Displays

The Messinian salinity crisis (MSC) is an extreme event in Earth history during which a salt giant (>1×10⁶ km³) accumulated on the Mediterranean seafloor within ~640 kyrs. The Messinian salt giant was formed about 6 million years ago when the restriction of water exchanges between the Atlantic Ocean and the Mediterranean Sea turned the Mediterranean into an enormous saline basin. After more than 40 years of research, the timing and the depositional environments of shallow (<200 m) and intermediate (200-1000 m) water-depth Messinian basins are known quite well from onshore outcrops. But what happened in the deepest portions of the Mediterranean Sea is still unclear, because the information about offshore successions is mainly based on geophysical data with no rock samples that can be dated.

The Levant Basin is the only deep Mediterranean basin where the entire Messinian section has been penetrated by wells tied to high resolution 3D seismic surveys. Here we present two studies challenging the desiccation paradigm dominating the MSC scientific literature for more than 40 years.

The first study focuses on the nearly flat top erosion surface (TES) that truncates a basinward-tilted Messinian evaporitic succession. This truncation is commonly interpreted to be the result of subaerial erosion at the end of the MSC. However, based on high resolution seismic surveys and wireline logs, we show that (1) the TES is actually an intra-Messinian truncation surface (IMTS) located ~100 m below the Messinian-Zanclean boundary; (2) the topmost, post-truncation, Messinian unit is very different from the underlying salt deposits and consists mostly of shale, sand, and anhydrite showing typical ⁸⁷Sr/⁸⁶Sr values and fauna assemblages from stage 3; and (3) the flat IMTS is a dissolution surface related to significant dilution and stratification of the water column during the transition from stage 2 to stage 3. We suggest that dissolution occurred upslope where salt rocks at the seabed were exposed to the upper diluted brine, while downslope the salt rocks were preserved because submerged in the deeper halite-saturated layer. The model, which requires a stratified water column, is inconsistent with a complete desiccation of the eastern Mediterranean Sea.

The second study focuses on the onset of the Messinian salinity crisis in the deep Eastern Mediterranean basin. Biostratigraphy and astronomical tuning of the Messinian pre-salt succession in the Levant Basin allows for the first time the reconstruction of a detailed chronology of the MSC events in deep setting and their correlation with marginal records that supports the CIESM (2008) 3-stage model. Our main conclusions are (1) MSC events were synchronous across marginal and deep basins, (2) MSC onset in deep basins occurred at 5.97 Ma, (3) only foraminifera-barren, evaporite-free shales accumulated in deep settings between 5.97 and 5.60 Ma, (4) deep evaporites (sulfate and halite) deposition started later, at 5.60 Ma. The wide synchrony of events implies inter-sub-basin connection during the whole salinity crisis and is not compatible with large sea-level fall that would have separated the eastern and western basins producing diachronic processes.

How to cite: Gvirtzman, Z., Manzi, V., Calvo, R., Gavrieli, I., Gennari, R., Lugli, S., Reghizzi, M., Persico, D., Schreiber, B. C., and Roveri, M.: Levant Basin as a key for Understanding the Messinian Salinity Crisis: Challenging the Desiccation Paradigm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4040, https://doi.org/10.5194/egusphere-egu2020-4040, 2020.

In August of 1970, during Mediterranean Sea Leg 13, when the Glomar challenger ventured Mediterranean waters, nobody was expecting to run into one of the most exiting scientific discoveries regarding the Mediterranean Sea evolution. Cores and seismic surveys made possible the discovery of a basin-wide Messinian evaporitic deposit buried beneath the deep-sea Pliocene sediments which was attributed to the Messinian Salinity Crises (MSC) already known and studied in onshore outcrops in the Apennines. Now, 50 years later the debate regarding the conditions and timing of the deposition of this salt giant is still ongoing as many theories are still open and in search for validating proof.

One of the main open questions certainly regards the base level drop during the MSC and the location, efficiency and dynamics of the Mediterranean – Atlantic connectivity. The Mediterranean level is thought to have dropped somewhere between a moderate 200 m up to an extreme high amplitude oscillation of 1500 m while according to different schools of thought the watergate to the Atlantic is considered as completely closed, intermittently open or to have been always open during the MSC. Gibraltar strait is the main candidate for a possible gateway during this time interval (5.96-5.33 Ma) as well as the leading cause of the re-establishment of open marine conditions in the Mediterranean. Consequently, understanding its evolution and opening is fundamental to endorse any of the MSC theories and a thorough investigation of the Messinian and early Pliocene sedimentological record of basins in its proximity is highly needed.

In this optic, the Alboran Sea is the place where many of those answers lie and its worth of further exploration. In the hope of a new oceanographic expedition in the near future, an effort should be made towards gathering and re-interpreting all the available data. We propose a refined planktonic foraminifer chronology of the Alboran DSDP and ODP sites 976B, 121 and 978A with a careful characterization of the main MSC facies that will clarify to a certain extent the MSC expression and the degree of Atlantic water influence in the Alboran basin.

How to cite: Bulian, F. and Sierro, F. J.: Revision of the Alboran sea Tortonian-Pliocene record: possible new insights on Mediterranean-Atlantic connectivity during the Messinian Salinity Crises, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4845, https://doi.org/10.5194/egusphere-egu2020-4845, 2020.

Dwarfism is a common feature affecting organism during and after extreme events that characterized the geological history. The organism size reductions are frequently referred as the result of “stressed condition”. Such changes occurred for instance during Oceanic Anoxic Events and are well recorded in the fossil assemblage of calcareous marine organisms. To date, no study addressed the morphological and biometric changes during the Messinian Salinity Crisis (MSC), one of the most recent and impacting event occurred in the Mediterranean Sea.

Here we focus on morphometric changes affecting calcareous nannofossils at the MSC onset in order to better constrain the paleoenvironmental changes and the “stressed conditions” that characterized this interval. Samples were collected in the Perales section (Sorbas Basin, West Mediterranean) in which size characterization of 50 specimens of 4 different calcareous nannofossil taxa (Helicosphaera carteri, Sphenolithus abies, Umbilicosphaera rotula and Coccolithus pelagicus) was performed in each sample, along with their absolute abundances (number of nannofossils over gram of dry sediment).  In order to test the reliability of the obtained data and demonstrate that the size change recorded at the MSC onset was a basin-scale event, 2 sections in the Piedmont Basin (Banengo and Pollenzo), encompassing the same time period were also analysed. In addition, size changes and cyclicity related to orbital forces were addressed in a high temporal resolution size and calcite mass analysis performed on Reticulofenestra minuta, using an automated image analyses system of calcareous nannofossils recognition (SYRACO) on several cycles encompassing the MSC onset.

A significant size reduction affected the calcareous nannofossil taxa involved in the MSC onset biostratrigraphic event in both the North and West Mediterranean sections. These morphometric changes were related to the restriction of the Mediterranean Basin, resulting in an increase in both productivity and environmental variability, stimulating  calcareous nannofossils growth rate and decreasing their cell and sizes. The R. minuta size and calcite mass correlate with the change in the orbital variability, governed mostly by precession, with minimum values recorded during the cyclical diatomite deposition in the Sorbas Basin. In this case, the size reduction was triggered by the precession-induced enhanced environmental variability that characterized the diatomitic deposition.

Our findings highlight the relevance of calcareous nannofossil morphometry and mass to trace the dynamics of extreme events, such as the MSC. Size and mass changes of selected calcareous nannofossils taxa at the MSC onset suggest that “stressed conditions” characterizing this event likely coincide with the instauration of a highly variable environment, linked to the restriction of the paleo Gibraltar strait. 

How to cite: Mancini, A. M., Ziveri, P., Grelaud, M., and Lozar, F.: Calcareous nannofossil size as a proxy for the Messinian Salinity Crisis dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21743, https://doi.org/10.5194/egusphere-egu2020-21743, 2020.

