Architecture and sequence stratigraphy of the Upper Coralline Limestone formation, Malta—Implications for Eastern Mediterranean restriction prior to the Messinian Salinity Crisis

Hydrocarbon escape systems can be regionally active on multi-million-year timescales. However, reconstructing the timing and evolution of repeated escape events can be challenging because their expression may overlap in time and space. In the northern Levant Basin, eastern Mediterranean, distinct fluid escape episodes from common leakage points formed discrete, cross-evaporite fluid escape pipes, which are preserved in the stratigraphic record due to the coeval Messinian salt tectonics.The pipes consistently originate at the crest of prominent sub-salt anticlines, where thinning and hydrofracturing of overlying salt permitted focused fluid flow. Sequential pipes are arranged in several kilometers-long trails that were progressively deformed due to basinward gravity-gliding of salt and its overburden. The correlation of the oldest pipes within 12 trails suggests that margin-wide fluid escape started in the Late Pliocene/Early Pleistocene, coincident with a major phase of uplift of the Levant margin. We interpret that the consequent transfer of overpressure from the deeper basin areas triggered seal failure and cross-evaporite fluid flow. We infer that other triggers, mainly associated with the Messinian Salinity Crisis and compressive tectonics, played a secondary role in the northern Levant Basin. Further phases of fluid escape are unique to each anticline and, despite a common initial cause, long-term fluid escape proceeded independently according to structure-specific characteristics, such as the local dynamics of fluid migration and anticline geometry.Whereas cross-evaporite fluid escape in the southern Levant Basin is mainly attributed to the Messinian Salinity Crisis and compaction disequilibrium, we argue that these mechanisms do not apply to the northern Levant Basin; here, fluid escape was mainly driven by the tectonic evolution of the margin. Within this context, our study shows that the causes of cross-evaporite fluid escape can vary over time, act in synergy, and have different impacts in different areas of large salt basins.

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Geochemical and micropaleontological evidence of the Messinian Salinity Crisis preconditioning phase in the West Alboran Basin

10.5194/egusphere-egu21-2126 ◽

2021 ◽

Author(s):

Francesca Bulian ◽

Tanja J. Kouwenhoven ◽

Francisco J. Sierro ◽

Wout Krijgsman

Keyword(s):

Bottom Water ◽

Eastern Mediterranean ◽

Sudden Change ◽

Global Ocean ◽

Messinian Salinity Crisis ◽

Benthic Foraminifer ◽

Low Oxygen ◽

North East ◽

Before And After ◽

The Mediterranean

The Messinian Salinity Crisis (MSC), still highly discussed within the scientific community, affected the Mediterranean Sea between 5.97 and 5.33 Ma and led to the deposition of huge evaporite accumulations both in its marginal and deep basins. During this profound palaeoecological change, the connections between the Atlantic Ocean and Mediterranean Basin were extremely reduced or even non-existing creating an environment where evaporation was dominant. However, the isolation from the global ocean was not a sudden change but most probably a stepwise process. At 7.17 Ma the first signs of restriction are visible in the sedimentological and micropaleontological records all over the Mediterranean.Particularly, several Italian, Greek and Cypriot locations register a reduced deep water marine ventilation to the sea floor since 7.17 Ma ago as reflected in the higher abundance of benthic low oxygen foraminifer species, indicators of stressed conditions like Bolivinia spp., Bulimina aculeata, Uvigerina peregrina. In these locations, the start of the progressive Mediterranean isolation coincides with the beginning of a more regular occurrence or even the first appearance of sapropel levels which further confirms the increasingly adverse conditions and increasingly dysoxygenated bottom waters. On the other hand, apart from the first opal-rich deposits in the Sorbas basin (Southern Spain) and the Messadit section (North-East Morocco), evidence from the Western Mediterranean is lacking and no studies have focused so far on the 7.17 Ma event.In this view, we conducted a detailed benthic foraminifer and stable isotope study of West Alboran Sea Site 976 before and after the 7.17 Ma event. This new record highlights the imprint that the early Atlantic-Mediterranean gateway restriction had on the Mediterranean sedimentological record, in a location proximal to the Messinian Gateways. Here, even if anoxic bottom water conditions were never reached, the benthic foraminifer association, paired with the benthic foraminifer carbon isotope record suggest a perturbation of the bottom water circulation and a decrease in bottom water oxygen levels starting ~7.17 Ma. In addition, a comparison of Western-Eastern Mediterranean records enabled us to make assumptions regarding the Mediterranean scale circulation before and after the 7.17 Ma event.

