Messinian Sequence Research Articles

Chemical and Mineralogical Characterization of Montevive Celestine Mineral

The Montevive celestine mineral deposit, set in the Granada Basin in a marine evaporitic uppermost Tortonian–lowermost Messinian sequence, is the largest reserve in Europe of this economically important strontium ore. Currently, the mine has a large amount of tailings resulting from the rejection of a manual dry screening of high-grade celestine mineral. This visual and density screening was carried out in the early days of mining (1954–1973). Concentrating the celestine mineral and increasing the ore recovery rate would reduce mine operation costs and the generation of new tailings, reducing the impact on the environment. In order to define more adequate concentration methods, we have used complementary analytical techniques such as optical (OM) and scanning and transmission electron microscopy (SEM and TEM), energy-dispersive X-rays (EDXs), X-ray fluorescence (XRF), and X-ray diffraction (XRD) to fully characterize the morphology, microstructure, chemistry, and mineralogy of the celestine mineral. The low-grade mineral is made of prismatic celestine crystals that are replacing a matrix of micro sparry calcite. Other minority minerals are strontianite, dolomite, quartz, and clays (kaolinite, paragonite, and illite). There is also a certain amount of iron oxides and hydroxides (mainly magnetite) associated with clays. We showed that the concentration of low-grade celestine mineral can be achieved through a low-cost and eco-friendly method based on grinding and size separation. The coarser fractions (>5 mm) have more celestine (up to 12 percent units higher than the starting unprocessed mineral) due to the selective loss of calcite and minority minerals (quartz, clays, and iron oxides) that are mainly found in the finer fraction (<1 mm). This process can make mine exploitation more sustainable, reducing the generation of residues that negatively impact the environment.

The Messinian of Agios Myron (Crete, Greece): A key to better understanding of diatomite formation on Gavdos (south of Crete)

The Agios Myron section in the NE of the Heraklion Basin on central Crete exposes a pre-evaporitic Messinian sequence of 24 sedimentary cycles of deep-marine homogeneous and laminated marls (sapropels). Planktonic foraminiferal biostratigraphy and ash layers show that the 24 cycles in section Agios Myron correlate to cycles M79 to M102 in the well-studied and orbitally tuned Metochia section on Gavdos Island. The correlation of the cycle patterns in sections Agios Myron and Metochia not only provides tuned ages for sedimentary cycles, planktonic foraminiferal bioevents, and ash layers in Agios Myron, but also reveals that the diatomites in Metochia cycles M94-M102 have no equivalents at Agios Myron. The onset of diatomite formation on Gavdos at 6.72 Ma is shown to coincide with eutrophication and related to a restriction-imposed increase in salinity 20 kyr earlier at 6.74 Ma. Geographic differences in productivity and possibly also the better preservation potential of siliceous microfossils on the much deeper seafloor at the Metochia site are believed to explain why diatomites are present on Gavdos and absent in time-equivalent levels at Agios Myron.

Cenozoic Marine Basin Evolution in the Western North Aegean trough Margin: Seismic Stratigraphic Evidence

This study investigates the interplay of evolving tectonic and submarine sedimentation processes in the northwest Aegean Sea using marine multichannel seismic profiles. We identify an extensive basin developing in the Thermaikos Gulf inner shelf, outer shelf, and slope leading to the 1500 m deep West North Aegean Trough (NAT). We establish the unconformable extent of Eocene and Oligocene sequences on the upper shelf and trace their continuation in the deeper shelf and slope of Thermaikos Gulf. The start of the Miocene and Middle Miocene developed below the well-established Messinian bounding reflectors that are mostly erosional. Important lateral variations are observed within the Messinian sequence, which is up to 0.8 s thick. Messinian prograding clinoforms are identified on the Thermaikos Gulf shelf and southeast of Chalkidiki, and a zone of irregular reflectors is attributed to the Messinian salt layer. The transpressional deformation of the Messinian in the southwestern margin constrains the timing of westward progradation of the North Anatolian Fault during Messinian. The Pliocene-Quaternary sediments are 0.6–1.8 s thick, showing the overwhelming effect of tectonics on sedimentation plus the northwards Quaternary activation at the Thermaikos apron.

