Deep Mediterranean Basins Research Articles

High-amplitude water-level fluctuations at the end of the Mediterranean Messinian Salinity Crisis: Implications for gypsum formation, connectivity and global climate

The formation and dissolution of salt giants impacts ocean chemistry on thousand-million year timescales. Gypsum precipitation and weathering changes the oceanic calcium concentration with implications for the carbon cycle and global temperatures. However, the connectivity of salt giants with the global ocean is necessarily restricted, making the timing of Ca2+ extraction and return more uncertain. Here we reconstruct the final phase of gypsum precipitation of the Late Miocene Mediterranean Salt Giant using micropaleontology, sedimentology and 87Sr/86Sr analyses on the most complete record preserved at Eraclea Minoa on Sicily and explore its implications for global climate. Precessional gypsum-marl couplets (Upper Gypsum) characterize the last 200 kyrs (Stage 3) of the Messinian Salinity Crisis (MSC; 5.97–5.332 Ma) in both intermediate (500–1000 m) and deep (>1000 m) Mediterranean basins. The interbedded selenitic gypsum layers contain well-preserved calcareous nannofossil assemblages dominated by Reticulofenestra minuta, a marine species which tolerates stressful conditions. Marine water is also required to explain the gypsum 87Sr/86Sr data, which describe a small range of ratios (0.708704–0.708813) lower than coeval ocean water. Mass-balance calculations indicate that during gypsum precipitation, the Atlantic made up ≤20% of a Mediterranean (“Lago-Mare”) water mass dominated by low salinity discharge from large river systems and Eastern Paratethys. This suggests episodic extraction of calcium and sulfate ions from the ocean throughout MSC Stage 3. The marls commonly contain shallow (30–100 m) brackish-water ostracods of Paratethyan (Black Sea) origin. Marls with Paratethyan ostracods are also found in both marginal (<500 m) and deep Mediterranean settings. This indicates that marl-deposition was not synchronous across the basin, but that it occurred in intermediate and deep basins during base-level lowstands at insolation minima and on the shallow Mediterranean margins during insolation maxima-driven highstands. These high-amplitude base-level fluctuations exposed the evaporites to weathering, but ponded the products in the Mediterranean basin until reconnection occurred at the beginning of the Pliocene.

Identifying Priorities for the Protection of Deep Mediterranean Sea Ecosystems Through an Integrated Approach

Benthic habitats of the deep Mediterranean Sea and the biodiversity they host are increasingly jeopardized by increasing human pressures, both direct and indirect, which encompass fisheries, chemical and acoustic pollution, littering, oil and gas exploration and production and marine infrastructures (i.e., cable and pipeline laying), and bioprospecting. To this, is added the pervasive and growing effects of human-induced perturbations of the climate system. International frameworks provide foundations for the protection of deep-sea ecosystems, but the lack of standardized criteria for the identification of areas deserving protection, insufficient legislative instruments and poor implementation hinder an efficient set up in practical terms. Here, we discuss the international legal frameworks and management measures in relation to the status of habitats and key species in the deep Mediterranean Basin. By comparing the results of a multi-criteria decision analysis (MCDA) and of expert evaluation (EE), we identify priority deep-sea areas for conservation and select five criteria for the designation of future protected areas in the deep Mediterranean Sea. Our results indicate that areas (1) with high ecological relevance (e.g., hosting endemic and locally endangered species and rare habitats),(2) ensuring shelf-slope connectivity (e.g., submarine canyons), and (3) subject to current and foreseeable intense anthropogenic impacts, should be prioritized for conservation. The results presented here provide an ecosystem-based conservation strategy for designating priority areas for protection in the deep Mediterranean Sea.