The formation of restricted basins isolates seawater from the global ocean and allows the formation of salt deposits, often because restricted basins can have minor connectivity to the global ocean and thus can fill and evaporate many times over. The formation of salts removes ions from the global ocean, potentially decreasing their concentration elsewhere and leading to an alteration of their biogeochemical cycle.  The subsequent exposure and chemical weathering of these salt deposits changes the source of these elements back into the global ocean and can influence their biogeochemical cycles for a long time after the formation of the restricted basin.   Sediment biogeochemistry in restricted basins also differs from most global continental shelf, slope, and deep-sea sediments. The formation of sedimentary minerals and their subsequent diagenesis means that the amount and isotopic composition of deposited minerals in restricted basins can differ greatly from those in the global ocean. In this talk I am going to explore how the formation of restricted basins, including epicontinental seas and isolated seas, has influenced the biogeochemical cycle of carbon and sulfur over the course of the last 65 million years.  I am going to use a combination of new measurements on the carbon and sulfur isotopic composition of the ocean over this time to explore how different types of restricted basins influence global biogeochemical cycles in the rest of the ocean. I will argue that the formation of restricted basins has been important in driving changes in the carbon and sulfur isotopic composition of the ocean over time, linking changes in ocean chemistry to tectonics.

How to cite: Turchyn, A.: The Role of Restricted Basins in Global Biogeochemical Cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7533, https://doi.org/10.5194/egusphere-egu2020-7533, 2020.

The Mediterranean Sea underwent restriction from the ocean and widespread salt deposition during the Messinian Salinity Crisis (MSC), allegedly leading to a kilometer-scale level drawdown by evaporation. One of the competing scenarios proposed for the termination of this environmental crisis 5.3 million years ago consists of a megaflooding event refilling the Mediterranean Sea through the Strait of Gibraltar: the Zanclean flood. The main evidence supporting this hypothesis is a nearly 390 km long and several hundred meters deep erosion channel extending from the Gulf of Cádiz (Atlantic Ocean) to the Algerian Basin (Western Mediterranean), implying the excavation of ca. 1000 km³ of Miocene sediment and bedrock.

How to cite: Garcia-Castellanos, D., Micallef, A., Camerlenghi, A., Estrada, F., Ercilla, G., Periañez, R., Abril, J. M., del Moral-Erencia, J. D., and Bohorquez, P.: The Zanclean megaflood of the Mediterranean. Searching for independent evidence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4996, https://doi.org/10.5194/egusphere-egu2020-4996, 2020.

Salt deposits found throughout the geological record and across the globe are witnesses of extreme paleoclimatic and paleoenvironmental conditions. However, little is known about the hydrological conditions that gave rise to these deposits, and the role of temperatures is even less constrained. Here we have used a new technique, Brillouin spectroscopy,  to investigate the paleoenvironmental and paleoclimatic conditions that led to the deposit of a thick salt sequence in the Dead Sea during the Last Interglacial (LIG, ~135,000 to 115,000 years before present). Through measuring the speed of sound inside halite fluid inclusions (FIs), this method provides the parent brine temperature and salinity at the moment of crystal growth. We applied it to several tens of halite intervals from the 450-meters-long core 5017-1 drilled in 2010-2011 in the deepest part of the Dead Sea in Palestine within the framework of the Dead Sea Deep Drilling Project (DSDDP). The application of Brillouin spectroscopy to this record provides a unique quantification of temperature and hydrological changes in this area during the LIG and outlines a radically new narrative for the climate of the region during this period. The example of the Dead Sea shows that Brillouin spectroscopy on halite FIs is in position to provide valuable data to test the efficiency of climate models and to better understand the processes that lead to the deposition of salt giants.

How to cite: Guillerm, E., Gardien, V., Brall, N., Schwab, M. J., Lach, A., Neugebauer, I., Ariztegui, D., and Caupin, F.: Unraveling temperature and hydrological conditions of salt deposits by measuring the speed of sound in halite fluid inclusions: the case of the Last Interglacial Dead Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8772, https://doi.org/10.5194/egusphere-egu2020-8772, 2020.

The tectonic opening and closure of oceans presents windows of opportunity for the formation of anomalous waterbodies which we term “trapped-sea-lakes” (TSL); poorly connected or isolated water basins characterized by anomalohaline (brackish, hyperhaline, mixohaline or limnetic according to the Venice system) conditions that change over time, reflecting the fluctuating connectivity with the global ocean and the climatic history of their watershed. TSLs contain elements typical for a sea (basin bathymetry, marine chemistry, faunistic elements), but also reflect lacustrine aspects like endemism and major environmental fluctuations over geological time. They are characterized by unusual large dimensions, long life-span (compared with classic lakes), anomalous environments with salinity and chemistry controlled by the limited connectivity with the global ocean and by climate forcing.

Here we present a classification of TSLs, supported by key studies, showing that Anoxic Giants, Salt Giants and brackish mega-basins are all related forms of TSLs and that transition between them is possible. We showcase several key TSLs that occurred over the last 100 Million years: the East African rift basins and the early South Atlantic basins providing a reference for the lacustrine - evaporitic transitions that characterize the opening of oceans and similarly the key moments in the closure of the Tethys ocean, presented to showcase the post-oceanic restriction episodes of the Paratethys waterworld in Central Eurasia, with its particular evaporite-brackish environment transitions.

The transition from marine basins to TSL is reversible and our model predicts that TSLs that lie in the proximity of the global ocean are likely to trigger cataclysmic floods during the partial or full reconnection with the global ocean if the reconnected water bodies have different water levels. These floods can be either in the form of marine flooding events, such as the Zanclean deluge of the Mediterranean, when TSL’s water level is below the global sea-level or in the form of “lake burst-floods”, if the isolated TSL evolves to a mega-lake with water levels above the global ocean. We present a first example of such lake burst-floods that scarred the Aegean Sea and likely turned the Mediterranean-Paratethys realm into a unique system of double-locked TSLs, in the eve of the Messinian Salinity Crisis.

How to cite: Palcu, D. V. and Krijgsman, W.: Trapped Sea-Lakes, the anomalous water bodies that herald the birth and demise of the oceans, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18963, https://doi.org/10.5194/egusphere-egu2020-18963, 2020.

Syntectonic growth strata in extensional settings are characterized by gross divergent geometries towards the master normal faults. Similar depositional patterns might be expected for evaporitic successions deposited during active extension although for salt-rich systems it might be very difficult to discern initial syn-tectonic depositional thickness variations from those caused by syn-depositional or early post-depositional halokinetic flow. Evaporites can be also passively infilling accommodation space that was created before their deposition either by tectonics or by erosion. Re-evaluation of regional coverage of seismic data from the Polish Basin provided evidences that, contrary to previous views, formation of Zechstein (Wuchiapingian – Changshingian) evaporites was significantly controlled by active extension. This sedimentary basin was located within the eastern periphery of the large epicontinental Permian-Mesozoic Central European Basin System and was filled with several kilometers of siliciclastics and carbonates, and thick Zechstein evaporites. Its axial part, the Mid-Polish Trough, characterized by the thickest Permo-Mesozoic sedimentary cover and developed partly above the Teisseyre–Tornquist Zone, underwent substantial Late Cretaceous–Paleogene inversion and currently forms a large regional anticlinal structure referred to as the Mid-Polish Swell. Some previous models of deposition of Zechstein evaporites assumed that evaporation started after catastrophic flooding of vast paleo-topographic depression (“hole in the ground” model). Regional coverage of seismic data was used to map major sub-Zechstein fault network that were responsible for crustal extension during development of the Polish Basin and were reactivated as reverse fault zones during its regional Late Cretaceous – Paleogene inversion. Those sub-Zechstein fault zones are often associated with locally increased thickness of Zechstein evaporites (salt pillows). It could be shown that such thickness increase could be in turn associated with gradual thickness increase of particular Zechstein cyclothems towards sub-Zechstein fault zones. All those observations were used to construct regional model of the Zechstein basin that was controlled by regional extension. As a consequence, Zechstein evaporites deposited within the axial part of the basin have been partly reinterpreted as growth strata related to active basement extensional tectonics.

How to cite: Krzywiec, P., Peryt, T. M., and Kiersnowski, H.: Was Zechstein basin in Poland just large “hole in the ground”? – new extensional model based on reinterpreted regional seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10756, https://doi.org/10.5194/egusphere-egu2020-10756, 2020.

