The Messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years (1–3). Earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated Mediterranean basin that had been repeatedly isolated from the Atlantic Ocean1,2, but elucidation of the causes of the isolation — whether driven largely by glacio-eustatic or tectonic processes — have been hampered by the absence of an accurate time frame. Here we present an astronomically calibrated chronology for the Mediterranean Messinian age based on an integrated high-resolution stratigraphy and ‘tuning’ of sedimentary cycle patterns to variations in the Earth's orbital parameters. We show that the onset of the Messinian salinity crisis is synchronous over the entire Mediterranean basin, dated at 5.96 ± 0.02 million years ago. Isolation from the Atlantic Ocean was established between 5.59 and 5.33 million years ago, causing a large fall in Mediterranean water level followed by erosion (5.59–5.50 million years ago) and deposition (5.50–5.33 million years ago) of non-marine sediments in a large ‘Lago Mare’ (Lake Sea) basin. Cyclic evaporite deposition is almost entirely related to circum-Mediterranean climate changes driven by changes in the Earth's precession, and not to obliquity-induced glacio-eustatic sea-level changes. We argue in favour of a dominantly tectonic origin for the Messinian salinity crisis, although its exact timing may well have been controlled by the ∼400-kyr component of the Earth's eccentricity cycle.

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Chronology, causes and progression of the Messinian salinity crisis

https://hal.archives-ouvertes.fr/hal-00199887/document

Phanerozoic geological evolution of Northern and Central Africa: An overview

The Messinian Salinity Crisis: Past and future of a great challenge for marine sciences

The Messinian salinity crisis in the Mediterranean basin: A reassessment of the data and an integrated scenario

The Mediterranean Sea became disconnected from the world's oceans and mostly desiccated by evaporation about 5.6 million years ago during the Messinian salinity crisis. The Atlantic waters found a way through the present Gibraltar Strait and rapidly refilled the Mediterranean 5.33 million years ago in an event known as the Zanclean flood. The nature, abruptness and evolution of this flood remain poorly constrained. Borehole and seismic data show incisions over 250 m deep on both sides of the Gibraltar Strait that have previously been attributed to fluvial erosion during the desiccation. Here we show the continuity of this 200-km-long channel across the strait and explain its morphology as the result of erosion by the flooding waters, adopting an incision model validated in mountain rivers. This model in turn allows us to estimate the duration of the flood. Although the available data are limited, our findings suggest that the feedback between water flow and incision in the early stages of flooding imply discharges of about 10(8) m(3) s(-1) (three orders of magnitude larger than the present Amazon River) and incision rates above 0.4 m per day. Although the flood started at low water discharges that may have lasted for up to several thousand years, our results suggest that 90 per cent of the water was transferred in a short period ranging from a few months to two years. This extremely abrupt flood may have involved peak rates of sea level rise in the Mediterranean of more than ten metres per day.

Catastrophic flood of the Mediterranean after the Messinian salinity crisis

A high-resolution chronology of the Mediterranean Messinian salinity crisis is proposed. Two types of evaporite deposition may be distinguished: those in marginal areas vs. those in basinal ones. Their diachroneity is deduced from the stratigraphic relationships linking these evaporites to a major Messinian erosional surface, A two-step model is proposed for the evolution of the salinity crisis through time. During the first phase (from 5.75 to 5.60 Ma), the deposition of marginal evaporites took place in response to a modest sea-level fall; in the second interval (from 5.60 to 5.32 Ma), the Mediterranean basin became isolated. During this later period, the deposition of basinal evaporites and the cutting of the Mediterranean canyons took place.

Alternate interpretation of the Messinian salinity crisis: Controversy resolved?