On the structure and evolution of the Sorbas basin, S.E. Spain

Geological mapping and gravity surveying were used to constrain the shape of the Serravallian and Tortonian (U. Miocene) rocks of the Sorbas basin, SE Spain, and hence its tectonic evolution and place in the overall regional tectonic scheme. The present-day basin floor forms a westerly-deepening trough ∼2.0km deep, infilled with mainly clastic turbidites and mass-flow deposits. Basin-fill rocks underwent broadly ENE-WSW extension during accumulation, with extensional faulting on the flank of the Sierra Cabrera to the east. Acoustic velocity measurements demonstrate a petrophysical impact of the syndepositional deformation. Post-deposition but prior to uplift and erosion, the sediments were folded into a large-scale monoclinal structure, inferred to have formed in response to gravitational sliding of sediments off the rising western flank of the Sierra Cabrera. This fold structure was deformed and rotated by 3km of extension-related uplift of the basement block to the south during late Tortonian time, then erosion and flooding to produce a shallow-marine Messinian sequence, partially burying the older rocks. The geodynamic setting was the back-arc sector (the Betic zone) produced by Serravallian-Tortonian rollback of the Gibraltar arc subduction zone. It is bounded to the south by the Carboneras stretching transform fault, that accumulated about 40km of left-lateral offset coevally with sediment deposition and deformation within the Sorbas basin. These events are inferred to be geodynamically linked.

Seismic stratigraphy and sedimentary facies analysis of the pre- and syn- Messinain salinity crisis sequences, onshore Nile Delta, Egypt: Implications for reservoir quality prediction

Abstract This study provides the first high-resolution outlines of the Messinian sequence in the Nile Delta based on an integrated sedimentological, petrophysical and seismic stratigraphic approach. The distribution, pattern and architecture of the Messinian facies deposited before, during and after the Messinian salinity crisis (MSC) have been investigated. In seismic, the pre-MSC Qawasim Formation constitutes parallel oblique seismic facies interpreted as deltaic system prograding northward from prodelta, distal sand bars into subaqueous distributary channels and mouthbars and subaerial delta-plain distributary channels. The MSC Abu Madi Formation consists of three seismic-stratigraphic units infilling the Eonile canyon. A seismically chaotic lower unit paving the canyon-floor is overlain by the continuous, high-amplitude reflectors of the middle unit which is capped by semi-chaotic, low-amplitude facies of the upper unit. The lower unit corresponds to the subaerial gravity-flow deposits synchronously accumulated during the Eonile incision; whereas the middle unit comprises the aggradational-progradational fluvial facies, and the upper unit constitutes the retrogradational estuarine facies. The superimposed diagenetic alterations on these various depositional facies produced complex reservoir heterogeneity. Fluid flow conduits are restricted to the coarse-grained delta distributary channels and fluvial facies with limited marine influence and minimal depositional clay content and traces of diagenetic kaolinite and chlorite. On the other hand, flow baffles and barriers are common in the fine-grained marine-influenced facies with pervasive depositional clays, diagenetic calcite and glauconite.

Depositional facies controls on the diagenesis and reservoir quality of the Messinian Qawasim and Abu Madi formations, onshore Nile Delta, Egypt

The Messinian Qawasim and Abu Madi formations are the main hydrocarbon exploration targets in the onshore Nile Delta. Qawasim Formation constitutes prograditional deltaic system from prodelta and distal delta‐front (distal deltaic facies) to proximal delta‐front and delta‐plain (proximal deltaic facies). Abu Madi sediments on the other hand change upward from continental subaerial gravity‐flow and fluvial facies to marginal‐marine estuarine facies. The seismic attribute (RMS amplitude) and petrophysical analyses revealed that solely the Qawasim proximal deltaic and Abu Madi fluvial facies define the potential reservoir targets. The reservoir quality of the Qawasim distal deltaic and the Abu Madi estuarine facies was completely deteriorated during eodiagenesis by calcite and glauconite cementation (mean > 7.3% and 4.5%, respectively). Conversely, the depositional setting of the Qawasim proximal deltaic and Abu Madi fluvial facies favoured a precipitation of scattered eodiagenetic calcite (mean < 2.5%), which supported the facies framework against mechanical compaction and preserved the intergranular volume (IGV). Chemical compaction, smectite infiltration, quartz cementation, and clay minerals authigenesis were more pronounced in the relatively deeper Abu Madi fluvial facies. These burial attributes caused a large‐scale reservoir heterogeneity. Therefore, the relatively shallower Qawasim proximal deltaic facies presents the best reservoir target in the Messinian sequence of the Nile Delta. This study reveals that in analogous systems, the depositional environment largely controls the diagenetic pathways and, hence, the reservoir quality.