Ages and stratigraphical architecture of late Miocene deposits in the Lorca Basin (Betics, SE Spain): New insights for the salinity crisis in marginal basins

Unlike most Neogene basins of the Betic Cordillera where the Salinity Crisis is dated to the Messinian, a contradictory Tortonian dating was proposed for evaporites of the Lorca Basin. As a consequence, complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites. In order to integrate the Lorca Basin into the geological context of the western Mediterranean domain during the Late Miocene, new sedimentological and stratigraphical studies coupled with new dating were performed, which allow us to propose a Messinian age for both diatomite-bearing deposits and evaporites of the Lorca Basin. These new ages challenge the idea of a Tortonian salinity crisis in the Lorca Basin. Three main events of base-level drop were evidenced during the Messinian. Each event is correlated with successive steps of basin restriction. Shallow salina evaporites were deposited after a base-level fall during the Messinian before a final base-level drop, which led to the entire exposure of the basin. This last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep Mediterranean basins. The reflooding which allowed the deposition of brackish deposits and a short-lived marine incursion occurred at the end of the Messinian. Base-level drops occurred during eustatic falls amplified by the gradual uplift of the Betic Cordillera. The exhumation of the Tercia ridge along the strike-slip Alhama de Murcia fault system during the Messinian probably favoured the gradual restriction of the basin. A discussion on correlations of main unconformities between several Neogene basins of the Betics is proposed, suggesting a similar structural evolution at the regional scale.

Deep Mediterranean's Messinian evaporite giant: How much salt?

Abstract Evaporite giants can precipitate out of high salinity waters in semi-enclosed ocean basins when the rate of evaporation outstrips the inflow of new saline and fresh waters. The thick saline series deposited in the deep Mediterranean during the Miocene Epoch's late Messinian age (between 5.97 and 5.3 Ma) is among the youngest of such salt giants in Earth history. During this event, also known as the Messinian Salinity Crisis, voluminous evaporites accumulated in the deep basins when the main inflow of saline water to the Mediterranean through the Gibraltar Straits was severely diminished. The evaporites are interbedded with sediments eroded from the shelves and slopes or mass-transported downslope. Recent advances in geochronology and better understanding of the geodynamic history of various basins have led to insights about the timing of the salinity crisis and the tectonics and role of Gibraltar passage and other western narrows from the Atlantic to the Mediterranean. New estimates based on ocean-wide seismic facies analysis presented here reveal that there is between 821 ± 50 and 927 ± 50 thousand cubic km of late Messinian salt, and a total of up to 1.2 ± 0.1 million cubic km of salt plus associated sediment tied up in the deep Mediterranean basins. This suggests that after the initial restriction the Mediterranean had to be either continuously supplied with brine, or partially to completely refilled several times to produce the total salt edifice. The amount of Atlantic saline water needed to amass this evaporite giant is between 7 and 8 times the modern-day Mediterranean's equivalent of saline water. Our new volumetric estimates have implications for the Mediterranean's Messinian sequestration and desiccation scenarios and should lead to more meaningful geodynamic models and provide constraints for many of the controversies that still surround this major event in geological history. Maps of salt distribution in various basins also have important implications for sub-salt exploration geoscience.

Uncovering the Mediterranean Salt Giant (MEDSALT) - Scientific Networking as Incubator of Cross-disciplinary Research in Earth Sciences

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.

Seismic markers of the Messinian salinity crisis in the deep Ionian Basin

AbstractWe conduct the seismic signal analysis on vintage and recently collected multichannel seismic reflection profiles from the Ionian Basin to characterize the deep basin Messinian evaporites. These evaporites were deposited in deep and marginal Mediterranean sedimentary basins as a consequence of the “salinity crisis” between 5.97 and 5.33 Ma, a basin‐wide oceanographic and ecological crisis whose origin remains poorly understood. The seismic markers of the Messinian evaporites in the deep Mediterranean basins can be divided in two end‐members, one of which is the typical “trilogy” of gypsum and clastics (Lower Unit – LU), halite (Mobile Unit – MU) and upper anhydrite and marl layers (Upper Unit – UU) traced in the Western Mediterranean Basins. The other end‐member is a single MU unit subdivided in seven sub‐units by clastic interlayers located in the Levant Basin. The causes of these different seismic expressions of the Messinian salinity crisis (MSC) appear to be related to a morphological separation between the two basins by the structural regional sill of the Sicily Channel. With the aid of velocity analyses and seismic imaging via prestack migration in time and depth domains, we define for the first time the seismic signature of the Messinian evaporites in the deep Ionian Basin, which differs from the known end‐members. In addition, we identify different evaporitic depositional settings suggesting a laterally discontinuous deposition. With the information gathered we quantify the volume of evaporitic deposits in the deep Ionian Basin as 500,000 km3 ± 10%. This figure allows us to speculate that the total volume of salts in the Mediterranean basin is larger than commonly assumed. Different depositional units in the Ionian Basin suggest that during the MSC it was separated from the Western Mediterranean by physical thresholds, from the Po Plain/Northern Adriatic Basin, and the Levant Basin, likely reflecting different hydrological and climatic conditions. Finally, the evidence of erosional surfaces and V‐shaped valleys at the top of the MSC unit, together with sharp evaporites pinch out on evaporite‐free pre‐Messinian structural highs, suggest an extreme Messinian Stage 3 base level draw down in the Ionian Basin. Such evidence should be carefully evaluated in the light of Messinian and post‐Messinian vertical crustal movements in the area. The results of this study demonstrates the importance of extracting from seismic data the Messinian paleotopography, the paleomorphology and the detailed stratal architecture in the in order to advance in the understanding of the deep basins Messinian depositional environments.

