Reconstructing the topography and water level of the Mediterranean Sea during the Messinian Salinity Crisis

[eng] During the Messinian Salinity Crisis (MSC, 5.97 – 5.33 Ma), an environmental crisis unparalleled in recent geological history, thick evaporites were deposited in the Mediterranean Basin associated with major erosion of the continental margins. The MSC is thought to have led to a kilometre-scale water level drop by evaporation due to restriction of the Atlantic-Mediterranean marine connection, but the timing and amplitude of this drop have remained controversial. This is due to uncertainty in the post-MSC vertical motions and lack of clear correlations between the marginal and abyssal sedimentary records. In this thesis I aim at constraining the Messinian water level by way of providing a paleobathymetric reconstruction of the Mediterranean sub-basins and depth estimates for the emplacement of evaporite deposits and erosional markers. I constrain the magnitude of vertical motions induced by the accumulation of evaporite and other sediment units, isostatic and thermal subsidence, and tectonic deformation in three key regions, being: the Alboran Basin, the rest of the Western Mediterranean, and the Nile Delta. In the Alboran Basin (Chapter 3), erosional terraces were formed originally at a wide depth range. The shallowest terrace is reconstructed to 250-550 m depth, while the deepest terrace has a reconstructed depth range of 750-1500 m. This variation is interpreted as the result of fluctuating water levels during the drawdown phase and to a high-energy basin reflooding event. In the Western Mediterranean (Chapter 4), we use the MSC “Mobile Unit” halite and “Upper Unit” gypsum as markers for paleoshorelines, and we estimate them as having formed at depths of 1500 m and 1100 m respectively. In addition, halite is found in small silled basins originally as shallow as 500 m along the Balearic Promontory, suggesting that halite deposition during the evaporative drawdown spanned a wider depth range than suggested by its current preservation, and was subsequently removed by erosion during subaerial exposure during the drawdown and lowstand phase of the Messinian Salinity Crisis. Physics- based box modelling (Chapter 6) of water and salt fluxes to the Central Mallorca Depression on the Balearic Promontory allow to further evaluate this hypothesis, showing that the gypsum identified in this silled basin could only have formed by overall salinification of the Western Mediterranean at high water level, while the volume of halite suggests that its precipitation started only after the water level had dropped by at least 850 m. Also, the new, smaller, estimate of halite volume in the deep Western Mediterranean is in agreement with precipitation starting at or soon after the onset of drawdown, in contrast to that in the Eastern Mediterranean. In the Nile Delta (Chapter 5) topographical restoration shows the original depth of the geomorphological base level of the Nile River at ~600-m below present sea level, with a 400 m waterfall separating the downstream Messinian canyon from the older upper valley. This baselevel drop is 2-4 times smaller than derived from other criteria for the Eastern basin, again suggesting fluctuations and diachronism of the MSC erosion episodes between the Western and Eastern Mediterranean. I show that the bathymetry of the Mediterranean basins was not radically different from the modern day in areas unaffected by fault tectonic deformation or plate subduction. Both the evaporites and the erosional features are found to have formed at a wide range of depths, not clearly linked to a single stable basinwide base level but rather affected by fluctuating water budgets in each subbasin. I propose that these variations in time and between subbasins were driven by variations in runoff from the continent and possibly by the capture of Paratethyan waters, during a stage of complete disconnection from the Atlantic.