Depositional and petrophysical controls on the volumes of hydrocarbons trapped in the Messinian reservoirs, onshore Nile Delta, Egypt

Abstract The Messinian sequence in the Nile Delta hosts the most prolific hydrocarbon reservoirs, and is therefore of great importance from the aspect of nonrenewable fuel sources exploration and development strategies. This study presents an investigation for the differential impacts of the depositional and petrophysical attributes on the hydrocarbon volumes trapped in the Messinian reservoirs. Analyses of the pressure data and pressure gradients revealed hydraulically-connected and homogeneous Messinian reservoir rocks. The amounts of Stock Tank Oil and Gas Initially In Places (STOIPP & GIIP) are typically controlled by the depositional primary attributes (matrix content and grain size) which induce several reservoir heterogeneities. The Lower Messinian Qawasim reservoir is subdivided into two main zones: the distal deltaic (zone 1) prograded into proximal deltaic facies (zone 2). The petrophysical reservoir quality in terms of porosity, permeability and water saturation increases upward from zone 1 to zone 2. These are largely controlled by the depositional attributes, and therefore zone 2 with a minimum matrix content, coarse-grained sandstones and mega pore spaces (>150 μm) hosts almost 90% of the STOIIP and 100% of the GIIP. Notably, approximately 78% and 65% of the total STOIIP and GIIP, respectively are confined within the coarse-grained delta-plain distributary channels of zone 2. Similarly, the fluvial sediments (zone 1) of the Upper Messinian Abu Madi Formation host 78% of the GIIP in West Al-Khilala Field and the other 22% is trapped in the overlying zone 2 and is mostly distributed within the sand-prone tidal channel and tidal sand bars facies. The channel width/thickness (W/T) ratio largely controls the STOIIP and GIIP values. STOIIP and GIIP display a progressive linear increase with increasing the channel width. This is likely due to increasing the percentage of the good reservoir quality facies within the geologic model as well as increasing the reservoir connectivity with increasing the channel width.

Geochemical constraints on the provenance and depositional environment of the Messinian sediments, onshore Nile Delta, Egypt: Implications for the late Miocene paleogeography of the Mediterranean

The Messinian sequence rocks in the Nile Delta present prolific hydrocarbon reservoirs and are, therefore, of great importance from the aspect of petroleum exploration and development strategies. Yet, little is known about their tectonic provenance and depositional setting. This study focuses on the geochemical signatures archived in the Messinian siliciclastic sediments to employ them as a powerful tool to elucidate the basin evolution during the Messinian salinity crisis (MSC). The pre-MSC Qawasim sediments are texturally and compositionally immature. They are enriched in lithic fragments, foraminiferal bioclasts, and rounded heavy minerals suggesting a significant contribution from the pre-existing Cretaceous-Eocene mixed carbonate-siliciclastic rocks bordering the Nile Delta. In contrast, the textural and mineralogical compositions as well as a range of geochemical proxies (e.g., chemical index of alteration and weathering CIA, CIW as well as index of chemical variability ICV and Zr/Sc ratio) are in favor of prolonged weathering and at least second-cycle origin of the MSC Abu Madi sediments. The mutually correspondent elemental ratios (e.g., Al2O3/TiO2, K2O/Na2O, Zr/Hf, Rb/Sr, Cr/Zr, and Cr/Th) and uniform weathering trends are indicatives for a similar provenance of the pre-MSC Qawasim and MSC Abu Madi sediments. Rare earth element (REE) distribution reveals a significant enrichment in LREE, depletion in HREE, relatively high (La/Yb)N (mean > 9), low (Gd/Yb)N (mean < 2) and a pronounced negative Eu anomaly (mean∼0.75) in the studied Messinian facies, characteristics of upper continental sources of mainly felsic to intermediate rock affiliations. Provenance proxy ratios (e.g., Al/Ti, La/Sc, Th/Sc, La/Co and Eu/Eu*) along with the low concentration of transition trace elements (Cr, Ni, Co, Ni) are effectively ruling out the contribution from mafic and ultramafic rocks.The investigated Messinian sedimentary facies have similar passive margin geotectonic setting and their source rocks were originated in a continental collision tectonic setting that lasted from Late Cretaceous to Oligo-Miocene time. This is confirmed by the Nb/Ta, Zr/Sm ratios coupled with the pronounced Nb, Ta, P, Ti anomalies and enrichments in Pb and U relative to primitive mantle typical of subduction zone environment. The petrographical and geochemical results suggest the MSC Abu Madi sediments to have been eroded and recycled from the older pre-MSC Qawasim sediments by gravity-flow processes and fluvial channels prior to redeposition as incised-valley-fills during the late stage of the MSC. The geochemical paleoenvironmental indicators such as C-value, Sr/Cu and Sr/Ba confirm arid-dry climatic conditions during the onset of the MSC consistent with the Mediterranean desiccation. These indicators also depict a transition from freshwater to relatively normal salinity conditions during the late stage of the MSC. Geochemical results presented in this study support the retrogradational depositional infill of the Messinian incised valleys in the Nile Delta, thus confirming an incipient rise in the Mediterranean Sea level prior to the major Zanclean flooding.

