scholarly journals The genesis of a giant mud canopy by catastrophic failure of a thick evaporite sealing layer

Geology ◽  
2020 ◽  
Vol 48 (8) ◽  
pp. 787-791
Author(s):  
Chris Kirkham ◽  
Joe Cartwright ◽  
Claudia Bertoni ◽  
Pieter Van Rensbergen
Keyword(s):  
Nile Delta ◽  
Eastern Mediterranean ◽  
Three Dimensional ◽  
Morphological Type ◽  
Fluid Migration ◽  
Messinian Salinity Crisis ◽  
Mud Volcanoes ◽  
Shelf Slope ◽  
Messinian Evaporites ◽  
Sealing Layer

Abstract Three-dimensional seismic imaging and well calibration reveal a large allochthonous mud edifice that is composed of several mud extrusions and covers an area >740 km2 on the outer shelf slope of the Nile Delta. The allochthonous material was sourced from beneath the ∼1-km-thick Messinian evaporites in the Eastern Mediterranean and extruded synchronously as eight large mud volcanoes directly on top of the Messinian evaporites in a catastrophic remobilization event at the end of the Messinian salinity crisis. These large extrusive flows coalesced to form a single edifice with an exceptional volume of ∼292 km3 that is connected to eight widely spaced conduits. We argue that this large mud body represents a new morphological type and scale of mud extrusion. We propose that mud extrusions that coalesce on a surface forming a multi-conduit-fed edifice be referred to as mud canopies, by analogy with salt canopies, with implications for basin reconstruction, paleo–overpressure release events, and fluid migration.

eastern and western med Messinian salinity crisis : comparison scenarii and propositions

2020 ◽  
Author(s):  
Christian Gorini ◽  
Romain Pellen ◽  
jean-loup Rubino ◽  
Benoit Didier ◽  
Lucien Montader ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Nile Delta ◽  
Eastern Mediterranean ◽  
Phase 1 ◽  
Threshold Effect ◽  
Western Mediterranean ◽  
Messinian Salinity Crisis ◽  
Central Mediterranean ◽  
Western Basin ◽  
The Mediterranean

<p>The partial sequestration of the Mediterranean Sea from adjacent oceans at the end of the Miocene caused an evaporation surfeit that increased the water salinity above the seafloor of the deep basins and peripheral basins. As a result, an up to 2-3 km-thick sequence of evaporites was deposited in the center of the deep basins. This coincided with the concomitantly intense subaerial erosion of the adjacent margins and important Mass transport deposit events all around the peri- Mediterranean slopes. The volume of evaporites deposited in the deep basins implies a periodic connection with the world oceans concomitant with a huge evaporation during all the MSC. “Deep basins” refers to their position in the deep central parts of the extant Messinian basins in the western basin, the central basins (Ionian) and the eastern basins. The configuration of these basins and the distribution and thickness of the evaporites were very different 6 Myr ago due to the Africa Europe convergence. Evaporites deposition at the edge of the evaporites basins was affected by the geodynamic nature of the margins: Tertiary or Mesozoic passive or transform margins (North Africa), strike slip margins (northern and eastern Levant), convergent margins in the North of the East Mediterranean with evaporites subducted or stacked in a fore arc position. We propose a kinematic reconstruction of the central Mediterranean sea to discuss the connections between the Atlantic waters and the eastern Mediterranean Sea. In this presentation, we show that: (1) There is no opposition between the deposition of the first deep water evaporites and a sea level fall of more than 1000 m. (2) by a threshold effect the eastern Mediterranean could have been more restricted than the western Mediterranean during the phase 1 of the MSC, which could explain the two major incisions observed in the Nile delta (3). At the end of the MSC, this threshold effect could have been maximal with an accommodation space almost filled up and a bathymetry probably not exceeding 50 m in the western Mediterranean and in the Central Mediterranean with deposition of K and Mg evaporates, and almost zero in the Eastern Mediterranean as shown by the fluvial network developed on a wide-spread erosional surface on top of the Levant basin salt. (4) The Messinian salinity crisis (MSC) ended with the rapid re-flooding of the Mediterranean sea. A two-step flooding in the western Mediterranean could find its origin in this threshold effect.</p>

scholarly journals Influence of chemosynthetic ecosystems on nematode community structure and biomass in the deep eastern Mediterranean Sea

