Τμήμα Γεωλογίας (ΔΔ)

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Open Access
Assessment of clayey raw material suitability for ceramic production in Northern Peloponnese : an archaeometric approach
Ξανθοπούλου, Βάια; Ηλιόπουλος, Ιωάννης; Montana, Giuseppe; Hein, Anno; Λυριτζής, Ιωάννης; Παπούλης, Δημήτριος; Αβραμίδης, Παύλος; Braekmans, Dennis; Xanthopoulou, Vayia
Τμήμα Γεωλογίας (ΔΔ)
The aim of this study is to examine possible sources of clayey raw materials, outcropping in the territory of the northern Peloponnese, which were potentially used for ceramic production during antiquity and also to provide a detailed characterization and comparison as to their compositional and technological properties. This was accomplished by the systematic sampling of Holocene, Plio-Pleistocene and Pliocene clayey raw materials (59 samples) from a wide area (31 sites) spanning all over the northern Peloponnese, extending from the region of Aigialeia (northwestern) to the region of Corinth (northeastern). In the case of the ceramic material, our selection was constrained by the recent important discoveries in the site of ancient Helike. The Early Bronze Age material unearthed therein highlights its significant role since then and possibly indicates one of the earliest ceramic productions attested in the area. Coeval archaeological sites do also exist in proximity to Ancient Helike, such as Aigion, or further to the East, such as Ancient Aigeira and Derveni. The ceramic analysis aims to provide a characterization mean for their comparison with the clayey raw materials sampled throughout the area and will help us unveil the early ceramic technology in the area and to make provenance inferences. In order to identify clay materials behavior during firing conditions and to access the eventual mineral phase transformations and use them subsequently as a mean for comparison with the archaeological ceramics, experimental briquettes from the studied raw material were manufactured. The experimental briquettes were fired at three temperatures 700, 900 and 1050oC under oxidizing conditions. In an attempt to characterize fully the raw materials, the experimental briquettes and the ancient ceramics, the integrated approach by using a series of analytical techniques, such as optical microscopy, scanning electron microscopy, cathodoluminescence, thermal analysis and geochemical analyses was indispensable. Clayey raw materials were further examined in terms of technological and physical properties, such as plasticity, grain size distribution and activity. The interpretation and elaboration of the whole data led us to the characterization of the raw materials as calcareous and calcareous-dolomitic clayey sediments and siliceous (only 2 samples). According to their clay minerals content and based on the sampling location were characterized as; Achaean samples: Illitic-chloritic and illitic-chloritic with mixed-phases presence; Corinthian samples: illitic and less chloritic with mixed-phases presence; Xylokastro samples: illitic and less chloritic and smectite with mixed-phases presence. Geochemical analyses revealed no compositional differentiation revealed among the various areas whereas the REE study suggests possible similar sources of origin. Plasticity results allowed us to characterize the studied materials as low and/or moderate plastic materials or silts of low plasticity, a fact that comes in in accordance with the low content of clay fraction and the abundant presence of illite. These data enabled us to infer that they cannot be used untreated as proper ceramic raw materials, but they may be used for large vessels or roofing tiles. Experimental briquettes showed that calcareous fine group and siliceous group resist over time, whereas the experimental briquettes of the calcareous coarse samples collapsed. The archaeometric approach led us to identify 5 main petrographic groups and various small groups and eventually infer about their local provenance. Furthermore the obtained data helps us to unveil the ancient technological processes i.e. levigation or sieving; the technique of tempering (rock fragments or/and grog). The aplastic inclusions as well as the composition (in terms of calcium content) of the clay paste were related with the local lithology, apart from a significant number of the ceramic samples, which even though contained the same inclusions encountered in the rest of the samples, they showed a different composition (non-calcareous). As far as it concerns the firing choices, it is observed the application of low firing temperature through open fires for the large vessels, whereas a wide range of firing temperatures was chosen in the case of tableware. The extensive number of the small groups and loners suggested the household production. We deduced that Helike potters used the same clayey raw material source for about half of the studies samples, but the query raised was about the source of those ceramic samples with the different composition. The characterization of the raw materials showed only one sampling location as potential source for those ceramics and close to Helike site. Another assumption is that the non-calcareous source was possibly depleted through time (naturally or by human activities). In summary the technological features of Helike pottery revealed a skillful pottery craftsmanship in Helike settlement, the existence of different workshops wherein were using different technology and different recipes.
Open Access
Assessment of marine litter in the Eastern Mediterranean Sea : a multi-perspective approach
Ιωακειμίδης, Χρήστος; Παπαθεοδώρου, Γεώργιος; Καραπαναγιώτη, Χρυσή; Ζέρη, Χριστίνα; Galgani, Francois; Παπαθανασίου, Ευάγγελος; Κουτσικόπουλος, Κωνσταντίνος; Γεραγά, Μαρία; Ioakeimidis, Christos
Τμήμα Γεωλογίας (ΔΔ)
Το θαλάσσιο περιβάλλον είναι άμεσα συνδεδεμένο με την ανθρώπινη ζωή, αποτελώντας βασικό συστατικό του πλανήτη σε ποσοστό περίπου 72%. Η υγιή κατάσταση των ωκεανών ήταν πάντα σημαντική για την ανθρωπότητα μιας και όλα τα είδη ζωής, συμπεριλαμβανομένης και της ανθρώπινης, εξαρτάται από αυτούς. Τα θαλάσσια απορρίμματα αποτελούν μια από τις σημαντικότερες απειλές για το θαλάσσιο περιβάλλον και τα οποία σήμερα συναντώνται παντού στο παγκόσμιο θαλάσσιο περιβάλλον. Τα θαλάσσια απορρίμματα ερευνήθηκαν στο υποθαλάσσιο περιβάλλον επιλεγμένων περιοχών στην Ανατολική Μεσόγειο (Ελλάδα, Κύπρος) και Μαύρη Θάλασσα (Ρουμανία). Διαφορετικές μέθοδοι δειγματοληψίας χρησιμοποιήθηκαν, ήτοι ερευνητική και εμπορική τράτα βυθού και υποβρύχια τηλεχειριζόμενα οχήματα (ROV). Ακολούθως έγινε σύγκριση των διαφορετικών μεθοδολογιών όπου αυτό ήταν δυνατό. Η αφθονία, η σύνθεση, η χωρική κατανομή και η κατανομή μεγέθους μελετήθηκαν, ενώ εντοπίστηκαν και οι αντίστοιχες πηγές. Πρωτότυποι χάρτες δημιουργήθηκαν για κάθε μια περιοχή μελέτης ξεχωριστά, στους οποίους απεικονίστηκαν οπτικά η αφθονία μαζί με τη χωρική κατανομή των θαλάσσιων απορριμμάτων. Επίσης, η παραγοντική στατιστική ανάλυση χρησιμοποιήθηκε προκειμένου να συγκεκριμενοποιηθούν οι πηγές των θαλάσσιων απορριμμάτων. Η πλειοψηφία των καταγεγραμμένων θαλάσσιων απορριμμάτων αποτελείτο από πλαστικά, εκ των οποίων τα πλαστικά μπουκάλια βρέθηκαν να απαντώνται σε σημαντικό ποσοστό. Η περιβαλλοντική αλλοίωση μπουκαλιών από πλαστικό PET (τερεφθαλικό πολυαιθυλένιο) τα οποία βρέθηκαν στο υποθαλάσσιο περιβάλλον ερευνήθηκε. Μια χρονική ένδειξη χρησιμοποιήθηκε ως ενδεικτικό των χρόνων απόρριψης των μπουκαλιών στο περιβάλλον. Τα πλαστικά μπουκάλια φαίνεται να παραμένουν στιβαρά για περίπου μια δεκαετία. Κατόπιν, η αλλοίωση των εγγενών λειτουργικών ομάδων φαίνεται να είναι σημαντική. Μερικές εξαφανίζονται ή νέες – όχι τυπικές των PET – δημιουργούνται. Είναι η πρώτη φορά που αντίστοιχη μελέτη πραγματοποιείται με δείγματα τα οποία έχουν αλλοιωθεί στο θαλάσσιο περιβάλλον. Επιπλέον, ερευνήθηκε η επίδραση των θαλάσσιων απορριμμάτων στη θαλάσσια βιοποικιλότητα. Εννέα διαφορετικά Μεσογειακά είδη ψαριών τα οποία ζουν σε διαφορετικά θαλάσσια ενδιαιτήματα ερευνήθηκαν σχετικά με την παρουσία σωματιδίων θαλάσσιων απορριμμάτων αποδιδόμενα σε κατάποση. Δεν βρέθηκε σημαντική παρουσία σωματιδίων θαλάσσιων απορριμμάτων. Τέλος, η κοινωνική αντίληψη και το κόστος των πολιτών για τα θαλάσσια απορρίμματα διερευνήθηκε χρησιμοποιώντας ένα πρωτότυπο πείραμα διακριτής επιλογής (DCE).
Open Access
The contribution of geophysics in the location of prehistoric settlements in Greece
(2010-07-14T05:48:54Z) Dogan, Meliha; Papamarinopoulos, Stavros; Papamarinopoulos, Stavros; Koukis, G.; Ferentinos, G.; Tsokas, G.; Lambrakis, N.; Karali, L.; Papadopoulos, T.
Τμήμα Γεωλογίας (ΔΔ)
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Open Access
Development of a system to access the earthquake damage potential for buildings : intensionmeter
(2008-11-11T11:20:08Z) Laurentiu, Danciu; Τσελέντης, Γεράσιμος; Τσελέντης, Γεράσιμος; Καρύδης, Παναγιώτης; Grecu, Vasile
Τμήμα Γεωλογίας (ΔΔ)
An earthquake damage warning system –called Intensiometer- has been proposed as a low cost alternative to the widely used traditional earthquake warnbased system. The rapid evaluation of integrated circuits, sensor and microcontrollers technologies over the last decades, as well as the reducing price and size, would make possible the development of such a low cost earthquake damage warning system. The most important improvement of the proposed system is the insertion of a new ground motion parameter CAV5 - cumulative absolute velocity after application of 5 cm/ sec2 threshold acceleration. In the present study, based on the relationship ground motion-damage, CAV5 have been found to be suitable parameter to describe the damage potential of a ground motion. The damage warning system was developed to quantify and report the earthquake intensity, with the aim of an Engineering Intensity Scale (EIS). Engineering Intensity Scale has been constructed based on the relationship between CAV5 parameter and Modified Mercalli Intensity (MMI) scale and embedded into the damage warning device. The Intensiometer has been developed to analyze the three components of an earthquake record and to trigger only the event of a damaging earthquake, typically MMI VI or greater. The Intensiometer is not triggered by smaller, non-damaging earthquakes or other sources of vibration such as vehicles, and construction equipment. Two were the aims of this research study. One was to detect an appropriate ground motion parameter capable to describe the damage potential of a ground motion. The second one was to incorporate the selected parameter into a damage warning system to minimize the hazards of catastrophic ground motion. The benefits of developing a damage potential warning system are multiple, including site specific applications, building automation strategy, shut off gas and water valves damage, shut down industrial processes, lock/unlock electronic doors, control elevators, protect assets and supplies, as well as a low-cost single user approach, such as for a typical homeowner.