Introduction to the thematic set: Exploring the Mediterranean – new concepts related to the Messinian salt

This thematic set of papers is derived from a workshop, dedicated to the Messinian sequence, which was convened during the 77th EAGE Conference and Exhibition in Madrid in 2015. The main goal of the workshop was to introduce a geological exploration topic to the EAGE meeting. With this objective, and in collaboration with Hector Gonzalez of REPSOL and Jean-Loup Rubino of TOTAL, we co-ordinated a dedicated meeting to bring together people studying the Mediterranean region, particularly those dealing with the Messinian sequence, from both academic and exploration viewpoints.

Anaerobic oxidation of methane in hypersaline Messinian environments revealed by 13C-depleted molecular fossils

The Messinian sequence of evaporitic deposits in Italy includes authigenic carbonates that have been suggested to derive from the microbial degradation of organic compounds, but the biogeochemical mechanisms that led to their formation remained unknown. To unravel these mechanisms, 13 C-depleted carbonate rocks including native sulphur-bearing limestone (Calcare Solfifero) from two locations in Sicily and bedded limestone from the northern Apennines have been studied. Their δ 13 C values as low as − 49‰ reflect incorporation of carbon derived from the oxidation of methane, which was previously suggested to have been linked to bacterial sulphate reduction. Molecular fossils extracted from the limestones reveal that methane was indeed oxidized in an anaerobic process by archaea and sulphate-reducing bacteria. The observed biomarker patterns resemble those of methane-seep carbonates, which form as a consequence of the anaerobic oxidation of methane (AOM). AOM-specific, 13 C-depleted archaeal biomarkers such as PMI (δ 13 C: − 101 to − 75‰) as well as compounds derived from sulphate-reducing bacteria ( iso- and anteiso-fatty acids; δ 13 C as low as − 85‰) were identified in the Messinian carbonates. Although the biomarker results clearly point to AOM, the compound inventory also revealed distinct differences to patterns found at marine methane-seeps. For example, sn3-hydroxyarchaeol is in some samples the only hydroxyarchaeol present, something usually not found at seeps. Archaeol is less depleted in 13 C than PMI at most sites (δ 13 C: − 55 to − 30‰), pointing to the co-occurrence of methanogenic or halophilic archaea with archaea involved in AOM. (1) The presence of calcite pseudomorphs after lenticular gypsum, (2) 18 O-enrichment in carbonates, and (3) the biomarkers O-phytanyl -O-sesterterpanyl glycerolether (extended archaeol), tetrahymanol, and possibly phytanylglycerol monoethers as well as non-isoprenoidal macrocyclic glycerol diethers confirm that carbonate formation took place under evaporitic conditions. AOM has previously been shown to be inhibited in some brine pools on the modern seafloor. Our observations, however, demonstrate that AOM functions in hypersaline environments as well.