The deep record of the Messinian salinity crisis: Evidence of a non-desiccated Mediterranean Sea

Abstract This research is focused on a complete reexamination of the evaporite facies present in all the cores that cut through the topmost deposits of the Messinian salinity crisis lying below the floor of the Mediterranean Sea (DSDP Legs 13 and 42A, ODP Legs 107 and 161). This review suggests that the uppermost evaporite units in both western and eastern deep Mediterranean basins consist mainly of clastic (gypsrudite, gypsarenite and gypsiltite) and fully subaqueous deposits (laminar gypsum, selenite and cumulate halite) that are partially affected by burial anhydritization and tectonic-induced recrystallization. No unequivocal evidence of shallow water or even supratidal (sabkha) deposition is in evidence, suggesting that at the very last phase of the salinity crisis the Mediterranean Sea did not experience desiccation, but that deposition took place under permanent subaqueous conditions.

New imaging of the salinity crisis: Dual Messinian lowstand megasequences recorded in the deep basin of both the eastern and western Mediterranean

Through several examples we show that following sea-level fall and marginal erosion during the Messinian salinity crisis (MSC), clastic inputs into the eastern and western Mediterranean Sea are not distributed evenly in space and time but are mainly limited to the lower section of the Messinian salinity crisis depositional megasequence. Significant similarities around the basin allow us to propose a Mediterranean Messinian salinity crisis depositional episode that can be divided into two seismic megasequences: the Messinian lower megasequence (MLM) and the Messinian upper megasequence (MUM). Their distinctive seismic facies correspond to systems tracts deposited during three main stages that represent a complete sea level cycle. (1) A falling stage systems tract including mass transport deposits and forced regressive clinoforms deposited in the early part of the falling stage, and related to the increasing rate of relative sea level fall. This stage is characterized by a marked shift in the depocenter towards the deep basins. (2) An early lowstand characterized by massive clastic inputs from major Messinian rivers (the Rhone, Nile, and Antalya Gulf rivers) or smaller river systems (offshore south Lebanon). These clastics were deposited in an oversaturated basin, as evidenced by the interfingering chaotic and transparent seismic facies of the Messinian lower megasequence (MLM). (3) A late lowstand, starting with rapid deposition of massive halite, with no detrital inputs into the deep basin. The upper part of the evaporites clearly onlaps the Messinian erosional surface at the margins and is evidence for a transition between a late lowstand stage and an early transgressive stage. These deposits belong to the Messinian upper megasequence (MUM). We interpret the transition between the two megasequences as the peak of the “salinity” crisis, the end of the relative sea level fall, and the maximum dispersal of sands into the deep Mediterranean basins.