The seismicity of southern France probably results from the convergence between Africa and Europe which proceeds at a rate of approximately 0,8 cm/year at the Provence longitude [Nuvell-DeMets et al., 1990]. The potentially active faults delimit a large panel in the Mesozoic cover. It includes E-W compressive structures (Mont-Ventoux, Montagne de Lure to the north, Luberon, Costes et Trevaresse to the south) and NE left-lateral strike slip (Durance to the east and Nimes, to the west, and possibly the Cevennes Fault) [e.g., Grellet et al., 1993; Sebrier et al., 1997; Lacassin et al., 1998]. The Nimes Fault, which is considered as one of the main faults of southeastern France [Combes, 1984; Grellet et al., 1993; Ghafiri, 1995] is associated with only few and small seismic events, but paleoseismic evidence for larger earthquakes, with magnitudes possibly as large as 6.5, were found on a subsidiary fault near Courthezon [Combes et al., 1993]. Here, we try to quantify fault activity over a longer period of time than that accessible from the usual geomorphic approach, by assessing possible displacement of Messinian markers on the Nimes fault. In the early Miocene a regional erosion surface of Burdigalian age (around-20 Ma) was formed. This surface is still preserved and has not been much deformed west of the Nimes fault. To the east, this surface is only gently folded due to E-W anticlines [Champion, 1999; Champion et al., 2000]. This contrast suggests that the Nimes fault has been active and has accommodated N-S shortening after the abandonment of the Burdigalian erosion surface. The Nimes and Pujaut faults can be followed in the topography between Nimes and Sauveterre where they are generally bounded by outcrops of Mesozoic limestone (fig. 2A-3). To the NE, the Nimes fault can be roughly traced across the Quaternary Rhone alluvium, between Sauveterre and the Mont Ventoux. It is marked by disruption of the continuity of the terrasses of Chateauneuf-du-Pape. The signal is only tenuous and cannot be used to infer precisely the fault location and segmentation but suggests that the faults have been active during the Quaternary. During the Messinian, starting at about -5.95 Ma, the Mediterranean sea level fell by about 1500 m [Clauzon, 1975; Krijgsman et al., 1999; Gautier et al., 1994; Cande et Kent, 1992-1995; Clauzon et al., 1995]. The major tributaries were forced to cut down and formed deep and narrow valleys. The Mediterranean sea rose up to an elevation of +80 m NGF at -5.32 Ma, flooding the canyons, and remained stable until about -3.8 Ma [Vail and Mitchum, 1979; Benson et al., 1991; Cita, 1975; Haq et al., 1987; Hilgen et Langeries, 1993]. After -5.32 Ma the canyons were filled with Pliocene sediments. The canyon formed by the Rhone incision during the Messinian crisis is well documented [Clauzon, 1982; Clauzon et al., 1995; Clauzon et al., 1999; Rubino et al., 2000]. We found evidence for a tributary canyon on an old seismic line ELF M2S8. The canyon strikes E-W between the "Barre de Roquemaure" and "Barre de Caderache" and should cross the Nimes Fault. In order to constrain more tightly its geometry near the Nimes Fault, we have implemented three seismic lines. If we trace the position of the southern border of the canyon using the different profiles and the surface geology, we find that the horizontal offset at the fault cannot be much larger than about 500 meters. In order to image a possible smaller offset we have determined the geometry of the canyon from a microseismic zoning technique [Nakamura, 1989; Duval et al., 1997; Ibs-von Seht M. and Wholenberg, 1999; Sabourault, 1999]. Measurements were conducted at 37 points which were used in complement. The depth to the canyon bottom was determined using the velocities derived from the seismic profiles and was cross-checked from the comparison with geological log at points F1 and F2. The geometry of the southern edge of the Messinian canyon, shows a left-lateral offset of 440 m + or -50 m, which might be taken to reflect post-Messinian fault motion. Assuming that the observed 440 m offset of the Messinian canyon at the Nimes fault is due to fault motion, and that the fault slip rate has not varied significantly since the Messinian crisis, we derive a left-lateral slip rate of 0.06 to 0.09 mm/year. Given that the observed deflection of the flank of the canyon might in part be of non tectonic origin, our study basically places an upper limit of 0.09 mm/yr on the slip rate on the Nimes faults. Such a low slip rate is comparable with estimates obtained on the Durance Fault [Baroux, 2000] and on the E-W folds and thrust faults east of the Nimes faults such as Ventoux-Lure and Alpilles-Costes-Trevaresse [Champion, 1999; Champion et al., 2000]. Although the details of the kinematics scheme of active deformation of Provence remain a matter of discussion, these various faults are probably linked and must have similar slip rates.