Shallow structures at the outer Calabrian accretionary wedge (NW Ionian Sea): new insights from recently migrated reflection data

Terra Nova, 00, 000–000, 2010 Abstract Post-stack time migration of a set of seismic reflection profiles reveals details of the stratigraphic–structural setting of the outermost Calabrian accretionary wedge, in the NW sector of the Ionian Sea, with particular emphasis on the Messinian stratigraphy and the deformation style of the thin frontal portion of this wedge. A structural style and seismic facies analysis, calibrated by refraction data, images a general bipartition of the Messinian evaporite deposits: the `lower subunit', consisting mainly of salt, appears to have undergone ductile-flow deformation, and the `upper subunit', consisting mainly of gypsum and marls, appears to be characterized by brittle deformation. Lateral variations in evaporite composition and/or thickness reflect a change in the deformation style of the accretionary wedge, with the development of double-verging imbricated thrust sheets of the whole Messinian sequence. Gravitational-slide tectonics of the unstable accretionary wedge, too steep to support a skinny evaporite-based top layer, characterize the outermost wedge, indicating here a near-surface `olistostrome' from the Late Messinian.

Onshore to offshore reconstruction of the Messinian erosion surface in Western Sardinia, Italy: Implications for the Messinian salinity crisis

New outcrops in the Sinis peninsula (Sardinia, Italy) allow a detailed description of the Messinian erosion surface. The correlation between outcrops, industrial seismic data and data collected offshore Oristano from a recent cruise permits reconstruction of the geometry of this surface from presently emerged interfluves to the deep canyons offshore, with: - onshore: an eroded karstic plateau presently cropping out over a 20 km × 5 km area. Well-preserved karst structures occur locally and can form several metres high reliefs. The southernmost edge of the plateau is limited by a cliff. The karstic plateau and the cliff are sealed by transgressive deposits of Pliocene age; - offshore, an interfluve zone with a mostly flat and low-angle dipping plateau, westward dissected by paleovalleys which were identified down to a depth of 2000 m. In the Oristano Gulf, Messinian paleovalleys were also identified. The Capo San Marco paleocliff was probably located on the edge of a canyon. Onshore, only one major erosion surface was identified, located at the top the Messinian sequence. Offshore, this surface extends down to the abyssal plain. The surface was emplaced above deposits related to the Terminal Carbonate Complex. This indicates that the marginal evaporites are older than the major drawdown of the Mediterranean sea-level. The major drawdown is related to the deposition of the deep evaporites.

Did the Mediterranean marine reflooding precede the Mio–Pliocene boundary? Paleontological and geochemical evidence from upper Messinian sequences of Tuscany, Italy

The events related to the Messinian salinity crisis are among the most deeply investigated of Earth's history. According to the current hypothesis of Neogene paleogeographic evolution, approximately 5.5 Ma ago, after evaporitic sedimentation and before the Mio–Pliocene boundary, the Mediterranean was characterized by the widespread development of non-marine environments inhabited by molluscs and ostracods of brackish affinity. The Messinian post-evaporitic deposits that testify such a dramatic environmental change are commonly referred to as ‘Lago-mare’ and have been reported from several outcrops and boreholes throughout the entire Mediterranean basin. The origin of ‘Lago-mare’ conditions is commonly interpreted as the result of the synergistic effect of both the humid climatic conditions and change of the drainage patterns at the Mediterranean scale, with the capture of Paratethyan brackish waters. A few recent studies, however, suggest that such a scenario probably represents an oversimplification of the original context, from both a paleogeographical and paleoenvironmental point of view. Unfortunately, the results of these studies have never been commonly accepted and the proposed evidences have been considered questionable. In this paper we describe the fish assemblages from the ‘Lago-mare’ deposits of two localities, Cava Serredi and Podere Torricella, located in the Neogene hinterland basins of Tuscany, central Italy. These assemblages consists of a mixture of marine euryhaline and stenohaline taxa suggesting that the depositional environments were characterized by permanently open connections with a marine basin filled with normal marine waters. In order to better define the paleontological significance of these upper Messinian fish assemblages, the oxygen, carbon and strontium isotopic composition of fish otoliths and other fossils has been measured. These isotopic compositions are strongly indicative of the presence of normal marine conditions close to the depositional environments testified by the sedimentary sequences, thereby implying that the interpretation of the geochemical results are consistent with those derived from the paleoecological analyses of the fish assemblages. Based on the integrated paleoichthyological–geochemical approach discussed in this paper it is possible to unambiguously demonstrate that normal marine rather than fresh- or brackish waters were present in the Mediterranean at least during the upper part of the ‘Lago-mare’ event, providing an unquestionable evidence that the marine refilling of the basin preceded the Mio–Pliocene boundary.