2012 ◽  
Vol 9 (12) ◽  
pp. 18131-18173
Author(s):  
N. Lampadariou ◽  
V. Kalogeropoulou ◽  
K. Sevastou ◽  
K. Keklikoglou ◽  
J. Sarrazin
Keyword(s):  
Species Richness ◽  
Mediterranean Sea ◽  
Eastern Mediterranean ◽  
Nematode Community ◽  
Cold Seep ◽  
Mud Volcanoes ◽  
Mussel Bed ◽  
Remotely Operated Vehicle ◽  
Eastern Mediterranean Sea ◽  
Density And Biomass

Abstract. Mud volcanoes are a special type of cold seeps where life is based on chemoautotrophic processes. They are considered as extreme environments and are characterised by unique megafaunal and macrofaunal communities. However, very few studies on mud volcanoes taking into account the smaller meiobenthic communities have been carried out. Two mud volcanoes were explored during the MEDECO cruise (2007) with the Remotely Operated Vehicle (ROV) Victor-6000; Amsterdam, located south of Turkey between 1700 and 2000 m depth (Anaximander mud field) and Napoli, south of Crete, located along the Mediterranean Ridge at about 2000 m depth (Olimpi mud field). The major aim of this study was to describe distributional patterns of meiofaunal communities and nematode assemblages from different seep microhabitats. Meiofaunal taxa and nematode assemblages at both mud volcanoes differed significantly from other Mediterranean sites in terms of standing stocks, dominance and species diversity. Density and biomass values were significantly higher at the seep sites, particularly at Amsterdam. Nematodes, the dominant meiofaunal taxon, displayed deeper penetration vertically into the sediment at the seep areas, indicating that biological rather than physicochemical factors are responsible for their vertical distribution. Patterns of nematode diversity varied, displaying both very high or very low species richness and dominance, depending on the habitat studied. The Lamellibrachia periphery and mussel bed of Napoli exhibited the highest species richness while the reduced sediments of Amsterdam yielded a species-poor nematode community, dominated by two successful species; one belonging to the genus Aponema and the other to the genus Sabatieria. Analysis of β-diversity showed that habitat heterogeneity of mud volcanoes contributed substantially to the total nematode species richness in the eastern Mediterranean Sea. These observations indicate a strong influence of mud volcanoes and cold-seep ecosystems on the meiofaunal communities and nematode assemblages.

scholarly journals A review of seawater intrusion in the Nile Delta groundwater system – the basis for assessing impacts due to climate changes and water resources development

2013 ◽  
Vol 10 (8) ◽  
pp. 10873-10911 ◽  
Author(s):  
M. B. Mabrouk ◽  
A. Jonoski ◽  
D. Solomatine ◽  
S. Uhlenbrook
Keyword(s):  
Climate Change ◽  
Nile Delta ◽  
Groundwater Resources ◽  
Scientific Evidence ◽  
Three Dimensional ◽  
Water Levels ◽  
Population Increase ◽  
Regional Process ◽  
Environmentally Sound ◽  
Resources Development

