The Messinian Salinity Crisis
The Levant Basin is the only deep Mediterranean basin where the entire section representing the Messinian Salinity Crisis (MSC) was penetrated by wells tied to high-resolution 3D seismic surveys. Based on the new data from the Levant, a series of recent studies challenge the desiccation paradigm dominating the MSC literature for >50 years. The first study (Gvirtzman et al., 2017) identified the transition from Stage 2 to Stage 3 of the MSC as an Intra-Messinian Truncation Surface (IMTS), separating the nearly 2 km thick salt sequence from the overlying ~100 m thick upper clastic-rich anhydrite unit. The origin of the flat IMTS was interpreted as a result of submarine dissolution in odds with previous interpretations that argued for subaerial erosion. Two following studies (Manzi et al., 2018, 2021) identified the Stage 1 deposits below the salt as a 10s-of-m thick foraminifera barren interval (FBI), composed of shales with no evaporites. This unit indicates that during Stage 1, salinity in the deep basin progressively increased and marine organisms gradually disappeared, but still with no salt deposition. The identification of Stage 1 deposits (shale) below the salt and Stage 3 deposits (sand+shale+anhydrite) above the salt, leads to the conclusion that the entire salt sequence was deposited during Stage 2, i.e., within a short period of 60 kyr. At that time, sedimentation rate jumped by an order of magnitude reaching a few cm/yr like the modern Dead Sea and artificial salinas. Following the suggestion that the top salt was truncated in deep waters by dissolution, Moneron and Gvirtzman (2022) further showed that the Stage 3 unit overlying the truncation surface contains a dense net of channels, characterized by submarine aggradation characteristics (levee height, channel depth, and channel-floodplain coupling). This adds up to the conclusion that evidence previously interpreted as indications for subaerial exposure (erosion and fluvial channels), are better explained by submarine processes (dissolution and turbidite channels). Finally, based on the reconstruction of the Messinian Nile River, Gvirtzman et al. (2022) estimate the amplitude of the MSC sea-level drop by ~600 m. Accordingly, salt was deposited in a water depth of >1 km in the Levant Basin and probably >2 km in the Herodotus Basin.
Intra-Messinian truncation surface in the Levant basin explained by subaqueous dissolution
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 k.y. Erosional unconformities extending from the continental margins into the deep basins are key features for reconstructing the MSC; however, the nature of the erosional processes and their subaerial versus subaqueous origin are highly controversial. This study focuses on the top erosion surface (TES) in the deep Levant Basin, which is notably flat, truncating a basinward tilted Messinian evaporitic succession. 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; 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. Dissolution occurred upslope where salt rocks at the seabed were exposed to the upper diluted brine, while downslope, submerged in the deeper halite-saturated layer, the salt rocks were preserved. The model, which requires a stratified water column, is inconsistent with a complete desiccation of the eastern Mediterranean Sea.
Published paper: Gvirtzman, Z., Manzi, V., Calvo, R., Lugli, S., Gennari, R., Gavrieli, I., Roveri, M., 2017, Intra-Messinian Dissolution Surface in the Levant Basin, Geology, doi:10.1130/G39113.1
Late Messinian submarine channel systems in the Levant Basin: Challenging the desiccation scenario
The question of whether the Mediterranean Sea desiccated during the Messinian salinity crisis (MSC) has been strongly debated for decades. In the Levant Basin, this debate was recently reignited in relation to the latest stage of the crisis after cessation of salt deposition. The desiccation supporters argue that salt truncation—and its subsequent burial by a latest Messinian, clastic-rich evaporitic unit—occurred subaerially on a desiccated seafloor. However, we show that this latest Messinian unit contains a dense net of channels with meanders, levees, and overspill deposits and is very similar to the turbidite channels observed on the modern seafloor. The aggradation characteristics of these buried channels (levee height, channel depth, and channel-floodplain coupling) indicate a marine rather than fluvial origin. Our conclusion adds to the findings of a previous study that salt truncation occurred in deep waters by dissolution. In a wider perspective, we suggest that the flush of clastics into the basin during the last stage of the MSC indicates a combination of wet climate and sea-level rise that started before the Zanclean (earliest Pliocene).
Published paper: Moneron, J. and Gvirtzman, Z., 2022. Late Messinian submarine channel systems in the Levant Basin: Challenging the desiccation scenario. Geology, 50(12), pp.1366-1371.
Limited Mediterranean sea-level drop during the Messinian salinity crisis inferred from the buried Nile canyon
The extreme Mediterranean sea-level drop during the Messinian salinity crisis has been known for >50 years, but its amplitude and duration remain a challenge. Here we estimate its amplitude by restoring the topography of the Messinian Nile canyon and the vertical position of the Messinian coastline by unloading of post-Messinian sediment and accounting for flexural isostasy and compaction. We estimate the original depth of the geomorphological base level of the Nile River at ~600m below present sea level, implying a drawdown 2–4 times smaller than previously estimated from the Nile canyon and suggesting that salt precipitated under 1–3 km deep waters. This conclusion is at odds with the nearly-desiccated basin model (>2 km drawdown) dominating the scientific literature for 50 years. Yet, a 600m drawdown is ca. five times larger than eustatic fluctuations and its impact on the Mediterranean continental margins is incomparable to any glacial sea-level fall.