Open Access
Fluid seepage on shore and offshore Western Greece
Κορδέλλα, Σταυρούλα; Kordella, Stavroula
Τμήμα Γεωλογίας (ΔΔ)
The present thesis is an integrated geological, geochemical, and oceanographic study of the environmental impact of hydrocarbon rich fluid seepage occurring in two areas located in Western Greece, Katakolo Bay and Amvrakikos Gulf. Western Greece is particularly affected by hydrocarbon seepage processes related to the presence of underground oil and gas reservoirs. The seepage is just the natural, upward migration of fluids from these reservoirs. Environmental impacts of hydrocarbon rich fluid seepage include:(a)the emission of greenhouse gases to the atmosphere, (b)hypoxia in aquatic systems(c)degradation of geotechnical properties of ground, soil, and sediments and,(d)geohazard due to explosiveness and toxicity of gas.This work is focused on points (a), (b) and (c).(a)Methane (CH4), the primary component of natural gas, is a powerful greenhouse gas and its seepage to the surface is an important natural source of greenhouse gas for the atmosphere. The seepage may occur on land (on shore) or in the marine environment (offshore), always associated to the presence of tectonic faults, as documented in this work. Measuring the flux of methane (generally expressed in mg m-2 per day, or tonnes per day) is the key task for addressing its atmospheric impact.(b)Hypoxia (i.e., oxygen depletion) in aquatic environments is an important environmental phenomenon with strong implications for life and its biodiversity, and as a result, aquatic ecosystem goods and services. Well oxygenated water bodies result from a fragile balance between production, transport and consumption. Hypoxia can be induced by natural and anthropogenic factors, such as water circulation, high water temperature, stratification of the water column, and anthropogenic pressures such as pollution. Hydrocarbon seepage is an additional natural factor that is yet poorly studied; it is known in theory that oxygen dissolved in water is consumed to oxidize methane released from the seabed. Knowing the conditions that regulate this process is still elusive. (c)Pockmarks are cone shaped deep depressions that are the result of erosion/degradation of the marine sediments caused by escaping fluids from below the seafloor (Amfilochia Bay in this thesis). Pockmarks constitute evidence that may illustrate and justify submarine fluid flow. On land gas seepage may be the cause of degradation of ground conditions, such as asphalt deformation and cracking. This occurs because the asphalt and concrete pavement over a seepage site (Katakolo Harbour in this thesis) acts as a cap for gas that gradually accumulates below. When the gas pressure increases the asphalt and concrete may swell and crack. In this study gas emission and hypoxia are investigated through geochemical and oceanographic methods, also using modern instrumentation such as benthic observatories. Katakolo Bay and Amvrakikos Gulf represent two different environments, hosting different type of seepage, geology, and seawater current circulation: Katakolo Bay is an open sea environment, but it includes a semi-enclosed harbor area where water circulation is limited. Amvrakikos Gulf is a naturally semi-enclosed basin receiving limited input from the open sea. The specific objectives of this study were: •Assessment of seepage distribution in the two studied areas•Estimate overall emission of methane into the atmosphere•Monitor over time oxygen concentration in seawater in relation to seepage•Determine the mechanism of hypoxia evolution due to seepageThe thesis is divided in two parts: -theoretical evaluation, describing general theory of hydrocarbon seepage and its environmental impact, with specific reference to hypoxia in seawater;-experimental study reporting original, experimental data, some of them acquired in the framework of an EU funded project, HYPOX. The data include marine geophysical data, methane flux from the ground and from the seawater/seabed, methane and oxygen concentration in seawater from areal surveys and from a temporal monitoring in a selected site within Katakolo Port. A descriptive model of the seepage/hypoxia relationship is provided for the first time and can be used to study hypoxia in other marine environments.
Open Access
Genesis, evolution and economic significance of the northern and the eastern parts of Karapınar-Ayrancı coal deposit
(2016-07-25) Oskay, Rıza Görkem; Χρηστάνης, Κίμων; Κοντόπουλος, Νίκος; Γεωργακόπουλος, Ανδρέας; Βαρνάβας, Σωτήριος; Παπούλης, Δημήτριος; Ιορδανίδης, Ανδρέας; Καλαϊτζίδης, Σταύρος
Τμήμα Γεωλογίας (ΔΔ)
During the last two decades electric power demand in Turkey is steadily increasing. As total installed capacity is being insufficient for covering the increasing demand, several new power plants fed with imported natural gas are being installed that increased the dependence of the country on imported resources. In this sense domestic coal, particularly this of low rank, is becoming important for the country to decrease the dependence on imported resources. Total coal reserves of Turkey amount to ~13 Gt with low-rank coals (i.e. lignite and sub-bituminous) sharing the greatest part. Karapınar-Ayrancı coal deposit is recently explored and proved being very important due to both its large reserves (1.8 Gt) and the geographical location in south central Turkey. There are plans to exploit the coal for power generation; therefore, determination of its potential environmental impacts and technical problems to be caused by coal is essential. The aim of the present study is to identify the palaeoenvironmental conditions during peat accumulation in the eastern and northern parts of Karapınar-Ayrancı coal deposit; furthermore, the potential environmental impacts from future coal mining and utilization, as well as potential technical problems from coal burning are assessed and measures are proposed. Several (coal and intercalating inorganic sediment) samples were picked up from cores obtained from the eastern and the northern parts of the deposit during the final exploration stages. The samples were analysed for mainly their petrological, mineralogical and geochemical features. Coal seam displays total thickness varying from 12.05 to 40.20 m with cumulative thickness of coal layers ranging from 2.00 to 9.10 m. The inorganic intercalations consist mainly of claystone, mudstone and marl, whereas the coal layers contain several mollusc-bearing layers. Matrix lithotype is the most common along with the mineral-rich one; char-rich lithotype is observed in the eastern part of the deposit only. The coal displays high ash yield (37.5 wt.%, on dry basis), and high contents in volatile matter (avg. 53.1 wt.%, on dry, ash-free basis), total sulphur (avg. 8.6%, on dry, ash-free basis) and hydrogen (avg. 6.8%, on dry, ash-free basis); its calorific value is low (avg. 11.71 MJ/kg, on moist, ash-free basis); it is a low-grade, low-rank coal (lignite). Huminite is the dominant maceral group in both parts of the deposit, whereas liptinite and inertinite display variable concentrations. In the northern part inertinite has generally lower values than in the eastern part. Telohuminite and detrohuminite are the most common huminite subgroups. Inertodetrinite and fusinite are the most common inertinite macerals. Liptinite is mostly represented by liptodetrinite and resinite (fluorinite type). X-ray diffractometry was performed on coal, inorganic sediments and coal ash residues produced after combustion at 750°C. Silicate minerals proved being common in coal; quartz is contained in all coal samples, whereas clay minerals, mica and feldspar show variable concentrations. Sulphur-bearing minerals are presented by sulphates and sulphides in coal. Bassanite is common and gypsum rare, whereas pyrite is the only sulphide contained mostly as minor phase. Carbonate is rarely detected in mollusc-bearing samples only. Halite is contained in coal from eastern part of the deposit. Inorganic samples display similar mineral composition, with the exception of carbonate minerals being dominant phases. Aluminosilicates and Ca-Mg silicates are dominant phases in the coal ash residues; oxides, sulphates (mostly anhydrite) and carbonate minerals (mostly dolomite) are usually contained as minor phases. The predominance of silicates can be explained by reaction of oxides with silicate melt or solid-phase reactions during ashing. Elemental composition of coal from both parts of the deposit shows slight variations due to different geological background and position within the palaeomire. Nevertheless, Al and Fe proved to be major elements (1.18% and 0.48%, respectively). From the remaining the following elements have been determined: As, B, Ba, Be, Bi, Cd, Cs, Co, Cr, Cs, Cu, F, Ga, Ge, Li, Mn, Mo, Ni, Pb, Rb, Re, Sr, Ti, U, V, W, Zn, and Zr. Most of these show intermediate affiliation; however, their mode of occurrence is variable from site to site in the deposit. In the northern part most elements are mostly affiliated with inorganic matter (mostly clastic-aluminosilicate minerals), whereas intermediate affiliation is more common in eastern part. Coal facies indices and lithological features of coal seam suggest that peat was accumulating under pure telmatic to limnotelmatic conditions; however, peat accumulation was ceased several times by water-level rising. Therefore, clastic (e.g. quartz, clay minerals) and authigenic (e.g. pyrite) mineral concentrations are variable. Similar trends are also obvious from elemental composition. High total sulphur, evaporite mineral (e.g. halite) and boron contents point to brackish-saline conditions during peat accumulation; however, high sulphur contents can be related to alkaline conditions. The presence of gastropod fragments along with silica-gel cavity infillings indicates alkaline conditions too. These can be related with a sulphate-rich karstic aquifer, which contributed to palaeomire water supply. Boron and chloride ions can be easily mobilised by circulating fluids within coal, thus, enriching it. Nevertheless, gathered gastropod and ostracod fauna also points to freshwater conditions. All these point out that in the studied parts of the deposit peat accumulated under mesotrophic conditions and the palaeomire was supplied by sulphate-rich, neutral to alkaline groundwater. The total geological reserves of entire Karapınar-Ayrancı deposit and the low calorific values of coal make it suitable as a feeding coal in power plants. On the other hand, the mineralogical and elemental compositions of the coal layers in the studied parts of the deposit could cause environmental impacts (e.g. acid mine drainage, hazardous and toxic gas emissions) and technical problems (e.g. corrosion, slagging) in the boilers of future power plants. These problems can be reduced applying proper coal beneficiation and flue gas control. Simple coal washing tests show some coal quality improvement. Thus, several further studies are essential before final decision on coal utilization and installation of power plants. Beyond these handicaps, Karapınar-Ayrancı coal’s exploitation might have great socio-economic importance at local, regional and national levels.