Abstract. Serious environmental problems are emerging in the River Nile basin and its groundwater resources. Recent years have brought scientific evidence of climate change and development-induced environmental impacts globally as well as over Egypt. Some impacts are subtle, like decline of the Nile River water levels, others are dramatic like the salinization of all coastal land in the Nile Delta – the agricultural engine of Egypt. These consequences have become a striking reality causing a set of interconnected groundwater management problems. Massive population increase that overwhelmed the Nile Delta region has amplified the problem. Many researchers have studied these problems from different perspectives using different methodologies, following different objectives and, consequently, arrived at different findings. However, they all confirmed that significant groundwater salinization has affected the Nile Delta and this is likely to become worse rapidly in the future. This article presents, categorizes and critically analyses and synthesizes the most relevant research regarding climate change and development challenges in relation to groundwater resources in the Nile Delta. It is shown that there is a gap in studies that focus on sustainable groundwater resources development and environmentally sound protection as an integrated regional process in Nile Delta. Moreover, there is also a knowledge gap related to the deterioration of groundwater quality. The article recommends further research that covers the groundwater resources and salinization in the whole Nile Delta based on integrated three-dimensional groundwater modelling of the Nile delta aquifer.

scholarly journals The structure of the lithosphere and upper mantle beneath the Eastern Mediterranean and Middle East

2020 ◽  
Vol 2 (3) ◽  
pp. 311-326 ◽  
Author(s):  
Dan McKenzie
Keyword(s):  
Middle East ◽  
Shear Wave ◽  
Upper Mantle ◽  
Eastern Mediterranean ◽  
Three Dimensional ◽  
Surface Velocity ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Surface Measurements ◽  
Lithosphere Thickness

AbstractSurface velocity measurements show that the Middle East is one of the most actively deforming regions of the continents. The structure of the underlying lithosphere and convecting upper mantle can be explored by combining three types of measurement. The gravity field from satellite and surface measurements is supported by the elastic properties of the lithosphere and by the underlying mantle convection. Three dimensional shear wave velocities can be determined by tomographic inversion of surface wave velocities. The shear wave velocities of the mantle are principally controlled by temperature, rather than by composition. The mantle composition can be obtained from that of young magmas. Application of these three types of observation to the Eastern Mediterranean and Middle East shows that the lithosphere thickness in most parts is no more than 50-70 km, and that the elastic thickness is less than 5 km. Because the lithosphere is so thin and weak the pattern of the underlying convection is clearly visible in the topography and gravity, as well as controlling the volcanism. The convection pattern takes the form of spokes: lines of hot upwelling mantle, joining hubs where the upwelling is three dimensional. It is the same as that seen in high Rayleigh number laboratory and numerical experiments. The lithospheric thicknesses beneath the seafloor to the SW of the Hellenic Arc and beneath the NE part of the Arabian Shield are more than 150 km and the elastic thicknesses are 30–40 km.

scholarly journals Biomarker evidence for nitrogen-fixing cyanobacterial blooms in a brackish surface layer in the Nile River plume during sapropel deposition

Geology ◽  
2019 ◽  
Vol 47 (11) ◽  
pp. 1088-1092 ◽  
Author(s):  
Nicole J. Bale ◽  
Rick Hennekam ◽  
Ellen C. Hopmans ◽  
Denise Dorhout ◽  
Gert-Jan Reichart ◽  
...  
Keyword(s):  
Surface Layer ◽  
Nile Delta ◽  
Eastern Mediterranean ◽  
Cyanobacterial Blooms ◽  
Nile River ◽  
Head Group ◽  
Free Living ◽  
Heterocystous Cyanobacteria ◽  
Primary Core ◽  
Sediment Layers