[spa] Durante la Crisis de Salinidad del Messiniense (MSC, 5,97 – 5,33 Ma), una crisis ambiental sin precedentes en la historia geológica reciente, se depositaron gruesas evaporitas en el Mar Mediterráneo asociadas con una gran erosión de los márgenes continentales. Se cree que el MSC provocó una caída del nivel del agua alrededor de un kilómetro debido a la evaporación provocada debido a la restricción en la conexión marina entre el Atlántico y el Mediterráneo. Debido a la incertidumbre en los movimientos verticales posteriores a la MSC y la falta de correlaciones claras entre los registros sedimentarios marginales y abisales, la amplitud de esta caída y su ubicación en el tiempo siguen estando en discusión. En esta tesis, mi objetivo es determinar el nivel del agua del Mediterráneo durante la MSC proporcionando una reconstrucción paleobatimétrica de las subcuencas mediterráneas y estimaciones de profundidad para el emplazamiento de depósitos de evaporita y marcadores de erosión. Estimo la magnitud de los movimientos verticales inducidos por la acumulación de evaporita y otras unidades de sedimentos, el hundimiento isostático y térmico y la deformación tectónica en tres regiones clave, que son: la cuenca de Alborán, el resto del Mediterráneo occidental y el delta del Nilo. En la Cuenca de Alborán (Capítulo 3), las terrazas erosionales se formaron originalmente en un amplio rango de profundidad. La terraza menos profunda se reconstruye a 250-550 m de profundidad, mientras que la terraza más profunda tiene un rango de profundidad reconstruido de 750-1500 m. Esta variación se interpreta como resultado de la fluctuación del nivel de agua durante la fase de evaporación y de un evento de inundación de alta energía de la cuenca. En el Mediterráneo occidental (Capítulo 4), utilizamos la halita de la “Unidad móvil” y el yeso de la “Unidad superior” del MSC como marcadores de las paleo-líneas costeras, y estimamos que se formaron a profundidades de 1500 m y 1100 m respectivamente. Además, la halita se encuentra en pequeñas cuencas restringidas originalmente hasta a una profundidad tan poco profundo como 500 m a lo largo del Promontorio Balear, lo que sugiere que la deposición de halita abarcó una profundidad más amplia que el sugerido por su conservación actual y posteriormente fue eliminada por la erosión durante la exposición subaérea durante la fase de descenso y nivel bajo de la crisis de salinidad de Messiniense. El modelo de caja basado en la física (Capítulo 6) de los flujos de agua y sal en la Depresión Central de Mallorca en el Promontorio Balear permite evaluar más a fondo esta hipótesis, mostrando que el yeso identificado en esta cuenca restringida solo podría haberse formado por la salinización general del Mediterráneo occidental en el nivel alto del agua, mientras que el volumen de halita sugiere que su precipitación comenzó solo después de que el nivel del agua había descendido al menos 850 m. Además, la nueva estimación del volumen de halita en el Mediterráneo occidental profundo concuerda con la precipitación que comienza con el inicio de la bajada del nivel del mar, en contraste con la del Mediterráneo oriental. En el Delta del Nilo (Capítulo 5), la restauración topográfica muestra la profundidad original del nivel base geomorfológico del río Nilo a ~600 m por debajo del nivel actual del mar, con una cascada de 400 m que separa el cañón Messiniense río abajo del valle superior más antiguo. Esta caída del nivel base es de 2 a 4 veces menor que la determinada por otros criterios para la cuenca oriental, lo que nuevamente sugiere fluctuaciones y diacronismo de los episodios de erosión de MSC entre el Mediterráneo occidental y oriental. Mi trabajo demuestra que la batimetría de las cuencas mediterráneas no fue radicalmente diferente de la actual en áreas no afectadas por la deformación tectónica de fallas o la subducción de placas. Se encontró que tanto las evaporitas como las evidencias de erosión se formaron en una amplia gama de profundidades, no vinculadas claramente a un único nivel base estable en toda la cuenca, sino más bien afectadas por los balances de agua fluctuantes en cada subcuenca. Propongo que estas variaciones temporales y entre subcuencas fueron impulsadas por variaciones en la escorrentía del continente y posiblemente por la captura de aguas del Paratethys, durante una etapa de desconexión total del Atlántico