Between 5.97-5.33 Ma several kilometre-thick evaporite units were deposited in the Mediterranean Basin during the Messinian Salinity Crisis (MSC). The MSC reflects a period featured by a negative hydrological budget, with a net evaporative loss of water exceeding precipitation and riverine runoff. The contemporary changes in continental and marine circum-Mediterranean temperature are, however, poorly constrained. Here we reconstruct continental mean annual temperatures (MAT) using branched glycerol dialkyl glycerol tetraether (GDGT) biomarkers for the time period corresponding to MSC Stage 3 (5.55-5.33 Ma). Additionally, for the same time interval, we estimate sea surface temperatures (SSTs) of the Mediterranean Sea using isoprenoidal GDGTs based TEX₈₆ proxy. The excellently preserved organic biomarkers were extracted from outcrops and DSDP cores spread over a large part of the onland (Malaga, Sicily, Cyprus) and offshore (holes 124 and 134 from the Balearic abyssal plane and hole 374 from the Ionian Basin) Mediterranean Basin domain. The calculated MATs for the 5.55 to 5.33 Ma interval show values around 16 to 18 ºC for the Malaga, Sicily and Cyprus outcrops. The MAT values calculated for DSDP Leg 13 holes 124, 134 and Leg 42A hole 374 are lower, around 11 to 13 ºC.

For samples where the branched and isoprenoid tetraether (BIT) index was lower than the 0.4 we could calculate TEX₈₆ derived SSTs averaging around 27 ºC for all sampled locations. Where available (i.e. Sicily), we compared the TEX₈₆ derived SSTs with alkenone based, U^k₃₇ derived SST estimates from the same samples. The TEX₈₆ derived SST values are slightly higher than the U^k₃₇ derived SST of 20 to 28 ºC. For the Mediterranean region, values between 19 and 27 ºC of the U^k₃₇ derived SSTs were calculated for the interval between the 8.0 and 6.4 Ma (Tzanova et al., 2015), close to our calculations for Sicily section (20 to 28 ºC). Independent of common pitfalls that may arise in using molecular biomarkers as temperature proxies, both SST estimates independently hint towards much warmer Mediterranean Sea water during the latest phase (Stage 3) of the MSC. These elevated temperatures coincide with higher δD values measured on alkenones and long chain n-alkanes (both records indicating for more arid and/or warmer conditions than today between 5.55 and 5.33 Ma). We therefore conclude that the climate between 5.55 to 5.33 Ma was warmer than present-day conditions, recorded both in the Mediterranean Sea and the land surrounding it.

How to cite: Vasiliev, I., Boehn, D., Volkovskaja, D., Schmitt, C., Agiadi, K., Andreetto, F., and Mulch, A.: A warmer Mediterranean region at the Miocene to Pliocene transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13577, https://doi.org/10.5194/egusphere-egu2020-13577, 2020.

Since the discovery of the late Miocene (Messinian) Mediterranean Salt Giant more than 50 years ago, the environmental conditions that caused its formation have been debated. Such reconstruction suffers from the absence of modern analogues, the lack or scarcity of fossils (calcareous plankton and benthos, but also pollens), and the inaccessibility of the evaporites buried beneath the present-day Mediterranean seafloor. We investigate the palaeoenvironmental changes, which drove the formation of the Mediterranean Salt Giant at the onset of the Messinian salinity crisis (MSC) through high resolution sedimentological, petrographical, and geochemical (lipid biomarkers, major and trace elements) analyses of sedimentary successions of the Piedmont Basin (NW Italy). Shale/marl couplets deposited in intermediate to deep-water settings (200 – 1000 m) are targeted, representing the lateral equivalent of primary sulphate evaporites from shallow-water settings that accumulated between 5.97 and 5.60 Ma. We suggest that climate and hydrological changes affected the northern Mediterranean in the earliest stage of the MSC event, leading to an intensification of water column stratification. An upper water layer of marine water influenced by freshwater input was separated through a pycnocline from more evaporated, denser and oxygen-depleted bottom waters. The water column structure and pycnocline oscillation exerted pivotal control over the sedimentary products pertaining to the first stage of the MSC.

How to cite: Sabino, M., Birgel, D., Dela Pierre, F., Natalicchio, M., and Peckmann, J.: Environmental changes across the onset of the Messinian salinity crisis: insights from the Piedmont Basin (NW Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3852, https://doi.org/10.5194/egusphere-egu2020-3852, 2020.

The thick saline series deposited in the deep Mediterranean during the latest Messinian (between 5.97 and 5.3 Ma) is among the youngest of salt giants in Earth history. During this Messinian Salinity Crisis (MSC) voluminous evaporites precipitated in the abyssal basins when the main inflow of saline water from the Atlantic through the Gibraltar Straits was severely restricted. Considerable volumes of sediments were also interbedded with evaporites, eroded from the shelves or mass-transported downslope during the oceanic drawdowns and thus this event was also a major erosional crisis.  Geochronologic advances 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. However, much of the new understanding comes from the Mediterranean’s shallow peripheral basins whereas knowledge of the nature of evaporites from the deep basins remains sketchy due to lack of deep drilling through the salt, and many controversies remain unresolved. An invaluable collaboration between academia and industry permitted access to most of the available seismic and core data from the Mediterranean allowing the total amount of salt (thicknesses and volumes) and associated interbedded sediment from all abyssal basins to be calculated. These new estimates are based on seismic facies analysis, which 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. First isochron maps of the MSC deposits (evaporites + sediment) in all the basins have been produced. These volumetrics 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. The volumetric data have implications for the MSC 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.

How to cite: Haq, B. and Gorini, C.: Mapping the abyssal Mediterranean's Messinian Evaporite Giant: Salt volumetrics from all deep basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5990, https://doi.org/10.5194/egusphere-egu2020-5990, 2020.

The Messinian Salinity Crisis (MSC), which affected the Mediterranean region during the latest Miocene, is mainly characterized by the deposition of thick evaporites in central basins and strong fluvial erosion of margins. The subaerial fluvial erosion, known as the Messinian Erosional Surface (MES), is for instance continuously followed from the Gulf of Lions up to 360 km from the present-day shoreline upstream the Rhône Valley. Short drainage systems limited by high coastal mountain ranges, must have been significantly affected by the Messinian erosion.

The Alboran Sea is similarly characterized by a geographic context and was the first Mediterranean area concerned by connection-disconnection to the Atlantic Ocean during the last millions years. A recent study suggested that the Alboran Sea remained always connected to the Atlantic Ocean during the MSC, being the marine refuge for the Mediterranean taxa.

In this work, we have performed an extensive research of the MES and MSC-related deposits in the Alboran region, both onshore and offshore, integrating outcrop descriptions, supported by new biostratigraphic data and seismic profile analyses. This study leads to an up-to-date geological and morphological map displaying the actual contours and morphology of the MES in the whole Alboran domain. The MES has a subaerial origin and is continuously followed from land to the offshore domain, sealed by post-MSC marine sediments. Both Spanish and Morrocan sides show three different erosive morphologies: downslope trending paleocanyons cut by a large reflooding channel crossing the entire Alboran basin from the Strait of Gibraltar to Algerian Basin, and alongslope   terraces. The occurrence of all these striking erosive features with basinal extension  questions the hypothesis of the permanent connection with the Atlantic Ocean.

How to cite: Do Couto, D., Estrada, F., Gorini, C., Ercilla, G., and Suc, J.-P.: Morphology of the Messinian Salinity Crisis surfaces and its related deposits in the Alboran Sea: a continuous Mediterranean-Atlantic connection?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15585, https://doi.org/10.5194/egusphere-egu2020-15585, 2020.

