Messinian Evaporites Research Articles

Evidence for isolated evolution of deep-sea ciliate communities through geological separation and environmental selection

BackgroundDeep hypersaline anoxic basins (DHABs) are isolated habitats at the bottom of the eastern Mediterranean Sea, which originate from the ancient dissolution of Messinian evaporites. The different basins have recruited their original biota from the same source, but their geological evolution eventually constituted sharp environmental barriers, restricting genetic exchange between the individual basins. Therefore, DHABs are unique model systems to assess the effect of geological events and environmental conditions on the evolution and diversification of protistan plankton. Here, we examine evidence for isolated evolution of unicellular eukaryote protistan plankton communities driven by geological separation and environmental selection. We specifically focused on ciliated protists as a major component of protistan DHAB plankton by pyrosequencing the hypervariable V4 fragment of the small subunit ribosomal RNA. Geospatial distributions and responses of marine ciliates to differential hydrochemistries suggest strong physical and chemical barriers to dispersal that influence the evolution of this plankton group.ResultsCiliate communities in the brines of four investigated DHABs are distinctively different from ciliate communities in the interfaces (haloclines) immediately above the brines. While the interface ciliate communities from different sites are relatively similar to each other, the brine ciliate communities are significantly different between sites. We found no distance-decay relationship, and canonical correspondence analyses identified oxygen and sodium as most important hydrochemical parameters explaining the partitioning of diversity between interface and brine ciliate communities. However, none of the analyzed hydrochemical parameters explained the significant differences between brine ciliate communities in different basins.ConclusionsOur data indicate a frequent genetic exchange in the deep-sea water above the brines. The “isolated island character” of the different brines, that resulted from geological events and contemporary environmental conditions, create selective pressures driving evolutionary processes, and with time, lead to speciation and shape protistan community composition. We conclude that community assembly in DHABs is a mixture of isolated evolution (as evidenced by small changes in V4 primary structure in some taxa) and species sorting (as indicated by the regional absence/presence of individual taxon groups on high levels in taxonomic hierarchy).

The Pozzo del Sale Groundwaters (Irpinia, Southern Apennines, Italy): Origin and Mechanisms of Salinization

Chemical and water isotope ratios data for groundwaters from the Pozzo del Sale area in the Irpinia sector of the Southern Apennines are presented. The water chemistry of the aquifer system may initially be regarded as the result of easy and common, low temperature interaction between meteoric water and Late Messinian evaporites, which produce Ca-bicarbonate and Na-chloride passing through Ca-sulfate waters. However, a closer inspection reveals a more complicated geochemical setting consisting of: (1) two further Na-sulfate and Ca(Mg)-sulfate waters; (2) the existence of different meteoric recharge areas; (3) the mixing between the different groundwaters and allochthonous fluids from terrestrial mud volcanoes. The salinization mechanism and the local mineralogy were inferred by classical and novel ternary and binary diagrams. The presence of MgSO4- and Na2SO4-bearing minerals of non-marine or mixed origin other than gypsum and halite within the local evaporites suggests a mineralogical heterogeneity within the local Messinian evaporites. The paleoenvironment of this sector of the Gessoso–Solfifera Formation might have been composed of relatively small playa-lakes fed by seawater but also large amounts of continental waters of meteoric origin.

Evidence for large-scale methane venting due to rapid drawdown of sea level during the Messinian Salinity Crisis

We report the discovery, from three-dimensional seismic mapping, of a field of pockmarks buried at present depths of ∼4 km in the Levant Basin (southeastern Mediterranean). The pockmarks cover an area of ∼1000 km 2 , have diameters as great as 2 km, and erode as much as 200 m into their substrate of deep-water clastic sediments, which immediately predate the Messinian Salinity Crisis (MSC, ca. 6.2–5.5 Ma). These craters are filled by the basal units of the Messinian evaporites, thus implying they formed at or close to the time of the earliest major drawdown of sea level. All the pockmarks are developed at a single, regionally correlatable surface, Horizon N, which is observed throughout the Mediterranean to coincide with the onset of the MSC. In the study area, this surface formed by erosion and drawdown with a magnitude of 900–1000 m. We propose that this rapid basinal drawdown led to a dramatic increase of the shallow subsurface pore-fluid overpressure regime in the mostly fine-grained pre-Messinian sediments. Subsequent pressure release then resulted in high flux fluid venting, sediment remobilization, and pockmark formation. The spatial association of the craters with an underlying canyon suggests that their formation is linked to biogenic methane generation. The model of drawdown-induced overpressuring and remobilization may be applicable to many other evaporitic basins, and represents a novel mechanism for inducing large-scale sediment remobilization of shallow buried depositional systems at the earliest stages of salt basin development.

