PRODELTAIC DEPOSITS. SEISMIC STRATIGRAPHY-SEDIMENTOLOGY-SLOPE STABILITY

THIS THESIS IS CONCERNED WITH THE ANALYSIS OF CONTINUOUS SEISMIC PROFILES (3.5 KHZ), THE STUDY OF GEOTECHNICAL PROPERTIES AND THE SLOPE STABILITY IN THE PRODELTA DEPOSITS OF PIROS, EVINOS, MORNOS AND PINIOS RIVERS. SEISMIC INDUCED MASS MOVEMENTS AND SEDIMENT FLOWS WERE CONCLUDED FROM 3.5 KHZ PROFILES SUCH AS: 1) CREEP IN EVINOS AND THE WESTERN SECTION OF MORNOS PRODELTA. 2) DEBRIS AND TRUBIDITY FLOWS, AS WELL AS INTENSE SLUMPING PHENOMENA IN THE EASTERN SECTION OF MORNOS PRODELTA. 3) POSSIBLE DEBRIS FLOWS OF RELATIVELY COARSE CLASTIC MATERIAL IN THE PRODELTA OF NORTH PELOPONNISOS SEASONAL RIVERS. THE GEOTECHNICAL PROPERTIES DISPLAYED HIGH VERTICAL AND SPATIAL DIVERSITY WITHIN THE PRODELTA SEQUENCES. THIS IS DUE TO FLUCTUATIONS OF NEAR BOTTOM HYDRODYNAMIC CONDITIONS, VARIATION OF DEPOSITIONAL MECHANISMS (ESPECIALLY THE SEDIMENTATION RATES), TO VARIOUS MASS MOVEMENTS AND FINALLY TO POSSIBLE DIFFERENCES IN CLAY MINERAL COMPOSITION. THE FACTOR OF SAFETY (F) OF PIROS AND PINIOS PRODELTA SLOPES WAS FOUND TO BE FAIRLY HIGH (STABLE CONDITIONS) WHILE LOW VALUES WERE ESTIMATED FOR THE PRODELTA SLOPES OF EVINOS AND MORNOS. IN THIS WAY THE PRODELTA SEQUENCES OF THE RIVERS EVINOSAND MORNOS DISPLAYED LIMITED EQUILIBRIUM ACCORDING TO THE INFINITE SLOPE STABILITY ANALYSIS UNDER UNDRAINED CONDITIONS.