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Calcareous dinoflagellate turnover in relation to the Messinian salinity crisis in the eastern Mediterranean Pissouri Basin, Cyprus

Journal of Micropalaeontology ◽

10.1144/jm.26.2.103 ◽

2007 ◽

Vol 26 (2) ◽

pp. 103-116 ◽

Cited By ~ 3

Author(s):

Katarzyna-Maria Bison ◽

Gerard J. M. Versteegh ◽

Frits J. Hilgen ◽

Helmut Willems

Keyword(s):

Mediterranean Basin ◽

Phytoplankton Community ◽

Environmental Changes ◽

Eastern Mediterranean ◽

Messinian Salinity Crisis ◽

Low Diversity ◽

Restricted Environment ◽

The Mediterranean ◽

Upper Tortonian ◽

The Mediterranean Basin

Abstract. The extent to which the Messinian salinity crisis modified the initially Tethyan, eastern Mediterranean phytoplankton community has been investigated by monitoring the fate of calcareous dinoflagellate cyst assemblages prior to, during and after the salinity crisis in the Pissouri section (Cyprus). A rich, but low diversity open oceanic assemblage, dominated by Calciodinellum albatrosianum, is found in the upper Tortonian and lower Messinian. The upper Messinian (pre-evaporitic) sediments yield only few cysts but the assemblage is much more diverse and reflects unstable more neritic conditions (Bicarinellum tricarinelloides), fluvial influence (Leonella granifera) and varying, temporally increased salinities (Pernambugia tuberosa), probably related to the increasingly restricted environment. The basal Pliocene sediments reflect the return to normal marine conditions; the dinoflagellate assemblage is rich in cysts and again has a low diversity. However, in contrast to the C. albatrosianum-dominated upper Tortonian and pre-evaporitic Messinian sediments, L. granifera clearly dominates the basal Pliocene association just after the replenishment of the Mediterranean basin. Apart from this shift in dominance, the onset of the Pliocene is furthermore marked by the first appearance of Calciodinellum elongatum, which must have immigrated from the Atlantic Ocean. Lebessphaera urania, a postulated remnant of the Tethyan Ocean survived the salinity crisis, possibly in as yet unidentified marine refuges in the Mediterranean itself. Although the environmental changes caused by the Messinian salinity crisis did not lead to an extinction of calcareous dinoflagellate species of the Pissouri Basin, it resulted in a significant change in the assemblages and contributed to a more modern character of the Pliocene dinoflagellate association in the eastern Mediterranean.

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Levant Basin as a key for Understanding the Messinian Salinity Crisis: Challenging the Desiccation Paradigm

10.5194/egusphere-egu2020-4040 ◽

2020 ◽

Author(s):

Zohar Gvirtzman ◽

Vinicio Manzi ◽

Ran Calvo ◽

Ittai Gavrieli ◽

Rocco Gennari ◽

...

Keyword(s):

High Resolution ◽

Mediterranean Sea ◽

Water Column ◽

Mediterranean Basin ◽

Eastern Mediterranean ◽

Messinian Salinity Crisis ◽

Seismic Surveys ◽

Salt Rocks ◽

The Mediterranean ◽

Levant Basin

The Messinian salinity crisis (MSC) is an extreme event in Earth history during which a salt giant (>1&#215;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.

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