Open Access
Holocene environmental evolution and climate variability inferred from multi-proxy coastal sediment records of southern Greece
Εμμανουηλίδης, Αλέξανδρος; Emmanouilidis, Alexandros
Τμήμα Γεωλογίας (ΔΔ)
This thesis presents a multi-proxy reconstruction from 5 different coastal wetlands of southern Greece spanning in the Holocene period and an in-depth review and application of non-destructive systems (CT scanning, X-ray Fluorescence) in paleoenvironmental research. During this thesis, the acquired dataset used consisted of a) X-ray Fluorescence scanning (XRF), b) Computed Tomography (CT) scanning, c) Stable isotopes δ18O and δ13C, d) micropaleontology (foraminifera, ostracods, diatoms, pollen), e) mineralogical analysis, and f) standard sedimentological techniques (grain size, magnetic susceptibility (MS), Total Organic Carbon (TOC), carbonates content). The chronological framework for the sediment cores was established through 14C radiocarbon dating. The wetlands studied are Aliki salt pond (NE Gulf of Corinth), Klisova lagoon (SW Greece), lake Vouliagmeni (E Gulf of Corinth), Agoulinitsa marsh field (W Peloponnese) and Pappas lagoon (NW Peloponnese). The sites form an EW transect of southern Greece, an area with high climatic and environmental spatial variability, whereas human occupancy on all areas is recorded from antiquity. Non-destructive, high-resolution techniques used in this thesis have been established as standard in the last decades and have been a great asset in geosciences. Computed Tomography (CT) was conducted in lake Vouliagmeni, Agoulinitsa marsh and Pappas lagoon cores. In contrast, XRF was performed on all core sections except for Pappas lagoon core, where the high assemblage of bivalve shells could lead to bias of Ca. The fundamental parameter behind CT analysis is the Hounsfield units that reflect relative density variations in the sediment. Correlation between HU values and heavy elements like Zr has been detected in all cores, whereas distinct sedimentological facies were recorded according to HU variations. In Agoulinitsa and Pappas lagoon, microstructural characteristics like shells/sediment ratio and root remnants were examined through 3D sections, in which HU boundaries were set accordingly. Lake Vouliagmeni sediment core was characterized by extreme stratigraphic variations with lamination structures alternating with homogenous deposits and event layers. Laminae thickness and boundaries were recorded through 3D rendered volumes with HU boundaries. Micro CT scanning and thin section analysis was also performed to cross-check possible variations. Event sedimentation layers were distinguished through the combined use of CT scanning, XRF and MS, with layers responding to increased HU, MS and Mn values. Statistical assessment of elemental distribution and HU revealed 3 different clusters. Cluster A responded to sedimentation during enhanced evaporation in the area, Cluster B emulated sedimentation during increased chemical weathering in the catchment, and Cluster C reflected the homogenous deposits. Aliki salt pond is located in a highly tectonic region, at the northeast part of the Gulf of Corinth in Greece. Beachrock deposits that form a barrier between the salt pond and the marine environment play an essential role in the evolution of the area. The chronological framework was set at ca. 3100 cal BP by four 14C radiocarbon dates and the established evolutionary model indicate four different changes taking place during this period in the study area. From around 3100 to 1600 cal BP, a transition from a closed to an open lagoonal environment, was identified, interrupted by a terrestrial fluvial deposit at ca. 2500 cal BP. A shift toward a closed lagoonal system at around 1600 cal BP and the establishment of a salt pond environment seem to correlate with tectonic activity. The study provides important information about the evolution of the coastal landscape in such an active tectonic region and points the interaction between regional human activity and climatic changes during the late-Holocene period. Klisova lagoon is located in the eastern part of Messolonghi-Etoliko wetland, the biggest lagoonal complex of Greece and an area of great environmental interest. For the last 4700 cal BP, the freshwater 1 influx, the progradation of the Evinos river delta and related geomorphological changes control the environmental conditions (e.g. depth and salinity) in the lagoon system. Considering the centennial temporal resolution of our analyses, small offsets of c.a. 50 years due to the lack of regional reservoir correction do not impact the reported radiocarbon ages considerably. Prior to 4000 cal BP, a relatively shallow water depth, significant terrestrial/freshwater input and increased weathering in the lagoon area are inferred. Elemental proxies and increased dinoflagellate and foraminifera abundances, which indicate marine conditions with prominent freshwater influxes, point to the gradual deepening of the lagoon recorded at the drilling site up to 2000 cal BP. The marine and freshwater conditions equilibrium sets at 1300 cal BP, and the lagoonal system seems to reach its present state. Maxima of anthropogenic pollen indicators during the Mycenaean (3200 cal BP), Hellenistic (2200 cal BP) and Late Byzantine (800 cal BP) periods suggest intervals of increased anthropogenic activities in the study area. Lake Vouliagmeni is subjected to intense climatically and tectonic forces, causing stratigraphic variations, with laminated sediments frequently interrupted by homogenous and event sedimentation deposits. Lamination couplets consist of aragonite layers alternating with detrital and organic residues and form during periods of seawater intrusion and stratification of the lake water. The discontinuous occurrence of laminated deposits excludes a varve based chronology from being established but still highlights the susceptibility of the lake to record environmental and climatically driven changes. Our synthesis model for regional climatic reconstruction and local environmental changes derives from δ18O and δ13C data from the laminated and homogenous sediments studied separately depending on the dominant carbonate mineral. This is further strengthened by high-resolution geochemical proxies, diatom and sedimentological data. Regional climatic trajectories from key sites and possible links to the lake Vouliagmeni record are explored in response to atmospheric circulation patterns variations. Phases of overall humid conditions are recorded by the increased inflow of siliciclastic material in the lake and negative δ18Obulk values. In contrast, periods of marine intrusion and enhanced evaporation are recorded by aragonite precipitation, increased δ18OAr values and laminations. The driving mechanism behind laminae formation seems to be marine intrusions, leading to pycnocline stabilization and increased evaporation of lake surface waters during summer months. Climatic oscillations recorded during the Holocene, apart from their duration, do not exceed events of the last millennia.
Open Access
Hydrological study of evapotranspiration types (ETo, ETa, MODIS ET) for Peloponnese (Greece) during 2016-2019, employing remote-sensed and meteorological stations’ data in GIS models, and pan evaporation measurements
Δημητριάδου, Σταυρούλα; Dimitriadou, Stavroula
Τμήμα Γεωλογίας (ΔΔ)
The present dissertation develops 14 GIS models, of which 10 models to implement six empirical and physical-based methods for the estimation of Reference Evapotranspiration (ETo) and Actual Evapotranspiration (ETa) and 4 models implementing statistical measures. Specifically, FAO-56 Penman–Monteith (FAO PM), Hargreaves–Samani (HS) and Hansen, with the former used as a reference, were the methods selected for ETo estimation and Turc, Turc modified and Coutagne were the methods selected for ETa estimation. The study area is Peloponnese, Greece, a suitable Mediterranean testbed with substantial changes of relief over short distances. The study period is years 2016-2019 which constitute four out of the five warmest years since pre-industrial era. For the same period, pan evaporation (Epan) measurements in daily step of two Class-A pan stations in Peloponnese (Patras University at the northmost edge and Ladonas lake at the central part) with different environmental conditions were collected and intercomparisons were made. Moreover, 304 MODIS products have been processed and used in the research. Specifically, 200 images of a global remote-sensed product which estimates actual ET, MODIS net ET (184 images), and MODIS potential ET (ETp; 16 images) were derived (as 8-day composites) and processed for different time scales to detect similarities and differences with the aforementioned ET types. In addition, 104 MODIS LST day and night products have served as inputs to models, in particular, 96 monthly scale and 8 annual scale. Besides the intercomparisons of ET types for an interesting testbed, another novelty of the dissertation is that all the six applied methods and the three most reliable statistical indices for ET studies were implemented after developing GIS models in ArcMap model builder environment and as python scripts. The models of empirical methods include all the stages of pre-procession and the intermediate steps and the inputs are images in raster format. Thus, the output (ETo or ETa) is a useful map for the study area. For the statistical analyses three models implementing statistical indices (RMSD, MB, NMB). Specifically, approximately the same pattern was followed for ETo and ETa investigation. For the first parameter, to investigate the variability in the daily mean reference evapotranspiration (ETo) for the months December and August during 2016–2019, as representative winter and summer months according to availability and qualitative criteria of the data. Furthermore, to investigate the agreement between the three methods’ ETo estimates, and then to examine the former along with MODIS ET (daily) averaged products and daily Epan values. For the second case annual ETa estimates by the three empirical methods were examined along with annual MODIS ET and annual Epan values.The inputs of the models were ground-based and remote-sensed data. Meteorological data from sixty-two stations (over or adjacent to Peloponnese) under the National Observatory of Athens (NOA), MODIS Terra LST day and night products, and MODIS net ET products (8-day composites) have been employed. The parameter differentiating FAO PM from the temperature-based Hansen and Hargreaves-Samani methods was wind speed. The method depicts interactions among climate parameters (T, evaporative demand and water availability) in the frame of climate change. The years 2016–2019 are four of the warmest since the preindustrial era. Hargreaves–Samani’s estimations for the month December of 2016–2019 were almost identical to MODIS ET, despite their different physical meaning. As expected, for month August, there were considerable discrepancies between the three methods’ and MODIS’s estimates, attributed to the higher evaporative demand in the summertime. Thus H-S could serve as an alternative to MODIS ET for month December of years 2016-2019 for Peloponnese. The latter needs further investigation to find out if this is the case for other winter months. Turc method’s outcomes resemble MODIS ET ranges for all years, followed by Coutagne. Estimates by Turc modified, were almost identical to those of MODIS ET. Moreover, unpaired Student T-test has been performed between each empirical method and MODIS ET which verified that the outcomes were statistically significant (p ≤ 0.05) and exhibited low effect size according to Cohen’s D value (< 0,24). Therefore, Turc modified could be used as an alternative to MODIS ET for Peloponnese for years 2016-2019. Their discrepancies are attributed to the uncertainty which MODIS ET involves as a global product. The GIS models were proved accurate, reliable, time-saving, and they are adjustable to any study area. Moreover, Epan for Patras University station (semi-urban, low-elevation) exhibits an upward trend which resembles FAO PM trend through study-years and the same pan coefficients were determined for both December and August of each year which is an indication of consistency that needs further investigation. In contrast, Epan of Ladonas station (lakeside, higher elevation) is more complex. Therefore, pan coefficients based on FAO PM substantially vary and require investigation on monthly time scale. Additionally, the gradual decrease in days of Ladonas pan-water icing could imply undergoing decrease in snowpack-storage retention over the mountains of Peloponnese.