ΣΤΗΝ ΠΑΡΟΥΣΑ ΔΙΑΤΡΙΒΗ ΑΝΑΛΥΟΝΤΑΙ ΚΑΙ ΕΡΜΗΝΕΥΟΝΤΑΙ ΣΕΙΣΜΙΚΕΣ ΤΟΜΟΓΡΑΦΙΕΣ, ΑΞΙΟΛΟΓΟΥΝΤΑΙ ΟΙ ΓΕΩΤΕΧΝΙΚΕΣ ΙΔΙΟΤΗΤΕΣ ΚΑΙ ΕΚΤΙΜΑΤΑΙ ΚΥΡΙΩΣ Η ΕΥΣΤΑΘΕΙΑ ΤΩΝ ΠΡΟΔΕΛΤΑΙΚΩΝ ΑΠΟΘΕΣΕΩΝ ΤΟΥ ΠΕΙΡΟΥ, ΕΝΥΗΝΟΥ, ΜΟΡΝΟΥ ΕΝΩ ΓΕΝΙΚΕΥΜΕΝΕΣ ΕΚΤΙΜΗΣΕΙΣ ΕΚΦΡΑΖΟΝΤΑΙ ΓΙΑ ΤΙΣ ΑΝΤΙΣΤΟΙΧΕΣ ΑΠΟΘΕΣΕΙΣ ΤΟΥ ΠΟΤΑΜΟΥ ΠΗΝΕΙΟΥ. 1) ΟΙ ΜΕΤΑΚΙΝΗΣΕΙΣ ΜΑΖΩΝ,ΠΟΥ ΕΝΕΡΓΟΠΟΙΗΘΗΚΑΝ ΚΥΡΙΩΣ ΚΑΤΩ ΑΠΟ ΤΗΝ ΕΠΙΔΡΑΣΗ ΤΗΣ ΣΕΙΣΜΙΚΗΣ ΔΡΑΣΤΗΡΙΟΤΗΤΑΣ,ΗΤΑΝ: (Α) ΕΡΠΥΣΜΟΣ ΣΤΟ ΔΕΛΤΑΙΚΟ ΜΕΤΩΠΟ ΤΟΥ ΠΟΤΑΜΟΥ ΕΥΗΝΟΥ ΚΑΙ ΣΤΟ ΔΥΤΙΚΟ ΤΜΗΜΑΤΟΥ ΔΕΛΤΑΙΚΟΥ ΜΕΤΩΠΟΥ ΤΟΥ ΜΟΡΝΟΥ. (Β) ΡΟΕΣ ΚΟΡΗΜΑΤΩΝ, ΤΟΥΡΒΙΔΙΤΙΚΕΣ ΡΟΕΣ ΚΑΙ ΕΝΤΟΝΕΣ ΚΑΤΟΛΙΣΘΗΣΕΙΣ ΣΤΟ ΤΜΗΜΑ ΤΩΝ ΑΠΟΘΕΣΕΩΝ ΤΟΥ ΜΟΡΝΟΥ. (Γ) ΠΙΘΑΝΕΣ ΡΟΕΣ ΚΟΡΗΜΑΤΩΝ ΜΕ ΕΥΜΕΓΕΘΗ ΧΟΝΔΡΟΚΛΑΣΤΙΚΑ ΤΕΜΑΧΗ ΣΤΙΣ ΑΠΟΘΕΣΕΙΣ ΤΩΝ ΠΟΤΑΜΟΧΕΙΜΑΡΡΩΝ ΤΩΝ ΒΟΡΕΙΩΝ ΑΚΤΩΝ ΤΗΣ ΠΕΛΟΠΟΝΝΗΣΟΥ. 2) ΟΙ ΓΕΩΤΕΧΝΙΚΕΣ ΙΔΙΟΤΗΤΕΣ ΤΩΝ ΙΖΗΜΑΤΩΝ ΤΩΝ ΠΡΟΔΕΛΤΑΙΚΩΝ ΑΠΟΘΕΣΕΩΝ ΠΑΡΟΥΣΙΑΣΑΝ ΜΕΓΑΛΗ ΔΙΑΚΥΜΑΝΣΗ ΚΑΙ ΕΥΡΟΣ ΤΙΜΩΝ, ΟΙ ΟΠΟΙΕΣ ΟΦΕΙΛΟΝΤΑΙ ΣΕ ΜΕΤΑΒΟΛΕΣ ΤΩΝ ΥΔΡΟΔΥΝΑΜΙΚΩΝ ΣΥΝΘΗΚΩΝ ΚΟΝΤΑ ΣΤΟ ΒΥΘΟ, ΣΕ ΑΛΛΑΓΕΣ ΤΩΝΜΗΧΑΝΙΣΜΩΝ ΑΠΟΘΕΣΗΣ ΚΑΙ ΙΔΙΑΙΤΕΡΑ ΤΩΝ ΡΥΘΜΩΝ ΙΖΗΜΑΤΟΓΕΝΕΣΗΣ, ΣΕ ΜΕΤΑΚΙΝΗΣΕΙΣ ΜΑΖΩΝ ΔΙΑΦΟΡΩΝ ΤΥΠΩΝ ΚΑΙ ΤΕΛΟΣ ΣΕ ΠΙΘΑΝΕΣ ΟΡΥΚΤΟΛΟΓΙΚΕΣ ΔΙΑΦΟΡΕΣ. 3) Ο ΣΥΝΤΕΛΕΣΤΗΣ ΑΣΦΑΛΕΙΑΣ (F) ΤΩΝ ΑΠΟΘΕΣΕΩΝ ΤΟΥ ΠΕΙΡΟΥ ΚΑΙ ΠΗΝΕΙΟΥ ΕΚΤΙΜΗΘΗΚΕ ΩΣ ΑΡΚΕΤΑ ΥΨΗΛΟΣ (ΕΥΣΤΑΘΕΙΣ ΣΥΝΘΗΚΕΣ) ΣΕ ΑΝΤΙΘΕΣΗ ΜΕ ΑΥΤΕΣ ΤΩΝ ΠΟΤΑΜΩΝ ΕΥΗΝΟΥ ΚΑΙ ΜΟΡΝΟΥ, ΟΠΟΥ ΠΑΡΟΥΣΙΑΖΕΙ ΧΑΜΗΛΕΣ ΤΙΜΕΣ. ΚΑΤΑ ΣΥΝΕΠΕΙΑ ΟΙ ΑΠΟΘΕΣΕΙΣ ΤΟΥ ΕΥΗΝΟΥ ΚΑΙ ΜΟΡΝΟΥ ΒΡΙΣΚΟΝΤΑΙ ΣΕ ΣΥΝΘΗΚΕΣ ΑΣΤΑΘΕΙΑΣ ΣΥΜΦΩΝΑ ΜΕ ΤΗ ΜΕΘΟΔΟ ΤΟΥ ΜΗ ΠΕΠΕΡΑΣΜΕΝΟΥ ΠΡΑΝΟΥΣ ΣΕ ΑΣΤΡΑΓΓΙΣΤΕΣ ΣΥΝΘΗΚΕΣ

