Добірка наукової літератури з теми "Mediterranean Salt Giant (MSG)"

Abstract The circum-Nile deformation belt (CNDB) demonstrates the interaction between a giant delta and a giant salt body. The semi-radial shape of the CNDB is commonly interpreted as the product of salt squeezing out from under the Nile Delta. We demonstrate, however, that this is not the dominant process, because the delta and its deep-sea fan do not reach the deep-basin salt. The distal part of the deep-sea fan overlies the edge of the salt giant, but squeezing this edge (<150 m thickness) should have had only little effect on the regional salt tectonics. Only on the easternmost side of the deep-sea fan, toward the Levant Basin, does the squeeze-out model work. Here, the delta front reaches the thick salt layer and differential loading promotes basinward salt flow, even upslope. On the western side of the delta, downslope gliding of the sediment-salt sequence toward the Herodotus Basin is driven by the elevation gradient toward the deepest part of the basin. Our analysis shows that salt squeezing by differential loading was previously overestimated in the Eastern Mediterranean and raises the need to carefully map the boundary of salt basins prior to any interpretation. This conclusion is especially relevant in young basins where deltas and shelves have not propagated far enough into the basin.

Interpretation of seismic profiles and results of scientific drillings in the Mediterranean subseafloor provided indication of gigantic salt deposits which rarely crop out on land, such as in Sicily. The salt giants were ascribed to the desiccation, driven by the solar energy, of the entire basin. Nevertheless, the evaporite model hardly explains deep-sea salt deposits. This paper considers a different hypothesis suggesting that seawater reached NaCl saturation during serpentinization of ultramafic rocks. Solid salts and brine pockets were buried within the serpentinite bodies being later (e.g., in the Messinian) released, due to serpentinite breakdown, and discharged at seafloor as hydrothermal heavy brines. Therefore, sea-bottom layers of brine at gypsum and halite saturation were formed. The model is applicable to the Mediterranean area since geophysical data revealed relicts of an aged (hence serpentinized) oceanic lithosphere, of Tethyan affinity, both in its western “Atlantic” extension (Gulf of Cádiz) and in eastern basins, and xenoliths from Hyblean diatremes (Sicily) provided evidence of buried serpentinites in the central area. In addition, the buoyant behavior of muddled serpentinite and salts (and hydrocarbons) gave rise to many composite diapirs throughout the Mediterranean area. Thus, the Mediterranean “salt giant” consists of several independent geobodies of serpentinite and salts.

About 6 million years ago, the Mediterranean basin was the location of one of the most extraordinary events in the recent geological history of the Earth: the Messinian Salinity Crisis. Restriction of the seawater exchange between the Atlantic and the Mediterranean led to excess evaporation and deposition on the bottom of the deep Mediterranean basins of a 1.5 km-thick salt layer. Research on this event initiated a long-term scientific controversy. COST (European Cooperation in Science and Technology) and Marie Skłodowska-Curie European Training Networks were identified as the most appropriate tools to address and solve the controversy using a highly cross-disciplinary approach.

Abstract There is a growing consensus that the sulfates and halite within the massive evaporite deposits on the shallow margin and deep floor of the Mediterranean sea formed in two steps. Both phases had geodynamic consequences. The current evidence indicates that during the first step when the first cycle “Lower Evaporites” were deposited primarily in marginal settings, the surface of the Mediterranean remained at or very close to the level of the external Atlantic. The geodynamic response resulted from the increasing weight of the brine layer as it concentrated from normal marine salinity to the threshold for sulfate precipitation and then to the threshold for halite precipitation. This weight alone significantly deepened the Mediterranean basins by isostatic loading. Flexure of the lithosphere caused a peripheral bulge to appear that may have been the agent to close off the further entry of Atlantic seawater. Step two began with the subsequent evaporative drawdown and the deposition of the second cycle “Upper Evaporites”. As the basins dried out the loss of weight of the water led to regional isostatic uplift that permanently closed the prior inlets. Sediments removed from the margins by early subaqueous mass-wasting and later subaerial erosion and delivered to the basin floors further accentuated uplift of the margins and subsidence of the depocenters. The principal result has been to progressively tilt the Mediterranean substrate downwards from the margin towards the basin centers. This tilting was enhanced with the flooding of the desiccated sea at the climax of the salinity crisis. Consequently the salt layer rests today out of equilibrium on a surface that is more inclined after precipitation than before. The current mobility and flowage of the salt away from its margins and towards the basin centers is therefore not so much a response to the differential thickness and weight of overlying sediments, but to the combination of geodynamic processes that have produced the seaward tilting. Other giant salt deposits seem to have experienced a similar two-step evolution.

