Τμήμα Γεωλογίας (ΜΔΕ)

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    A review on sediment samples from a deep hypersaline anoxic basin : Tyros
    Νικητίδου, Αγγελική; Γεραγά, Μαρία; Γεραγά, Μαρία; Nikitidou, Angeliki
    The Tyros basin is a presently deep hypersaline anoxic depression in the eastern part of the Mediterranean Sea. Its presence attributes to a combination of submarine dissolution of outcropping or subcropping evaporates (Messinian) which accumulate at the slopes of the basin and at its tectonic subsidence (pull-apart mechanism) that occurs in the western Strabos trench. Therefore, this unique environment consists of two major factors. The first one is a high density stagnant bottom-water column and the second is the preservation of the organic-rich sediments of the area due to the anoxic conditions. The core (TYRO5) that was retrieved from that basin had a total length of 285cm and comprises a complex lithostratigraphic sequence due to the strong geodynamic regime of the area. The analysis conducted on sediment samples from the core TYR05 included granulometry, mineralogy, micropaleontology, bulk geochemistry and total CHNS/organic carbon (TOC). The grain size distribution along with the planktonic foraminifera presents fluctuations which coincide with changes in the lithology of the core. The mineralogical composition of the sediments confirm the evaporate influence developed on the bottom of the basin, while both geochemistry and total CHNS/TOC verify the present anoxic conditions and the existence of organic-rich sediments. The synthesis of all the above analysis suggests that the sediment core consist mostly of sapropel to sapropelic layers and that it has a rather homogeneous character, because of its high re-sedimentation rate. Subsequently, it is indicated that the sapropel units refer to an S1 type, but further analyses are needed in order to be safely determine, such as radiocarbon dating C14 and stable isotopes of O, C.
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    Biogeochemistry and microbial ecology of shallow marine sediments from methane seeps, Katakolo Bay, Western Greece
    Βαζιουράκης, Κωνσταντίνος-Μάριος; Παπαθεοδώρου, Γεώργιος; Κορμάς, Κωνσταντίνος; Teske, Andreas; Vaziourakis, Konstantinos-Marios
    Anaerobic oxidation of methane (AOM) and other hydrocarbons prevents methane emission from marine sediments into the atmosphere. This study tries to illuminate aspects of AOM investigating shallow marine core sediments from Katakolo bay (W. Greece), one of the vastest thermogenic gas seepage fields in Europe. Belonging to the central Ionian geotectonic zone of the external units of the Hellenides, Katakolo has attracted the interest of scientists due to the vast seepage occurring in the harbor and can be considered as a unique natural laboratory in studying O2 versus gas seepage by long term monitoring. In the terms of this master dissertation, a number of multidisciplinary methodologies was implemented in order to shed light on the key biogeochemical process and the microbial ecology of nearshore (less than eight meter water depth) organic carbon depleted silty sands. We combined pore-water geochemical measurements, bulk geochemical and mineralogical analyses with 16S rRNA sequencing-based community analysis for both Archaea and Bacteria and fluorescence in situ hybridization (CARD-FISH) to investigate and visualize the microbial communities in this environment. Although the sediments are highly disturbed by natural and anthropogenic activities at the port area, several geochemical proxies indicated the presence of recent and paleo-redox changes along the sediment cores. Congruent with the existence of a seep microbiome, a distinct microbial community shift was observed in deeper sediment horizons (25-35cm below seafloor). The archaeal community from surface sediments was characterized by Bathyarchaeia and the recently discovered, Woesarchaeota, whose metabolic potential is possible consistent with methanogenesis in hypoxic surface marine sediments. By contrast, in the deeper layer with methane as the dominant hydrocarbon, strictly anaerobic methane oxidation is likely the main process controlled by the governance of the clade of ANME-2c in conjunction with the presence of ethane and butane oxidizers. In the same depth, bacterial communities are characterized by the presence of Parcubacteria (Candidatus Moranbacteria). The latter coincides with the anoxic environment of the sediments but it differs from the typical governance of the sulfate reducing bacteria that were expected. Slight decrease of sulfate, formation of free sulfide and the presence of aggregates consisted of ANME-2c indicate the predominance of sulfate-coupled AOM in these anoxic shallow marine sediments.
