Seismicity of the Eastern Mediterranean and Some Tectonic Features of the Mediterranean Ridge

Author(s):  
P. E. COMNINAKIS ◽  
B. C. PAPAZACHOS
1977 ◽  
Vol 8 (2) ◽  
pp. 205-235 ◽  
Author(s):  
Maria Bianca Cita ◽  
Colette Vergnaud-Grazzini ◽  
Christian Robert ◽  
Hervé Chamley ◽  
Neri Ciaranfi ◽  
...  

A deep-sea core over 16 m long from the crestal area of the Mediterranean Ridge has been investigated with different techniques, including quantitative micropaleontology, stable isotopes (measured on the epipelagic species Globigerinoides ruber and on the mesopelagic species Globorotalia inflata), and clay mineralogy. The resulting record of climatic fluctuations can be cross correlated to other Mediterranean cores by means of isochronous lithologies (tephra layers and sapropels). The climatic record of the Mediterranean is similar in character, phase, and chronology to the records investigated in the equatorial Pacific and in the Caribbean. Isotope stages 1 to 17 have been recognized. Cyclically repeated stagnant cycles resulting in sapropel deposition complicate both the isotopic and the faunal signal. The isotopic investigations reveal that the temperature change in the surface layers of the eastern Mediterranean was no greater than 8°C in the late “glacial” Pleistocene. The chronostratigraphic and biostratigraphic interpretation of Core KS09 indicate that the mean sedimentation rate was 2.4 cm/1000 years, a value very close to the 2.5 cm/1000 years calculated for the entire Quaternary section at DSDP Site 125, also located in the crestal area of the Mediterranean Ridge in the Ionian Basin. The base of KS09 is likely to be very close to the Brunhes/Matuyama boundary dated at 0.7 my.


Extensive surveys with long range side-scan sonar, as well as an air-gun sub-bottom profiler and a narrow beam echo-sounder, are described for the eastern half of the Mediterranean Sea. The main structural trends are shown in plan view to follow the curve of the Hellenic Outer Ridge (previously known as the Mediterranean Ridge, East Mediterranean Ridge or Mediterranean Rise), and suggest a structural continuation into the Ionian Islands west of Greece. To the west a similar but smaller feature, the Calabrian Outer Ridge (external to the Calabrian Arc) is described. This is partly welded to the Hellenic Outer Ridge along a narrow suture zone. To the east the Hellenic Outer Ridge is shown to merge into the Cyprus Outer Ridge (external to the Cyprus Arc). The Hellenic Outer Ridge is clearly asymmetrical in cross section, with its steeper slope facing towards the interior of its Arc System. Folds and strike faults have been recognized on sonographs, particularly those of the Hellenic Outer Ridge. Cross-faults (possibly strike-slip) are numerous on the northern slope of this Outer Ridge. Cross-faults are especially well developed where the Ridge is narrowest and highest between Crete and North Africa, and where it may have been thickened by thrusting. In general the intensity of deformation decreases southwards across the Hellenic Outer Ridge. Slumping is probably responsible for progressively reducing the height of the relief produced by folding and faulting. The Hellenic, Calabrian and Cyprus Outer Ridges are interpreted as miogeanticlines related to the Plio-Quaternary phase of the continuing southwards outgrowth of the Hellenic, Calabrian and Cyprus Arc Systems. The large and small scale structures are of particular interest because they show the surface relief of some early evolutionary stages of dominantly compressional submarine mountain ranges before they are subject to subaerial erosion or modified by later tectonism. The driving force of the continuing orogeny is seen as resulting from local mantle diapirs spreading outwards from the Tyrrhenian, Aegean and Turkish regions, rather than from a simple closure of the Eastern Mediterranean due to the supposed convergence of the Eurasian and African ‘Plates’.


Author(s):  
Alba Rey-Iglesia ◽  
Philippe Gaubert ◽  
Gonçalo Espregueira Themudo ◽  
Rosa Pires ◽  
Constanza De La Fuente ◽  
...  

Abstract The Mediterranean monk seal Monachus monachus is one of the most threatened marine mammals, with only 600–700 individuals restricted to three populations off the coast of Western Sahara and Madeira (North Atlantic) and between Greece and Turkey (eastern Mediterranean). Its original range was from the Black Sea (eastern Mediterranean) to Gambia (western African coast), but was drastically reduced by commercial hunting and human persecution since the early stages of marine exploitation. We here analyse 42 mitogenomes of Mediterranean monk seals, from across their present and historical geographic ranges to assess the species population dynamics over time. Our data show a decrease in genetic diversity in the last 200 years. Extant individuals presented an almost four-fold reduction in genetic diversity when compared to historical specimens. We also detect, for the first time, a clear segregation between the two North Atlantic populations, Madeira and Cabo Blanco, regardless of their geographical proximity. Moreover, we show the presence of historical gene-flow between the two water basins, the Atlantic Ocean and the Mediterranean Sea, and the presence of at least one extinct maternal lineage in the Mediterranean. Our work demonstrates the advantages of using full mitogenomes in phylogeographic and conservation genomic studies of threatened species.


2021 ◽  
pp. 1-12
Author(s):  
Zalmen Henkin

Abstract Encroachment of woody plants into grasslands and subsequent brush management are among the most prominent changes occurring in arid and semiarid ecosystems over the past century. The reduced number of farms, the abandonment of marginal land and the decline of traditional farming practices have led to encroachment of the woody and shrubby components into grasslands. This phenomenon, specifically in the Mediterranean region, which is followed by a reduction in herbage production, biodiversity and increased fire risk, is generally considered an undesirable process. Sarcopoterium spinosum has had great success in the eastern Mediterranean as a colonizer and dominant bush species on a wide variety of sites and climatic conditions. In the Mediterranean dehesa, the high magnitude and intensity of shrub encroachment effects on pastures and on tree production were shown to be dependent on temporal variation. Accordingly, there are attempts to transform shrublands into grassland-woodland matrices by using different techniques. The main management interventions that are commonly used include grazing, woodcutting, shrub control with herbicides or by mechanical means, amelioration of plant mineral deficits in the soil, and fire. However, the effects of these various treatments on the shrubs under diverse environmental conditions were found to be largely context-specific. As such, the most efficient option for suppressing encroachment of shrubs is combining different interventions. Appropriate management of grazing, periodic control of the shrub component, and occasional soil nutrient amelioration can lead to the development of attractive open woodland with a productive herbaceous understory that provides a wider range of ecological services.


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