Open Access
Landslide monitoring using remote sensing, GNSS, GIS methods and interferometric techniques
Κυρίου, Αγγελική; Kyriou, Aggeliki
Τμήμα Γεωλογίας (ΔΔ)
Landslides constitute one of the most widespread natural disasters with severe and devastating consequences for both human beings and the environment worldwide. In the upcoming years more, and more landslides are expected and thus researchers are trying to develop methodologies, practices and plans towards ensuring safety and reducing risk. The enormous progress and diversity of remote sensing technologies has significantly enhanced scientific capabilities for landslide mapping and monitoring. The specific thesis aims to provide knowledge regarding landslide mapping and monitoring using low cost remote sensing data, Global Navigation Satellite System (GNSS) measurements and GIS methods. In that context, a variety of different remote sensing data, including Synthetic Aperture Radar (SAR) imagery, multispectral imagery, Unmanned Aerial Vehicles (UAV) imagery, Terrestrial Laser Scanning (TLS) point clouds were obtained and processed appropriately. Remote sensing data were supported by the execution of GNSS measurements, while multiple GIS methods were implemented. Four areas of instability with diverse characteristics (area, topography, lithology, mechanism of failure etc.) were selected as case studies. A different combination of remote sensing data was selected for each case study in order to identify the most appropriate type for landslide mapping and monitoring. The assessment of the results revealed that a multidisciplinary use of various remote sensing data and techniques could contribute to a more comprehensive landslide investigation. Moreover, an attempt for the establishment of a guide on the proper selection of remote sensing data in accordance to the characteristics of the landslide (size, volume, topography etc.) was carried out.
Embargo
Magmatic and post-magmatic processes recorded in Cr-PGE ores and mantle peridotites, Chalkidiki ophiolites, Greece : a mineralogical, geochemical and petrological investigation
(2023-03-01) Σιδερίδης, Αλκιβιάδης; Sideridis, Alkiviadis
Τμήμα Γεωλογίας (ΔΔ)
Along the Chalkidiki peninsula there are two separate ophiolite zones, the West and the East Chalkidiki, both comprise of well exposed mantle sections which host podiform chromitite bodies. The West Chalkidiki (occurrences of Vavdos and Gerakini-Ormylia) comprises a highly depleted mantle section, which, based on the present research, consists of highly depleted harzburgite, transitional to dunite harzburgite, massive dunite and Cr-rich chromitite - dunite envelope assemblages. Using the chemistry of magnesiochromite hosted within the Cr-rich chromitite, the calculated parental melts demonstrate boninitic affinities, generated after high partial melting degrees in a forearc above a subducted slab. This led to the depletion of the mantle source and subsequent melt-rock interaction consumed orthopyroxene, leaving dunite residues. Dunite acted as pathways for the melt percolation and subsequent formation of chromitite. The PGE concentrations are typical of Cr-rich podiform Tethyan chromitites and their distribution is controlled by partial melting. The primary PGM revealed a) initial crystallization temperatures of ~1200 ◦C under low sulfur fugacity (Os-Ir alloys and Ru-rich laurite) and b) subsequent cooling of the system with increasing sulfur fugacity (erlichmanite and Ru-poor laurite). The high temperature PGM are hosted in the massive chromitite and the lower temperature in non-massive counterparts. These results demonstrate a common mantle evolution in the Vardar ophiolites. Apart from the described primary features, it was deemed important to study a) the effect of post-magmatic processes and b) the geotectonic settings that these took place. The major post-magmatic process is listwaenitization, which has led to complete silicification (silica listwaenite) of the peridotite protoliths which are dominated by a rusty silica pseudo-mesh texture mass. The listwaenite hosted chromitites do not preserve any primary silicate, just serpentine relics and chlorite. This supports a serpentinization effect prior to listwaenitization. The effect of listwaenitization upon chromitite has never been addressed. Study of the major and trace element chemistry of magnesiochromite showed that there were no significant chemical variations due to the listwaenitization. The encountered PGM were desulfurized and listwaenitized chromitite display Pd-Au enrichments. The listwaenitization took place within a mantle wedge, where CO2-bearing fluids originating from dehydrated subducted Mesozoic sediments, interacted with the protoliths, forming serpentinite and finally silica listwaenite. The meta-ultramafic bodies of Gomati and Nea Roda (East Chalkidiki) are situated in the Serbomacedonian Massif. They demonstrate bimodal character in terms of chromitite chemistry with both Cr- and Al-rich chromitites outcropping in proximity, with no obvious tectonic structure intercepting those two varieties. Based on the trace element abundances in spinel grains, metamorphosis reached amphibolite facies, forming porous spinel. Chromitite-hosted chlorite and garnet chemistry correlates with greenschist facies temperatures and formation of zoned spinel grains. Despite the metamorphic overprint, some of the primary features of the chromitites have been preserved. The PGE contents demonstrate an increase in Pd/Ir ratios in some chromitites pointing to fractionation, whereas low ratios of mostly Cr-rich chromitites point to partial melting being the main mechanism that controls PGE mineralization. The normalized trace element patterns of spinel-group minerals revealed that Al-rich chromitites were generated in spreading settings in a back-arc and the Cr-rich counterparts in SSZ environment. The parental melts of Al-rich and Cr-rich chromitites demonstrate MORB and boninitic affinities, respectively. The meta-ultramafic protoliths were modified within a subduction zone, with significant input of a sedimentary source, as confirmed by the chemistry of serpentinite, diopside and Sb-mineralization. These results suggest common geotectonic processes within the Rhodope and the Serbomacedonian massif, that have affected the ultramafic bodies and chromitite occurrences.
Open Access
Mapping of high priority marine habitats in Greece, the case of coralligenous formations
(2023-03-03) Δήμας, Ξενοφών; Dimas, Xenofon
Τμήμα Γεωλογίας (ΔΔ)
The 1st chapter is the introduction of the thesis and is an overview of the present knowledge about the coralligenous formations found in the Mediterranean Sea in general and in the Greek Seas more specifically. Several aspects and the mechanisms that control the presence and growth of coralligenous formations are presented in this chapter. Coralligenous formations are under immense pressure due to the impact of human activities. These pressures and the conservation methods and acts that have been established are also part of this chapter. In order to map the coralligenous formations on the seafloor marine scientists use a plethora of different techniques. All these techniques as well as some new emerging state-of-the-art high-resolution techniques and the different seafloor classification schemes that are used are also described. The final part of the chapter is dedicated to gathering and presenting all the available information regarding the presence and status of the coralligenous formations of the Greek Seas that have been published in scientific studies. The 2nd chapter presents the survey areas that were selected for the application of the methodologies proposed in this PhD. For the probability model, the study area is the whole span of the Greek Seas. Key features of the Ionian and the Aegean Seas are presented, in addition, a further note is given to some very important gulfs of these seas. Gyaros Island (Cyclades Archipelago, South Aegean) was selected to be the survey area for testing and application of the down-scale, high-resolution marine remote sensing survey. In the 3rd chapter methodologies that are used for the objectives of the PhD are analysed. The first part describes the steps taken for the creation of a probability map of coralligenous formation presence in the Greek Seas. The steps are the collection of seafloor mapping data from the archive of the Laboratory of Marine Geology and Physical Oceanography, the collection of data regarding the seafloor morphology and its physico-chemical attributes for the areas mapped and the Greek Seas in general. The methodology of the applied random forest algorithm analysis is the final step of this part. The second part is the description and analysis of the downscale seafloor mapping survey techniques on Gyaros Island. This part presents both the survey planning and execution phase as well as the processing of the data collected through the survey. Chapter 4 presents the results of the methodologies described in chapter 3. The results are also divided into two parts; the first refers to the mapped coralligenous formations and the probability model of the spatial distribution of coralligenous assemblages in Greece, while the second present the results of the high-detail mapping in Gyaros Island At first the result of the combination of the mapping data of the LMGPO archive is presented in the form of the most complete coralligenous formations presence map of the Greek Seas. The results of the statistical analysis and the creation of violin plots for the parameters collected from the open-access portals are the next part of this chapter. In this part, the violins plots are used to detect common attributes and differences between the formation found in the Greek Seas by segmenting it into three different geographical areas (Ionia, S and N Aegean Seas). The results of the probability model close the presentation of the first part of the results. In the second part, the results of the marine remote sensing and ground truthing survey are presented through thematic maps for each of the techniques applied. The combination of these maps allowed the segmentation of the seafloor based on three different seafloor classification schemes and their results are analysed. The final part of this chapter is the statistical analysis of the coralligenous formation mapped in the area of Gyaros seafloor in respect to the bathymetry and the sediment thickness. The 5th and last chapter of the thesis is the synthesis of this thesis. The key results of each applied methodology are presented and their contribution to the process of understanding the coralligenous formation is highlighted Moreover, the limitations and/or gaps in each of the implemented methodological approaches are mentioned and ways to solve or fill them are also presented. The presentation of methodologies and instrumentations that will further enhance future mapping surveys is the last part of the PhD.