Messinian evaporite deposition during sea level rise in the Gulf of Lions (Western Mediterranean)

The Messinian Salinity Crisis resulted from desiccation of the Mediterranean Sea after its isolation from the Atlantic Ocean at the end of the Miocene. Stratal geometry tied to borehole data in the Gulf of Lions show that the pre-crisis continental shelf has been eroded during a major sea-level fall and that sediments from this erosion have been deposited in the basin. This detrital package is onlapped by high amplitude seismic reflectors overlain by the “Messinian Salt” and the “Upper Evaporites”. Towards the shelf, the transition between regressive deposits and overlying onlapping sediments is characterised by a wave-ravinement surface, suggesting that a significant part of the onlapping reflectors and overlying Messinian Evaporites were deposited during a relatively slow landward migration of the shoreline. The clear boundary between the smooth wave-ravinement surface and the subaerial Messinian Erosional Surface observed on the Gulf of Lions shelf and onshore in the Rhône valley is interpreted to have resulted from a rapid acceleration of the Mediterranean sea level rise at the end of the Messinian Salinity Crisis. Numerical simulation of this cycle of sea level change during the Messinian Salinity Crisis and of precipitation of thick evaporites during the slow sea level rise shows that this scenario can be modelled assuming a value of evaporation minus precipitation of 1.75 m3/m2/yr in the deep Mediterranean basins.

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

Forty years after the image of the Mediterranean transformed into a giant salty lake was first conceived, the fascinating history of the Messinian Salinity Crisis (MSC) still arouses great interest across a large and diverse scientific community. Early outcrop studies which identified severe palaeoenvironmental changes affecting the circum-Mediterranean at the end of the Miocene, were followed by investigations of the marine geology during the 1950s to 1970s. These were fundamental to understanding the true scale and importance of the Messinian event. Now, after a long period of debate over several entrenched but largely untested hypotheses, a unifying stratigraphic framework of MSC events has been constructed. This scenario is derived mainly from onshore data and observations, but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep Mediterranean basins. The MSC was an ecological crisis, induced by a powerful combination of geodynamic and climatic drivers, which had a great impact on the subsequent geological history of the Mediterranean area, and on the salinity of the global oceans. These changed the Mediterranean's connections with both the Atlantic Ocean and the freshwater Paratethyan basins, causing high-amplitude fluctuations in the hydrology of the Mediterranean. The MSC developed in three main stages, each of them characterized by different palaeoenvironmental conditions. During the first stage, evaporites precipitated in shallow sub-basins; the MSC peaked in the second stage, when evaporite precipitation shifted to the deepest depocentres; and the third stage was characterized by large-scale environmental fluctuations in a Mediterranean transformed into a brackish water lake. The very high-resolution timescale available for some Late Miocene intervals in the Mediterranean makes it possible to consider environmental variability on extremely short time scales including, in some places, annual changes. Despite this, fundamental questions remain, some of which could be answered through new cores from the deepest Mediterranean basins. Improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal Messinian succession for the first time. The resulting data would allow us to decipher the causes of this extreme environmental change and its global-scale consequences.

High-resolution strontium isotope stratigraphy of the Messinian deep Mediterranean basins: Implications for marginal to central basins correlation

New 87Sr/86Sr data from DSDP–ODP Messinian cores from deep Mediterranean basins suggest that the usually envisaged correlation of offshore Upper Evaporites with onshore Upper Gypsum deposits of Sicily, Cyprus and Crete recording the stage 3 (5.53–5.33 Ma) of the Messinian salinity crisis may be not entirely correct. High-resolution stratigraphic calibration of Sr isotope data indicates that only a very thin unit (commonly < 50 m) in the uppermost part of the “seismic” Upper Evaporites is characterized by the typically lower values for Sr isotopes with respect to the global Ocean which characterize stage 3 onshore successions (“Lago Mare event”). These deposits mainly consist of interbedded clastic or cumulate gypsum and marls; halite recovered from cores in the Upper Evaporites unit is actually characterized by Sr isotope values consistent with stage 2 deposits of onshore successions. According to these results, the Messinian trilogy of the western Mediterranean basin could be as a whole correlated with the halite unit of the eastern basin, suggesting that different hydrologic conditions characterized the two deep areas during the peak of the salinity crisis.