A song of volumes, surfaces and fluxes: The case study of the Central Mallorca Depression (Balearic Promontory) during the Messinian Salinity Crisis

The Central Mallorca Depression (CMD) located in the Balearic Promontory (Western Mediterranean) contains a well-preserved evaporitic sequence belonging to the Messinian Salinity Crisis (MSC) salt giant, densely covered by high- and low-resolution seismic reflection data. It has been proposed recently that the MSC evaporitic sequence in the CMD could be a non-deformed analogue of the key MSC area represented by the Caltanissetta Basin in Sicily. This presumed similarity makes the CMD an interesting system to better understand the MSC events. Physics-based box models of the water mixing between sub-basins, built on conservation of mass of water and salt, help constrain the hydrological conditions under which evaporites formed during the MSC. Those models have been widely used in the literature of the MSC in the past two decades. They have been mostly applied to the Mediterranean Sea as a whole focusing on the Mediterranean–Atlantic connection, or focusing on the influence of the Sicily Sill connecting the Western and Eastern Mediterranean Sea. In this study, we apply a downscaled version of such modelling technique to the CMD. First, we quantify the present-day volumes of the MSC units. We then use a reconstructed pre-MSC paleo-bathymetry to model salinity changes as a function of flux exchanges between the CMD and the Mediterranean. We show that a persistent connection between the CMD and the Mediterranean brine near gypsum saturation can explain volume of Primary Lower Gypsum under a sea level similar to the present. For the halite, on the contrary, we show that the observed halite volume cannot be deposited from a connected CMD-Mediterranean scenario, suggesting a drawdown of at least 850 m (sill depth) is necessary. Comparison between the deep basin halite volume and that of the CMD shows that it is possible to obtain the observed halite volume in both basins from a disconnected Mediterranean basin undergoing drawdown, although determining the average salinity of the Western Mediterranean basin at the onset of drawdown requires further investigation

Was the Mediterranean once a desert? Messinian Salinity Crisis: 50 years of controversy and recent advances from a modelling perspective

Severo Ochoa Coffee Talk - LectureAbout 5.5 million years ago the Mediterranean Sea underwent a dramatic hydrological, environmental and biological crisis, as its connection to the global ocean and water supply was disrupted. This Messinian Salinity Crisis (MSC) left a salt deposit of thousands of cubic kilometers on the basin floor, and caused deep incision of rivers on its margins as they adjusted to a lowered water level. This makes it one of the largest salt deposits on earth, and by far the youngest, least affected by subsequent tectonic events. After 50 years of scientific effort by geologists, geochemists, geophysicists and others some of the large controversies surrounding the MSC remain unresolved. In this talk I will discuss the advances in MSC research since its discovery during the first oceanic drilling campaign in the Mediterranean in 1970, and illustrate how the vast amount of data gathered in these efforts now allow us to use modelling to decipher some of its mysteries

Flexural-isostatic reconstruction of the Western Mediterranean vertical motions after the Messinian Salinity Crisis: implications for sea level and basin connectivity

EGU2020: Sharing Geoscience Online, 4-8 may 2020The 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 subbasins 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

Constraining Arabia-Eurasia convergence accommodated in the Greater Caucasus: Paleomagnetism and inematic evolution of the Talesh, NW Iran

EGU General Assembly 2019 in Vienna, Austria, 7–12 April 2019The Arabia-Eurasia collision zone is an area of relatively young continental collision of which the kinematic evolution is poorly understood due to complex interactions of blocks accreting to the Eurasian plate after subduction of various oceanic domains, most notably the Paleotethys and Neotethys. The way in which convergence between the Arabian and European plates was accommodated and even the timing of collision is poorly constrained. Quantifying the mechanisms and processes active in the collision zone which extends from the Zagros mountains in the southwest of Iran to the Greater Caucasus in the northwest is a crucial step towards better understanding this young collision zone. Here, we constrain the amount of convergence accommodated by oroclinal bending and block rotation of the Talesh mountains to the west of the South Caspian Basin, in order to estimate the size of a reconstructed Greater Caucasus Basin north of the Talesh. New paleomagnetic data from the Eocene volcanics in the Talesh in NW Iran and Azerbaijan combined with previously published data allow us to provide a new subdivision of structural domains which are in accordance with trends in regional strikes, fold axes and faults. We define three blocks based on variations in both regional structural trends and rotations. These are used in a new Gplates reconstruction of the collision zone since the Eocene. The Talesh and lesser Caucasus were located at similar latitudes at 35 Ma, allowing for approximately 300 km of Arabia-Eurasia convergence to be accommodated during subduction of the Greater Caucasus Basin, accompanied by 120 km of arcparallel extension, as well as 220 km of convergence between the South Caspian Basin and the Talesh due to rotation. We identify structures which accommodated shortening and extension during block rotation and oroclinal bending. Our results allow for a more detailed understanding of the kinematic development of the Arabia-Eurasia collision zone since the Eocene, providing crucial insight into a young and still active collision zone

