the endoreic Messinian regression of an unusual amplitude (Clauzon, 1973, 1975a, b, 1976). The total absence of marine formations of this age on land as well as on the continental margin supports this continental geodynamic episode. CONCLUSION

It is probable that during the epeirogenic Plio-Quaternary uplift already mentioned the continental margin was downflexured. This differential movement would accentuate the longitudinal profile of the canyon but it does not affect the measured depths. We cannot evoke marginal flexure to counter any of the conclusions reached by calculated measurements of the relative relief of the canyon thalweg in respect to the strata into which it is incised. The existence of the Var canyon demonstrates that the Balearic Basin (Auzende et al., 1973) shared abyssal depths since the Miocene. It is worthwhile mentioning that the Vat canyon is not an isolated example. At least three additional examples concur in the southern continental margin of France, namely (1) the canyon of Cassidaigne (Fernex et al., 1974), (2) the Pliocene rias of the RhSne (Denizot, 1953; Beaufort et al., 1954; Ball~sio, 1972; Clauzon, 1973,1975b) and (3) of the Durance (Clauzon, 1972, 1975a). The common presence of these paleoforms is a strong support that the general configuration of the Provenqal margin of the Balearic Basin was already in existence in Messinian times and that the abyssal plain cannot have resulted uniquely from Plio-Quaternary foundering (Bellaiche, 1972; Leenhardt, 1973; Nesteroff, 1973; Burollet and Byramjee, 1974; Stanley et al., 1974; Irr, 1975).

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If it is inconceivable under this circumstance to imagine that the Messinian evaporites could be deposited in a shallow basin, then on the contrary the deep-basin desiccation model receives a powerful confirmation. ACKNOWLEDGMENTS T h e p r e s e n t m a n u s c r i p t has b e e n critically reviewed b y M.B. Cita, W.B.F. R y a n , K.J. Hsfi, X. Le P i c h o n and D.J. Stanley. REFERENCES Auzende, J.M., Bonnin, J. and Olivet, J.L., 1973. The origin of the western Mediterranean basin. J. Geol, Soc. London, 129: 607--620. Ball~sio, R., 1972. Etude stratigraphique du Plioc~ne rhodanien. Doc. Lab. Geol. Fac. Sci. Lyon, 53:333 pp. Beaufort, L., Bruneau, J., Gr~pin, A. and JuUian, Y., 1954. Ampleur de l'~rosion pontienne et du comblement plioc/me en Camargue. Bull. Soc. Geol. Fr., (6), 4: 175--184. Bellaiche, G., 1972. Pr~l~vement par 2000 m de profondeur d'un r~flecteur acoustique d'~ge plioc~ne inf~rieur ~ faciespeu profond (canyon des Stoechades, M~diterran~e nord-occidentale). Nouvelles donn~es sur le creusement des canyons sous-marins et l'amplitude des mouvements verticaux ponto-plio-quaternaires. C.R. Acad. Sci.,Ser. D, 275: 321--324. Bertrand, L., 1905. Sur les grandes lignes de la g~ologie de la partie alpine des AlpesMaritimes. Bull. Soc. Geol. Fr., (4), 2: 638--675. Bertrand, L. and Ziircher, P., 1902. Notice de la feuillede Nice au 1/80 000 ° , 1° ~d. Bourcart, J.. 1948. Sur la gdologie sous-marine du "rech" Lacaze--Duthiers, canyon sousmarin du Roussillon. C.R. Acad. Sci., Set. D, 226: 1827--1829. Bourcart, J., 1958a. Probl~mes de g~ologie sous-marine. Masson, Paris, 127 pp. Bourcart, J., 1958b. Carte du Pr~continent sous-marin entre Antibes et G~nes, no.1. Mus~e oc~anographique, Monaco. Bourcart, J., 1959. Morphologie du pr~continent des Pyrenees ~ la Sardaigne. In: La topographie et la g~ologie des profondeurs ocdaniques. Colloq. C.N.R.S., Villefranche, pp.33--52. Bourcart, J., 1960. Carte topographique du fond de la M~diterran~e occidentale. Bull. Inst. Oceanogr. Monaco, 1163 : 3--20. Bourcart, J., 1963. La M~diterran~e et la r~volution du Plioc~ne. In: Livre Ala m~moire du Professeur P. Fallot. Mere. Soc. Geol. Fr., 1: 105--116. Bourcart, J., Gennesseaux, M. and Klimek, E., 1961. Sur le remplissage des canyons sousmarins de la M~diterran6e fran~aise. C.R. Acad. Sci., Ser. D, 252: 3695M3698. Bulard, P.F., 1975. Sur la gen~se et les structures de l'Arc de Nice. Bull. Soc. Geol. Fr., (7), 17: 939--944. Burollet, P.F. and Byramjee, R., 1974. Evolution g~odynamique de la M~diterrande occidentale. C.R. Acad. Sci., Ser. D, 278: 1321--1324. Campredon, R. and Boucarut, M., 1975. Alpes-Maritimes, Maures, Esterel. Masson, Paris, 175 pp. Cita, M.B., 1973. Mediterranean evaporite: paleontological arguments for a deep-basin dessication model. In: C.W. Drooger (Editor), Messinian Events in the Mediterranean. North-Holland, Amsterdam, pp.206--228. Cita, M.B., 1974. Stratigraphie du N~og~ne dans les fonds matins de la M~diterran~e. In: 5 Congr. Ndog~ne M~diterr., Lyon, 1971. Mere. B.R.G.M., 78: 387--397. Clauzon, G., 1972. Sur la presence d'une br~che syntectonique d'~ge miocene sup~rieur surle flanc sud du Petit Luberon (Vaucluse). C.R. Acad. Sci., Ser. D, 273: 1963--1966.

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