The Albian Gap is an enigmatic salt-related feature in the Santos Basin, offshore Brazil. It is a uniquely large, up to 65 km wide and >450 km long structure, located in the updip portion of the basin and trending NE (i.e. sub-parallel to the coast). The gap is characterized by the near-complete absence of Albian strata above depleted Aptian salt. Its most remarkable feature is an equivalently large, post-Albian seaward-dipping rollover that is up to 9 km thick. Due to its unique geometry, size, and counter-regional aspect, the Albian Gap has been the centre of debate for >25 years. This debate revolves around two competing models for its origin and evolution; i.e. did it form due to thin-skinned extension, or progradation loading and expulsion? The extension-driven model invokes that the rollover and the Albian Gap formed due to post-Albian gravity-driven extension associated with a large, counter-regional, listric normal fault, the Cabo Frio Fault. Conversely, the expulsion-driven hypothesis suggests that the Albian Gap was established earlier, during the Albian, and that post-Albian deformation was controlled by differential loading, vertical subsidence, and basinward salt expulsion without significant lateral extension. This study utilizes a large (c. 76,000 km²) and dense depth-migrated, 2D seismic dataset that covers and which thus permit a detailed, 3D structural analysis of the entire Albian Gap, focusing on i) base-salt relief and original salt thickness variations and ii) the geometry of the post-Albian rollover, and its related faults and salt structures. We also apply novel structural restoration workflows incorporating flexural isostasy, along with a detailed sequential reconstruction of the rollover sequences, to constrain the kinematics of the Albian Gap, and how this relates to base-salt relief. Our results show that the geometry and kinematics of the Albian Gap vary along-strike and that both post-Albian extension and expulsion play a significant role on its evolution. Seaward-dipping growth wedges, salt rollers and normal listric faults evidence extension, whereas sigmoidal wedges, halokinetic sequences, and upturned near-diapir flaps, the latter two associated with inflated diapirs bounding the downdip edge of the gap, indicate basinward salt expulsion and inflation. Where the Albian gap is relatively wide (>50 km), these processes alternate and operate at approximately equal proportions. Our results are consistent with the observed amount of basinward translation further downdip within ramp basins in the Sao Paulo Plateau and seemingly reconciles one of the longest-running debates in salt tectonics. Our results have implications for understanding the regional kinematics and dynamics of salt-related structures in other salt basins, in particular, the controls on the development of large, salt-detached, counter-regional faults.

How to cite: Muniz Pichel, L. and Jackson, C.: The enigma of the Albian Gap: spatial variability and the competition between salt expulsion and extension, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18341, https://doi.org/10.5194/egusphere-egu2020-18341, 2020.

Large deposits of gypsum accumulated in the marginal basins of the Mediterranean Sea during the Messinian Salinity Crisis. These form the marginal portions of the Mediterranean Salt Giant (MSG) that also occupies the deep, central Mediterranean basins. Although the marine, evaporitic origin of the MSG is undisputed, the analysis of gypsum fluid inclusions and of gypsum-bound water (d¹⁸O_H2O and dD_H2O) suggest that marginal basin gypsum formed from low- to moderate-salinity water masses (5 - 60 ‰), rather than from high-salinity brines (130 - 320 ‰), as expected during the evaporation of seawater.  The formation of low-salinity gypsum poses a fundamental geochemical problem: how can gypsum saturation conditions be met in marginal basins if evaporation does not concentrate marine water to high salinity? In other words, can gypsum saturation be attained by adding Ca²⁺ and/or SO₄^2- ions rather than by extracting water? We are exploring two geochemical scenarios to explain this phenomenon: (1) the addition of Ca²⁺ and SO₄^2- to marginal basins by continental runoff, and (2) the non-steady state addition of SO₄^2- to marginal basins via the biogeochemical oxidation of reduced sulfur. Both scenarios may lead - at least theoretically - to the decoupling of saturation state from salinity that is suggested by gypsum geochemical signatures.

How to cite: Aloisi, G., Natalicchio, M., Guibourdenche, L., Caruso, A., and Dela Pierre, F.: The geochemical riddle of Mediterranean low-salinity gypsum deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4533, https://doi.org/10.5194/egusphere-egu2020-4533, 2020.

During the so-called Messinian Salinity Crisis (MSC: 5.97-5.33 Myr ago), reduced exchange with the Atlantic Ocean caused the Mediterranean to develop into a “saline giant” wherein ~1 million km³ of evaporites (gypsum and halite) were deposited. Despite decades of research it is still poorly understood exactly how and where in the water column these evaporites formed. Gypsum formation commonly requires enhanced dry conditions (evaporation exceeding precipitation), but recent studies also suggested major freshwater inputs into the Mediterranean during MSC-gypsum formation. Here we use strontium isotope ratios of ostracods to show that low-saline water from the Paratethys Seas actually contributed to the precipitation of Mediterranean evaporites. This apparent paradox urges for an alternative mechanism underlying gypsum precipitation. We propose that Paratethys inflow would enhance stratification in the Mediterranean and result in a low-salinity surface-water layer with high Ca/Cl and SO₄/Cl ratios. We show that evaporation of this surface water can become saturated in gypsum at a salinity of ~40, in line with salinities reported from fluid inclusions in MSC evaporites.

How to cite: Krijgsman, W., Grothe, A., Andreetto, F., Reichart, G.-J., Wolthers, M., van Baak, C., Vasiliev, I., Stoica, M., Sangiorgi, F., Middelburg, J., and Davies, G.: Paratethys pacing of the Messinian Salinity Crisis: low salinity waters contributing to gypsum precipitation?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11563, https://doi.org/10.5194/egusphere-egu2020-11563, 2020.

Sulfur is a key element to understand ocean biogeochemical processes. Since decades, numerous studies have explained sulfur isotopic variations registred in the geological record as reflecting changes in continental sulfur inputs, biogeochemical recycling of sulfur and the relative proportion of oxidized (gypsum) vs reduced (e.g. pyrite) sulfur burial fluxes. Geochemical and petrographic studies have showed that these processes were active during the formation of the Mediterranean Salt Giant (MSG), a giant salt deposit formed at the end of the Messinian period (5.9-5.33 Ma) following the restriction of hydrological exchanges between the Mediterranean Sea and the Atlantic Ocean. To date, the biogeochemical sulfur cycle during the formation of the MSG has been investigated by analyzing the sulfur and oxygen isotope composition (δ³⁴S and δ¹⁸O, respectively) of the sulfate ion in gypsum accumulated in the deep and marginal Mediterranean basins. In the uppermost gypsum layers (Upper Gypsum unit), significantly higher δ¹⁸O isotopic ratios (averaging at 12,7‰) than Messinian marine values suggest implications of microbial sulfate reduction activity followed by complete re-oxidation of sulfide back to sulfate in evaporated marine waters.

 Nevertheless, these different microbial processes can overprint each other δ³⁴S and δ¹⁸O isotopic signatures and could have been provoked by various type of microbial metabolisms, involving different hydrological and environmental conditions. Here we present for the first time a multiple sulfur isotope (δ³⁴S, Δ³³S, Δ³⁶S) investigation of samples from the well-known sections of Vena del Gesso (Apennines) and Pollenzo (Piedmont basin) in order to identify and understand how microbial mechanisms were coupled during the MSG formation. We designed a simple steady-state, three-box model representing the analysed S-bearing fractions (SO₄^2-, S⁰, FeS₂) and the different hydrological and biogeochemical S fluxes involved in marginal basin S-cycling. This system of 18 equations allows us to explain the strong isotopic variations we measured (-40.2 to 25.4‰ in δ³⁴S, -0.001 to 0.160‰ in Δ³³S and -1.79 to 0.001 in Δ³⁶S‰) as produced by a huge variability in sulfate reduction activity reflecting fluctuations in the availability of organic matter. Moreover, our results, with relatively high λ³³_net (0.513 to 0.516) suggest than more than 90% of the hydrogen sulfide produced was re-oxidized by disproportionation reactions. Large, cyclic fluctuations of the Mediterranean hydrological cycle, and the presence of easily accessible S-compounds with a variety of oxidation states, makes the MSG a key system to understand the dynamics of the S biogeochemical cycle in the geological past.

How to cite: Guibourdenche, L., Cartigny, P., Dela Pierre, F., Natalicchio, M., Caruso, A., and Aloisi, G.: The biogeochemical sulfur cycle during the formation of the Mediterranean Salt Giant, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19087, https://doi.org/10.5194/egusphere-egu2020-19087, 2020.

New high-resolution imaging of recently acquired data in the Levant basin shed light on very dense channel systems. The processes behind their origin, timing and direction - during the different stages of the Messinian Salinity Crisis (MSC) - is still unresolved and partly understood. Discoveries of such drainage systems raise questions on a past topography and mechanisms responsible for the channel morphologies, the understanding of these channel patterns is thus essential for a meaningful assessment of such mechanisms involved in the context of the MSC and its aftermath. Our results show that the drainage direction was undergoing extreme changes during short time intervals in the Levant Basin. Indeed, new maps presented here indicate different past drainage orientations, which is in contrast to the current-day turbidite channels - draining the Sinai-Levant continental margin northward towards the Cyprus Arc. We hypothesize from these results that drainage change, from southwest to north, expresses northward tilting of the basin towards the Cyprus subduction zone, however, when exactly did this tilting occur? Deciphering the timing of such events is important in order to get a better understanding of tectonostratigraphic settings, controlling depocenter locations in the Levant basin in the MSC. We also suggest that the unique pattern of channels over the Intra-Messinian Truncation Surface (IMTS), expresses a complex seafloor relief which was mainly controlled by salt tectonics induced thrusts faults.