Published paper: Gvirtzman, Z., Heida, H., Garcia-Castellanos, D., Bar, O., Zucker, E. and Enzel, Y., 2022. Limited Mediterranean sea-level drop during the Messinian salinity crisis inferred from the buried Nile canyon. Communications Earth & Environment, 3(1), p.216.
Freshening of the Mediterranean Salt Giant: controversies and certainties around the terminal (Upper Gypsum and Lago-Mare) phases of the Messinian Salinity Crisis
The late Miocene evolution of the Mediterranean Basin is characterized by major changes in connectivity, climate and tectonic activity resulting in unprecedented environmental and ecological disruptions. During the Messinian Salinity Crisis (MSC, 5.97-5.33 Ma) this culminated in most scenarios first in the precipitation of gypsum around the Mediterranean margins (Stage 1, 5.97-5.60 Ma) and subsequently > 2 km of halite on the basin floor, which formed the so-called Mediterranean Salt Giant (Stage 2, 5.60-5.55 Ma). The final MSC Stage 3, however, was characterized by a "low-salinity crisis", when a second calcium-sulfate unit (Upper Gypsum; substage 3.1, 5.55- 5.42 Ma) showing (bio)geochemical evidence of substantial brine dilution and brackish biota-bearing terrigenous sediments (substage 3.2 or Lago-Mare phase, 5.42-5.33 Ma) deposited in a Mediterranean that received relatively large amounts of riverine and Paratethys-derived low-salinity waters. The transition from hypersaline evaporitic (halite) to brackish facies implies a major change in the Mediterranean’s hydrological regime. However, even after nearly 50 years of research, causes and modalities are poorly understood and the original scientific debate between a largely isolated and (partly) desiccated Mediterranean or a fully connected and filled basin is still vibrant. Here we present a comprehensive overview that brings together (chrono)stratigraphic, sedimentological, paleontological, geochemical and seismic data from all over the Mediterranean. We summarize the paleoenvironmental, paleohydrological and paleoconnectivity scenarios that arose from this cross-disciplinary dataset and we discuss arguments in favour of and against each scenario.
Published paper: Andreetto, F., Aloisi, G., Raad, F., Heida, H., Flecker, R., Agiadi, K., Lofi, J., Blondel, S., Bulian, F., Camerlenghi, A. and Caruso, A., 2021. Freshening of the Mediterranean Salt Giant: controversies and certainties around the terminal (Upper Gypsum and Lago-Mare) phases of the Messinian Salinity Crisis. Earth-Science Reviews, 216, p.103577.
https://www.sciencedirect.com/science/article/pii/S0012825221000763?via%3Dihub
The onset of the Messinian salinity crisis in the deep Eastern Mediterranean basin
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 Messinian salinity crisis (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 (anhydrite and halite) deposition started later, at 5.60 Ma and (5) new and published
87Sr/86Sr data indicate that during all stages, evaporites precipitated from the same water body in all the Mediterranean sub-basins. The wide synchrony of events and 87Sr/86Sr homogeneity implies inter-sub-basin connection during the whole MSC and is not compatible with large sea-level fall and desiccation of the Mediterranean.
Published paper: Manzi V, Gennari R, Lugli S, Persico, Matteo R, Roveri, M, Schreiber, M C, Calvo R, Gavrieli I, Gvirtzman Z, 2018. The onset of the Messinian salinity crisis in the deep Eastern Mediterranean basin, Terra Nova; doi.org/10.1111/ter.12325
Synchronous onset of the Messinian salinity crisis and diachronous evaporite deposition: New evidences from the deep Eastern Mediterranean basin
We present a basin-wide correlation of the pre-evaporitic succession across the deep Levant basin, based on integrated bio- and cyclostratigraphy. The onset of Messinian salinity crisis (MSC) can be placed in all studied wells where oraminifers suddenly disappear and normal marine calcareous nannofossils are replaced by opportunistic assemblages. These changes mark the base of the Foraminifers Barren Interval (FBI), a 10s-of-m-thick (below seismic resolution), evaporite-free, shale unit that records the entire duration of the first stage. Moving towards the basin margin the FBI is progressively truncated on top by the Messinian erosional surface (MES), a regional-scale discontinuity sealed by a thin clastic evaporite units overlain by thick halite deposits. Our results confirm previous hypothesis suggesting that the crisis started in deep- as well as in shallow-water settings at 5.97 Ma and pointing to a synchronous onset of the MSC but diachronous deposition of evaporites. During stage 1 of the crisis, coeval with gypsum deposition in marginal basins, the salinity in deep basins progressively increased (with possible oxygen reduction) hindering the life of marine organisms. Then, at 5.60 Ma, when salinity in deep basins exceeded halite saturation, massive halite precipitation started, and a nearly 2-km-thick salt sequence accumulated in deep basins within a short period of 60 kyr. At that time (stage 2), sedimentation rate jumped by an order of magnitude reaching a few cm/yr. Similar sedimentation rates are inferred for the Realmonte salt mine (Sicily) and observed in the modern Dead Sea and artificial salinas.
Published paper: Manzi, V., Gennari, R., Lugli, S., Persico, D., Roveri, M., Gavrieli, I. and Gvirtzman, Z., 2021. Synchronous onset of the Messinian salinity crisis and diachronous evaporite deposition: New evidences from the deep Eastern Mediterranean basin. Palaeogeography, Palaeoclimatology, Palaeoecology, 584, p.110685.
https://www.sciencedirect.com/science/article/pii/S0031018221004703?via%3Dihub