Major erosion at the end of the Messinian Salinity Crisis: evidence from the Levant Basin, Eastern Mediterranean

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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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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The role of the Nahr Menashe in the Messinian Salinity Crisis: formation, dissolution and fluvial incision of the top evaporite unit in the NE Levant Basin, Eastern Mediterranean

10.5194/egusphere-egu21-10318 ◽

2021 ◽

Author(s):

SM Mainul Kabir ◽

David Iacopini ◽

Adrian Hartley ◽

Vittorio Maselli ◽

Davide Oppo

Keyword(s):

Eastern Mediterranean ◽

Messinian Salinity Crisis ◽

3D Seismic ◽

Fluvial Erosion ◽

Base Level ◽

Fluvial Incision ◽

Formation And Evolution ◽

New Interpretation ◽

Levant Basin

The Nahr Menashe Unit (NMU), which forms the uppermost part of the Messinian succession, &#160;is one of the most cryptic and elusive sedimentary units present in the Levant basin (Eastern Mediterranean). We use a high-resolution 3D seismic dataset from offshore Lebanon to propose a new interpretation for its formation and evolution. The NMU varies laterally across the basin both in thickness and internal seismic characteristics. The variably coherent cyclic seismic packages affected by fracturing, faulting suggests that the NMU represent a reworked, layered evaporite succession interbedded with siliciclastics derived from both the Lebanon Highlands and the Latakia Ridge. Widespread semi-circular depressions, random linear imprints, passive surface collapsing and residual mound features within the NMU suggest that post depositional diagenetic and/or strong dissolution process often affected its evaporite-rich subunits. The well-known extended valley and tributary channel systems characterising the uppermost NMU shows mainly erosional rather than depositional features. Erosion started after deposition of NMU as a consequence of the maximum base level fall during the last phase of the Messinian Salinity Crisis (MSC). The channel and valley system were subsequently infilled by layered sediments here interpreted to represent post-MSC deep water marine reflooding. In conclusion, our analyses suggest the NMU can be interpreted as a mixed evaporite-siliciclastic system deposited in a shallow marine or marginal environment, which subsequently experienced fluvial erosion and later burial by transgressive/high-stand sediments.

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Intra-salt deformation: Implications for the evolution of the Messinian evaporites in the Levant Basin, eastern Mediterranean

Marine and Petroleum Geology ◽

10.1016/j.marpetgeo.2017.08.027 ◽

2017 ◽

Vol 88 ◽

pp. 251-267 ◽

Cited By ~ 5

Author(s):

Ye E. Feng ◽

Josh Steinberg ◽

Moshe Reshef

Keyword(s):

Eastern Mediterranean ◽

Messinian Evaporites ◽

Levant Basin

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Structural characteristics and petroleum exploration of Levant Basin in Eastern Mediterranean

Petroleum Exploration and Development ◽

10.1016/s1876-3804(17)30066-6 ◽

2017 ◽

Vol 44 (4) ◽

pp. 573-581

Author(s):

Xiaobing LIU ◽

Guangya ZHANG ◽

Zhixin WEN ◽

Zhaoming WANG ◽

Chengpeng SONG ◽

...

Keyword(s):

Eastern Mediterranean ◽

Structural Characteristics ◽

Petroleum Exploration ◽

Levant Basin

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Source rock characterization of mesozoic to cenozoic organic matter rich marls and shales of the Eratosthenes Seamount, Eastern Mediterranean Sea

Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles ◽

10.2516/ogst/2018036 ◽

2018 ◽

Vol 73 ◽

pp. 49 ◽

Cited By ~ 8

Author(s):

Sebastian Grohmann ◽

Susanne W. Fietz ◽

Ralf Littke ◽

Samer Bou Daher ◽

Maria Fernanda Romero-Sarmiento ◽

...

Keyword(s):

Organic Matter ◽

Mediterranean Sea ◽

Source Rock ◽

Eastern Mediterranean ◽

Source Rocks ◽

Eastern Mediterranean Sea ◽

Potential Source Rock ◽

Levant Basin ◽

Rock Characterization ◽

Rock Eval

Several significant hydrocarbon accumulations were discovered over the past decade in the Levant Basin, Eastern Mediterranean Sea. Onshore studies have investigated potential source rock intervals to the east and south of the Levant Basin, whereas its offshore western margin is still relatively underexplored. Only a few cores were recovered from four boreholes offshore southern Cyprus by the Ocean Drilling Program (ODP) during the drilling campaign Leg 160 in 1995. These wells transect the Eratosthenes Seamount, a drowned bathymetric high, and recovered a thick sequence of both pre- and post-Messinian sedimentary rocks, containing mainly marine marls and shales. In this study, 122 core samples of Late Cretaceous to Messinian age were analyzed in order to identify organic-matter-rich intervals and to determine their depositional environment as well as their source rock potential and thermal maturity. Both Total Organic and Inorganic Carbon (TOC, TIC) analyses as well as Rock-Eval pyrolysis were firstly performed for the complete set of samples whereas Total Sulfur (TS) analysis was only carried out on samples containing significant amount of organic matter (>0.3 wt.% TOC). Based on the Rock-Eval results, eight samples were selected for organic petrographic investigations and twelve samples for analysis of major aliphatic hydrocarbon compounds. The organic content is highly variable in the analyzed samples (0–9.3 wt.%). TS/TOC as well as several biomarker ratios (e.g. Pr/Ph < 2) indicate a deposition under dysoxic conditions for the organic matter-rich sections, which were probably reached during sporadically active upwelling periods. Results prove potential oil prone Type II kerogen source rock intervals of fair to very good quality being present in Turonian to Coniacian (average: TOC = 0.93 wt.%, HI = 319 mg HC/g TOC) and in Bartonian to Priabonian (average: TOC = 4.8 wt.%, HI = 469 mg HC/g TOC) intervals. A precise determination of the actual source rock thickness is prevented by low core recovery rates for the respective intervals. All analyzed samples are immature to early mature. However, the presence of deeper buried, thermally mature source rocks and hydrocarbon migration is indicated by the observation of solid bitumen impregnation in one Upper Cretaceous and in one Lower Eocene sample.

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