Abstract Three-dimensional seismic imaging and well calibration reveal a large allochthonous mud edifice that is composed of several mud extrusions and covers an area >740 km2 on the outer shelf slope of the Nile Delta. The allochthonous material was sourced from beneath the ∼1-km-thick Messinian evaporites in the Eastern Mediterranean and extruded synchronously as eight large mud volcanoes directly on top of the Messinian evaporites in a catastrophic remobilization event at the end of the Messinian salinity crisis. These large extrusive flows coalesced to form a single edifice with an exceptional volume of ∼292 km3 that is connected to eight widely spaced conduits. We argue that this large mud body represents a new morphological type and scale of mud extrusion. We propose that mud extrusions that coalesce on a surface forming a multi-conduit-fed edifice be referred to as mud canopies, by analogy with salt canopies, with implications for basin reconstruction, paleo–overpressure release events, and fluid migration.

Abstract. The Chemistry-Aerosol Mediterranean Experiment (ChArMEx; http://charmex.lsce.ipsl.fr) is a collaborative research program federating international activities to investigate Mediterranean regional chemistry-climate interactions. A special observing period (SOP-1a) including intensive airborne measurements was performed in the framework of the Aerosol Direct Radiative Forcing on the Mediterranean Climate (ADRIMED) project during the Mediterranean dry season over the western and central Mediterranean basins, with a focus on aerosol-radiation measurements and their modeling. The SOP-1a took place from 11 June to 5 July 2013. Airborne measurements were made by both the ATR-42 and F-20 French research aircraft operated from Sardinia (Italy) and instrumented for in situ and remote-sensing measurements, respectively, and by sounding and drifting balloons, launched in Minorca. The experimental set-up also involved several ground-based measurement sites on islands including two ground-based reference stations in Corsica and Lampedusa and secondary monitoring sites in Minorca and Sicily. Additional measurements including lidar profiling were also performed on alert during aircraft operations at EARLINET/ACTRIS stations at Granada and Barcelona in Spain, and in southern Italy. Remote sensing aerosol products from satellites (MSG/SEVIRI, MODIS) and from the AERONET/PHOTONS network were also used. Dedicated meso-scale and regional modelling experiments were performed in relation to this observational effort. We provide here an overview of the different surface and aircraft observations deployed during the ChArMEx/ADRIMED period and of associated modeling studies together with an analysis of the synoptic conditions that determined the aerosol emission and transport. Meteorological conditions observed during this campaign (moderate temperatures and southern flows) were not favorable to produce high level of atmospheric pollutants nor intense biomass burning events in the region. However, numerous mineral dust plumes were observed during the campaign with main sources located in Morocco, Algeria and Tunisia, leading to aerosol optical depth (AOD) values ranging between 0.2 to 0.6 (at 440 nm) over the western and central Mediterranean basins. Associated aerosol extinction values measured on-board the ATR-42 within the dust plume show local maxima reaching up to 150 Mm−1. Non negligible aerosol extinction (about 50 Mm−1) was also been observed within the Marine Boundary Layer (MBL). By combining ATR-42 extinction, absorption and scattering measurements, a complete optical closure has been made revealing excellent agreement with estimated optical properties. Associated calculations of the dust single scattering albedo (SSA) have been conducted, which show a moderate variability (from 0.90 to 1.00 at 530 nm). In parallel, active remote-sensing observations from the surface and onboard the F-20 aircraft suggest a complex vertical structure of particles and distinct aerosol layers with sea-salt and pollution located within the MBL, and mineral dust and/or aged north American smoke particles located above (up to 6–7 km in altitude). Aircraft and balloon-borne observations show particle size distributions characterized by large aerosols (> 10 μm in diameter) within dust plumes. In terms of shortwave (SW) direct forcing, in-situ surface and aircraft observations have been merged and used as inputs in 1-D radiative transfer codes for calculating the direct radiative forcing (DRF). Results show significant surface SW instantaneous forcing (up to −90 W m−2 at noon). Associated 3-D modeling studies from regional climate (RCM) and chemistry transport (CTM) models indicate a relatively good agreement for simulated AOD compared with measurements/observations from the AERONET/PHOTONS network and satellite data, especially for long-range dust transport. Calculations of the 3-D SW (clear-sky) surface DRF indicate an average of about −10 to −20 W m−2 (for the whole period) over the Mediterranean Sea together with maxima (−50 W m−2) over northern Africa. The top of the atmosphere (TOA) DRF is shown to be highly variable within the domain, due to moderate absorbing properties of dust and changes in the surface albedo. Indeed, 3-D simulations indicate negative forcing over the Mediterranean Sea and Europe and positive forcing over northern Africa.