Rise and fall of the Paratethys Sea during the Messinian Salinity Crisis

Extremely thick evaporite units were deposited during the so-called Messinian Salinity Crisis (MSC: 5.96–5.33 Ma) in a deep Mediterranean basin that was progressively disconnected from the Atlantic Ocean. A crucial, but still poorly understood component in Messinian evaporite models is the connectivity between Mediterranean and Paratethys, i.e. the former Black Sea domain. Inadequate stratigraphic correlations and insufficient age control for Paratethys sediments have so far hampered a thorough understanding of hydrological fluxes and paleoenvironmental changes. Here, we present a new chronology for the Eastern Paratethys by integrating biostratigraphic and paleomagnetic data from Mio–Pliocene sedimentary successions of Romania and Russia. We show that a major flooding event from the Mediterranean surged the Paratethys basins at the Maeotian–Pontian boundary, 6.04 million years ago. This indicates that sea level in both Mediterranean and Paratethys was high at the beginning of the MSC. We argue in favor of changes in Paratethys–Mediterranean connectivity to initiate the MSC in combination with elusive tectonic processes in the Gibraltar arc. A subsequent fall of Paratethyan water level closely coincides to the Mediterranean isolation-event, corresponding in age to the glacial cycles TG12–14 (5.60–5.50 Myr). In the latest Messinian, a major climate change towards more humid conditions produced a positive hydrological balance and likely a transgression in the Paratethys, although our stratigraphic resolution cannot exclude a possible relation to the Pliocene flooding of the Mediterranean here.

Across margin export of organic matter by cascading events traced by stable isotopes, northwestern Mediterranean Sea

We present a 1‐yr (2005‐2006) record of organic carbon (OC) and total nitrogen (TN) contents and their isotopic ratios (Δ13COC and Δ15N) in sinking particles from the western Gulf of Lions. Maximum OC and TN fluxes recorded in January 2006 and March‐April 2006 were associated with negative near‐bottom temperature anomalies. This reveals large inputs of resuspended organic matter from the shelf basinwards to depths ≫1500 m by dense shelf‐water cascading. The first pulse of organic matter had low Δ13COC (‐25.5‰) and N:C (0.08) and high Δ15N (6.6‰) values, indicative of the arrival of organic matter of terrestrial origin. In contrast, the second pulse had high Δ13COC (‐21.9‰) and N:C (0.15) and extremely low Δ15N (0.0‰) values, indicative of the transfer of organic matter with higher marine contribution. Though downslope export of organic matter from the adjacent shelf predominated, particles escaping from surface waters remained an important source of organic matter during low‐energy and low‐flux periods and especially during summer conditions, with significant contribution of N2 fixation to organic matter export. Overall, our results suggest the export of organic matter from different sources to the deep Mediterranean basin, which in turn might alter within a couple of months the quality of the sedimentary organic matter deposited on the sea floor and thus the dynamics of the deep ecosystems.

Depositional environments of the Mediterranean “Lower Evaporites” of the Messinian salinity crisis: Constraints from quantitative analyses

We use simple quantitative analyses to evaluate controversial water level scenarios for the Mediterranean “Lower Evaporites” of the Messinian salinity crisis. Our results indicate that a shallow-water scenario for the Lower Gypsum units – with Mediterranean water level lower than the sill at Gibraltar – would imply unrealistic salt thicknesses on the order of 3 km. Some outflow to the open ocean must have persisted, implying that the Mediterranean was a deep-water basin during Lower Gypsum formation. Since glacio-eustatic fluctuations do not seem to have had a major influence on Lower Gypsum deposits, Mediterranean water level was even substantially higher than the Gibraltar sill. Our analyses furthermore show that precessional changes in the freshwater budget may explain the observed cyclic lithological changes of gypsum and non-evaporitic sediments. Potential precipitation of gypsum in the deep Mediterranean basins would have critically depended on the availability of oxygen and thus on the stratification of the water column. Finally, our results indicate that the deep Mediterranean halite units could have been deposited under shallow conditions, assuming that they correspond to the ~ 70 kyr time interval between glacials TG12 and TG14, when Mediterranean outflow to the Atlantic was blocked.

