Late Miocene Messinian Salinity Crisis Research Articles

Deciphering the termination of the Messinian salinity crisis: The alkenone record of the Miocene-Pliocene transition in the northern Mediterranean.

The late Miocene Messinian salinity crisis (MSC; 5.97–5.33 Ma) transformed the Mediterranean basin into the youngest salt giant in Earth history. The paleoenvironment and the paleodepth of the Mediterranean basin during the terminal phase of the MSC (i.e., the Lago-Mare event), are still uncertain, primarily due to the contradicting presence of in-situ, fully marine vs brackish to freshwater fossils, with different palaeoecological affinity, found in the same rock record. This study uses the distribution of C37, C38 and C39 long-chain unsaturated methyl and ethyl n-ketones (alkenones), produced by haptophyte algae, in combination with micropaleontological and stable oxygen isotope data, to reconstruct the surface water temperatures and paleoenvironmental conditions in the Northern Mediterranean basin across the transition between the latest Miocene Lago-Mare phase to the re-establishment of marine conditions starting in Pliocene, at 5.33 Ma. The results suggest that the Mediterranean basin was already receiving influxes from the Atlantic Ocean before the end of the MSC, resulting in a progressive return to marine conditions proceeding from south to north, i.e., from the more distal to proximal areas. Finally, fully marine conditions were established at the base of the Pliocene (5.33 Ma). The study highlights the reliability of alkenone-based paleo proxies for environmental reconstruction, especially when body fossil records of primary producers are scarce or problematic.

Time‐probabilistic approach to the late Miocene Messinian salinity crisis: Implications for a disconnected Paratethys

Time‐probabilistic approach to the late Miocene Messinian salinity crisis: Implications for a disconnected Paratethys

Discovery of vast fluvial deposits provides evidence for drawdown during the late Miocene Messinian salinity crisis

The late Miocene Messinian salinity crisis (MSC) was a significant oceanographic event that caused widespread evaporitic accumulation throughout the Mediterranean Basin. Although multiple hypotheses exist regarding the origin of evaporitic and post-evaporitic deposits, researchers remain divided on the magnitude of base-level fall, and on whether these accumulations record deep-water or non-marine conditions. Here, we introduce a previously unknown, upper Messinian fluvial deposit comparable in size to the late Miocene Nile River fluvial valley fill and show that near-complete desiccation of the eastern Mediterranean was responsible for its development. The basin-wide accumulation, which is located offshore Cyprus, Syria, Lebanon, and Israel, lies directly atop deep-basin evaporites and related erosional surfaces, and is one of the largest known riverine deposits associated with the terminal MSC. From marked onshore incision and basinward thinning trends, the source of the accumulation is presumed to be a formerly unidentified drainage basin in southern Turkey and western Syria; the deposit extends > 500 km into the western Levant Basin, where its depositional sink is marked by six well-developed backstepping lobes. Based on the deposit's seismic stratigraphy and morphology, which provide clear evidence of subaerial exposure, we question current hypotheses proposing a deepwater origin for late Messinian accumulations. We also draw specific attention to the development of extensive circum-Mediterranean nonmarine conditions prior to Zanclean marine transgression, and to the previously overlooked role of fluvial systems in diluting hypersaline lakes in evaporitic basins.

Neogene palaeochannel deposits in Sudan – Remnants of a trans-Saharan river system?

The start of Nile-type trans-Saharan drainage systems in NE Africa during the Cenozoic is disputed. Stratigraphical and sedimentological data in Egypt are partly in conflict with the uplift history of potential source areas of water and sediment in East Africa. Here, we investigate outcrops of the Wadi Awatib Conglomerate in Sudan that provide the first evidence of northerly flowing Neogene rivers in the region. Dimension and relief of basal erosion surfaces, overall geometry of deposits and palaeocurrent indicators demonstrate that the deposits represent the fill of northward-oriented incised valleys. The conglomerates were deposited in deep gravel-bed rivers, by hyperconcentrated flows, tractions carpets and gravel bars, primarily during heavily sediment-laden floods of probably monsoonal origin. Stratigraphical and geomorphological relationships show that the deposits are between Eocene and Pliocene in age. Considering the structural history of the region and periods in the Cenozoic with palaeoclimatic conditions suitable for the production and transport of gravels, we hypothesize that the dramatic base-level fall during the Late Miocene Messinian salinity crisis in combination with a favorable palaeoclimate caused the incision of valleys and their subsequent filling with conglomerates. Sea-level change in the Mediterranean Sea and headward erosion of streams that were connected to the Egyptian Nile might have been the primary cause of valley incision and deposition of conglomerates, despite a location far inland from the coastline. We suggest that the deposits document a relatively young Neogene (Messinian to early Pliocene) trans-Saharan river system unrelated to uplift of the Ethiopian Plateau.