Paratethyan–Mediterranean connectivity in the Sea of Marmara region (NW Turkey) during the Messinian

The Sea of Marmara region is thought to have been a gateway between Paratethys and the Mediterranean since the Middle Miocene, and is therefore an important control on water mass exchange between the two realms. The Miocene successions in the northeastern Aegean and northwestern Marmara regions indicate that the first Mediterranean marine transgression to affect these areas occurred during the late Serravallian. In the northeastern Aegean region, frequent marine incursions occurred during the Tortonian and Messinian stages. The Messinian stage in this area is represented by a package of brackish- to fresh-water carbonates with some marine sandstone–siltstone interbeds (Alçıtepe Formation), which conformably overlies the Tortonian Kirazlı Formation. The Messinian sequence is overlain with an erosional contact by a shallow marine siliciclastic sequence (Göztepe Formation) of Zanclean age. With its brackish- to fresh-water carbonates and broadly constrained age, the Messinian sequence is interpreted as being coeval with the Upper Evaporite–Lago Mare sequence observed in western Mediterranean basins. In the western Marmara region, the Pontian (Messinian) Alçıtepe Formation consists of bioclastic and oolitic limestones with basal clastic rocks. It conformably overlies the fluvio-lacustrine siliciclastic sediments of the Middle to Upper Miocene Kirazlı Formation and is overlain by fluvio-lacustrine sediments of the Kimmerian (5.5–3.2 Ma) Truva and Tevfikiye formations with an erosional contact. The bioclastic limestones of the Alçıtepe Formation in the western Marmara region contain a molluscan and ostracod fauna that are endemic to Paratethys. These fauna indicate deposition in a shallow, brackish- to fresh-water environment. Faunal and paleomagnetic analyses of a section of the Alçıtepe Formation at Yenimahalle (Çanakkale) confirm that the formation is of Pontian age and represents chron C3r (6.04–5.24 Ma). The ostracod analysis indicates that during deposition of the Alçıtepe Formation, salinity increased from brackish in the lower part to more saline conditions in the upper part. Ostracod valves have low 87Sr / 86Sr values relative to coeval Late Miocene ocean water. This indicates that exchange between the Sea of Marmara region and the global ocean was restricted throughout this period. Fossil and Sr-isotope evidence suggests, however, that there was a Paratethyan–Marmara connection during the deposition of the lower part of the Alçıtepe Formation, with Paratethyan influence reaching the north Aegean. Connection via Marmara between Paratethys and the Mediterranean was not re-established until the late Aktchagylian (Late Pliocene). The re-connection was caused by both increased activity on the North Anatolian Fault and global sea level rise.

Testing models for the Messinian salinity crisis: The Messinian record in Almería, SE Spain

Neogene intermontane basins in Almería Province, SE Spain, display excellent exposures of Messinian (Late Miocene) sequences. The Sorbas, Almería-Níjar and Vera basins maintained connection with the Mediterranean throughout the Messinian, except during the major desiccation phase leading to the formation of salt in the deep centre of the Western Mediterranean. These basins were part of the Western Mediterranean with no separate link to the Atlantic Ocean. The presence of normal marine sediments in these basins reflects the Western Mediterranean watermass. Messinian pre-evaporitic sediments in the basins of southeastern Almería do not show gradual change towards evaporite deposits. Instead they contain stenohaline invertebrates right up to a major erosion surface that separates them from overlying gypsum deposits. This contradicts suggestion of progressive salinity increase in this part of the Western Mediterranean prior to the Messinian Salinity Crisis (MSC); it also indicates that initiation of evaporite precipitation was not synchronous throughout the Mediterranean Basin. There is no major erosion surface within or at the top of the evaporites in these Almería basins, and the gypsum beds exhibit upward transition to siliciclastic and carbonate deposits. This is inconsistent with a model of Messinian Mediterranean evaporite formation whereby deposition of marginal evaporites was followed by their erosion during drawdown that resulted in formation of evaporites in the centre of the Western Mediterranean. The presence of stenohaline biotas in siliciclastic deposits interbedded with the gypsum and in the Messinian post-evaporitic sediments, challenges the view that a long-standing large body of brackish water (the Lago Mare) filled the Western Mediterranean following the MSC and prior to Early Pliocene flooding. It also contradicts the concept of many relatively small brackish basins spread across an otherwise desiccated Western Mediterranean basin. The basins of southeastern Almería record normal marine Early Messinian sedimentation that was abruptly interrupted by sealevel fall. This drawdown most likely resulted in precipitation of evaporites in the central deep Western Mediterranean basin. Following this episode, final marine reflooding of the Western Mediterranean took place during the Late Messinian, and the Mediterranean Sea rose to a level similar to, or higher than, that preceding the Salinity Crisis.