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 ~600 m 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 600 m 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.The article was supported by COST Action “Uncovering the Mediterranean salt giant” (MEDSALT), funded by the European Cooperation in Science and Technology. It was also supported by the SALTGIANT program, a European project funded by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska Curie grant agreement number 765256.Peer reviewe

Flexural‐isostatic reconstruction of the Western Mediterranean during the Messinian Salinity Crisis: Implications for water level and basin connectivity

International audienc

Topography of the Balearic Promontory during the Messinian Salinity Crisis: Isostatic response to desiccation and evaporite deposition.

Topo-Europe Conference in Granada, Spain, 5–10 May 2019The Messinian Salinity Crisis was a period of rapid and extreme environmental changes in the Mediterranean occurring from 5.96 to 5.33 Ma1¿, 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 base level commonly associated with the deposition of massive halite deposits at the `acme¿ of the crisis. However, the timing and magnitude of this sea level drawdown are not well constrained2¿, while this has important implications for the conditions under which the different MSC sedimentary units were deposited and the connectivity of various sub-basins during the crisis. Previous studies yield a sea level drop ranging from 400 m (Martínez et al. 2004) to 1500 m (Urgeles et al., 2010) for the Western Mediterranean, with values up to 2250 m reported for the Eastern Mediterranean. A pseudo 3-D (planform) flexural backstripping approach allows us to restore the Messinian topography in tectonically quiescent areas, estimating the isostatic subsidence due to the Plioquaternary sediment and restoring the elevation of paleoshorelines and the original depth of erosional surfaces and other stratigraphic markers.3¿ Here, we apply this method to the area spanning the Valencia Basin, Balearic Promontory and the Algero-Provençal Basin, to restore the Messinian Erosion Surface which formed above base level during the drawdown to its original elevation, constraining the minimum required base level drop for subaerial erosion at this elevation. Our results can be compared to previously obtained paleogeographies and checked for consistency with Messinian mammal migration onto the Balearic Islands (Mas et al., 2018)

Plio-Quaternary strike-slip tectonics in the Central Mallorca Depression, Balearic Promontory: Land-sea correlation

International audienceThe Balearic Promontory (Spain) is of key importance to understand the tectonic kinematics of the westernmost Mediterranean, because its continued marine sedimentation has recorded the contrasting effects expected from competing geodynamic models proposed for the region. Near the center of this promontory, between the islands of Mallorca and Ibiza, the Miocene to Pleistocene stratigraphy of the Central Mallorca Depression presents an ideal record of the tectonic deformation that has received only limited attention. We use a widespread dataset of 2D seismic reflection profiles to identify, interpret and map the main prominent reflectors and extrapolate the thickness of the pre-Messinian and Pliocene-Quaternary sedimentary units. We then quantify the timing and style of deformation related to the various fault systems. Our results reveal for the first time a series of aligned small depressions bounded by extensional and strike-slip faults and filled with Plio-Quaternary sediment, perfectly aligned with the sub-basins of the onshore Mallorca Graben. A subsidence analysis confirms this correlation. We identify non-cylindrical deformation within the Plio-Quaternary unit that is remarkably similar to that observed onshore, suggesting continuous fault zones from the Central Mallorca Depression to Mallorca Island. We interpret an intra-PQ unconformity as the marker of a transition from extensional to strike-slip tectonic regime. The strike-slip stage is represented by both transpressional and transtensional structures, interpreted as restraining/releasing bends respectively and step overs along the faults. We show that these offshore faults in the Central Mallorca Depression overlap well with seismic epicenters and suggest major active strike-slip corridors that have an onshore continuity both until eastern Mallorca and in the southwestern Ibiza margin. The role of previous tectonic inherited structures (rifting, Betic thrusts, post-orogenic collapse) on the deformation reported here is discussed and we propose a tentative sketch that integrates our results in a Miocene to Present-day evolution at regional scale