Keywords: Messinian Salinity Crisis, Channel systems, Evaporites, Seismic Reflection Profiles

How to cite: Moneron, J. and Gvirtzman, Z.: Drainage systems and their relations to the Messinian Salinity Crisis in the Levant Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22621, https://doi.org/10.5194/egusphere-egu2020-22621, 2020.

The objective of this study is to constrain the formation conditions of deposition of the Middle Miocene marine evaporite in the Transylvanian Basin (TB).  The salt rock, formed during the Badenian Salinity Crisis (BSC), consists principally of halite (> 90%).  Representative samples were collected from Praid salt diapir.

Detailed petrographic study was carried out in order to distinguish primary features of the salt rock and to exclude secondary movements and their impacts.  Two types of salt rock can be distinguished: 1/ massive grey salt with large, elongated halite crystals, containing primary fluid inclusions (FIp), surrounded by submicrometer size halite grains and clay matrix, and 2/ layered salt building up greyish (clay rich) and white (clear halite) layers.  This type has quasi mosaic structure and contains very rarely FIps.

The primary fluid inclusions in halite, containing aqueous solutes, are expected to record compositions and isotopic characters of paleo-seawater during the BSC of the Paratethys.  Beside halite, authigenic anhydrite and dolomite are also present, which precipitated in marine environment and their compositions also reflect the geochemical conditions of the seawater.

Microthermometry of FIp in both types of halite shows low homogenization temperature (10-24 °C) which is typical for marine environment.  Isotopic characteristics of FIp are -15.55 – -7.07 ‰ for δ¹⁸O and -87,9 – -74.17 ‰ for δ²H.  Sulfate isotope values measured in anhydrite are ranging δ³⁴S 20.4 – 22.4 ‰ and δ¹⁸O 12.9 – 14.5 ‰ that coincide with the Middle Miocene Outer Carpathians salt deposits (Halas & Krouse, 1981) and support evaporated seawater origin.  The geochemical signatures (Fe-zonation) and isotopic characters (δ¹⁸O -7.07 – -4.55 ‰ and δ¹³C -9.03 – -8.31 ‰) of the rombohedral translucent dolomite suggest mainly meteoric origin.  They possibly precipitated from an upper level of the seawater.  All of these isotopic and geochemical characters of the evaporite reveal a complex restricted hydrogeologic evolution environment.

How to cite: Gelencsér, O., Palcsu, L., Futó, I., and Szabó, C.: Isotopic analyses of the Middle Miocene evaporite assemblage and its fluid inclusions (Praid, Transylvanian Basin, Romania), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1201, https://doi.org/10.5194/egusphere-egu2020-1201, 2020.

The Messinian Salinity Crisis was a period of rapid and extreme environmental change in the Mediterranean occurring from 5.96 to 5.33 Ma, leading to deposition of a huge amount of evaporites in the deep basins and erosion on the margins. Erosional surfaces located deep below current sea level suggest a kilometric drop in sea level commonly associated with the deposition of massive halite deposits during the crisis. However, the timing and magnitude of this sea level drawdown are not well constrained in spite of its important implications for the conditions under which the different MSC sedimentary units were deposited and the connectivity of various sub-basins during the crisis. A 2D (planform) flexural backstripping allows us to restore the Messinian topography in tectonically quiescent areas, constraining the isostatic subsidence due to the (post)Messinian sediment, and the potential effect of falling sea level during the crisis. In this way we restore the elevation of paleoshorelines and the original depth of erosional surfaces and other stratigraphic markers. We apply this method to the area spanning the Valencia Basin, Balearic Promontory and the Algero-Provençal Basin, to restore the Messinian Erosion Surfaces which formed subaerially during the drawdown to their original depth, constraining the minimum base level drop required to erode the margins at these locations. We reconstruct three key moments in the basin history: the pre-crisis basin, the end of halite deposition, and the end of the crisis. We consider multiple scenarios in terms of timing of sea level fall. Preliminary results indicate that over 1 km of sea level drop is required at the end of the Messinian, and over 2 km at the crisis acme to reproduce the observed location of the paleoshorelines, with only small sensitivity to crustal strength. This is in good agreement with estimates from previous backstripping investigations, and provides constraints on the progression of the MSC in the Western Mediterranean.

How to cite: Heida, H., Garcia-Castellanos, D., Jiménez-Munt, I., Raad, F., Maillard, A., and Lofi, J.: Flexural-isostatic reconstruction of the Western Mediterranean vertical motions after the Messinian Salinity Crisis: implications for sea level and basin connectivity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3097, https://doi.org/10.5194/egusphere-egu2020-3097, 2020.

Although the Mediterranean is known for its equable climate, this does not apply on geological timescales. At the end of the Miocene, salinity of the Mediterranean Sea exceeded gypsum and halite saturation, leading to the youngest known salt giant to form in a relatively short time span. This event is called the Messinian Salinity Crisis. Insight into the exact circumstances leading to this extreme situation would increase our understanding of today’s system and how it would react to climatic changes. Some of the theories rely on a drastic change in circulation, leading to a stably stratified water column at high salinities. It is yet to be determined how realistic these ideas are.

Conceptual box models can help to find answers to this. In a previous study it was already shown that a decrease in the rate of deep water formation in the margins can lead to a stratified water column. Here we used a predefined value for the overturning. In contrast, in the present study, the circulation, including the exchange through the strait of Gibraltar, is dynamically driven by density differences. By modelling stratification for various assumptions regarding the efficiency of the strait of Gibraltar, evaporation and the connectivity of the margins, this set-up ables us to get in-depth insights regarding the system in general, and the influence of climate and bathymetry on the circulation, specifically.

This model brings us one step closer to an understanding of the circumstances of this extreme state of the Mediterranean Sea

How to cite: Ebner, R. and Meijer, P.: Slowing down the overturning – Insights from conceptual modelling on a stably stratified Mediterranean Sea during the Messinian Salinity Crisis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10338, https://doi.org/10.5194/egusphere-egu2020-10338, 2020.

This study intends to contribute to the understanding of the Mediterranean Salt Giant in the Western Mediterranean, formed about 6 Ma ago during the Messinian Salinity Crisis. It provides reprocessed multichannel seismic reflection data that aim at improving our knowledge of the stratigraphy in the Algero-Balearic deepwater basin and its continental margins, in the absence of lithological information from wells.

We investigate the seismic expression of the Messinian salinity crisis from the south-east of the Balearic promontory to the central Algero-Balearic abyssal basin and the salt tectonic processes associated to these facies. Here the segmentation of salt structures has been previously described using shallow chirp sonar data, low-resolution vintage multichannel seismic data and high-resolution multi-channel seismic data post-stack migrated with a constant velocity field. The structure of the northern Algero-Balearic basin is controlled by two abrupt fault scarps oriented SW–NE (mainly the Emile Baudot Escarpment transform fault) and WSW-ENE (mainly the Mazarron Escarpment transform fault) emplaced during the basin extension, and later intruded by steep and narrow volcanic ridges of Pleistocene age. It is a good analogue to early stage salt tectonic for older and more complex salt giants in the North Sea or the Gulf of Mexico.

We reprocessed 2D Kirchhoff PSTM multichannel seismic data acquired by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS (SBALDEEP Cruise of 2005 and SALTFLU cruise of 2012; the latter within a Eurofleet cruise) spanning the South-East continental margin of the Balearic islands and the Algero-Balearic basin. The reprocessing was designed for improving the continuity of the reflectors by applying Kirchhoff PSTM using a detailed velocity model, while preserving amplitude information. The objectives are to better apprehend the structural complexity of the area and to retrieve the amplitude variation within the Messinian units, in an attempt to derive the composition of the salt and the pressure regime.

We present preliminary results where we delineate four different domains based on i) the seismic facies, ii) the amount of salt deformation, iii) the thickness of the overburden and iv) the pre-salt configuration. We try to assess the presence of the Messinian trilogy in the south-eastern continental slope. We attempt to reconstitute the paleo-depositionnal environment of the various depositional units, and the effect of crustal structures and salt tectonic gravity spreading and gliding on their syn to post-depositional evolution. Finally, we search for evidence of fluid circulation within the Messinian and the Plio-Quaternary deposits over the study area.