Open Access
Modelling of environmental parameters in lake environmnets using neural networks
Χατζησολωμού, Αικατερίνη; Παπαθεοδώρου, Γεώργιος; Παπαθεοδώρου, Γεώργιος; Λαμπράκης, Νικόλαος; Παπαστεργιάδου, Ευανθία; Γεραγά, Μαρία; Φερεντίνος, Γεώργιος; Ζαχαρίας, Ιερόθεος; Καμπάνης, Νικόλαος; Hadjisolomou, Ekaterini
Τμήμα Γεωλογίας (ΔΔ)
Aquatic pollution is one of the most serious environmental issues that the human kind has to deal, especially the last decades. Therefore, the aquatic environments are suffering a great environmental pressure as well. Since the lakes are having about the 90% of the Earth’s liquid freshwater, their proper management is a crucial task in order to maintain their good water quality. Eutrophication is one of the major problems that are observed in the limnetic environments. The eutrophic water is related with a series of environmental problems like anoxia, the existence of harmful cyanotoxins etc. Therefore, this study is focused on the assessment of the environmental parameters that are related with the phenomenon of the eutrophication. The mathematical models are capable to contribute positively to the restoration of the good water quality status of a limnetic environment. The mathematical models can act as a mean to describe several environmental processes with the use of mathematical relationships. Several types of mathematical models have been applied into the area of environmental sciences, including the artificial neural networks. During the last decades the artificial neural networks have been applied successfully into the field of limnology. It has been documented that the artificial neural networks are superior to other modelling techniques (e.g. multiple linear regression model). This is attributed to the fact that the artificial neural networks can simulate with good correlation the complex non-linear relationships that are describing the environmental processes. Therefore, several categories of artificial neural networks are applied in this study. The artificial neural networks can be divided into two main categories, those with supervised learning and those with non-supervised learning. In Application 1 and Application 2 supervised artificial neural networks are developed aiming to predict the chlorophyll parameter. Afterwards several sensitivity analysis (one way-sensitivity analysis) algorithms are applied in order to evaluate the environmental parameters with the biggest impact on the artificial neural network, which managed to simulate well (produced small error) the chlorophyll parameter. The synergistic effect of the parameters (two-way sensitivity analysis) is calculated with the use of the “PaD2” algorithm. In Application 3 a self-organizing map (SOM), which is a non-supervised artificial neural network, is presented. Based on that SOM neural network it is possible the limnological data to be clustered and at the same time the interactions among the environmental parameters to be examined. Furthermore, the statistical methods of Principal Components Analysis and Cluster Analysis are applied and their results are compared with the results produced by the SOM. The results of the Principal Components Analysis and Cluster Analysis methods are with agreement with those produced by the SOM, although the SOM is a superior modelling method because of its advanced visualization abilities to assess the parameters interactions.
Open Access
Nanocomposites based on halloysite as carriers for anticancer drugs : experimental data and molecular simulations
Γιαννή, Ελένη; Gianni, Eleni
Τμήμα Γεωλογίας (ΔΔ)
Halloysite is a clay mineral of kaolinite group with tubular morphology. Due to its special characteristics, it is widely used for the encapsulation of a variety of molecules and therefore it is used as a drug delivery system. In this study, halloysite was investigated as a potential delivery system of irinotecan for the treatment of colon cancer by oral administration. The drug-loaded halloysite nanocomposites were coated with Eudragit S100 copolymer, for the targeted release of the active substance only in colon conditions. The drug entrapment efficiency was reached a satisfactory value of 84.42 ± 3.10 %, as it was found from UV-Vis Spectrophotometry. The nanocomposites were characterized for their physicochemical and morphological properties via TGA, XRD, TEM, SEM, and DLS methods. Quantum Mechanics and Classical Molecular Simulations methods were used for a deeper view on mutual interactions between individual compounds. The bacterial load of the halloysite was examined in order to support its use in pharmaceutical applications. Release studies were performed in simulated conditions of the human body, determined a minimum release of the drug under stomach conditions (0.7 % in 2 h), a low release at pH 4.5 (24.8 % total release after 2 h in pH 1.2 and 2 h in pH 4.5) followed by a rapid release after 1 h in intestinal conditions (> 90 %). Cellular studies (viability, apoptosis and hemolysis) were performed in order to prove the cytocompatibility of the samples. The drug carrier was found to be non-toxic in small concentrations, while the irinotecan-loaded halloysite exhibits higher anticancer activity than free irinotecan (45 ± 6 % and 26 ± 6 % viability at 24 h and 48 h, respectively). From Molecular Simulations was showed that halloysite can interact effectively with all the different forms of the drug, resulting a promising drug delivery system for irinotecan.
Open Access
Palaeoenvironmental and taphonomical study based on the microvertebrate assemblages of three upper pleistocene cave sites from Mani and central Greece
Κολενδριανού, Μαρία; Kolendrianou, Maria
Τμήμα Γεωλογίας (ΔΔ)
The present thesis is a discussion of the palaeoenvironmental conditions in the wider area of Kythros islet (Lefkas) and Mani Peninsula (Peloponnese) during the last hundred thousand years, based on the taxonomic determination of microvertebrate fossil material from three cave sites: Panthera cave (Kythros islet, Inner Ionian Archipelago, central Greece), Kalamakia cave and Melitzia cave (Mani Peninsula, Peloponnese). The taphonomical history of these caves was also reconstructed with regard to the assemblages’ agent of accumulation and the post- depositional processes they went through. In this context, 74916 teeth and skeletal elements from amphibians, lizards, snakes, insectivores and rodents were examined from the three Upper Pleistocene cave sites, in what was the first attempt to apply taphonomical indices for the identification of predators and taphonomical processes and to conduct palaeoenvironmental reconstructions using the Taxonomic Habitat Index (THI) upon microvertebrate palaeontological material from Greece and the southern Balkans. 62 taxa and 2388 individuals were identified in all three sites with Melitzia being the richest and Panthera cave the poorest in both species richness and individual abundance. Herpetofauna was the most diverse animal group, but rodents were the most numerically abundant animal group in every cave. Out of the taxa identified for all three cave sites, 16 are reported for the first time in the Greek fossil record, 2 are reported for the first time in mainland Greece and 10 are reported for the first time in Upper Pleistocene deposits. Regarding the palaeoenvironmental analysis, the reconstructions revealed the existence of mixed habitats varying between relative expansions mainly of shrublands, grasslands, deciduous forests and rocky areas with the occasional presence of water bodies of a local character in the caves’ wider areas. There were no major shifts between the percentages of different habitats but those that were detected could be correlated with climatic events within a geochronological context (Kalamakia, Melitzia). However, local factors and/ or site taphonomy are also believed to have affected the analyses to some extent. Consequently, it is suggested that- in the future- these palaeoenvironmental reconstructions should be complemented by palaeoclimatic analyses and interpreted in conjunction. Concerning taphonomy, the most common agent of microvertebrate accumulation was predation, since digestion was always present in every unit of every site in the present study. Different predators were identified in every site while, in some cases, predation by multiple predators is believed to have taken place simultaneously or successively. In Panthera cave, assemblages are believed to have been formed by category 3-4 mammalian or owl predators in the lowermost unit, while the uppermost units seem to have been significantly affected by post- depositional processes that either affected the signature(s) of the accumulating agent(s) beyond identification (unit 1) or caused the accumulation of material themselves (water transport in unit 0). In the case of Kalamakia, barn owls were the accumulative agents while for Melitzia category 3 and 4 predators were responsible for the accumulation of microvertebrate material (mixed with predation by category 1-2 predators in some units). Other than digestion, additional alterations were identified in the sites that were related to post- depositional natural processes occurring in a cave (black staining by water dripping, weathering, cave corrosion, rootmarks) or caused by the human or animal residents of the caves (burning, trampling). These processes seem to have significantly affected some of the results and interpretation efforts of the present study, either directly by altering the preservation state of the material or indirectly by producing inconclusive results. In both cases, the introduced biases were taken into consideration during interpretations. Moreover, palaeozoogeographical implications regarding the identification of 10 taxa that were found to be outside their modern geographical ranges were considered, regarding previous identifications in the Greek fossil record. Possible corridors of dispersal are, therefore, proposed based on the Greek relief and the water bodies that could have acted as barriers during the animals’ descent southwards/ ascent northwards. Finally, rare dental phenotypic anomalies on the occlusal surface of Microtus molars were identified that may be considered as a hint of closed breeding and bottleneck events in the beginning and at the end of the last glacial period, cautiously adding further information into the already complex phylogeographic history of the genus, since these rare traits are only an indication of said processes.
Open Access
Paleoceanographic and stratigraphic investigation in two semi-closed basins during Late Quaternary : the southern Red Sea and the Gulf of Corinth
(2022-10-26) Σεργίου, Σπυρίδων; Sergiou, Spyridon
Τμήμα Γεωλογίας (ΔΔ)
Marginal marine environments with a restricted connection to the open ocean have been considered excellent for tracking the concurrent impact of both regional processes and the influence of the adjoining open sea. Consequently, the investigation of sedimentary successions from such settings provides essential information on the regional paleoclimatic signals and the impact of global sea level changes in hydrographic systems over time. The present thesis is concentrated on core sediments from the southern Red Sea (Saudi Arabia) and the Gulf of Corinth (Greece) aiming to examine the hydrological response of a semi-closed, sill-controlled basin to highly variable climatic conditions and intense sea-level fluctuations during late Quaternary time intervals: the last 30 ka for the southern Red Sea and the period between ca. 130-70 ka (Marine Isotope Stage 5) for the Gulf of Corinth. Chronological framework was built on radiocarbon datings for the Red Sea record while a combination of absolute (Th/U) and relative (biostratigraphic) age markers was applied for the Gulf of Corinth succession. Gravity core FA09 was retrieved from the deep outer part of the southern Red Sea continental shelf within the frameworks of DISPERSE project. The combination of lithological, micropaleontological (planktic and benthic foraminifera), stable isotope (δ18Ο, δ13C), and transfer function (Artificial Neural Networks) analyses of sea-surface temperature and salinity revealed the effects of sea level changes and the South Asian Monsoon System (SAMS) on the oceanographic regime and the seafloor conditions of the area. Moreover, extended comparisons with records from the central and northern Red Sea, the Gulf of Aden, and the northwestern Arabian Sea provided insights into the overall interaction between the Red Sea and the Indian Ocean. Results showed that over the total investigated interval the Red Sea was connected to the Arabian Sea favoring the deposition of hemipelagic beds in the outer shelf of the southern Red Sea. However, a strong glacial/interglacial variability trend was imprinted in the sedimentary succession. The continuous intrusions of inflows from the Gulf of Aden during the glacial section (30–15 ka) induced common sea-surface temperature variations in these regions and prevented hypersalinity in the southern Red Sea, while seafloor conditions were characterized by rather low oxygen levels and high accumulation of terrestrial sediments. The MIS 2 sea-level lowstand (ca. 22-15 ka) was marked by a gradual reduction in planktic foraminiferal abundance together with the highest salinity (~38 psu) and lowest temperature (~23.5 °C) reconstruction estimates, while organic-rich seafloor conditions were indicative of efficient preservation of the organic matter in the oxygen-depleted sediments. Deglacial sea level rise improved the water mass exchange between the northwestern Arabian Sea, the Gulf of Aden, and the entire Red Sea, while in the early Holocene these three areas shared relatively similar surface water conditions. Southwest (summer) Monsoon was dominant