Abstract Sapropels are organic-rich sediment layers deposited in the eastern Mediterranean Sea during precession minima, resulting from an increase in export productivity and/or preservation. Increased freshwater delivery from the African continent resulted in stratification, causing deepwater anoxia, while nutrient input stimulated productivity, presumably at the deep chlorophyll maximum. Previous studies have suggested that during sapropel deposition, nitrogen fixation was widespread in the highly stratified surface waters, and that cyanobacteria symbiotic with diatoms (diatom-diazotroph associations, DDAs) were responsible. Here we analyzed sapropel S5 sediments for heterocyst glycolipids (HGs) from three locations in the eastern Mediterranean. HG biomarkers can differentiate between those heterocystous cyanobacteria that are free living (found predominately in freshwater or brackish environments) and those that are from DDAs (found in marine settings). In our primary core, from a location which would have been influenced by the Nile River outflow, we detected a HG with a pentose (C5) head group specific for DDAs. However, HGs with a hexose (C6) head group, specific to free-living cyanobacteria, were present in substantially (up to 60×) higher concentration. These data suggest that at our study location, free-living cyanobacteria were the dominant diazotrophs, rather than DDAs. The C6 HGs increased substantially at the onset of sapropel S5 deposition, suggesting that substantial seasonal cyanobacterial blooms were associated with a brackish surface layer flowing from the Nile into the eastern Mediterranean. Two additional S5 sapropels were analyzed, one also from the Nile delta region and one from the region between Libya and southwestern Crete. Overall, comparison of the HG distribution in the three S5 sapropels provides evidence that all three locations were initially influenced by surface salinities that were sufficiently low to support free-living heterocystous cyanobacteria. While free-living heterocystous cyanobacteria continued to outnumber DDAs during sapropel deposition at the two Nile-influenced sites, DDAs, indicators of persistent marine salinities, were the dominant diazotrophs in the upper part of the sapropel at the more westerly site. These results indicate that N2 fixation by free-living cyanobacteria offers an important additional mechanism to stimulate productivity in regions with strong river discharge during sapropel deposition.

scholarly journals A three-dimensional palaeohydrogeological reconstruction of the groundwater salinity distribution in the Nile Delta Aquifer

2019 ◽  
Vol 23 (12) ◽  
pp. 5175-5198 ◽  
Author(s):  
Joeri van Engelen ◽  
Jarno Verkaik ◽  
Jude King ◽  
Eman R. Nofal ◽  
Marc F. P. Bierkens ◽  
...  
Keyword(s):  
Steady State ◽  
Nile Delta ◽  
Three Dimensional ◽  
Computer Code ◽  
Variable Density ◽  
Groundwater Salinity ◽  
Fresh Groundwater ◽  
Marine Transgression ◽  
Transient Simulations ◽  
Clay Layers

Abstract. Holocene marine transgressions are often put forward to explain observed groundwater salinities that extend far inland in deltas. This hypothesis was also proposed in the literature to explain the large land-inward extent of saline groundwater in the Nile Delta. The groundwater models previously built for the area used very large dispersivities to reconstruct this saline and brackish groundwater zone. However, this approach cannot explain the observed freshening of this zone. Here, we investigated the physical plausibility of the Holocene-transgression hypothesis to explain observed salinities by conducting a palaeohydrogeological reconstruction of groundwater salinity for the last 32 ka with a complex 3-D variable-density groundwater flow model, using a state-of-the-art version of the SEAWAT computer code that allows for parallel computation. Several scenarios with different lithologies and hypersaline groundwater provenances were simulated, of which five were selected that showed the best match with the observations. Amongst these selections, total freshwater volumes varied strongly, ranging from 1526 to 2659 km3, mainly due to uncertainties in the lithology offshore and at larger depths. This range is smaller (1511–1989 km3) when we only consider the volumes of onshore fresh groundwater within 300 m depth. In all five selected scenarios the total volume of hypersaline groundwater exceeded that of seawater. We also show that during the last 32 ka, total freshwater volumes significantly declined, with a factor ranging from 2 to 5, due to the rising sea level. Furthermore, the time period required to reach a steady state under current boundary conditions exceeded 5.5 ka for all scenarios. Finally, under highly permeable conditions the marine transgression simulated with the palaeohydrogeological reconstruction led to a steeper fresh–salt interface compared to its steady-state equivalent, while low-permeable clay layers allowed for the preservation of fresh groundwater volumes. This shows that long-term transient simulations are needed when estimating present-day fresh–salt groundwater distributions in large deltas. The insights of this study are also applicable to other major deltaic areas, since many also experienced a Holocene marine transgression.

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