Abstract. Since the 1980s several spaceborne sensors have been used to retrieve the aerosol optical depth (AOD) over the Mediterranean region. In parallel, AOD climatologies coming from different numerical model simulations are now also available, permitting to distinguish the contribution of several aerosol types to the total AOD. In this work, we perform a comparative analysis of this unique multi-year database in terms of total AOD and of its apportionment by the five main aerosol types (soil dust, sea-salt, sulfate, black and organic carbon). We use 9 different satellite-derived monthly AOD products: NOAA/AVHRR, SeaWiFS (2 products), TERRA/MISR, TERRA/MODIS, AQUA/MODIS, ENVISAT/MERIS, PARASOL/POLDER and MSG/SEVIRI, as well as 3 more historical datasets: NIMBUS7/CZCS, TOMS (onboard NIMBUS7 and Earth-Probe) and METEOSAT/MVIRI. Monthly model datasets include the aerosol climatology from Tegen et al. (1997), the climate-chemistry models LMDz-OR-INCA and RegCM-4, the multi-model mean coming from the ACCMIP exercise, and the reanalyses GEMS and MACC. Ground-based Level-2 AERONET AOD observations from 47 stations around the basin are used here to evaluate the model and satellite data. The sensor MODIS (on AQUA and TERRA) has the best average AOD scores over this region, showing a relevant spatio-temporal variability and highlighting high dust loads over Northern Africa and the sea (spring and summer), and sulfate aerosols over continental Europe (summer). The comparison also shows limitations of certain datasets (especially MERIS and SeaWiFS standard products). Models reproduce the main patterns of the AOD variability over the basin. The MACC reanalysis is the closest to AERONET data, but appears to underestimate dust over Northern Africa, where RegCM-4 is found closer to MODIS thanks to its interactive scheme for dust emissions. The vertical dimension is also investigated using the CALIOP instrument. This study confirms differences of vertical distribution between dust aerosols showing a large vertical spread, and other continental and marine aerosols which are confined in the boundary layer. From this compilation, we propose a 4-D blended product from model and satellite data, consisting in monthly time series of 3-D aerosol distribution at a 50 km horizontal resolution over the Euro-Mediterranean marine and continental region for the 2003–2009 period. The product is based on the total AOD from AQUA/MODIS, apportioned into sulfates, black and organic carbon from the MACC reanalysis, and into dust and sea-salt aerosols from RegCM-4 simulations, which are distributed vertically based on CALIOP climatology. We extend the 2003–2009 reconstruction to the past up to 1979 using the 2003–2009 average and applying the decreasing trend in sulfate aerosols from LMDz-OR-INCA, whose AOD trends over Europe and the Mediterranean are median among the ACCMIP models. Finally optical properties of the different aerosol types in this region are proposed from Mie calculations so that this reconstruction can be included in regional climate models for aerosol radiative forcing and aerosol-climate studies.