Propagation of a lithospheric tear fault (STEP) through the western boundary of the Calabrian accretionary wedge offshore eastern Sicily (Southern Italy)

The rollback of a segmented slab of oceanic lithosphere is typically accompanied by vertical lithospheric tear fault(s) along the lateral slab edge(s) and by strike slip movement in the upper plate, defined as a STEP fault (Subduction Tear Edge Propagator). The Neogene evolution of the Central Mediterranean is dominated by the interaction between the slow Africa–Eurasia convergence and the SE-ward rollback of the Ionian slab, that leads to the back-arc opening of the Tyrrhenian Sea. Here, we present post-stack time migrated and pre-stack depth migrated Archimede (1997) multichannel seismic lines, that were acquired offshore eastern Sicily, at the foot of the Malta escarpment . First, we identify the recent deformation along the lateral ramp of the Calabrian accretionary wedge. Towards the east, the Calabrian wedge is formed by the accretion of the post-evaporitic sediments, above a decollement at the base of the Messinian evaporites . At the latitude of Syracuse, 50 km east of the Malta escarpment, a major N150°E trending crustal scale and vertical fault slices through the entire accretionary wedge. This fault cuts by several kilometers, through the pre-evaporitic Messinian sediments and into the basement. The vertical offset along this vertical fault decreases from north to south, and the fault is no longer observed on the seismic lines, 50 km SE of the Alfeo seamount . A previously published Moho depth isocontour map, offshore Sicily and the recent GPS data, combined with the presence of strike slip movements NE onshore Sicily, allow us to identify this 200 km long crustal-scale fault as the surface expression of a STEP fault. The presence of syntectonic Pleistocene sediments on top this crustal-scale fault suggests a recent lithospheric vertical movement of the STEP fault, in response to the rollback of the Ionian slab and to the SE-ward advance of the Calabria-Peloritan block. ► Depth migrated seismic reflection profiles from the Calabria/Sicily active margin. ► A N150°E striking, lithospheric scale fault, 50 km east of the Malta escarpment ► Interpreted to be a “Subduction Tear Edge Propagator” (STEP) fault ► Fault offset decreases to the S until termination (at the propagating tip) ► Deformed sediments suggest recent fault activity (related to Calabrian subduction).

Impact of the Messinian Salinity Crisis on Black Sea hydrology—Insights from hydrogen isotopes analysis on biomarkers

The Messinian Salinity Crisis (5.96–5.33Ma ago) was a dramatic oceanographic event, when evaporites kilometers thick precipitated in a desiccating Mediterranean basin, trapping more than 5% of the world's oceanic salt. Hydrological changes in the adjacent Black Sea and water exchange with the Mediterranean region are crucial, but poorly understood factors, influencing Messinian evaporite formation. Here, we present compound specific hydrogen isotope (δD) data from Messinian Black Sea sedimentary rocks that show a rapid change to heavy waters at 5.8Ma, when major glaciations occurred. At the same time, highly depleted δD values of long chain n-alkanes derived from plant waxes indicate that fresh, river transported water originated from colder northern latitudes. The δD values of alkenones, biosynthesized by haptophyte algae, show an unprecedented increase of 60‰ within ∼100kyr. The corresponding rapid change to +110‰ for δD of the Black Sea waters seem unrealistic, being heavier than anywhere in the present day oceans. Regardless of the applied relation between the δD values of the alkenones and δD of the waters where they were produced, the 60‰ enrichment in the δD values of alkenones indicates strongly enhanced evaporitic conditions. Still, the relative distribution of the alkenones implies in-situ growth and reproduction of haptophyte algae, requiring sustained marine conditions in the Black Sea up to 5.6Ma. This indicates that Mediterranean–Black Sea connectivity persisted during the first MSC phase when gypsum precipitated in the Mediterranean basin. When the Black Sea became isolated, at the peak of the MSC (∼5.6Ma), it had a strongly negative hydrological budget and rapidly desiccated due to excess evaporation.