An archaeal biomarker record of paleoenvironmental change across the onset of the Messinian salinity crisis in the absence of evaporites (Piedmont Basin, Italy)

A sudden change from normal marine to extreme paleoenvironmental conditions occurred approximately 6Ma ago in the Mediterranean Basin at the onset of the late Miocene Messinian salinity crisis, one of the most severe ecological crises in Earth history. Strong evaporation and tectonics led to hypersaline conditions, resulting in widespread deposition of evaporites and the apparent annihilation of the marine metazoan biosphere. In contrast to the prominent occurrence of evaporites elsewhere in the Mediterranean, evaporites did not form in the deeper part of some marginal basins at the onset of the crisis. The strata of the Pollenzo section (Piedmont Basin, NW Italy) studied here were deposited in such a paleogeographic setting. Instead of evaporites, a cyclic succession of organic-rich shales and carbonates formed during the early phase of the crisis in the study area. These sediments record a sharp increase in the contents of archaeal molecular fossils that are mostly represented by isoprenoidal dialkyl glycerol diethers (DGDs) and isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs). Such an expansion of archaeal biomass is best explained by a change of the archaeal communities at the onset of the Messinian salinity crisis. In particular, the appearance of molecular fossils of extremophilic archaea, mostly producing DGDs (archaeol and extended archaeol), suggests the emergence of halophilic archaea. At the same time, lipids of planktonic Thaumarchaeota, especially crenarchaeol, are present across the entire section, suggesting the local persistence of normal marine conditions. In agreement with the sudden appearance of tetrahymanol in the upper part of the section, the persistence of crenarchaeol indicates the establishment of water column stratification after the advent of the Messinian salinity crisis. To further investigate the Piedmont Basin paleoenvironmental conditions, we test the Archaeol Caldarchaeol Ecometric (ACE), a proxy developed for identifying high paleosalinities in waters and possibly in sediments. Despite high ACE values found for the Messinian salinity crisis samples, these values are in contrast with the absence of any lithological evidence for high salinities as well with other biomarker-independent information, indicating low to normal seawater salinities. This apparent contradiction is likely explained by the complexity of the sources of archaeal lipids, especially of caldarchaeol and archaeol, limiting the utility of the ACE for the reconstruction of paleosalinities for Messinian strata.

Black Sea desiccation during the Messinian Salinity Crisis: Fact or fiction?

The late Miocene Messinian Salinity Crisis (MSC) was an extraordinary geologic event in the Mediterranean Basin marked by massive salt accumulation and presumably basin desiccation as a consequence of the reduced water exchange with the Atlantic Ocean. The discovery of a desiccation deposit in the Black Sea, the so-called Pebbly Breccia unit, was used to claim that the Black Sea also became desiccated during the MSC. Erosional features interpreted from seismic profiles of the Black Sea margin, correlated by some to the Pebbly Breccia unit, were used to support this hypothesis. However, the age of the Pebbly Breccia is poorly constrained, and its origin and relevance to the MSC subject to controversy. Here we present new biostratigraphic (dinoflagellate cyst) data from two key sedimentary successions located in a deep and a marginal setting of the Black Sea Basin. These records demonstrate that the Pebbly Breccia predates the Mediterranean water-level drop during the MSC. We argue that the presumed erosional features in the Black Sea Basin are not related to the MSC and likely represent an older Miocene event.

Modelling global-scale climate impacts of the late Miocene Messinian Salinity Crisis