during the late glacial and early-middle Holocene and favored a strong coupling between surface productivity levels and organic matter accumulation of both marine and terrestrial sources, thus implying combined effects of nutrient-enriched inflow from the Gulf of Aden and increased riverine runoff in the southern Red Sea. For most of the late glacial era, laminated sediments accumulated in association with oxygen-poor and organic-rich seafloor conditions under a well-stratified water column. Northeast (winter) Monsoon dominated during glacial times and especially around the Heinrich stadials 2 and 1, associated with reduced sea surface temperature and productivity levels in the southern Red Sea. The MIS 5 succession of the Corinth rift sediments corresponds to the subunit 1.3 of hole M0079A, drilled during IODP Expedition 381 in the central basin. Sedimentological (granulometry, composition), micropaleontological (planktic and benthic foraminifera), and isotopic (δ18O and δ13C) analyses were combined with additional data from the expedition overview and records from the surrounding area. The sedimentary succession is characterized by the alternation of a) bioturbated, foraminifera-rich hemipelagites with b) detrital-rich, partly bedded intervals likely corresponding to intrabasinal gravitational mass movements and low oxic sea-surface conditions and c) aragonite-rich, laminated deposits, indicating either marginal conditions between marine and isolated environment or highly stratified water column and anoxic seafloor conditions. Water exchange with the open sea was efficiently established during the MIS 5e and 5c sea level highstands as indicated by the similar planktic faunal biozones between hemipelagic intervals of M0079A and core records from the adjoining Ionian and Adriatic Seas. In contrast, seawater interaction was restricted during the MIS 5b when the sea level fluctuated very close to the sill height. Notably, no imprints of the MIS 5a highstand exist in the studied successions. The combined effects of Ionian Sea inflows and enhanced riverine runoff led to increased water column stratification and low oxygen, eutrophic seafloor conditions in the Gulf of Corinth during times of enhanced humidity and precipitation rates in southern Europe and deposition of sapropel S5 and S4 throughout the eastern Mediterranean (MIS 5e, 5c). However, the high abundance of benthic foraminifera suggests the deposition of sapropel-equivalent sediments rather than sapropel layers within the GoCb. Primary productivity was principally regulated by high riverine runoff in the gulf during S5 whereas at the time of S4 deposition nutrient availability was concentrated in a well-developed DCM layer. Comparing the overall findings of the two records, and despite the several differences in terms of the climatic, oceanographic, and geomorphological regime in the two areas, several similar features have been identified which provide a wide perspective on the environmental response of a northern Hemisphere marginal sea of either tropical or temperate latitudes to sea level fluctuations and modifications in regional climate. 1) Efficient water exchange with the open ocean coincides with the deposition of fine-grained hemipelagites in the semi-closed basin, marked by high numbers of planktic foraminifera. 2) High evaporation, increased sea surface salinity (SSS) and drastic reduction of the planktic foraminifera assemblages are recorded during maximum sea level lowstands when water exchange with the open sea is limited with respect to the sill height. 3) High summer insolation intensity and enhanced humidity lead to a well-stratified water column characterized by low salinity, light δ18O, and elevated productivity sea surface conditions above a low oxygen and organic-rich seafloor. At insolation maxima, the highest stack of planktic foraminiferal numbers is observed in both records driven by increased surficial productivity. 4) Drastic reduction in planktic foraminifera abundance can result from either a) restricted inflows of nutrient-rich waters from the open ocean during sea level lowstands, b) low oxygenated seawater surface, and c) dilution effects triggered by intrabasinal mass transport deposits. 5) Both records are considered highly valuable wider-scale paleoclimatic archives: The southern Red Sea record is excellent for reconstructing past monsoon dynamics while the Gulf of Corinth succession includes imprints of sapropel-equivalent conditions in a semi-closed environment. 6) Several multi-millennial, widespread cooling events of the northern Hemisphere are captured in the investigated records, causing a coupling between cool seawater surface and well-oxygenated seafloor conditions attributed to a temporal breakdown of thermal stratification.
Open Access
Passive seismic interferometry & shear wave splitting in the investigation of the Earth's crust
Γιαννόπουλος, Δημήτριος; Σώκος, Ευθύμιος; Σώκος, Ευθύμιος; Οικονόμου, Γεώργιος; Τσελέντης, Γεράσιμος; Κουκουβέλας, Ιωάννης; Κυρατζή, Αναστασία; Παπαδημητρίου, Παναγιώτης; Ευαγγελίδης, Χρήστος; Giannopoulos, Dimitrios
Τμήμα Γεωλογίας (ΔΔ)
The Corinth Rift is an active intra-continental structure on the western edge of the Aegean Arc, Greece. It is a region which has been in the limelight of the geo-scientific interest for more than three decades, as it is one of the most seismically active rifts in the Euro-Mediterranean region, presenting one of the highest geodetically measured rates of extension. Despite the large amount of multidisciplinary observations and the proposed models, there is still a considerable discussion concerning the relationship between seismic activity, fault mechanics and the rifting process. In the framework of the on-going research aimed to understand the tectonic evolution of the area, this thesis is trying to investigate the velocity structure and the physical characteristics of the upper crust beneath the western Corinth Rift derived by two different techniques: Passive Seismic Interferometry using ambient seismic noise and Shear-Wave Splitting using locally recorded shear-waves. We use passive seismic interferometric techniques to constrain the velocity structure in the upper crust of the western Corinth Rift. The method of Seismic Interferometry aims to retrieve the Green's function of the medium between two sensors by just utilizing ambient seismic noise recordings at the Earth's surface. Seismic Interferometry is considered as a revolutionary method characterized by a rapid development during the last decade. Seismic Interferometry was initially based on the fact that "by cross-correlating random wave fields of ambient seismic noise recorded on two locations on the Earth's surface, we can retrieve the wave field that would be recorded at one of the locations if there was a source at the other". After the mathematical representation of the previous conjecture, a plethora of studies have been performed using ambient noise Seismic Interferometry showing how useful the Green's function extraction can be in practical applications, either by monitoring temporal changes in material properties associated with volcanic processes and fault zones or by imaging the subsurface of the Earth at different scales (from reservoir to continental scale). Following this rule, we applied Passive Seismic Interferometry technique on long time-series of ambient seismic noise recorded at all available seismic stations which are deployed in the western Corinth Rift. We cross-correlated all vertical-vertical component time-series from all stations, turning each station into a virtual source emitting Rayleigh-waves (Green's functions). Then Rayleigh-wave group velocity dispersion curves were measured for each station-pair by applying frequency-time analysis and finally we performed straight-ray surface-wave tomographic inversions to produce an ambient noise tomography of the western Corinth Rift at different periods between 1 and 6 s. Since no other ambient noise tomography has been performed until today in the area, the first part of this thesis is considered as the first attempt to study the crustal velocity structure of the Corinth Rift by using ambient seismic noise recordings. In general, our results highlight the complexity of the geological and tectonic regime of the western Corinth Rift. Tomographic images at periods up to ~3 s (up to ~2.5 km depth) revealed that the overall distribution of the Rayleigh-wave velocity is mostly coincident with the geology context of the area. Low velocity zones are mostly observed where Plio-Quaternary syn-rift sediments are present, while higher velocities are due to the pre-rift basement structures. At periods above ~3 s (> 2.5 km depth), where Rayleigh-wave velocity measurements are sensitive to deeper structures, the results highlight a low velocity zone located in the southern part of the Corinth Rift with a preferential elongation in the WNW-SSE direction, sub-parallel to the strike of the rift. The low velocity anomaly is the most interesting and profound feature in the velocity maps between 4 and 6 s. Interestingly, this zone is still highlighted at depths even greater than ~5 km (especially around Aigion area), namely much deeper than the estimated sedimentary layer in the area. We interpret the presence of the low velocity anomaly below the southern part of the rift in relation with the present-day active tectonic regime giving also special attention on possible involvement of fluid circulation processes at depth within a highly fractured crust. Prompted by the observations derived from our ambient noise tomography study and motivated by previous studies in the literature noting that possible fluid circulation processes at depth play a key role in the overall evolution of the western Corinth Rift (crustal stress, faulting, seismicity etc.), in the second part of this thesis, we concentrated on locally recorded shear-waves to investigate possible changes in the seismic waves propagation properties of the crust (S-wave anisotropy), related to the occurrence of seismic events in the area. Shear-wave splitting (anisotropy) is a phenomenon in which shear-waves are separated into two components with almost vertical polarizations and different propagation velocities. This can occur during shear-wave propagation through an anisotropic medium. The two splitting parameters that can be measured through a shear-wave splitting analysis are the polarization direction of the fast component of the splitted shear-waves, and the time-delay between the two components. Significant variations of the crustal anisotropy parameters have been observed in relation to earthquakes worldwide, reflecting spatial and/or temporal changes in the characteristics of the medium and the stress field. Towards this purpose, we performed a local shear-wave splitting analysis in a time-period that includes the occurrence of two moderate earthquakes. On January 2010 two earthquakes of MW ~5.2 occurred near the village of Efpalio located at the northern coast of the western Corinth Rift. For the needs of our study, we used a 2-year long dataset, covering one year before and one year after the January 2010 Efpalio earthquakes, to study the temporal variability of the splitting parameters related to the earthquakes occurrence. In general, our analysis revealed the presence of an anisotropic upper crust in the western Corinth Rift, as well as a significant temporal variation of the splitting parameters in relation with the earthquakes. In order to have additional information about the average properties of the medium along the studied ray- paths, we accompanied each shear-wave splitting measurement with apparent Vp, Vs and average Vp/Vs ratio calculations. A distinct increase in time-delay values and Vp/Vs ratios was observed soon after the Efpalio earthquakes, followed by a decrease after the end of the aftershock sequence. The measurements of the apparent Vp and Vs showed that the observed changes in Vp/Vs ratios after the Efpalio earthquakes were due to an increase in Vp and a decrease in Vs. Considering the above, we attempted to interpret the causative factors of the observed temporal variations associated with the Efpalio earthquakes, in terms of the regional stress field and fluids involvement. We suggest that a migration of over-pressured fluids through the earthquake produced fractured damage zone is most probably the main cause of the observed increase in time delays and Vp/Vs ratios. The observed variations in the time-delays and Vp/Vs ratios after the Efpalio earthquakes seemed to be slightly stronger close to the hypocentral areas, which are possibly reflecting minor post-earthquake related changes in the properties of the crust. Fast shear-wave polarizations present a general E-W orientation, which is in agreement with the regional stress field. On the contrary, the Efpalio earthquakes seemed to have little or no influence on this parameter since fast polarization directions did not present any significant change after the Efpalio earthquakes. A notable conclusion drawn from both the shear-wave anisotropy analysis and the noise-based tomography includes evidence of fluids interactions not only within the more seismically active southern margins of the Corinth Rift, but also along the less active northern region. Furthermore, fluids interactions appear to be more intense and permanent in time in the southern part of the rift than the detected ones along the northern part which they mostly triggered by the Efpalio earthquakes occurrence. The observed variations in time delays and Vp/Vs ratio after the earthquakes were slightly stronger close to the rupture areas than outside of them and they appeared to have a decreasing trend, moving to background values a few months later.