The end of the Messinian salinity crisis: Evidences from the Chelif Basin (Algeria)

How did the Messinian Salinity Crisis end is a matter of intense debate between two opposite concepts i.e., the generalised dilution event, the so-called Lago–Mare, followed by the sudden restoration of the marine conditions at the base of the Zanclean, or the early partial or complete marine refill that would have happened earlier during the upper Messinian. The Chelif Basin of Northwestern Algeria, one of the greatest Messinian marginal basins of the Mediterranean, provides an exceptional opportunity to study in detail how this major paleoenvironmental change occurred through continuous sedimentary records of the Miocene–Pliocene boundary. Five sections representative of both the central and marginal areas of the Chelif basin were analysed in detail for sedimentology, mineralogy, foraminifera and ostracod assemblages, and stable isotope composition of carbonates. The late Messinian deposits exhibit a great lithological variability with predominant clastic deposits (sandstones, siltstones, conglomerates, carbonates) with, in some marginal areas, large slided masses of lower Messinian (Tripoli Unit) that settled just before the base of the Zanclean. Most sediments are either azoic or contain microfossils typical of hyposaline conditions sometimes mixed with benthic foraminifera known to be adapted to stressed environments and even to lacustrine conditions. Fewer types of sediment contain assemblages of planktonic foraminifera, including typical Messinian species, which are thought to be reworked. In contrast, diversified communities of benthic and planktonic foraminifera returned suddenly at the base of the Zanclean; the Messinian–Pliocene transition was marked by an abrupt change of the δ 18O values of carbonates from variable but predominantly negative values characteristic of low salinity conditions in the upper Messinian to higher and more stable values in the Zanclean typifying marine conditions. The southern margin continued, however, to be submitted to large inputs of continental waters. The beginning of the marine inundation was a transitional period with poorly diversified assemblages of planktonic foraminifera and benthic communities tolerant to oxygen deficient bottom conditions; more stable marine conditions with better bottom water ventilation were set up after a lag time which would roughly correspond to a precession cycle. Except for the more marginal areas where conglomerates and erosional features are observed, the restoration of marine conditions occurred, without any significant erosion in the more central areas where the contact is well marked by strong burrowing activity by benthic organisms. This indicates the rapid substitution in the basin of brackish waters by marine waters. Both mixing of these two kinds of waters and permanence of freshwater inputs in the initial stage of the Pliocene transgression may explain why the community of marine planktonic foraminifera, introduced by the inflowing Atlantic waters, hardly survived in such unfavourable ecological conditions in the Mediterranean and reached a normal development later when more stable marine conditions settled. This study and the comparison with other sections from both marginal and deep Mediterranean basins confirm that the Lago–Mare was a widespread dilution event that affected the whole Mediterranean at the end of the Messinian which was abruptly interrupted by the sudden marine inundation at the base of the Zanclean.

Evaporite deposition and coeval volcanism in the Fortuna Basin (Neogene, Murcia, Spain)

The Neogene basins of the Eastern Betic Mountains were placed in a marginal position with respect to the deep Mediterranean basin during the Tortonian to the Messinian. They contain thick gypsum–anhydrite formations resulting from the Upper Miocene salinity crisis. The evaporitic sedimentation reached its maximum extension and stratigraphic complexity in the Fortuna basin, which belongs to this geological setting. Five stratigraphic units are distinguished in the Fortuna basin: (1) Lower Gypsum, (2) Chicamo Gypsum, (3) Chicamo diatomitic–evaporitic cycles, (4) Ribera Gypsum and (5) Rambla Salada Gypsum units. Some of these units occur locally, whereas others can be laterally correlated with those of the Archena-Mula, Guadalentín corridor and Lorca basins. Most of the gypsum units consist of nodular-laminated secondary gypsum, however, primary selenitic, laminated gypsarenites and fine-grained microlenticular burrowed gypsum lithofacies are also present. The evaporite units can also be characterized by the geochemical composition of the gypsum (the sulphur and oxygen of the sulphate and the strontium isotopes), which display a wide range of values. The extreme values indicate precipitation from Tertiary marine brines, or from meteoric waters that recycled Triassic sulphate anion and additional non-marine contributions from country rocks and hydrothermal solutions. The intermediate values are attributed to mixing between seawater and non-marine parent brines. The Fortuna basin contains several outcrops of volcanic to subvolcanic igneous lamproites (Cabezos Negros, Derramadores, El Tale). These lamproites, the so-called fortunites, crop out as individual domic volcanoes with lava flows (Cabezos Negros) or as intrusive subvertical dikes (Derramadores, El Tale). There is good evidence of several magma–sediment interactions that produced macro and microglobular peperitic lithofacies in the Fortuna basin. A peperite is produced when two liquids (a hot magma and a fluidized water-rich sediment) interact and no mixing is possible due to the sharp contrast of viscosity between them. This implies that the eruption was nearly coeval with the deposition of the host-sediment, that was water-rich. The latest evaporitic event (Rambla Salada Gypsum Unit) in the Fortuna basin took place coevally to the emplacement of the Cabezos Negros dome and related lavic-structures, and the intrusion of the Tale and Derramadores dikes. This paper illustrates the presence of peperitic lithofacies in the fortunites and discusses their implications in assigning an age to these evaporitic sediments, which in turn allows us to date the evaporitic units of the Fortuna–Lorca basins.