A modeling perspective on spatial and temporal variations in Messinian evaporite deposits

Abstract During the Messinian Salinity Crisis (MSC), evaporite-dominated sequences formed in marginal and deep basins of the Mediterranean Sea. In the marginal basins, the onset of the MSC is synchronous and a single depositional framework fits all sequences. In contrast, MSC sequences of the western and eastern deep basins appear to comprise a different number of units and differ greatly in thickness. Even though there exist numerous scenarios for deposition in the marginal and deep basins, the link between the two settings is difficult and scenarios are rarely quantitatively supported. We employ a simple box model for the Messinian Mediterranean to examine the causes of (1) spatial variation in thickness and (2) differences in the time of onset of deposition. Model results are compared with actual observations on the MSC sequences. The results show that a large connection between the western and eastern basin is necessary for, and some degree of water column stratification is conducive to, synchronous onset of the MSC in the marginal basins. Moreover, halite deposits in the deep basins are likely to be coeval and have formed in ≈ 60 ka after a (further) restriction of the Atlantic–Mediterranean connection during the MSC, but without a significant sea level drop. A difference in the net salt gain per unit volume caused the different halite deposition rates in the two basins. A scenario with only a simple restriction of the Atlantic–Mediterranean connection during the Late Miocene – without significant changes in the Mediterranean sea level, the fresh water budget, or the size of the Strait of Sicily – is able to explain the synchronous onset of the MSC, the synchronous marginal evaporite formation and the differences in the deep basinal sequences.

Two-stage growth of the Calabrian accretionary wedge in the Ionian Sea (Central Mediterranean): Constraints from depth‐migrated multichannel seismic data

New structural images of the Calabrian accretionary wedge are presented from depth‐migrated multichannel seismic data. A combined interpretation swath‐mapping bathymetry allows us to identify five morphological domains on the basis of their tectonic style. (1) Beneath the undeformed Abyssal Plain, a set of deep, NW vergent reverse faults cuts the Ionian oceanic crust and thick pre-Messinian sediments. (2) Towards the NW, the low-taper post-Messinian wedge overlying a shallow NW dipping décollement, at the base of the Messinian evaporites and exhibiting strong tectonic thickening. (3) Beneath the flat Central Transition Zone, a backthrust marks the contact between the post- and pre-Messinian wedges. Here, the décollement dip increases (>3°) cutting through deeper sediments to reach 10km depth. (4) Beneath the pre-Messinian Calabrian wedge, some steep landward dipping features are imaged where underplating may occur. (5) Beneath the inner plateau, a fore‐arc basin lies above the top of the Calabrian continental basement imaged at 8km depth. The architecture of the Calabrian accretionary complex is very similar to the Mediterranean Ridge. Both systems consist of (a) an external low-taper post-Messinian wedge overlying a thick undeformed section of underthrust Mesozoic sediments and (b) an internal pre-Messinian wedge where the décollement steps down and where the underthrust section is presumably underplated. We perform area balancing and show that since the Messinian, the Calabrian accretionary wedge has undergone extremely rapid outward growth at an average rate of 30km/Ma, which makes it the fastest growing accretionary wedge over the past 5Ma.

The utilization of seismic interpretation to identify and describe the shallow subsurface structures in the southeastern Mediterranean Sea

The shallow subsurface structures of the offshore Nile Delta particularly in the southeastern Mediterranean were dealt through the interpretation of 40 two-dimensional seismic reflection lines. The interpretations of seismic reflection data indicated that the principle sedimentary processes affecting the study area include three main structural groups according to their origin and development. The first group of structures comprises of gravity-driven structures, which include slides, slumps, turbidities, and debris flow. Slides are present in three different forms on seismic sections: slide sheets, slides with scar, and wedges of slide materials. Slumps have many geometrical shapes: lenses, spoon-shaped slumps, and slumped blocks bound by growth faults. Debris flows are present as transparent unit (due to the dispersion of seismic waves at debris boundaries), whereas turbidities appear on the seismic profiles, which are formed of closely spaced parallel thin reflectors analogous to their thin stratified bedded layers. The second group of structures is syn-depositional structures, which include growth faults, and tilted and rotated fault blocks. Growth faults are listric in shape and usually dip seaward; displacements along the fault plane increase with depth. Some of these faults are incipient, and some are complicated and intersected by secondary antithetic faults. Most of the growth faults soles out basin wards and in the evaporites layer. Fault blocks are formed due to the Messinian evaporite movement vertically and horizontally due to its mobility as a consequence to the pressure resulted from the overloading of Pliocene sediment. The third group of structures comprises evaporite flow structures such as diapiric structures and graben collapse structures. The surface of the Messinian evaporites was folded during its flow as a consequence to the lateral compression acted on the mobile strata of the Messinian evaporites to form diapiric triangular structures and creates a stress zone faulting and fractures system. These conditions led to the formation of collapse structures or graben collapse structures.