Precise 40Ar/39Ar dating of volcanic tuffs within the upper Messinian sequences in the Melilla carbonate complex (NE Morocco): implications for the Messinian Salinity Crisis

The Melilla carbonate complex (NE Morocco) is the only area of the Paleo-Mediterranean Sea where volcanic activity was present throughout most of the Messinian. 40Ar/39Ar dating of volcanic tuffs interbedded within the upper Messinian sedimentary deposits, known as the Terminal Carbonate Complex (TCC), yields accurate ages of paleoenvironmental and sea-level changes related to the Messinian Salinity Crisis. The new chronologic data (1) provide an average of 5.95–5.99 Ma for the base of the TCC, thus being synchronous with the onset of the Messinian Salinity Crisis, (2) demonstrate for the first time that the basal unconformity of the TCC does not represent a hiatus of long duration, (3) define a precise time line at 5.87±0.02 Ma (2σ) corresponding to sedimentary rocks exhibiting a lateral transition between continental and marine deposits typical of the TCC and (4) yield evidence that emersion of the Melilla platform during deposition of the TCC is partly related to tectono-magmatic activity. An erosional surface, capping the TCC deposits in the Melilla basin, is related to the major Messinian Mediterranean drawdown. The duration of the hiatus, associated with this surface, is estimated to be at most 450 kyr, but is probably shorter.

Post-Messinian evolution of the Southeastern Levant Basin based on two-dimensional stratigraphic simulation

The evolution of the southeastern Levant Basin following the Messinian salinity crisis was interpreted, using observations derived from seismic sections and well data, and from output of a two-dimensional forward stratigraphic simulation program (SEDPAK). The working assumption was that the thick evaporitic Messinian sequence was generated in a shallow-water, albeit a topographically deep basin. The sea-level dropped at least 800 m below its present level and may have been as low as 1300 m, the latter value representing the reconstructed depth of the top Messinian in the deep part of the basin. The top of the evaporitic sequence in that part of the basin was virtually horizontal at the end of the Messinian crisis and thus may be used as a regional datum. Subsidence rates measured for the shelf and coastal plain of Israel indicate a reduction of these rates for the Pleistocene when compared to the Pliocene. During the Pleistocene subsidence rates for the base slope increased and dictated the modern physiography of the margin. Earlier, in the Middle to Late Pliocene, small-scale salt movements occurred in the deep basin, producing the fragmented and irregular shape of the “M” horizon (the seismic event marking the top of the evaporitic sequence) and deforming the overlying Pliocene section. The simulated rate of sediment supply indicates a constant increase over time for the Pliocene and the Pleistocene, probably in response to an increased influx of Nile-derived, along-shelf sediment transport.

Modeling deformation and salt tectonics in the eastern Mediterranean Ridge accretionary wedge

This study addresses some aspects of the kinematics and structural setting of the Mediterranean Ridge accretionary complex, particularly those aspects related to the occurrence and distribution of Messinian evaporites. The approach is by (1) identification of the geometry of deformation through reprocessing of existing multichannel seismic reflection data from the Levantine Basin, aimed at the definition of the velocity field and depth imaging; (2) physical modeling in the laboratory, aimed at the study of the kinematics of shortening of sedimentary sequences detaching on viscous decollements; and (3) comparison between the results of the two approaches. We conclude that the thick Messinian sequence of the Levantine Basin is composed primarily of salt, so that the entire evaporitic sequence can be expected to behave as a viscous material. It follows that the main detachment of the post-Messinian wedge is located at the base of the Messinian salt layer. A viscous (salt) decollement would produce thrusting trending normal to the shortening direction, but boundary conditions affect structural trends even more than stress and/or movement direction. Both strain partitioning and the formation of major strike-slip faults within the post-Messinian wedge are prevented by the high angle of convergence between the African and Aegean plates as well as by the low intraplate friction. In addition, we show that curved and anastomosing thrust fronts are reflected in the cobblestone topography of the Mediterranean Ridge. We finally postulate that extension may occur in the central Mediterranean Ridge as a result of the geometry of the plate boundaries. This extension is considered as a possible cause of mud volcanism and mud diapirism.