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    Open Access
    Geographical reconstrustion of the area of the ancient harbour of Lechaion using marine geophysical methods
    Γκριμπούλη, Μαρία-Αφροδίτη; Παπαθεοδώρου, Γεώργιος; Παπαθεοδώρου, Γεώργιος; Γεραγά, Μαρία; Καλαιτζίδης, Σταύρος; Gkrimpouli, Maria-Afroditi
    The Gulf of Corinth is the second most active continental rift in the world and thus a much-studied natural laboratory for analyzing details of rift history. The Gulf of Lechaion sited S-E of the Corinth Gulf is the least studied area of the active Corinth graben. Although, the study of the Lechaion Gulf renders great importance as its formation is estimated to constitute an early rifting stage, where the evolution of the Corinth Gulf started. Therefore, more offshore seismic surveys combined with the already acquired data in this least studied part, will shed light to the tectono- sedimentary evolution of the eastern end of the Corinth rift. Besides the geological importance, Lechaion Gulf hosts the ancient harbour of Lechaion, which is of great archaeological significance and was built at 600BC, a period of zenith for ancient Corinth when its military and naval activities flourished. The coastal installations of the ancient harbor are still visible today, though part of them are partly or completely submerged due to the glacio- eustatic and tectonic movements in the area during Quaternary. The present thesis aims to the reconstruction of the coastal palaeoenvironment of the ancient harbour of Lechaion and the recent geological activities nearby the submerged installations through the interpretation of the seismic stratigraphy and the seafloor morphology data. The survey was conductedin three sessions, at November 2013, 2014 and 2015 and the data were collected with high frequency 3.5 kHz Pinger type subbotom profiler, where an area of 8,5 km2was scanned and 146 routes with 145,4 km length of seismic data were collected, reaching a maximum depth of 60m below the sea surface. The seismic profiles were then processed with specialized programs at the Laboratory of Marine Geology and Physical Oceanography. The digital process enabled the design of bathymetric maps, isopach maps and also 3D models depicting the marine geomorphology around the harbor area and the sediment distribution near the ancient installations. The composition and processing of all these seismic data enabled the estimation of the chrono- stratigraphy, paleo- morphology and geological regime of the ancient harbour of Lechaion.
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    IODP-expedition 381, site 79A. Palaeoceanographic evolution of the Corinth gulf during the MIS5, based on the downhole distribution of foraminiferal assemblages
    Αντωνίου, Δήμητρα; Γεραγά, Μαρία; Παπαθεωδόρου, Γεώργιος; Σακελλαρίου, Δημήτριος; Antoniou, Dimitra
    As an early continental rift with high strain rates, the Gulf of Corinth has mainly attracted many geoscientists due to its preservation of the synrift succession both onshore and offshore. This feature was recognized by the International Ocean Discovery Program (IODP) when marine scientists proposed Corinth Gulf as a study area in European Consortium for Ocean Research Drilling during the program “Exploring the Earth under the sea”. One of the expedition objectives was the generation of a new high-resolution record of the Quaternary paleoclimate. Throughout this expedition three different sites (Site M0078, M0079, M0080) in the Corinth Gulf were drilled, cored and logged. After this phase, the holes were submitted to many and different methods and techniques whereby new data and information for lithostratigraphy, structural geology, geochemistry and micropaleontology of the sediments were arisen. Regarding the micropaleontology, preliminary results of the holes showed that there were temporal intervals when Gulf of Corinth was connected with the open sea and isolated from it. To reinforce the previous results, in the terms of the master thesis, 58 sediment samples from hole M0079 studied in 125μm and 63μm fractions for the existence of planktonic and benthic foraminifers. The present master thesis aims to study the environmental conditions which contributed to the formation of Corinth Gulf throughout the SU3 deposition (149.2-183.87 mbsf; meter below sea floor) and the upper part of SU4 (186.37-201.01 mbsf). The distribution of foraminifers during the deposition of SU3 sediments shows a high variety and quantity of planktonic and benthic foraminifers with the former be more abundant. Below SU3, foraminifers are significantly decreased. These results in conjunction with the curves of global sea-level fluctuations signify that during SU3 deposition the distribution of planktonic foraminifers along the hole coincides with the substages of Marine Isotope Stage 5 (5a, b, c, d, e) when the rift was connected with the open sea. Finally, the transition from the SU3 to SU4 is characterized by the rapid depletion of foraminifers indicating the onset of MIS 6 when the rift was an isolated/semi-isolated environment.
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    Foraminiferal analysis of marine sediments from the last interglacial period. IODP expedition 381, Corinth gulf
    Καστανά, Αικατερίνη; Kastana, Aikaterini
    This thesis examines the benthic foraminifera composition in specific sedimentary intervals from the core M0079 recovered from the Corinth rift in the framework of IODP Expedition 381. These intervals are parts of the lithostratigraphic subunit 1.3 (LSU 1.3) deposited from 154.47 mbsf to 179.8 mbsf. LSU 1.3 appears to coincide broadly with the prevalence of MIS 5 which is dated between 75 ka and 122 ka. The aim of this work is to assess the variation of the seafloor environmental conditions of the Corinth gulf within this period.