Entre 5.97 et 5.33Ma, à la fin du Miocène, un événement géologique exceptionnel aux conséquences majeures a affecté le bassin méditerranéen : la Crise de Salinité Messinienne (CSM). Cet épisode, dont le scénario exact reste encore énigmatique, est responsable du dépôt d’un volume considérable d’évaporites connu sous le nom de Géant Salifère de Méditerranée (GSM). Aujourd'hui, plus de 90 % des dépôts évaporitiques du MSG sont situés dans les bassins profonds de la Méditerranée et sont enfouis sous une épaisse couche de sédiments Plio- Quaternaire. Ces évaporites ont donc été étudiées principalement par imagerie sismique. Dans ce mémoire, nous nous intéressons aux dépôts de la crise enregistrés sur Promontoire des Baléares (BP), un haut topographique situé dans bassin de la Méditerranée occidentale. Du fait qu’il contient une succession de bassins en position intermédiaire stratégique, étagés entre les bassins marginaux du pourtour Méditerranéen et les bassins profonds, le BP se révèle un lieu unique avec des dépôts évaporitiques variés, ubiquistes et peu déformés tectoniquement, permettant d’accéder à une vision complète de l’enregistrement de la crise et pouvant mener à un scénario global cohérent.Cette thèse de doctorat a été réalisée dans le cadre d’un projet transdisciplinaire : « European Training Network (ETN) SaltGiant », dont l'objectif est de comprendre le GSM. Une approche pluridisciplinaire a été appliquée sur la zone d’étude choisie pour apporter des contraintes afin de répondre à certaines des nombreuses questions encore sans réponses sur la crise de salinité messinienne. Le travail de base a consisté en l'interprétation d'un large ensemble de données de sismique réflexion en Méditerranée occidentale, particulièrement concentré sur les dépôts messiniens du BP. Ceci a permis de préciser la cartographie des unités messiniennes de cette région et de définir leurs inter-relations géométriques. Une comparaison détaillée de ces unités évaporitiques avec celles du bassin messinien sicilien de Caltanissetta a été menée afin de reconstituer l'histoire de leur dépôt pour la confronter au modèle chrono-stratigraphique « consensuel » à trois phases. Pour reconstituer la paléo-bathymétrie de la dépression centrale de Majorque (CMD), le bassin le moins déformé situé dans sa partie centrale du BP, une interprétation structurale a permis d’identifier les principaux mouvements tectoniques post-MSC, modérés et localisés dans des corridors de décrochement. L'analyse par backstripping 2D et pseudo-3D, en collaboration avec d’autres collègues du projet SaltGiant, a alors permis de restaurer la paléo-bathymétrie de la CMD. Enfin, ces résultats ont été utilisés comme contraintes bathyétriques et de volumes pour modéliser le dépôt des évaporites observées, par des modèles physiques basés sur la théorie du contrôle hydraulique des détroits. Les résultats montrent que les unités messiniennes de la CMD pourraient constituer un analogue non déformé de celles qui affleurent à terre dans le bassin sicilien de Caltanissetta. Ils démontrent aussi qu'une baisse générale du niveau marin de grande amplitude (>850m) est nécessaire pour précipiter le volume de halite observé dans la CMD. Ces résultats, très bien contraints par ces études précises, remettent en cause certaines idées parfois encore largement acceptées. Ces doutes concernent en particulier l'apparition synchrone du sel à l'échelle du bassin méditerranéen, la profondeur maximale de dépôt du gypse inférieur primaire (PLG) et le moment de la formation du gypse inférieur resédimenté (RLG). En conclusion, ce mémoire montre la nécessité de réviser le scénario consensus actuel de la CSM, et l’importance de réaliser des forages en mer dans la région clef du BP, ce qui permettrait de révéler de nombreux mystères encore enfouis sous le géant salifère de Méditerranée
The Messinian Salinity Crisis (MSC; 5.97– 5.33 Ma) is one of the most controversial geological events that influenced the evolution of the Mediterranean Basin in the late Miocene, leaving behind an immense volume of evaporites known as the Mediterranean Salt Giant (MSG). Today, more than 90% of the MSG evaporitic deposits are located offshore, buried below thick sediments that are Pliocene to Quaternary in age, and have thus been studied mainly by marine seismic reflection imaging. The Balearic Promontory (BP), a prominent topographic high in the Western Mediterranean basin, contains a unique and tectonically poorly deformed MSC record that resembles the evaporitic record of other peri-Mediterranean marginal and intermediate basins.This PhD thesis was performed in the framework of the SaltGiant European Training Network (ETN), a cross-disciplinary project whose objective is to understand the formation of the MSG. The work of the thesis is focused on the MSC deposits of the BP. Multi-disciplinary approach was applied to answer some of the still open questions concerning the MSC event. As a first step, seismic interpretation of a wide seismic reflection dataset in the Western Mediterranean in general and in the BP in particular was performed, with the aim of refining the mapping of the Messinian units covering the area. To restitute the depositional history of the MSC evaporites of the BP, a detailed comparison with the Messinian evaporitic units of the Sicilian Caltanissetta Basin was carried out, in which a discussion on how this history matches the existing 3-stages chrono-stratigraphic ‘consensus model’ is illustrated. The next step consisted in the restoration of the paleo-bathymetry of the BP at the beginning of the MSC, focusing on the relatively less-deformed basin located in the central part of the BP and called the Central Mallorca Depression (CMD). To achieve this restoration, structural interpretation in the CMD area was done where the main post-MSC tectonic-related vertical movements that altered the MSC paleo-bathymetry were identified. Then 2D and pseudo-3D backstripping analysis were applied in collaboration with other colleagues from the SaltGiant project, to restore the paleo-bathymetry. In the final step, the paleo-bathymetry was used to model the deposition of the MSC evaporite volumes observed in the CMD using physics-based models built on strait hydraulic-control theory. The results show that the MSC units of the CMD could constitute an undeformed analog of those outcropping on-land in the Sicilian Caltanissetta Basin. Moderate post-MSC deformation acted along MSC strike-slip corridors in the CMD following the MSC evaporites deposition, thus altering only locally the paleo-bathymetry. A high amplitude drawdown (>850m) is required during the halite stage of the MSC. The results rise a series of doubts about the current consensus model, still widely accepted. Doubts concern the synchronous onset of salt at the basin scale, the maximum depth of deposition of the Primary Lower Gypsum (PLG) and the timing of formation of the Resedimented Lower Gypsum (RLG). All the results and discussions hint to the need of revision of the current MSC consensus model, as well as the importance of initiating drillings offshore over the BP area, which would help revealing many of the mysteries still buried with the MSG