Introduction to this special section: The Mediterranean region

When it comes to the Mediterranean, the figure of Odysseus, as the archetypal “explorer”, may spring to mind. The Mediterranean region represents an incredibly colorful region, not only from a historical and cultural perspective, but also from a hydrocarbon exploration point of view. Located between Europe, Africa, and the Near East, this region also has a long history of geological and geophysical activities. During the last few decades, a few segments of the Mediterranean became significant from an exploration and production point of view, the most important example being the Nile Delta of Egypt. Some segments have numerous offshore oil and gas fields (e.g., Libya or Croatia) but with a much smaller contribution to the petroleum production of the entire Mediterranean. One reason to have a TLE special section dedicated to this region is the exploration breakthrough happening in the Israeli sector of the eastern Mediterranean. Large, multi-TCF gas accumulations (e.g., Leviathan and Tamar) have been found in the deep-water Levantine Basin. The biogenic gas is reservoired in Miocene turbidites, in large inverted structures beneath the Messinian evaporite sequence. The sheer size of these recent discoveries (total recoverable reserves of about 40 TCF!) made the broader Levantine Basin an emerging major petroleum province, just in the last few years.

Chemical and isotopic characterization of the thermomineral water of Terme Sibarite springs (Northern Calabria, Italy)

The Terme Sibarite and nearby thermomineral water discharges have Ca-SO4 to Ca-SO4-HCO3 composition, near neutral pH value of 6.9 to 7.6, outlet temperatures of 16° to 25.5°C, variable redox potentials (-0.23 to 0.2 V) and total dissolved solids from 20 to 35 meq L-1. The total flow rate of the Terme Sibarite springs is about 130 L s-1. Solubility of chalcedony and the K-Mg geothermometer show a full equilibrium reservoir temperature of 33°C. The δ34S values of dissolved sulfate are constrained by mixing of thermomineral waters with cold waters, both interacting with Upper Triassic carbonate-evaporite rocks, as well as occurrence of bacterial sulfate reduction. In the light of the geological and hydrogeological framework of the study area, this chemical and isotopic evidence suggests that the thermal circuit develops entirely into the Upper Triassic sedimentary sequence, without any interaction with the Messinian evaporites which are possibly present below the Upper Triassic sedimentary sequence. The thermomineral waters are meteoric precipitations infiltrating in the Pollino Massif, at average altitudes of 950-1090 m a.s.l, as indicated by the δ18O values of water. These waters descend to maximum depths of 600 m below the Sibari Plain, where the geothermal reservoir is situated. Circulating into it, waters extract heat from reservoir rocks, attaining thermo-chemical equilibrium at the temperature suggested by chemical geothermometers. Then, the thermomineral waters locally rise relatively quickly to the surface, along subvertical faults and fractures, preserving part of their physical and chemical characteristics. The methodological approach utilized in this research may be applied to other fault-controlled, low-temperature geothermal systems in other zones of Italy and other nations.

Strain partitioning in gravity-driven shortening of a thick, multilayered evaporite sequence

Abstract Three-dimensional seismic data from the Levant Basin, eastern Mediterranean, was used to quantify longitudinal strains in thick, multilayered Messinian evaporites at an early stage of salt tectonics. Gravity-spreading is driven by basin subsidence and tilting of the Levant margin and by progradation of the Nile Cone. Similar styles of shortening in two separate 3D survey areas comprise detachment folds, thrust-ramp folds and conjugate arrays of strike-slip faults. These Pleistocene structures can be explained with a single deformation phase with a tectonic transport direction of NE to ENE, obliquely opposed to the extension updip, which began in the Late Pliocene. Four major detachments within the Messinian are probably halite-rich intervals in the multilayer. Shortening of competent interlayers varies from 1–2% near the base to c. 7% near the top of the Messinian, with a sharp reduction in shortening at the top Messinian and roof to 1–2%. This shortening profile is attributed to asymmetric Poiseuille flow, indicating that salt is flowing downdip faster than the overburden is translating. Physical modelling supports the inferred flow profile, showing that each mobile layer flows faster than adjoining competent layers and that strains in evaporites can be far greater than in the overburden. This is the first published use of seismic data to demonstrate the flow regime within salt on a regional scale.