How to cite: Blondel, S., Raad, F., Camerlenghi, A., Lofi, J., and Del Ben, A.: Image improvement of Late Miocene (Messinian) to Plio-Quaternary units in the Algero-Balearic basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13769, https://doi.org/10.5194/egusphere-egu2020-13769, 2020.

The Messinian Salinity Crisis (MSC) was an environmental perturbation with dramatic environmental consequences that greatly affected marine organisms. Messinian deposits are found in several locations around the Mediterranean, but few offer marine faunas rich in molluscs. A section near Heraklion, central Crete, has provided new material that contains a well preserved and rich molluscan fauna that includes many micromorphic species. The section is of early Messinian age, belongs to Agios Miron Formation, and bears several layers of fossiliferous marly sands.

Molluscs from a fossiliferous bed of the section are presented here for the first time. Gastropods and bivalves are most common, but scaphopods and chitons are not infrequent. The assemblage seems to be composed of transported elements from nearby environments and the most frequent species are present in comparable abundances for gastropods and bivalves. The gastropod fauna is represented by Bittium sp. and Gibbula sp., accompanied by Diodora cf. graeca, Turritella sp., Jujubinus sp., species of Pyramidellidae and rarer Homalopoma sp. and Haliotis sp. The presence of Bittium sp. together with Jujubinus sp. suggests vegetated environments. Bivalves are represented by species dwelling mostly in sandy environments such as Glycymeris cf. inflata (also occurring in larger specimens), Spisula sp., Timoclea sp. and various cardiids. Exceptionally well-preserved chitons indicate the presence of hard substrates such as rocks, pebbles or roots of seagrass beds. This is confirmed by the presence of the gastropods Diodora cf. graeca and Haliotis sp.

The assemblage points towards normal salinity shallow marine conditions of sandy bottoms with patches of seagrass-type vegetation before the onset of the MSC.

How to cite: Koskeridou, E. and Thivaiou, D.: A new molluscan assemblage from the pre-evaporitic Messinian of Crete (Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15647, https://doi.org/10.5194/egusphere-egu2020-15647, 2020.

As the Messinian sea-level drawdown associated with the Messinian Salinity Crisis is still questioned, we propose to show that the widely spread erosion surface affecting the Mediterranean margins is indeed linked to an exondation demonstrated from offshore and onshore data.

Our study presents for the first time a comprehensive onshore to offshore correlation of the Messinian erosional surface, and it is focused on small drainage systems or interfluve areas, outside of evaporite basins or incised canyons, where the Messinian erosion had not yet been studied previously: around Ibiza on the Balearic Promontory and around Orosei on the Eastern Sardinian margin, Tyrrhenian Basin, both areas where new offshore data were recently acquired. We show that the late Messinian erosion formed in subaerial settings, as testified by evidence of continentalization events, and attests for a regression phase that was correlated from the offshore continental slopes to the onshore paleo-platforms in both areas. Characteristics of this erosion in both study areas strengthen the scenario with at least one important low-stand sea-level for the Messinian Salinity Crisis with evaporites subbasins lying at different depths and possibly disconnected.

How to cite: Maillard, A., Gaullier, V., Lézin, C., Chanier, F., Odonne, F., and Lofi, J.: New onshore/offshore evidence of the Messinian Erosion Surface from key areas: the Ibiza-Balearic Promontory and the Orosei-Eastern Sardinian margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19545, https://doi.org/10.5194/egusphere-egu2020-19545, 2020.

We 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 Å} 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.

How to cite: Camerlenghi, A., Del Ben, A., Hübscher, C., Forlin, E., Geletti, R., Brancatelli, G., Micallef, A., Saule, M., and Facchin, L.: Seismic markers of the Messinian salinity crisis in the deep Ionian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3903, https://doi.org/10.5194/egusphere-egu2020-3903, 2020.

Since the discovery of widespread Salt and Gypsum deposits of the Mediterranean Sea in the early ’50s, a large number of scientists tried to unravel the mystery related to this huge deposition of evaporites. Evidence of the later so-called “Messinian Salinity Crisis” (MSC) are largely distributed all around the Mediterranean Basin and widely studied. Although gypsum deposits were recognized in some peripheral or marginal basins (e.g. Sorbas Basin in Spain, Northern Apennines in Italy), mechanism of their deposition and formation are still uncertain. Particularly, the so-called Gessoso-Solfifera formation (GS Fm) was recognized in the ’50s by Selli in several outcrops in Northern Apennines and it is nowadays well known and mapped in the on-shore outcrops.  A regional analysis in the Adriatic Sea is still incomplete, even though a large amount of data is available (2D multichannel seismic lines, boreholes, exploration reports). In the Adriatic Sea, the MSC event can be recognized in the 2D seismic lines as actual thin deposit (maximum GS Fm thickness of about 120 ms TWT) or Messinian erosional surface (MES). In both cases, a strong and clear reflector at the Pliocene base is picked and calibrated by the boreholes reaching its depth. Along the main part of the available seismic profiles it is sometimes very hard to ascribe this strong reflector to the MES or to the presence of a thin gypsum layer.
Calibration of 2D seismic lines with boreholes, also integrated by physical properties derived from geophysical well logs and core data) of the Plio-Quaternary sediments, allowed a detailed seismic facies analysis useful for this purpose. A structural map of the Plio-Quaternary base describes the Plio-Quaternary deformation that affected the study area mainly as Apennine foreland. The thickness map of the GS Fm describes the subsidence and the erosional effect occurred during the MSC. Both these maps are here presented as a first result of a regional study, that intends cover the whole Adria offshore.

How to cite: Lanzoni, A., Del Ben, A., Edy, F., and Martina, B.: Mapping of the Gessoso-Solfifera layer and Messinian Erosional Surface in the Northern and Central Adriatic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4823, https://doi.org/10.5194/egusphere-egu2020-4823, 2020.

The Messinian Salinity Crisis (MSC) is a prominent and still misunderstood event that influenced the Mediterranean basin in the late Miocene leaving behind a Salt Giant (SG) widespread all over the Mediterranean basin. More than 90% of the Messinian Evaporitic deposits are located offshore with reduced access via boreholes, and thus has been studied mainly by seismic imaging. Onshore-Offshore should be considered a key for a better understanding and answering some of the controversies on the MSC.

The Balearic Promontory (BP) contains a series of small perched basins presently lying at different water depths, stepped from the present-day coastline down to the deep basin. These topographic lows trapped sedimentary series up to 500m thick, interpreted as MSC in age.
The reduced tectonic movements in the BP since the late Miocene (Messinian) till recent days, favored the conservation of the MSC records in this area. Moreover, recent studies revealed the presence of a Salt layer in the Central Mallorca Depression (CMD).

Considering: 1- the bathymetry of the BP, classified as an intermediate perched basin; 2- the distribution of the MSC records accumulated in a series of sub-basins more or less connected between each other; 3- the geometries of the evaporitic formations, provided by how these records appear on the seismic data; this might recall similarities between the BP records (especially the ones in the CMD) and the MSC reference records outcropping in Sicily (especially in the Caltanissetta Basin).

We perform seismic interpretation of a wide seismic reflection dataset in the study area with the aim of refining the mapping of the Messinian evaporites covering the study area. Four seismic units were identified in the BP based on their seismic facies and their seismo-stratigraphic position. We try to match up these units to the consensus Messinian 3-stages chrono-stratigraphic model proposed during the CIESM in 2008.
We also attempt to find similarities in geometries, facies and distribution of the MSC between the sub-basins of the BP and those described in the Sicilian sub-basins.

How to cite: Raad, F., Lofi, J., Maillard, A., Caruso, A., and Tzevahirtzian, A.: The Messinian Salinity Crisis (MSC) deposits in the Balearic Promontory: An undeformed analog of the MSC Sicilian basins??, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7690, https://doi.org/10.5194/egusphere-egu2020-7690, 2020.

