Messinian erosional and salinity crises: View from the Provence Basin (Gulf of Lions, Western Mediterranean)

International audienceThough the late Miocene “Messinian Salinity Crisis” has been intensely researched along the circum-Mediterranean basins, few studies have focused on the central part of the Mediterranean Basin and, especially, the pre-salt deposits. To improve our knowledge of the Messinian events, it is imperative to better understand this domain. In this study, we provide a more complete understanding of this central domain in the Provence Basin. We were able to recognize: a) thick marine detrital series (up to 1000 m) derived from the Messinian subaerial erosion which is partly prolongated in the distal part by b) a thick unit of deep marine deposits (up to 800 m) prior to the evaporites; c) a thick presumed alternation of detritals and evaporites (1500 m) below the mobile halite; and d) a two-step transgression at the end of the Messinian. Spatially, we document the eroded shelf to the deep basin (and from the western to the eastern parts of the Gulf of Lions), and temporally, we extend the interpretations from the early deposition of detritic sediments to the final sea-level rise. The results provide a new basis for discussion not only for the development of the Messinian Salinity Crisis but also for the reconstruction of the subsidence history of the Provence Basin

Évolution Oligo Miocène des marges du micro océan Liguro-Provençal

La marge du Golfe du Lion est issue d une période de rifting Oligo-Aquitanienne suivie de l ouverture océanique du bassin Provençal ver le Burdigalien. Deux périodes ont été étudiées au cours de cette thèse. L événement messinien constitue un jalon de l histoire du bassin. Trois résultats principaux se dégagent de son étude. Le premier est l identification, à la transition entre la plate-forme érodée par les fleuves messiniens et le bassin, d une épaisse série détritique (jusqu à 1000m d épaisseur). Le deuxième élément est l identification, entre l épisode détritique initial et la halite messinienne, d une épaisse série à évaporites inférieures (environ 1500m). Un troisième résultat concerne le ré ennoiement du bassin juste après le dépôt de la halite. Nous identifions au total près de 3500 m de sédiments messiniens déposés dans le bassin. La plate-forme enregistre une perte sédimentaire (due à l érosion) pouvant atteindre 1000 m. Ces transferts sédimentaires énormes ont des conséquences importantes sur l évolution de la marge. Les premiers résultats issus d un backstriping 1D et prenant en considération ces interprétations suggèrent une profondeur du bassin de 3500m avant la crise messinienne. L étude de la période de formation du Golfe du Lion, des débuts de l extension continentale à l océanisation nous permet de proposer un histoire en trois temps. Tout d abord un évènement thermique profond maintient la plate-forme exondée pendant l épisode de rifting. Dan un deuxième temps la rupture se fait et le premier socle océanique atypique (zone de transition) se met en place. Le troisième temps correspond à la mise en place de la croûte océanique au centre du bassin.The Gulf of Lion margin has been created by an Oligo-Aquitanian rifting followed by oceanic accretion in the Provencal basin during the Burdigalian. Two main periods have been detailed in this thesis. The study of sedimentary geometries on the margin and in the deep basin gave new elements for the understanding of the messinian crisis. The fïrst element is the identification of a thick detritic series (up to 1000m) at the transition between the sub aerially eroded shelf and the slope. The second important element is the identification of a thick stratum of lower evaporites (over 1500m), between the first detritic episode and the deposition of halite in the deep basin. A third result concerns the flooding of the basin, just after halite deposition associated to the lowest sea level during the crisis. We therefore identified about 3500m of sediments deposited during the messinian crisis. The shelf registered a loss of up to 1000m thick of sediments. This implies enormous amount of sediment transfer from the shelf to the slope and the deep sea. First attempts of 1 D backstrippings, taking into account our new observations, showed that the basin might have been 3500m deep just before the messinian crisis. The study of crustal structures and early sedimentation led us to propose a model for the formation of the Gulf of Lion in three steps. First of ail, a deep thermic event keeps the shelf subaerially exposed during early phase of rifting. In a second step, rupture occurs (during Upper Aquitanian, around 20 Ma ago and the first unusual oceanic crust (transitional zone) is built. The third step corresponds to the formation of typical oceanic crust at the centre of the basin.BREST-BU Droit-Sciences-Sports (290192103) / SudocPLOUZANE-Bibl.La Pérouse (290195209) / SudocSudocFranceF

La marge sud-marocaine et les premières phases d'ouverture de l'Océan Atlantique central

BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

La cinématique de l'Atlantique nord (la question de la déformation intraplaque)

BREST-BU Droit-Sciences-Sports (290192103) / SudocRENNES-Géosciences (352382209) / SudocSudocFranceF

Campagne CYAGOR - Submersible Cyana - 25 juillet-26 août 1977

We present in this paper raw data and preliminary results of CYAGOR dives (July-August 1977) on Gorringe bank (SW Portugal). A series of eight dives with submersible SP 3000 Cyana, from 2 600 to 40 m depth, enabled us to observe the outcrop of the bank flanks, a nearly complete cross-section of oceanic crust and upper mantle. The structure seems to be little affected by fracturing and is slightly rocked to the NE. Cross-sections made during the dives show characteristics similar to those of an ophiolitic complex.Nous présentons ici les données brutes ou résultant d'un dépouillement encore préliminaire de la campagne de plongée profonde CYAGOR (Juillet-Août 1977) sur le banc de Gorringe (SW du Portugal). Une série de huit plongées avec l'engin submersible SP 3000 CYANA entre 2 600 et 40 mètres de profon­deur a permis de reconnaître l'affleurement sur les flancs du Banc, une coupe presque complète de la croûte océanique et du manteau supérieur. L'ensemble à première vue, peu affecté par une tectonique de type cassant, est légèrement basculé vers le NE. Les coupes réalisées au cours de cette série de plongées présentent des caractéristiques très voisines de celles d'un complexe ophiolitique

Evolution of rifted continental margins: The case of the Gulf of Lions (Western Mediterranean Basin)

International audienceThe formation of rifted continental margins has long been explained by numerous physical models. However, field observations are still lacking to validate or constrain these models. This study presents major new observations on the broad continental margin of the Gulf of Lions, based on a large amount of varied data. Two contrasting regions characterize the thinned continental crust of this margin. One of these regions corresponds to a narrow rift zone (40–50 km wide) that was highly thinned and stretched during rifting. In contrast with this domain, a large part of the margin subsided slowly during rifting and then rapidly after rifting. The thinning of this domain cannot be explained by stretching of the upper crust. We can thus recognize a zonation of the stretching in both time and space. In addition, the Provencal Basin is characterized by a segmentation of the order of 100–150 km. These observations have important consequences on the formation and evolution of the Gulf of Lions margin. Independently of the geodynamic context, we can propose some general features that characterize the formation of rifted continental margins