Prokaryotic community structure and diversity in the sediment of Kazan mud volcano

We investigated 16S rRNA gene diversity at a high sediment depth resolution (every 5 cm, top 30 cm) in an active site of the Kazan mud volcano, East Mediterranean Sea. A total of 242 archaeal and 374 bacterial clones were analysed, which were attributed to 38 and 205 unique phylotypes, respectively (>=98% similarity). Most of the archaeal phylotypes were related to ANME-1, -2 and -3 members originating from habitats where anaerobic oxidation of methane (AOM) occurs, although they occurred in sediment layers with no apparent AOM (below the sulphate depletion depth). Proteobacteria were the most abundant and diverse bacterial group, with the Gammaproteobacteria dominating in most sediment layers and these were related to phylotypes involved in methane cycling. The Deltaproteobacteria included several of the sulphate-reducers related to AOM. The rest of the bacterial phylotypes belonged to 15 known phyla and three unaffiliated groups, with representatives from similar habitats. Diversity index H was in the range 0.56-1.73 and 1.47-3.82 for Archaea and Bacteria, respectively, revealing different depth patterns for the two groups. At 15 and 20 cm below the sea floor, the prokaryotic communities were highly similar, hosting AOM-specific Archaea and Bacteria. Our study revealed different dominant phyla in proximate sediment layers

Organic carbon distribution and isotopic composition in three records from the eastern Mediterranean Sea during the Holocene

International audienceWe investigated the distribution of organic carbon (TOC) and bulk organic δ 13C org values in two cores from the Aegean Sea and one from the Libyan Sea, eastern Mediterranean Sea (EMS) with a focus on the timing and regional expression of sapropel S 1 deposition in the early Holocene. Our data indicate that the onset of S 1 occurred earlier in the Libyan Sea (∼9.8 kyr BP) than in the Aegean Sea (∼8.9 kyr BP), implying that dysoxia/anoxia started earlier in the deeper sites of the EMS than in the shallower sites in the Aegean Sea. Accumulation rates of organic matter (OM) during the S 1 period have a clear decreasing gradient from north to south, with higher values in the Aegean Sea and TOC contents higher in the deep basin. The three sedimentary sequences exhibit δ 13C org values that fall within the range of algal OM (-25‰ to -20‰). Shifts to lighter δ 13C org values within sapropel intervals in the Aegean sites can be interpreted as the result of elevated marine production, enhanced inflow of light terrestrial dissolved inorganic carbon and/or of the shoaling of the pycnocline, along with the presence of a deep chlorophyll maximum (DCM) during the S 1 period

Coccolith Sr/Ca ratios in the eastern Mediterranean: Production versus export processes

Samples collected by two sediment traps located southwest of Crete in the eastern Mediterranean (EMED) [48A (1953 m) and 48B (950 m)] from June 2005 to May 2006 were used to study fluxes of organic carbon, carbonate and coccolithophores in combination with the variations of Sr/Ca ratios in different individually picked coccolith species. Considering the complexity of the EMED, we validate the use of Sr/Ca ratios as productivity proxy and unravel the varied processes which may influence it. We examined the relationship between the seasonal peaks in export fluxes and the Sr/Ca ratio in coccoliths of three upper photic zone coccolithophores species collected in the traps, Calcidiscus leptoporus, Helicosphaera carteri and Emiliania huxleyi. We aimed at testing whether high export fluxes are correlated with high Sr/Ca ratios, suggestive of higher nutrient-stimulated production, or Sr/Ca ratios are unchanged during high export periods, suggestive of increased export efficiency or scavenging. Periods of enhanced trap fluxes in March and June result from surface water blooms recognized in satellite imagery. An additional peak flux was found in January, but this peak represents re-suspended or recycled material in the water column. The amplitude of seasonal variations in the Sr/Ca ratios of the three investigated species is small in both traps. In the shallow trap, a decrease in the Sr/Ca ratio of C. leptoporus occurred synchronously with minimal fluxes. The other two species were not measured for this period. In the deep trap, no such decrease in Sr/Ca was observed during minimal fluxes, in either C. leptoporus or H. carteri, probably due to a long residence of coccoliths in the water column, recycling and low export efficiency. Absolute Sr/Ca ratios for all species are lower than in other more productive environments like the Bay of Bengal, Arabian Sea, or Sargasso Sea. We conclude that Sr/Ca ratios in coccoliths of surface sediments in the EMED reflect mainly spring-summer bloom conditions averaged over hundreds to thousands of years. In addition, the origin of varying calcite thickness in H. carteri was investigated. The similarity of average Sr/Ca ratios in differently-calcified specimens confirms that coccolith thickness variations in this species result from primary biomineralization processes and not from variable overgrowth by (low Sr) abiogenic calcite in the water column or the sediments. © 2009 Elsevier B.V. All rights reserved