The Calcare di Base Formation (CdB) mostly (but not exclusively) represents a microbial-mediated carbonate body formed during Messinian and extending for more than 500 km across the Southern Italy, along the accretionary wedges of Calabria and Sicily Apennine chain. In these areas, the microbial carbonates, frequently associated with evaporites, are stratigraphically positioned at the onset of the Messinian Salinity Crisis, pre-dating the massive basinal sulphates and halite deposition in the Mediterranean Circum.

The CdB highlights a wide spectrum of different facies positioned along a prograding carbonate platform to slope system. The inner platform environments are characterized by sabkhas, flood-influenced salinas and peritidal mudflats, rich of planar to domal laminated microbial boundstones associated with evaporites, solution breccias and local cross-laminated detrital carbonates. Megabreccias with plarform-derived clasts and a local siliciclastic input prevail in the upper slope, whereas debris flows and high-density turbidity currents occurred in the lower slope. Basinward, thinly laminated clay and marlstones associated to low-density turbidites characterize the outer-platform.

In a newly-proposed general sequential stratigraphic model of the Messinian Salinity Crisis, the carbonate platform systems represent a high-stand phase of at least two depositional cycles that follow one another. Each cycle begins with a relative sea-level fall responsible for the emplacement of prograding wedges composed of terrigenous and evaporitic deposits that, subsequently, evolve in the deposition of huge deposits of primary basin-fill evaporites. This latter phase is followed by open marine transgression due to relative sea-level rise that predates the development of another carbonate platform.

Despite the intense syn-sedimentary tectonic activity, responsible for huge basinward sediments exportation and fast decreasing in the accommodation space, the defined systems tracts succession has been mainly controlled by eustatic sea-level variations.

How to cite: Borrelli, M. and Perri, E.: PRE-SALT CARBONATES DEFINE A NEW STRATIGRAPHIC MODEL FOR THE MESSINIAN SALINITY CRISIS IN THE CENTRAL MEDITERRANEAN (CALCARE DI BASE Fm, SOUTHERN ITALY), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8141, https://doi.org/10.5194/egusphere-egu2020-8141, 2020.

While the Mediterranean Sea is, since the Middle Miocene, a nearly completely land-locked basin indeed, it is itself comprised of several smaller semi-enclosed seas. What the Mediterranean Sea as a whole is to the Atlantic Ocean, are the Adriatic Sea or Aegean Sea to the Ionian-Levantine basin, for example. In the discussions regarding the Messinian salinity crisis the marginal basins of the Mediterranean play a prominent role because it is from these parts that the sedimentary record has been uplifted and become exposed.

In view of this and with an aim to contribute insight from the field of modelling, we focus on the basic element: a single marginal basin, subject to atmospheric forcing and exchanging water through a seaway with an adjacent larger basin. The equations are derived in dimensionless form and a universal, scale-independent, solution for basin salinity obtained. The analysis yields two dimensionless ratios which control basin behaviour in terms of salinity and response time. 

Application of the theoretical model to the Messinian salinity crisis sheds new light on the formation of gypsum in marginal basins that were separated from the main Mediterranean by a sill, gives insight about the role of atmospheric heat exchange, and underlines the previous finding that, at elevated salinity, marginal basins respond to periodic climate variation (e.g. due to precession) with a significant lag.

How to cite: Meijer, P.: A scale-independent model for land-locked seas with application to the Messinian salinity crisis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10494, https://doi.org/10.5194/egusphere-egu2020-10494, 2020.

The discovery in the 70’s of the km-thick Mediterranean salt giant alongside the seismic observance of Pliocene-filled engravings along its shelf-slope systems concurred together to postulate that the Mediterranean-Atlantic seaway terminated during the late Messinian. The resulting changes in paleogeographic, paleohydrological and biological conditions, acknowledged as Messinian Salinity Crisis (MSC, 5.97-5.33 Ma), find their expression in the marginal sedimentary record in fauna-depleted gypsum and halite-bearing successions (5.97-5.42 Ma). During the Lago-Mare phase (5.42-5.33) that terminates the MSC the evaporitic deposition endures in the intermediate basins (e.g. Caltanissetta Basin, Sicily), whilst all the marginal basins fill with fluvio-lacustrine terrigenous sediments. Up to five conglomerate to sandstone-laminated pelite alternations thought to be precession controlled are counted underneath the Zanclean marine deposits featuring the restoration of a marine environment. Finer hemicycles tuned to insolation maxima period stand out above all for the occurrence of faunal assemblages consisting of brackish water ostracods, mollusks and dinoflagellate cysts. The affinity of these faunal elements with the coeval inhabitants of the Eastern Paratethys region, fragmented in isolated, long-lived brackish lakes (i.e. Euxinic and Caspian Basin), led to the primordial hypothesis of a similar paleoenvironment in force during the Lago-Mare phase for the Mediterranean, coherent with the paleoenvironment subsisting immediately prior to it. However, the progress of scientific research provided additional evidence arguing against the desiccation theory and supporting a basin filled even during the Lago-Mare phase. Within the full Mediterranean model controversial views exist on the hydrochemistry of the water mass, disputed between marine, brackish and density-stratified. To elucidate Mediterranean base level and hydrology just preceding the restoration of open marine conditions we merge together new and published ostracod biostratigraphic data and radiogenic strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) from locations (SE Spain, Piedmont, Sicily and Cyprus) covering the whole extent of the Mediterranean Basin. Ostracod faunal assemblages share approximately the same species and the same distribution pattern. Within a single pelitic bed, richness varies from oligotypic assemblages dominated by Cyprideis torosa to heterotypic assemblages with up to 17 Black Sea-derived species. Consequently, we conclude that it is most likely that the Mediterranean water level during the final phase of the MSC was high enough to let the Paratethyan fauna to reach and spread throughout the shallow Mediterranean depositional environments. ⁸⁷Sr/⁸⁶Sr ratios measured on ostracod valves range between 0.709131-0.708715. The generally lower and higher Sr isotopic composition than contemporary seawater (∼0.709024) alongside the data spreading are considered as a further proof of the presence of multiple lakes acquiring their own isotopic composition. We demonstrate that, when taken individually, none of the marginal basins yields an isotopic signature that matches that of the local rivers. If anything, these ⁸⁷Sr/⁸⁶Sr values arise from the mixing of local river water with Mediterranean water and we show that the discrepancies among each basin are consistent with variations in the lithologies of the contributing catchments. Lastly, we show that multiple, isotopically different water sources of both internal (major peri-Mediterranean rivers) and external (Atlantic and Eastern Paratethys) contributed to building up the Mediterranean water mass.

How to cite: Andreetto, F., Flecker, R., and Stoica, M.: Crunching of the primordial interpretation of the Lago-Mare phase: new insights from integrated ostracod biostratigraphy and Sr isotope ratios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18814, https://doi.org/10.5194/egusphere-egu2020-18814, 2020.

The origin of massive dolomite deposits has been an enduring and challenging problem for carbonate sedimentologists since the initial recognition of dolomite as a discrete carbonate mineral [CaMg(CO₃)₂]. The dolomite problem or enigma involves the fact that the mineral is very abundant in the geologic record, but it is rarely found forming in modern environments.  However, when modern dolomite is observed, it is generally, but not exclusively, found forming in hypersaline environments and in minor amounts.  Although the geologic record indicates that many ancient massive dolomite deposits formed in association with evaporites, modern examples of extensive amounts of dolomite being deposited under hypersaline conditions have not, or only rarely, been reported.   

One example of a massive hypersaline dolomite deposit of relatively recent origin may be the dolomite units associated with the end phase, at approximately 5.33 Ma, of the Messinian Salinity Crisis (MSC) in the Ionian Basin, Central Mediterranean (Hsü, Montadert, et al., 1978, Initial Reports of DSDP, Vol. 42, Part 1).  Drill core and interstitial waters obtained at DSDP Leg 42A, Site 374 in the Ionian abyssal plain revealed the presence of approximately 25 m of latest Miocene dolomitic mudstone (Lithologic Unit IIIa) capped by 8.5 m of earliest Pliocene dolomite (Lithologic Unit II).  Significantly, the pore-water geochemical data indicate that the dolomitization of the overlying earliest Pliocene nannofossil ooze may be an ongoing process.  Deeper drilling below the two dolomite units (Lithologic Unit II and IIIa) to the bottom of Site 374 recovered a further 29.5 m of gypsum/dolomitic mudstone cycles (Lithologic Unit IIIb) followed by 21 m of anhydrite and salts (Lithologic Unit IIIc).  Hence, the latest Miocene/earliest Pliocene dolomite sequence recovered at DSDP Site 374 is directly associated with the Messinian Salt Giant and potentially represents a massive dolomite deposit of an undetermined horizontal extent.