Fast deep sinking in Mediterranean eddies

Large (up to 0.03 m s−1) downward vertical water velocities (w) are observed using yearlong moored ADCP at ∼2400 m in the deep Mediterranean Sea's Algerian basin. Once every 2–3 months, ∣w∣ rapidly increases to O(0.01 ± 0.002 m s−1) before slowly decreasing during a few weeks, in association with the passage of mesoscale eddies formed nearby. These amplitudes of negative w are O(100) times larger than those commonly linked to mesoscale eddies near the surface (subduction), and O(10) times larger than settling velocities for marine snow. Our observations suggest that mesoscale eddies, which are important for biological productivity near the surface, can also convect nearly fresh material down to the bottom (∼3000 m there) within a few days.

Pliocene Transgression in the Western Mediterranean Sea: Strontium Isotopes from Cuevas Del Almanzora (Se Spain)

The deposition of marine sediments in the deep Mediterranean basins following the Messinian salinity crisis (“Zanclean Deluge”) began at 4.9 Ma and continued until normal marine conditions prevailed at 4.6 Ma. The Betic Strait of southeast Spain, the Rif Strait of northern Morocco, and the Strait of Gibraltar have been postulated as possible entry ways for the marine waters into the Mediterranean. Two possible explanations have been offered for the timing of the deposition of marine hemipelagic marls in the Vera Basin (Cuevas del Almanzora section) within the Betic Strait: (1) early Pliocene, representing the “Zanclean Deluge” (Cita et al., 1980), (2) Messinian (∼5.7 Ma), representing the last marine stage before the Messinian salinity crisis (Benson and Rakic‐El Bied, 1991; Benson et al., 1991). The strontium isotopic ratio on mixed assemblages of foraminifers from these marine marls was determined in order to assess their ages. The average 87Sr/86Sr (0.709033±24) of the seven measured samples is, compared to the base of the Miocene/Pliocene boundary stratotype at Capo Rossello, Sicily, higher by 38 × 10−6 and yields an age of 4.6±0.5 Ma when compared to the established open ocean Sr seawater curve. The determined age indicates that (1) the first 3.6 m of marine deposits of the Cuevas del Almanzora section sensu Cita et al. (1980) including the passage zone are Pliocene, (2) the earliest marine Pliocene might not be represented at Cuevas del Almanzora indicating that this marginal basin at the edge of the Mediterranean Sea, yet within the former Betic Strait, was filled progressively by a marine transgression originating from the Mediterranean Sea around 4.6 Ma. The absence of lowermost Pliocene sediments could suggest that the Betic Strait did not serve as a conduit for the water masses entering the Mediterranean basins during the early Pliocene; and (3) the presence of an early evolutionary stage of Globorotalia margaritae in the Moroccan Bou Regreg section (approximately 5.8–5.6 Ma) and in the Spanish Cuevas del Almanzora section (later than 4.6±0.5 Ma) are diachronous suggesting that straightforward correlations of micropaleontological events within the Mediterranean area with micropaleontologic events of open marine sections should be tested thoroughly by independent methods like Sr isotopes.