A Miocene tectonic inversion in the Ionian Sea (central Mediterranean): Evidence from multichannel seismic data

It is widely accepted that the Central and Eastern Mediterranean are remnants of the Neo-Tethys. However, the orientation and timing of spreading of this domain remain controversial. Here, we present time migrated and pre-stack depth migrated NW-SE oriented Archimede (1997) lines together with the PrisMed01 (1993) profile to constrain the evolution of the Ionian basin. Our interpretation allows us to identify a large-scale set of SW-NE striking reverse faults beneath the Ionian Abyssal Plain. These primarily NW vergent faults are characterized by a spacing comprised between 10 to 20 km and a dip ranging from 60 to 65{degree sign}. Following very recent paleogeographic reconstructions, we propose that the set of N{degree sign}55 features initially formed as normal faults during the NW-SE trending seafloor spreading of the Ionian basin after its late Triassic-early Jurassic rifting. Based on geometric comparisons with the intraplate deformation observed beneath the Central Indian Ocean, we show that the inherited oceanic normal faults were reactivated under compression as reverse faults. Well-developed Tortonian syntectonic basins developed NW of the major faults and the base of the Messinian evaporites (Mobile Unit) is slightly folded by the activity of the faults. We show that 3-4 km of total shortening occurs over a 80 km wide area beneath the Ionian Abyssal Plain, resulting in a bulk shortening of 3.5-5 %. We propose a link between the Tortonian-early Messinian inversion of the fault pattern and a plate tectonic reorganization prior to the main phase of back-arc opening of the Tyrrhenian domain.

New knowledge on the Monte Conca gypsum karst system (Central-western Sicily, Italy)

The Monte Conca karst system is located in Central-Western Sicily, where Messinian evaporites are widespread. Here, the evaporites lie on lower Messinian-middle Serravallian clayey-marly-sandy deposits and are overlain locally by Pliocene marly limestones. These successions are affected by E-W, and to a lesser degree N-S and NW-SE, high-angle faults that have also produced lateral contacts between the gypsum units and the clayey-marly deposits. The cave passages reachaltogether about 2.4 km in lengthand 130 m in depth, and the system consists of a sink cave, a resurgence and a relict resurgence. At large scale it is characterized by superimposed levels of sub-horizontal galleries connected by vertical shafts, whichare developed in adjustment to the contemporary geomorphological setting. Until 2003, the sink cave was known to have been formed by a stream-sink, an upper horizontal gallery, a sequence of four shafts and a lower gallery. New explorations have discovered 1.5 km of relict passages that are correlatable withthe inactive resurgence level and that occur at intermediate elevations between the two stories of galleries. Sinks of these relict branches are located headward of the actual sink point, but they have been sealed and covered by thick debris and alluvial deposits from the surface slopes. The resurgence consists of two superimposed galleries, the upper one inactive and the lower one active in equilibrium withthe current local base level. The relict resurgence is located about 40 m above the resurgence and is characterized by a sub-horizontal gallery partially filled by copious alluvial deposits. Analysis of the gallery patterns and of the cave landforms suggests that the karst system is a multi-layer system formed under unconfined conditions. Additionally, analysis suggests that its evolution is due to a succession of stillstand and lowering phases of the karst base level, according to a regional uplifting trend, and to surface slope processes, whichhave complicated the structure of the karst system.