Mouvement post-messinien sur la faille de Nîmes: Implications pour la sismotectonique de la Provence

Commentaire sur l’article " Mouvement post-messinien sur la faille de Nîmes : implications pour la sismotectonique de la Provence "

The Messinian salinity crisis is typically recorded by evaporites in the abyssal plains of the Mediterranean Sea and by canyons incised into the Mediterranean margins and their hinterlands However, the impacts of crisis on geomorphology and surface dynamics lasted, until canyons were filled by sediments in the Pliocene (fig 2)

In the mid-Rhone valley, the Ardeche Cretaceous carbonate platform is incised over 600 m by the Rhone Messinian canyon The canyon thalweg is located -- 236 m bsl (below sea level) in the borehole of Pierrelatte [Demarcq, 1960; fig 1] During the Pliocene, this canyon was flooded as a ria and infilled by a Gilbert type fan delta [Clauzon and Rubino, 1992; Clauzon et al, 1995] The whole Messinian-Pliocene third order cycle [Haq et al, 1987] generated four benchmark levels

The first two are [Clauzon, 1996]: (i) The pre-evaporitic abandonment surface which is mapped around the belvedere of Saint-Restitut (fig 1) This surface is synchronous [Clauzon, 1996] of the crisis onset (595 Ma) [Gautier et al, 1994; Krigjsman et al, 1999] and, consequently, is an isochronous benchmark (ii) The Messinian erosional surface is also an isochronous benchmark due to the fast flooding [Blanc, 2002] of the Rhone canyon, becoming a ria at 532 Ma [Hilgen and Langereis, 1988] These surfaces are the result of endoreic Mediterranean sea level fall more than a thousand meters below the Atlantic Ocean

A huge accommodation space (up to more than 1000 m) was created as sea-level rose up to 80 m above its present-day level (asl) during the Pliocene highstand of cycle TB 34 (from 532 to 38 Ma) During the Lower Pliocene this accommodation space was filled by a Gilbert fan delta This history yields two other benchmark levels: (i) the marine/non marine Pliocene transition which is an heterochronous surface produced by the Gilbert delta progradation This surface recorded the Pliocene highstand sea level; (ii) the Pliocene abandonment surface at the top of the Gilbert delta continental wedge

Close to the Rhone-Ardeche confluence, the present day elevations of the four reference levels are (evolution of base-level synthesized in fig 4): (1) 312 m asl, (2) 236 m bsl, (3) 130 m asl, (4) 190 m asl

The Ardeche carbonate platform underwent karstification both surficial and at depth The endokarst is characterized by numerous cavities organised in networks Saint-Marcel Cave is one of those networks providing the most complete record (fig 5) It opens out on the northern side of the Ardeche canyon at an altitude of 100 m It is made up by three superposed levels extending over 45 km in length The lower level (1) is flooded and functionnal It extends beneath the Ardeche thalweg down to the depth of 10 m bsl reached by divers The observations collected in the galleries lead us to the conclusion that the karst originated in the vadose area [Brunet, 2000] The coeval base-level was necessarily below those galleries The two other levels (middle (2) and upper (3)) are today abandoned and perched The middle level is about 115 m asl and the upper one is about 185 m asl They are horizontal and have morphologies specific to the phreatic and temporary phreatic zone of the karst (fig 6)

In literature, the terracing of the Saint-Marcel Cave had been systematically interpreted as the result of the lowering by steps of the Ardeche base-level [Guerin, 1973; Blanc, 1995; Gombert, 1988; Debard, 1997] In this interpretation, each deepening phase of the base level induces the genesis of the gravitary shaft and the abandonment of the previous horizontal level The next stillstand of base level leads to the elaboration of a new horizontal level (fig 7) This explanation is valid for most of Quaternary karsts, that are related to glacioeustatic falls of sea-level However our study on the Saint-Marcel Cave contests this interpretation because all the shafts show an upward digging dynamism and no hint of vadose sections The same "per ascensum" hydrodynamism was prevailing during the development of the whole network (figs 8 and 9)