In order to measure the lateral dimensions of the combined dolomite/evaporite lithologic units in the central Ionian Sea, the University of Hamburg, using the facilities of the RV Meteor, conducted a multi-channel reflection seismic survey centered at DSDP Leg 42A, Site 374.  A powerful 6 kJoule sparker created the seismic signals, while a digital 144-channel streamer with an active length of 600 m recorded the data. The lowermost Pliocene reveals high lateral continuity and low reflection amplitudes, which is typical for the entire Pan-Mediterranean realm. The uppermost Messinian unit is characterized by a package of strong and positive reflection amplitudes (High Amplitude Reflection Package, HARP). The lateral continuity of the corresponding reflections is very low and the upper boundary is quite irregular. It is unlikely that the reflection configuration results from depositional processes, but it rather suggests diagenetic processes. We correlate the HARP with the dolomite- and gypsum-bearing sediments cored at DSDP Site 374 (Lithologic Unit IIIa, IIIb, IIIc), which is also consistent with the calculated depth. Based on preliminary estimates derived from the seismic survey, the areal extent of the dolomite deposit beneath the Ionian abyssal plain corresponds to a few 10’000 Km², potentially representing a massive hypersaline dolomite deposit.

How to cite: McKenzie, J. A., Huebscher, C., and Camerlenghi, A.: Seismic Mapping of Massive Dolomite Deposit Associated with Demise of MSC Salt Giant in Ionian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18964, https://doi.org/10.5194/egusphere-egu2020-18964, 2020.

The partial sequestration of the Mediterranean Sea from adjacent oceans at the end of the Miocene caused an evaporation surfeit that increased the water salinity above the seafloor of the deep basins and peripheral basins. As a result, an up to 2-3 km-thick sequence of evaporites was deposited in the center of the deep basins. This coincided with the concomitantly intense subaerial erosion of the adjacent margins and important Mass transport deposit events all around the peri- Mediterranean slopes. The volume of evaporites deposited in the deep basins implies a periodic connection with the world oceans concomitant with a huge evaporation during all the MSC. “Deep basins” refers to their position in the deep central parts of the extant Messinian basins in the western basin, the central basins (Ionian) and the eastern basins. The configuration of these basins and the distribution and thickness of the evaporites were very different 6 Myr ago due to the Africa Europe convergence. Evaporites deposition at the edge of the evaporites basins was affected by the geodynamic nature of the margins: Tertiary or Mesozoic passive or transform margins (North Africa), strike slip margins (northern and eastern Levant), convergent margins in the North of the East Mediterranean with evaporites subducted or stacked in a fore arc position. We propose a kinematic reconstruction of the central Mediterranean sea to discuss the connections between the Atlantic waters and the eastern Mediterranean Sea. In this presentation, we show that: (1) There is no opposition between the deposition of the first deep water evaporites and a sea level fall of more than 1000 m. (2) by a threshold effect the eastern Mediterranean could have been more restricted than the western Mediterranean during the phase 1 of the MSC, which could explain the two major incisions observed in the Nile delta (3). At the end of the MSC, this threshold effect could have been maximal with an accommodation space almost filled up and a bathymetry probably not exceeding 50 m in the western Mediterranean and in the Central Mediterranean with deposition of K and Mg evaporates, and almost zero in the Eastern Mediterranean as shown by the fluvial network developed on a wide-spread erosional surface on top of the Levant basin salt. (4) The Messinian salinity crisis (MSC) ended with the rapid re-flooding of the Mediterranean sea. A two-step flooding in the western Mediterranean could find its origin in this threshold effect.

How to cite: Gorini, C., Pellen, R., Rubino, J., Didier, B., Montader, L., and do Couto, D.: eastern and western med Messinian salinity crisis : comparison scenarii and propositions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19209, https://doi.org/10.5194/egusphere-egu2020-19209, 2020.

A detailed biostratigraphical and cyclostratigraphical study provided the opportunity of cycle-by-cycle correlations between sections from the marginal and deep areas of the Caltanissetta Basin (Sicily), and the northern Calabrian Rossano Basin. All the sections were compared with the Falconara-Gibliscemi composite section. We present new mineralogical and geochemical data on the transition from Tripoli to Calcare di Base (CdB), based on the study of several field sections. The outcrops display good record of the paleoceanographical changes that affected the Mediterranean Sea during the transition from slightly restricted conditions to the onset of the Mediterranean Salinity Crisis (MSC). This approach permitted to better constrain depositional conditions and highlighted a new palaeogeographical pattern characterized by separated sub-basins. The sedimentological and geochemical parameters of these basins introduced a different and diachronous response to the global constraints of the MSC. Our preliminary results display already evidences of paleoenvironmental changes: (1) a lithological transition passing from the Tripoli’s triplet (grey marls, reddish laminites and diatomites) to the complex carbonates of CdB; (2) the appearance of evaporite pseudomorphs implying early stage diagenesis; (3) the presence of sulphur-rich deposits involving process of bacterial sulphate reduction. The local transition from the uppermost part of the Tripoli cycles to the CdB reflects the worsening of the marine connections, leading to the individualisation of semi-closed settings where the marine inputs were not great enough to balance the effects of the climate fluctuations and especially of the evaporation/precipitation budget.

How to cite: Tzevahirtzian, A., Blanc-Valleron, M.-M., Rouchy, J.-M., and Caruso, A.: New insights of Tripoli and “Calcare di Base” Formations from Caltanissetta (Sicily) and Rossano (Calabria) Basins: a detailed geochemical, sedimentological and bio-cyclostratigraphical study., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19511, https://doi.org/10.5194/egusphere-egu2020-19511, 2020.

During the Messinian salinity crisis (MSC), the Mediterranean Sea was gradually isolated from the Atlantic Ocean due to tectonics, ultimately resulting in the deposition of enormous volumes of evaporites on the Mediterranean seafloor. In marginal Mediterranean sub-basins, the first phase of the MSC is represented by a cyclic succession of gypsum and shales (Primary Lower Gypsum unit; PLG), changing laterally into an alternation of shales, marls and carbonates towards the deeper parts of the basins. The current consensus is that the lithological cyclicity is the expression of precession-paced climate oscillations, with shales deposited during insolation maxima (precession minima) and gypsum deposited during insolation minima (precession maxima). However, this hypothesis has yet to be validated, because this assumption is primarily based on the continuation of sedimentary cyclicity from the open marine pre-MSC sediments into the Primary Lower Gypsum unit. To assess the possible role of orbitally-driven paleoclimate change on the deposition of the PLG unit, we have analysed molecular fossils (lipid biomarkers) preserved in shales and gypsum of the Pollenzo section (Piedmont basin, NW Italy).

Long-chain n-alkanes are reliable biomarkers that are used to track the input of terrestrial organic matter and allow to reconstruct paleovegetation. By using the distribution of higher plant-derived long chain n-alkanes and their compound specific carbon isotope signature (δ¹³C), we show that the sedimentary cyclicity in the PLG unit is indeed controlled by precession. Our high-resolution paleoclimatic proxy records cover approximately 300 Ka (6.003 Ma – 5.721 Ma) and comprise the onset of the MSC (5.971 Ma) and the first 12 cycles of the PLG unit. Cyclic fluctuation of δ¹³C values is observed, with higher δ¹³C values typifying long-chain n-alkanes extracted for gypsum, while lower values correspond to shales.

Our results, which represent the first paleoclimatic proxy data derived from Messinian gypsum, show that riverine flux of organic matter to the basin varied significantly during the first phase of the MSC. In agreement with a precessional control on paleoclimate, lower n-alkane abundance in gypsum reflects drier conditions, while higher n-alkane abundance in shales indicates more humid climate and increased input of terrestrial organic matter to the basin.

How to cite: Stolwijk, D., Natalicchio, M., Dela Pierre, F., Birgel, D., and Peckmann, J.: Precession-paced climate oscillations in Messinian sulphate evaporites recorded by carbon stable isotopes of leaf wax derived n-alkanes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20640, https://doi.org/10.5194/egusphere-egu2020-20640, 2020.