(Table 2) Age determination of Aegean Sea sediments

The modern Aegean Sea is an important source of deep water for the eastern Mediterranean. Its contribution to deep water ventilation is known to fluctuate in response to climatic variation on a decadal timescale. This study uses marine micropalaeontological and stable isotope data to investigate longer-term variability during the late glacial and Holocene, in particular that associated with the deposition of the early Holocene dysoxic/anoxic sapropel S1. Concentrating on the onset of sapropel-forming conditions, we identify the start of 'seasonal' stratification and highlight a lag in d18O response of the planktonic foraminifer N. pachyderma to termination T1b as identified in the d18O record of G. ruber. By use of a simple model we determine that this offset cannot be a function of bioturbation effects. The lag is of the order of 1 kyr and suggests that isolation of intermediate/deep water preceded the start of sapropel formation by up to 1.5 kyr. Using this discovery, we propose an explanation for the major unresolved problem in sapropel studies, namely, the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition. We suggest that nutrients had been accumulating in a stagnant basin for 1-1.5 kyr and that these accumulated resources were utilized during the deposition of S1. In addition, we provide a first quantitative estimate of the diffusive (1/e) mixing timescale for the eastern Mediterranean in its "stratified" sapropel mode, which is of the order of 450 years

Climate variability in the Eastern and Western Mediterranean Sea over the last two millennia: a contribution of PaleoMex/MISTRALS

International audienceRecent compilations of Mediterranean 2k paleoclimate archives (Luterbacher et al., 2012, MedClivar Book) stressed the lack of high-resolution/ continuous marine records. The two new high-resolution sea surface temperature (SSTs) time-series presented here from the shallow coastal shelf sediments of the Gulf of Lions and deeper ocean one of the Aegean Sea using alkenone paleothermometry, are thus an important contribution. SST values are roughly 2°C warmer in the Eastern than Western Mediterranean sites in agreement with our knowledge of the production pattern of the main alkenone producer Emiliania huxleyi in the two basins. Both SST-record reveal significant variability of cool/warm intervals, corresponding to the continental European and Northern Hemisphere climatic variability. While distant from each other, SSTs at the two sites show some degree of similarity: increasing SSTs from ~ 600 to 1300 AD followed by a significant cooling till the early 1600's marking the onset of an outstanding warm period reaching values similar to present day. After a sharp decrease ending around 1700 yrs AD, the last three centuries indicate gradually rising SSTs by about 1°C/100 yrs. To our knowledge the latter feature has been undocumented in North Atlantic cores but often observed in paleoclimate reconstructions of the European climate, though with different regional timing and amplitude. This unexpected finding may reflect feedbacks from the surrounding land-masses contributing to "continentalize" the Mediterranean climate. Another notable feature is the short-lived abrupt cooling in the Aegean record between 1816 and 1824 yr AD, possibly expressing the surface water cooling subsequent to the Tambora volcanic eruption of 1815 yrs AD. * We acknowledge financial support from MEDECOS (Marin-ERA, EU/FP6) Project and the Greek General Secretary of Research and Technology. Luterbacher J, Garcia-Herrera R, Allan R, Alvarez-Castro BG, Benito G, Booth J, Büntgen U, Colombaroli D, Davis B, Esper J, Felis T, Fleitmann D, Frank D, Gallego D, Gonzalez-Rouco FJ, Goosse H, Kiefer T, Macklin MG, Montagna P, Newmann L, Rath V, Ribera P, Roberts N, Silenzi S, Tinner W, Valero-Garces B, van der Schrier G, Vanniere B, Wanner H, Werner JP, Willett G, Xoplaki E, Zerefos CS, Zorita E (2012) A review of 2000 years of paleoclimatic evidence in the Mediterranean. In: Lionello, P. (Ed.), The Climate of the Mediterranean region: From the Past to the Future. Elsevier, Amsterdam, 87-185