Open Access
Petrological factors controlling abiotic methane formation in mafic-ultramafic rocks
Υφαντή, Ελένη; Yfanti, Eleni
Τμήμα Γεωλογίας (ΔΔ)
Abiotic methane occurrence in ultramafic rocks produced via CO2 hydrogenation, is an emerging research topic. It is considered that metals occurring in mineral phases of some ultramafic rocks catalysed the Sabatier reaction. However, it is still unclear which mineralogical features and/or petrological factors control its formation, and which lithotype is the gas source. The occurrence and isotopic composition of gas occluded in rocks, is routinely quantified via whole-rock analysis, after crushing and milling of rock samples. The purpose of this study is to give new insights into the literature gaps mentioned above. The aim was to identify mineral reactions, which indicate the formation of methane and to locate the mineral-catalysts indicating past or ongoing, gas-rock reactions. Deep understanding on the petrological aspects that control the formation of abiotic methane during continental serpentinisation, would allow the extraction of research criteria that could be used in other studies to predict the potential of abiotic methane occurrence in unstudied areas. This study was performed in two parts. The first part of the thesis, focused in determining which lithologies host abiotic methane among samples deriving from different ophiolitic suites and various flood basalt localities in Greece. The results were used to investigate the mineralogical aspects that affect the formation of abiotic methane, and extract research criteria for investigation in unstudied areas. In the second part, the mineralogical and geochemical indicators of abiotic gas synthesis set in the first part, were tested for their suitability to assess the potential of a prospecting ophiolite complex to host abiotic methane. For this purpose, the Ranau peridotites in Sabah, east Malaysia, was chosen. The results of this study showed the chromitites from Moschokarya and Aetorraches areas host the highest amount of methane. Moreover the chromitites from Moschokarya are enriched in IPGE, which occur as laurite and IPGE-Ni sulphides. The secondary IPGE alloys in the Moschokarya chromitites resemble deactivated and spent catalysts, after extensive gas-rock reactions with a fluid phase. Furthermore, four main categories of research criteria were set to assist future investigation of abiotic methane in new areas (field evidence, lithologies to act as reagents, source lithology, catalyst indicators). These criteria set were used to investigate the potential of abiotic methane occurrence in an unstudied area (Ranau peridotites). Preliminary data showed that the Ranau peridotites host methane of potential abiotic origin. In summary, this research showed that massive chromitites are the catalyst-bearing lithologies that host the highest amount of abiotic methane and are considered as its source lithology. The Ru-bearing PGM are the potential minerals catalysts of the Sabatier reaction, while alteration of PGM under reducing conditions resembles a deactivated and spent catalyst, after extensive gas-rock reactions with the fluid phase.
Open Access
Quaternary paleogeographic & sea-level change reconstructions in the Eastern Mediterranean
Γεωργίου, Νίκος; Georgiou, Nikos
Τμήμα Γεωλογίας (ΔΔ)
Coastal areas provide multiple support for life on earth and are expected to play a major role in society’s development in the near future. The rising human activities and resources exploitation have increased pressure in the coastal zone and the marine environment, causing marine pollution, climatic crisis, and nature-cultural heritage loss. This has forced the governments to enact Marine Spatial and Integrated Coastal Zone Management plans. However, before establishing these plans, stakeholders and decision-makers should be aware of the resources' spatial extent in order to plan a sustainable future that will allow the balanced management of sea resources’ exploitation and nature-cultural heritage preservation. The main pillar for achieving this purpose in the marine environment is the establishment of multileveled and multi-thematic geodatabases that will allow users to correlate, join and combine datasets of different spatial analyses and information. This thesis is separated into six chapters: ▪ The 1st chapter is the introduction of the thesis and is dedicated to the description of the main processes that affect the sea level through the geological time. These are separated in the eustatic and the relative sea-level change processes that affect the sea level in a global and regional/local scale respectively. Scientists use the geological and archaeological remains, for the reconstruction of the past sea-level, which are called “Relative sea-level indicators” (RSLi). These RSLi consist of geological formations such as marine terraces, notches, coral reefs etc. and archaeological indicators such as harbor facilities, fish tanks etc, while each one allows specific precision in the sealevel change reconstruction. The analysis of these indicators are playing a major role in the climate reconstruction, especially during Interglacial periods, during the Last Interglacial periods (Georgiou et al. 2019), when the climatic conditions were similar to the present. In this way, we will be able to evaluate the modern accelerating rates and estimate/model the future ones. Such an example is presented in an article related to sealevel reconstruction through a tidal notch shape analysis which was published during the Ph.D. period and is included in the dissertation’s broader scientific field: Georgiou N., Stocchi P., Rovere A., Elisa Casella E. (2020) IMEKO TC-19 International Workshop on Metrology for the Sea Naples, Italy, October 5-7, 2020 Reconstructing past sea level through notches: Orosei Gulf (Indexed in Scopus) The Eastern Mediterranean is one of the most complete and diverse databases of global sea-level and human history. The Underwater Cultural Heritage (UCH) in the Eastern Mediterranean and the testimonies that are laying on the seafloor constitute part of our history which should be mapped, protected and preserved for the future generations. Marine geophysics are the main tool to map and delimit the submerged archaeological remains and consists the pillar to the creation of extended databases of different spatial resolution and information regarding the seafloor. Extensive work has been performed in the marine environment raising the awareness in the Greek UCH, in the context of the dissertation’s broader scientific field: Papatheodorou G., Geraga M., Christodoulou D., Fakiris E., Iatrou M., Georgiou N., Dimas X., Ferentinos G. (2021). The Battle of Lepanto search and survey mission (1971-72) by Throckmorton, Edgerton and Yalouris: Following their traces a half century later using marine geophysics. Remote Sensing.; (Q1) (ISSN 2072-4292) https://doi.org/10.3390/rs13163292 Geraga M, Christodoulou D, Eleftherakis D, Papatheodorou G, Fakiris E, Dimas X, Georgiou N., Kordella S, Prevenios M, Iatrou M, Zoura D, Kekebanou S, Sotiropoulos M, Ferentinos G. (2020). Atlas of Shipwrecks in Inner Ionian Sea (Greece): A Remote Sensing Approach. Heritage.; 3(4):1210-1236. https://doi.org/10.3390/heritage3040067 Ferentinos G., Fakiris E., Christodoulou D., Geraga M., Dimas X., Georgiou N., Kordella S., Papatheodorou G., Prevenios M., Sotiropoulos M. (2020). Optimal sidescan sonar and sub-bottom profiler surveying of ancient wrecks: The ‘Fiskardo’ wreck, Kefallinia Island, Ionian Sea, Journal of Archaeological Science, Volume 113, 105032, ISSN 0305-4403, (Q1) https://doi.org/10.1016/j.jas.2019.105032. Geraga M., Papatheodorou G., Ferentinos G., Fakiris E., Christodoulou D., Georgiou N., Dimas X., Iatrou M., Kordella S., Sotiropoulos G., Mentogiannis V., Delaporta K. The study of an ancient shipwreck using marine remote sensing techniques, in Kefalonia Island (Ionian Sea), Greece, Archaeologia Μaritima Μediterranea - International Journal on Underwater Archaeology, v. 12, pp. 183-200. (Q4) The two areas presented in the current thesis are situated in the Eastern Mediterranean and more specifically in the countries of Lebanon and Greece. Byblos (Lebanon) and Aegina (Greece) are two of the most continuously inhabited ancient cities which are both globally known as two of the greatest maritime centers during the Bronze age, renowned primarily as chief harbours either for trading or naval purposes. As expected, for the cities to serve this purpose, important harbour facilities must have been built to support their status. ▪ The 2nd chapter describes the chronicles of the field trips and the equipment used in each survey. More specifically, the offshore surveys in Byblos were completed in three different phases (2014, 2016, 2017). During the first survey in 2014 a first approach was made in the offshore coastal zone using the available marine geophysical equipment: i)Side-scan sonar, ii) sub-bottom profiler (3.5kHz) and iii) a single beam echosounder. In 2016 the survey was divided in an offshore marine geophysical survey (using sub-bottom profiler-“Chirp”, ADCP, single-beam echosounder) and a sampling survey along the coastal zone of Byblos. The last survey in Byblos, was operated during 2017 and was focused on a focused detailed geomorphological mapping of the geological sea-level indicators detected during the previous surveys using a multibeam echosounder and on an underwater diving survey that aimed in the acquisition of underwater images of these findings. The second survey area, Aegina-Greece, was mapped during 2018. A research vessel was equipped with a side-scan sonar, a sub-bottom profiler and a multibeam echosounder, in order to map in detail, the geomorphology of the area and the extent of the submerged archaeological remains. An ROV was also used to ground-truth the findings of the survey and perform photogrammetry on one of the archaeological findings. The methodology that was used for the data acquisition is described below. ▪ The 3rd one (Chapter 3) is based on the article: “Integrated Methodological Approach for the Detection and Mapping of Marine Priority Habitat Types and Submerged Antiquities: examples implemented in the Saronic Gulf, Greece” Georgiou N., Dimas X., Papatheodorou G. which was published in Sustainability-MDPI (I.F. 3.25) Q1. & The book chapter: The palaeogeography of the strait of Salamis: Marine geoarchaeological survey in the strait of Salamis and the Ampelakia Bay. In Salamis 480 B.C; Papatheodorou, G.; Geraga, M.; Georgiou, N.; Christodoulou, D.; Dimas, X.; Fakiris, E.; Ferentinos, G. Hellenic Maritime Museum, 2020, 2020; pp. 392–411 ISBN 13 9786188218178. This article proposes an integrated downscale methodological approach that summarizes the existing and developing methodologies for mapping the seafloor/substrate in offshore coastal environments and detecting archaeologicalgeomorphological features and marine priority habitats. The methodology proposed is based on three main methodological axes of increasing spatial resolution: i) desk-based research, ii) marine geophysics/ seafloor classification, and iii) in-depth visual inspection /3D mapping. In this way, it is possible to produce datasets of different spatial analyses (meter to millimeter scale). The results of this methodology were integrated into a Marine Spatial Planning map regarding the area of the Saronic Gulf in Greece. Regarding the main parts of the thesis the 4th (Chapter 4) and 5th (Chapter 5) parts, they are dedicated to the implementation of the previously proposed methodology especially for the detection of underwater cultural heritage and geomorphological-geological features which were finally