Deep Mediterranean Basins and Their Oil Potential: ABSTRACT

deep basins are surrounded by oil and gas producing areas, either onshore or beneath the continental shelf. The main zones are the Ebro delta and the Valencia Gulf (Spain); the Pelagian Sea off Tunisia, western Libya; Sicily; the Adriatic Sea; the Prinou basin in the Greek Aegean Sea; and the Nile delta. In other areas, as in the Adana basin (Turkey), offshore Cyprus (DSDP Leg 42A), and west of Sardinia (DSDP Leg 13), oil and gas shows were present in boreholes. In general, the basins have relatively flat and uniform bottoms with water depths of the order of 2,800-3,000 m (9,200-9,850 ft). Several major exceptions are the Tyrrhenian Sea and the Aegean Sea, which are internal parts of the Alpine orogenies with a stretched structure of a back-arc type. The Ionian Sea has gradual northward slopes. The Eastern basin occupies a typical external position with the front of the Hellenic and Tauric nappes and the external overthrust zone known as the Mediterranean ridge. In terms of the crust, the problem can be approached with the aid of geophysical studies (gravimetry, magnetism, and seismic) and variations in heat flow. The superposition of these varied data thus enables us to schematize the nature of crust of the basins. The western has a high heat flow that is surpassed only at certain points in the Tyrrhenian Sea. In contrast, the eastern in general has a very low heat flow, even in the Ionian Sea where a very considerable positive gravimetric anomaly is known to exist. Without reaching the high Tyrrhenian levels, the Aegean Sea has relatively high heat values. This is normal because of the area's volcanic activity. The main potential oil and gas objectives are the Oligocene and Miocene Series, deposited after and during the main orogenic phases, and covered by thick Messinian evaporites and Pliocene-Pleistocene marine sediments. Underlying the Ionian Sea, the ridge, and the eastern basins, Mesozoic and Paleogene rocks may be possible targets. The zone at the shelf limit of the African platform and the alpine chains resembles many of the productive areas around the globe. In conclusion, the deep basins could hide large targets. The exploration effort will require various improvements (excluding that of the price of crude oil): a better comprehension of the deep structure, seismic techniques capable of obtaining reflection beneath the evaporites and in the overthrust sectors, and technology that allows drilling in 3,000-4,000 m (10,000-13,000 ft) of water with the requisite security safeguards. End_of_Article - Last_Page 1200------------

Stable isotope study of the cyclic diatomite—Claystones from the tripoli formation, Sicily: A prelude to the Messenian salinity crisis

The Tripoli Formation, underlying the Messenian evaporites of Sicily, comprises cyclic alternations of diatomites and claystones that commonly contain dolomite. An oxygen- and carbon-isotope study on the carbonate component of the diatomaceous interbeds records normal marine conditions, whereas the 18O values (+4.0 to +8.5‰) of the dolomite in the claystones signify dolomitization by highly evaporated waters. Extremely negative 13C values (−3.5 to −22.0‰) of this dolomite, certain interbedded limestones, and the overlying Calcare di base denote an organic source of carbon dioxide, the origin of which could be explained by the metabolic activity of sulfate-reducing bacteria in anoxic sediments. This, in turn, implies the former presence of evaporites (?gypsum) before the onset of the Messenian salinity crisis. Eustatic sea-level changes dependent upon the waxing and waning of the Antarctic ice sheet are proposed as the cause of the periodic restrictions in the Tripoli Sea. During high sea-level stands, diatomaceous sedimentation took place under normal marine conditions; during low sea-level stands, restriction and subsequent evaporation of water entering the Tripoli Sea favored the formation of dolomitizing solutions which diagenetically altered the carbonates in the clay-rich sediments. The restriction of the Tripoli Sea during low sea-level stands required the presence of a shallow Atlantic—Mediterranean sill. Progressive tectonic constriction of the connection between the two water bodies, or global eustatic sea-level lowering, is indicated by the extensive dolomitization of the uppermost transitional unit of the Tripoli Formation and the calcitized “evaporite” beds of the Calcare di base. The final phase was total restriction which led to the desiccation of the deep Mediterranean basins and the onset of the Messinian salinity crisis.