Abstract. Late Miocene tectonic changes in Mediterranean–Atlantic connectivity and climatic changes caused Mediterranean salinity to fluctuate dramatically, including a ten-fold increase and near-freshening. Recent proxy- and model-based evidence suggests that at times during this Messinian Salinity Crisis (MSC, 5.96–5.33 Ma), highly saline and highly fresh Mediterranean water flowed into the North Atlantic Ocean, whilst at others, no Mediterranean Outflow Water (MOW) reached the Atlantic. By running extreme, sensitivity-type experiments with a fully coupled ocean–atmosphere general circulation model, we investigate the potential of these various MSC MOW scenarios to impact global-scale climate. The simulations suggest that although the effect remains relatively small, MOW had a greater influence on North Atlantic Ocean circulation and climate than it does today. We also find that depending on the presence, strength and salinity of MOW, the MSC could have been capable of cooling mid–high northern latitudes by a few degrees, with the greatest cooling taking place in the Labrador, Greenland–Iceland–Norwegian and Barents seas. With hypersaline MOW, a component of North Atlantic Deep Water formation shifts to the Mediterranean, strengthening the Atlantic Meridional Overturning Circulation (AMOC) south of 35° N by 1.5–6 Sv. With hyposaline MOW, AMOC completely shuts down, inducing a bipolar climate anomaly with strong cooling in the north (mainly −1 to −3 °C, but up to −8 °C) and weaker warming in the south (up to +0.5 to +2.7 °C). These simulations identify key target regions and climate variables for future proxy reconstructions to provide the best and most robust test cases for (a) assessing Messinian model performance, (b) evaluating Mediterranean–Atlantic connectivity during the MSC and (c) establishing whether or not the MSC could ever have affected global-scale climate.

First Nd isotope record of Mediterranean–Atlantic water exchange through the Moroccan Rifian Corridor during the Messinian Salinity Crisis

We present the first neodymium isotope reconstruction of Mediterranean–Atlantic water exchange through the Moroccan (‘Rifian’) Corridor 8–5Ma. This covers the late Miocene Messinian Salinity Crisis (MSC); a period when progressive tectonic restriction of the Mediterranean–Atlantic seaways resulted in extreme, basin-wide Mediterranean salinity fluctuations. The Rifian Corridor was one of these seaways and until now, relatively poor age constraints existed for the timing of Corridor closure, due to the impact of uplift and erosion on the sedimentary record. The bottom water Nd isotope record from the continuous Bou Regreg Valley succession in northwest Morocco allows us to explore corridor connectivity with the Atlantic. Data from the interior and Mediterranean edge of the Rifian Corridor (respectively, the Taza–Guercif and Melilla basins, northern Morocco) provide new information on corridor shallowing and the provenance of water flowing through the seaway. As a result, we can constrain the age of Rifian Corridor closure to 6.64–6.44Ma. We also find no evidence of the siphoning of Atlantic waters through the seaway (7.20–6.58Ma). Our results cannot exclude the possibility that at times during the Messinian Salinity Crisis, Mediterranean Outflow Water reached the Atlantic.

Choking the Mediterranean to dehydration: The Messinian salinity crisis

Strait uplift due to isostasy played a pivotal role in the development and maintenance of a desiccated Mediterranean basin during the Late Miocene Messinian salinity crisis. New three-dimensional flexure models for the western Mediterranean suggest that most of the giant evaporite body was deposited before sea-level lowering. Any mechanism that subsequently caused a Mediterranean sea-level lowering by a few hundred meters during several thousand years sufficed to cause isostatic uplift and closure of the gateways, thus choking the Mediterranean to desiccation. Due to this isostatic feedback, multiple desiccation and reflooding phases driven by Milankovitch cycles are unlikely. When the Atlantic connection had been lost and sea level had dropped, a sizeable regional uplift of the Strait of Gibraltar developed that presented a formidable obstacle to reflooding. Rollback and steepening of the Gibraltar slab may have played a key role at the end of the Miocene by dynamically lowering the sill region, thus reinstating the oceanic connection.

The endurance of endemism: the Mediterranean freshwater gobies and their prospects for survival

Gobies (Teleostei: Gobiidae), spawning in fresh waters of the Mediterranean catchment area, are listed, and their diagnostic features and relationships summarized. The species, by zoogeographic category, include (i) Mediterranean: Padogobius martensii (Günther, 1861) and P. nigricans (Canestrini, 1867) from the northern Adriatic and west‐central Italy, (ii) West Balkanian: Economidichthys pygmaeus (Holly, 1929) and E. trichonis Economidis & Miller, 1990, and (iii) Ponto‐Caspian: Prorerorhinus marmoratus (Pallas, 1811) and Knipowitschia caucasica (Kawrajsky, in Berg, 1916), from the northern Aegean area but otherwise widespread in the Ponto‐Caspian region, and the endemic Mediterranean K. punctatissima (Canestrini, 1864) (north‐eastern Italy) and K. thessala (Vinciguerra, 1921) (Thessaly). Scenarios for differentiation following the late Miocene Messinian salinity crisis are outlined. The vulnerability of these species is discussed, and their present status reviewed. Populations no longer exist at the precise type localities of E. pygmaeus (Lefkas) and K. thessala (Hasabali spring, Pinios river system). Special features of scientific and cultural interest are noted, and the biological capability for species recovery is assessed.