THE PETROLEUM PROSPECTIVITY OF LEBANON: AN OVERVIEW

This paper presents an updated review of the petroleum prospectivity of Lebanon. It is based on a re‐assessment of the tectono‐stratigraphic succession in Lebanon, correlation with nearby countries and the results of a recent offshore seismic survey. A generalized model illustrating potential petroleum system(s) in Lebanon is presented with data on Palaeozoic, Mesozoic and Cenozoic plays. Major lithological units are described with respect to their source, reservoir and cap‐rock potential.Based on a general review of previous studies and existing data, Lebanese exploration prospects may comprise on‐ and offshore as well as coastal (margin) targets. They include potential Triassic reservoirs in onshore central‐northern Lebanon including those at the Qartaba structure. Offshore plays are discussed with reference to recent seismic profiles; potential offshore targets comprise Oligo‐Miocene reservoirs sealed by Messinian evaporites as well as deeper Mesozoic reservoirs.

Present-day stress-field rotations associated with evaporites in the offshore Nile Delta

Evaporitic horizons are routinely interpreted to act as mechanical detachment sequences and thus signifi cantly infl uence the structural evolution of sedimentary basins and fold-thrust belts. However, over 30 years of global in situ stress analysis have provided only poor evidence to support this widespread assumption. This study examines present-day stress orientations inferred from borehole breakout and drilling-induced fractures in 44 boreholes in the offshore Nile Delta. A total of 446 breakouts and 19 drilling-induced fractures from 37 wells reveal sharply contrasting present-day maximum horizontal stress (SHmax) orientations in sequences above and below the extensive Messinian evaporites of the eastern Nile Delta. A typical deltaic margin-parallel SHmax (E-W in the central and ESE-WNW in the eastern Nile Delta) is observed in parts of the Nile Delta that are below or do not contain evaporites. However, a scattered but largely margin-normal (NNE-SSW) SHmax is observed in sequences underlain by evaporites. The ~90° variation in present-day SHmax orientation above and below the Messinian salts provides the fi rst convincing in situ evidence that evaporite sequences can act as major mechanical detachment horizons. In addition, the margin-normal SHmax orientation is subperpendicular to the strike of nearby active extensional faults, indicating the existence of non-Andersonian faulting in the suprasalt region. Furthermore, the evidence that the Messinian evaporites act as an effective mechanical detachment suggests that suprasalt faulting in the eastern Nile Delta is not the result of basement-related deformation and thus raises doubts about the often postulated extension of the Suez fault zone into the eastern Mediterranean.

Gypsum whiskers in Messinian evaporites identified by μ-XRD2

The gypsum mineralogy of hair-like, so-called whisker crystals was determined by micro X-ray diffractometry equipped with a focusing X-ray optic and a two-dimensional detector (μ-XRD2). Gypsum whiskers typically form by efflorescence on surfaces that are in contact with water. The delicate whiskers studied here formed within a Messinian evaporite mostly consisting of anhydrite. They project from alabastrine gypsum into former cavities. The gypsum resulted from hydration of anhydrite. Whiskers were finally engulfed by biogenic, native sulphur, which filled the cavities in the course of microbial alteration of the host lithology. The sulphur protected the delicate whisker crystals from destruction, including a period of exposure to weathering on a dumping site of a former mine where the rocks have been sampled. To the best of our knowledge, this is the first report of gypsum whiskers in evaporites. More significantly, this study reveals that μ-XRD2 has great potential for sedimentary petrology, allowing the in situ identification of minute mineral phases that cannot be identified with conventional techniques.

Characteristic features of salt tectonics offshore North Sinai, Egypt

Salt tectonic along offshore North Sinai was studied using seismic reflection data. The study revealed and identified various types of salt tectonics and structures in the study area. The triggering mechanism of salt tectonics was attributed to the pressure regime initiated from overloading sediments on the Messinian evaporites. The sediment load of 3,000 m exceeds the critical load (more than 1,000 m) and hence creates a pressure zone. The salt-generated structures resulted from thin-skinned extension that is driven by gravity gliding of the overloading sediments above the Messinian evaporite boundary, which acts as a detachment layer. These structures comprise normal growth faults and keystone grabens, trending roughly perpendicular to the slope of the continental margin. Salt tectonics in the study area were also triggered by the deformation of the movement of evaporite layer that causes stretching and fragmentation of the evaporite layer. Moving salt layer took place laterally and vertically, causing lateral and vertical pressures inside the Pliocene sediments. These movements of sediments led to the formation of salt rollers, salt weld, salt diapirs, rollover structures, and fault blocks. The interpretation of seismic data illustrates that the evaporite layer was switched off between the famous reflector M at its top and another reflector N at its base. M reflector is present and can be traced across the whole study area, while the N reflector pinched out in some parts of the study area.