Mediterranean Messinian Salinity Crisis: constraints from a coeval marginal basin, Sorbas, southeastern Spain

The extent, timing and effects of Late Miocene desiccation and evaporite deposition in the Mediterranean Sea remain controversial. Marginal basins containing Messinian (5.3–7.1 Ma) sequences now exposed onland supplement information from the deep Mediterranean, but have evaporites of a variety of ages. Some of these Messinian evaporites pre-date, and others post-date, deep desiccation. None appears to be exactly coeval with those of the deep Mediterranean. In the Betic Cordillera of southern Spain, basins (e.g. Granada Basin) far from the present-day Mediterranean lost connection with the Mediterranean due to uplift ∼1 Ma before the Salinity Crisis, and have marine evaporites of early, not late, Messinian age. In contrast, basins such as the Sorbas Basin in southeastern Spain, adjacent to the present-day Mediterranean, record events directly reflecting the course of the Salinity Crisis. The Sorbas Basin retained marine connection with the western Mediterranean up until evaporative drawdown in the mid-Messinian and was rapidly reflooded immediately afterwards. The Sorbas Messinian sequence is up to 320 m thick. It is complete and normal marine, except for an incised basinwide erosion surface overlain by a 130 m thick gypsum deposit. We propose that this surface marks the interval of deep desiccation of the adjacent Mediterranean basin. Erosion occurred shortly after 5.9 Ma and the irregular unconformity has relief of at least 240 m, confirming Mediterranean drawdown significantly below the Atlantic level. Sorbas gypsum deposits overlie the unconformity and are intercalated with marls estimated at ∼5.5 Ma containing normal marine Messinian biotas. These gypsum deposits therefore post-date deep desiccation and formed in a silled basin immediately following marine reflooding. They mark the end of the Salinity Crisis and are overlain by 70 m of normal marine sediments containing unreworked foraminifers of latest Messinian age. This succession demonstrates that the Salinity Crisis occurred faster and was completed sooner than previously believed. It took place within ∼0.4 Ma (time-scale of Berggren et al., 1995b, is ∼0.2 Ma on the time-scale of Baksi, 1993) and was completed before the end of the Messinian. This corrects previous views that the Salinity Crisis continued until the Early Pliocene. There is no evidence in the Sorbas Basin for brackish `Lago Mare' conditions, and the normal marine biotas that directly precede and follow drawdown rebut earlier suggestions of prolonged salinity effects.

Bacterial and algal markers in sedimentary organic matter deposited under natural sulphurization conditions (Lorca Basin, Murcia, Spain)

Free lipids, sulphur-bound lipids present in macromolecular fractions and kerogen pyrolysis products have been studied in shales and early diagenetic carbonates replacing gypsum from a Messinian sequence of Lorca Basin. The high abundance of phytane, 2,3-dimethyl-5-(2,6,10-trimethylundecyl)thiophene, mid-chain C 20 isoprenoid thiophenes and bithiophenes and bis-O-phytanyl and O-phytanyl-O-sesterterpanyl glycerol ethers indicates that the organic matter in all these samples was deposited under hypersaline conditions. The isopranyl glycerol ethers are essentially found in the sulphur-bound macromolecular matter which contrasts with the low concentrations of these compounds as free lipids. However, the distributions of these isopranyl glycerols is paralleled by the occurrence of free phytanic acid (shales and laminated carbonate) and 3,7,11,15,19-pentamethyleicosanoic acid (only in the laminated carbonate). The bacterial inputs are represented by 2-hydroxytetracosanoic acid, n-octadec-11-enoic acid, hopanoic acids and the distributions of iso- and anteiso-C 15 and C 17 homologues and minor amounts of iso-C 16 and anteiso-C 14. These branched fatty acids are characteristic of sulphate-reducing bacteria. The relative proportions of the iso- and anteiso-compounds in the total fatty acid distributions are correlated with the proportion of reduced sulphur in the sediments.