We interpret the development of the Ardeche endokarst as related to the eustatic Messinian-Pliocene cycle TB 34/35 recorded by the Rhone river The diving investigations in the flooded part of the Saint-Marcel Cave and also in the vauclusian springs of Bourg-Saint-Andeol reached - 154 m bsl Those depths are compatible only with the incision of the Messinian Rhone canyon at the same altitude (-236 m bsl) The Saint-Marcel lower level would have develop at that time The ascending shaping of levels 2 and 3 is thus likely to have formed during the ensuing sea-level rise and highstand during the Pliocene, in mainly two steps: (i) the ria stage controlled by the Mediterranean sea level rise and stillstand; (ii) the rhodanian Gilbert delta progradation, that controlled the genesis of the upper level (fig 10)

The Ardèche endokarstic responses to the eustatic variations resulting from the Messinian salinity crisis

Le plateau de Saint-Remeze est forme d'une plate-forme carbonatee d'âge mesozoique qui borde la moyenne vallee du Rhone. Cette plate-forme est intensement karstifiee, comme l'atteste la grotte de Saint-Marcel dont le developpement depasse 53 km. La grotte de Saint-Marcel presente un etagement des reseaux sur plusieurs niveaux. Deux de ces niveaux (intermediaire et superieur) presentent des conduits dont une grande partie est abandonnee par les ecoulements, ils presentent de grandes sections de conduits qui se developpent horizontalement sur plusieurs kilometres. Le troisieme niveau (inferieur) est actif et partiellement noye, il a ete reconnu en plongee jusqu'a 65 m sous le niveau de l'Ardeche. L'etagement des niveaux horizontaux n'a aucun lien avec la structure geologique qui est recoupee sans distinction. Cette observation permet de saisir le role structurant du niveau de base et de prendre en compte son evolution dans la formation du karst ardechois. Dans le perimetre des gorges de l'Ardeche et de la moyenne vallee du Rhone, l'investigation des niveaux reperes generes par la crise de salinite messinienne permet une restitution de l'evolution du niveau de base regional. Cette restitution de l'evolution des niveaux a permis d'etudier la grotte de Saint-Marcel dans un cadre geodynamique et chronologique d'une duree de six millions d'annees. Couplees aux variations du niveau de base, les investigations morphologiques menees dans la grotte ont restitue trois grandes phases de speleogenese et deux grands modes de circulation des eaux souterraines. Il s'agit en premier lieu de la structuration en profondeur du drainage du plateau de Saint-Remeze lors du creusement des canyons messiniens durant la crise de salinite. Au lendemain de la crise, a 5,32 Ma, la transgression pliocene a provoque une brusque remontee du niveau de base produisant un refoulement hydrologique aux exutoires du karst messinien. La resistance hydraulique a declenche le creusement per ascensum de conduits vaudusiens : les puits-cheminees. La reponse du systeme de drainage s'est reproduite au cours du Pliocene a chaque stade de la remontee du niveau de base. Durant le Pliocene (5,32 a 2 Ma), lors du remblaiement des rias, l'Ardeche a aussi connu de longues phases de stabilite propices a la speleogenese. Il s'agit d'un drainage des eaux du plateau de Saint-Remeze sur lequel se sont connectes de larges recoupements souterrains de meandre de l'Ardeche. L'observation detaillee des grands niveaux de l'endokarst a revele en retour l'existence de stades intermediaires dans l'evolution du niveau de base et permis d'affiner et d'enrichir la connaissance de l'evolution du niveau de base regional.

Georges Clauzon

Papers

Alternate interpretation of the Messinian salinity crisis: Controversy resolved?

Mouvement post-messinien sur la faille de Nîmes: Implications pour la sismotectonique de la Provence

Commentaire sur l’article " Mouvement post-messinien sur la faille de Nîmes : implications pour la sismotectonique de la Provence "

The Ardèche endokarstic responses to the eustatic variations resulting from the Messinian salinity crisis

La grotte de Saint-Marcel (Ardèche) : un référentiel pour l'évolution des endokarsts méditerranéens depuis 6 Ma