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.

Mud diapirs, mud volcanoes and fluid flow in the rear of the Calabrian Arc Orogenic Wedge (southeastern Tyrrhenian sea)

ABSTRACTIn the northern Calabrian margin offshore, the Paola Ridge, seaward from the 700 m deep Paola intraslope basin, tops at a depth of around 600 m. Multibeam bathymetry, seafloor reflectivity and seismic data are available. The Paola Ridge consists of circular or elongated ridges cored by a transparent seismic facies that are interpreted as mud diapirs. The diapirs have radius in the order of 5 km and elevate on average 200 m from the adjacent seafloor. The elongated shape of the diapirs is an evidence of a tectonic influence on the pathways exploited by the rising structures. The most recent seismic unit drapes the topographic relief associated with the diapirs showing that diapir rise is at present mainly quiescent. Pockmarks fields and evidence of gas charged sediments are due to degassing from the inactive diapirs. Two mud volcanoes, shown by high backscatter mud flows fed from circular high backscatter areas centred by a collapse feature, are also present on top of one of the dormant diapirs. The only diapir that is actively rising and deforming the seafloor is not associated with pockmarks. Thus, a relationship between fluid expulsion from the diapiric mass and the arrest of the diapir rise is apparent. The increased seafloor steepness due to diapir rise and the presence of gas within the sedimentary succession promotes sediment instability as shown by a thick slump deposit and numerous mass‐wasting scars. Sometimes, the diapirs rise in coincidence with extensional faults that offset the Messinian evaporites. The mud remobilization structures are located along a NW–SE trending belt characterized by active extensional faulting. Hence, genetic processes similar to many of the mud diapir and volcano provinces of the Mediterranean, consisting of pre‐Messinian source rocks mobilized along discrete belts of active tectonic deformation, is advanced as controlling the setting of the study area.

Sedimentology and paleoenvironmental evolution of Messinian evaporites in the Iskenderun–Hatay basin complex, Southern Turkey

Messinian evaporites, which resulted from the salinity crisis during the final closure of the Mediterranean Sea, are exposed in SE Turkey. These evaporites formed in two isolated sub-basins, Iskenderun–Arsuz (IA) and Hatay–Samandağ (HS), which belong to different depositional configurations and tectonic structures. The Neogene fill of these sub-basins consists of a thick sedimentary succession that started with Early Miocene terrestrial clastics, followed by reefs (Middle Miocene) and shallow water siliciclastics (Tortonian – Early to Late Miocene) and finally Messinian evaporates. These sub-basins accumulated in a diverse range of depositional environments from very shallow to deeper water. Evaporite facies in the IA sub-basin consist of sabkhas, saline lagoons and ponds. They are mainly represented by chemical deposits such as scattered gypsum nodules and balls, nodular bedded gypsum, laminated gypsum (Type-A) and selenites (Type-S1). Evaporites in the HS sub-basin mainly consist of detrital gypsum composed of gypsum laminae (Type-B, C), gypsum arenite–rudites and deeper water selenites (≤ 20 m), and resedimented selenites (Type-S2), which were deposited on a sulfate platform with a slope-basin transitional zone. Secondary gypsum with alabastrine and porphyroblastic textures as well as satin spar veins is commonly associated with the sabkha-type evaporites of the IA sub-basin. Deeper-water clastic evaporites of the HS sub-basin have generally remained as primary gypsum or have only been slightly affected by diagenetic alterations. The isotope values ( 87/86Sr; δ 18O SMOW; and δ 34S CDT) from the different kinds of gypsum lithofacies of the sub-basin are similar to those of the Messinian evaporites in other peri-Mediterranean basins, indicating an origin from marine water without external or basinal contributions. The Messinian evaporites examined in this paper are overlain by Early Pliocene (Zanclean) deposits composed of shallow- and deep-water siliciclastics and carbonates with local intercalations of Lago–Mare-type strata. Throughout the Messinian evaporitic stage, the IA sub-basin was mainly comprised of shallow water evaporites, while the HS sub-basin underwent deepening related to regional tectonics induced by the Dead Sea Fault during the construction of the Hatay Graben.