ABSTRACT Two-dimensional depth-migrated seismic data were used to interpret and analyze extension and salt deposition in the ocean-continent transition (OCT) along 720 km of the southern Gulf of Mexico rifted margin. The OCT is characterized by alternating areas of salt-filled, fault-bounded outer troughs overlying a shallow Moho and salt perched at a level above the top of oceanic crust. Normal faults and the limit of oceanic crust are both offset by two sets of transfer faults and paleo–transform faults, respectively, that trend NNW-SSE and N-S. The patterns define five OCT segments that show propagation of both rifting and spreading to the NE, an abrupt jump in pole location, and rifting/spreading nuclei that link up laterally. Salt was deposited during outer trough formation to the SW but prior to it in the NE, where salt consequently flowed from proximal locations into the growing trough during decoupled thick-skinned extension. The salt was deposited at least 0.5–1.5 km below global sea level, with precipitation initially confined to the oldest troughs (in the west) and subsequently spreading to cover the entire basin in a deep brine over a period of at least 5 m.y. Possible siliciclastic strata interbedded with the salt were likely sourced from the south and southeast, and hypersaline conditions waned gradually during punctuated marine flooding over another 5–10 m.y. The Gulf of Mexico was thus a giant evaporite basin formed in a deep depression during late-synrift mantle exhumation in a magma-poor setting, analogous to the South Atlantic salt basins and possibly the Red Sea and southern Moroccan/Scotian margins.