interpreted as relative sea-level indicators. Sea level rise drove to the submersion of coastal archaeological remains, disappearing their traces and risking their very existence while submerging important evidence related to sea-level fluctuation, human evolution, and dispersal. In addition, sea-level change research through geological/geomorphological indicators is of crucial importance against climatic change. At present, it is important to know the extent of natural phenomena based on natural variability and be able to quantify the influence of humans on them. To do so, it is essential to reconstruct past sea-level using the RSLi and establish the sea level rise rate during the late Holocene but also during the Last Interglacial periods, when climatic conditions were similar to the present. In this way, we will be able to evaluate the modern accelerating rates and model the future ones. The two survey areas that combine both those archaeological and geomorphological criteria are Byblos in Lebanon (Chapter 4) and Aegina in Greece (Chapter 5). ▪ Regarding the 4th part of the thesis (Chapter 4): Chapter 4.1, 4.2 & 4.4 is based on the final report to the DGA (Directorate General of Antiquities) titled “Offshore Geo-archaeological Research in Byblos, Lebanon”. Chapter 4.1 is based on the article: “Marine geophysical survey offshore Byblos: preliminary results” Papatheodorou G., Geraga, M., Georgiou N., Christodoulou D. published in BAAL: bulletin d'archéologie et d'architecture libanaises (BAAL is the annual journal issued by the Directorate General of Antiquities in cooperation with the Lebanese Ministry of Culture since 1996) & Chapter 4.3 is based on the article: “Late Pleistocene submarine terraces in the Eastern Mediterranean, central Lebanon, Byblos: Revealing their formation time frame through modeling” Georgiou N., Papatheodorou G., Francis-Allouche M., Geraga M., Christodoulou D., Stocchi P., Fakiris E., Dimas X., Zoura D., Iatrou M. submitted in Quaternary International-Elsevier (I.F. 2.13) Q1 This chapter describes the implementation of the proposed methodology (Chapter 3) in the area of Byblos, Lebanon, primarily contributing to detecting the location of the renowned Phoenician harbor. To add to that, two different sequences of submarine terraces (nearshore, distant sequences) were mapped in detail, at the offshore coastal area of Byblos and interpreted as relative sea-level indicators. A semi-automatic technique for the analysis of the acoustic data was used to detect the submarine terraces and acquire their morphometry. Then, this was combined with a model that uses their morphometry as input, and which is set to test it towards existing sea-level curves, uplift rates, and cliff retreat rates in order to find the most possible time frame of the submarine terraces’ formation. In this way, it was revealed that the distant sequence was possibly formed during the MIS3 interglacial period, ranking them among the unique MIS3 submarine terraces found in the Eastern Mediterranean. Finally, this contributed to the paleogeographic reconstruction of the area. The 5th part of the thesis (Chapter 5) is based on the article: “A multidisciplinary approach for the detection, mapping and morphometric analysis of ancient coastal installations: The case study of the ancient Aegina harbour complex” Georgiou N., Dimas X., Fakiris E., Christodoulou D., Geraga M., Koutsoumpa D., Baika K., Kalamara P., Papatheodorou G., Ferentinos G. published in Remote Sensing-MDPI (I.F. 4.84) Q1. This chapter uses the proposed methodology (Chapter 3) in the coastal area of Aegina island in Greece, where a one-of-a-kind submerged harbour complex is apparent. This approach succeeded in obtaining information that serves both geomorphological and archaeological purposes in a time- and cost-effective way, while obtaining information of centimeters to millimeters scale. The geomorphology of the area was mapped in detail through marine geophysical means while ancient submerged conical rubble structures and breakwaters were delimited using automatic seafloor segmentation techniques, revealing previously unknown sites of archaeological interest. Part of the seafloor classification techniques were developed and used in the articles below, which were also included in the dissertation’s broader scientific field: Fakiris E., Blondel P., Papatheodorou G., Christodoulou D., Dimas X., Georgiou N., Kordella S., Dimitriadis C., Rzhanov Y., Geraga M., Ferentinos G. (2019). Multi-Frequency, Multi-Sonar Mapping of Shallow Habitats—Efficacy and Management Implications in the National Marine Park of Zakynthos, Greece. Remote Sensing; 11(4):461. (Q1) https://doi.org/10.3390/rs11040461 Fakiris E., Zoura D., Ramfos A., Spinos E., Georgiou N., Ferentinos G., Papatheodorou G., (2018). Objectbased classification of sub-bottom profiling data for benthic habitat mapping. Comparison with sidescan and RoxAnn in a Greek shallow-water habitat, Estuarine, Coastal and Shelf Science, Volume 208, p. 219-234, ISSN 0272-7714, (Q1) https://doi.org/10.1016/j.ecss.2018.04.028. The structures’ parameters were extracted from the acoustic data to analyze their morphometry, while photogrammetry was realized using a Remotely Operated Vessel to expose their microstructure. The spatial distribution of the structures revealed the construction of a well-planned harbour complex with multiple entrances, while based on different sea-level scenarios in the Holocene, different possible functionalities were assumed (shielding-sheltering). Finally, through the structures’ morphometric analysis (geometry and terrain statistical parameters) their preservation status was revealed, uncovering the anthropogenic impact on the submerged antiquities due to the modern harbor activity. ▪ The 6th and last chapter of the thesis (Chapter 6) is the synthesis of this thesis where a summary of the surveys’ results is presented and questions of broader scientific context but also of site-specific scientific interest are answered. Finally, the limitations of the implemented methodological approach are referred, and the future/missing directions are proposed.
Embargo
Southern Pindos foreland basin : Late Eocene – Early Oligocene stratigraphic evolution and geochemical constraints on the provenance and tectonic setting
Μποτζιολής, Χρύσανθος; Botziolis, Chrysanthos
Τμήμα Γεωλογίας (ΔΔ)
Pindos foreland basin in western Greece is a tectonic depression that lodges about 2500 meters of Upper Eocene to Lower Oligocene sub-marine fan deposits. This research presents a sedimentological, stratigraphic and paleocurrent analysis of the submarine fan deposits that occur in the central part of Pindos foreland basin, western Greece. Facies analysis suggests that the studied succession includes thirteen sedimentary facies and eleven facies and sub-facies associations. The environments of deposition comprise abyssal plain, outer fan, inner fan, and slope deposits. The stratigraphic analysis documents an upward transition from carbonates to abyssal plain, to outer and eventually to inner fan deposits suggesting progradation of the submarine fan system and progressive infilling of a deep-water sediment depocenter. Sediments suggest deposition close to the onset of Pindos orogen, when sedimentation was unable to exceed the accommodation space created by lithospheric flexure. Paleocurrent data from sole marks reveal two main directional flows. The NE-SW direction suggests that axial flows were dominant during the sediment deposition. The deposition in Pindos Foreland basin is dated to Eocene/Oligocene epoch. However, the exact stratigraphic position of the Eocene-Oligocene boundary is still uncertain. A qualitative analysis has been conducted on calcareous nannofossils and planktonic foraminifera, constraining the depositional age. Pindos Thrust is a crustal-scale structural element that formed Pindos foreland. Thus, Pindos foreland accommodates a syn-orogenic sedimentary succession with thick clastic deposits affected by compressional movements. The present research was based on detailed field campaign mapping and on standard structural techniques and aims to compile the main tectonic elements that shaped the Pindos foreland. The study area is part of the external Hellenides located on the Pindos foreland (SE Aetoloakarnania region). The activation of the NNW Gavrovo Thrust resulted on significant fault-related structures, such as the Varasova, Froxilia and Klokova anticlines. The existence of dextral strike-slip faults like Evinos Fault partitioned the westwards propagating thrusting deformation and acted as a barrier for the emergence of carbonate sediments at the southern part of the study area during the deformation. Based on the registration of bedding orientation, kinematics of meso and large-scale faults at different field outcrops, the relationship between sedimentation and orogenic processes in the area is defined providing new evidence of the evolution of the Pindos foreland basin. Furthermore, this study documents new petrographic and geochemical data for evaluating the composition, weathering condition, provenance, and tectonic setting of the central part of Pindos foreland basin. Conglomerate clast composition analysis suggests that the studied deposits contain mainly limestone clasts, followed by sandstone and chert clasts. It also suggests an additional low-grade metamorphic source, which is confirmed by the Cathodoluminence analysis. Microfacies analysis of the conglomerates clasts further restricts the source rocks that contributed to the basin sedimentation. An upward increase of lithic fragments abundances is documented and ascribed to the progressive unroofing of the Pindos orogenic source regions. This study links for the first time the stratigraphic evolution of the deep-sea fan deposits with the evolutionary stages and the geochemical constrains of the Pindos Foreland system. Multi-dimensional discrimination diagrams suggest a collisional setting and agree with an active continental margin. Geochemical and petrographic analysis suggests that the succession derived from sedimentary, felsic to intermediate igneous and low-grade metamorphic source rocks.
Open Access
Stratigraphic processes and Ionian basin evolution in Kastos Island from Triassic to Eocene, for hydrocarbon fields development. Correlation with NW Peloponnesus (Araxos peninsula) outcrops
Μπουρλή, Νικολίνα; Bourli, Nicolina
Τμήμα Γεωλογίας (ΔΔ)
Microfacies analysis, facies zones and age determination: In Kastos Island based on lithological and sedimentological characteristics, the following depositional environments have been recognized: deep sea and deep shelf, toe of slope-to-slope and open marine to restricted. Calciturbidites and basin evolution: Calciturbidites include Ta to Te Bouma sub-divisions and are organized in cycles that form channelized deposits with a high degree of amalgamation. Statistical analysis confirms the presence of order in the sub-division sequence. The thickness of event beds in the studied section shows a lognormal statistical distribution, typical of turbidite successions. Limestone microfacies suggest deep-water deposits and reworked shelf deposits. The intense extensional tectonic activity in the Ionian basin during the Early Cretaceous, with synthetic and antithetic faults, produced active platform margins and asymmetrical grabens. The Early Cretaceous to early Eocene depositional history in the Ionian Basin indicates that the regional tectonic activity, rather than the eustatic sea-level changes, was the major factor that influenced the basin evolution, suggesting a syn-rift stage being active from the Jurassic to the early Eocene. Cherty layers and nodules diagenesis: The lower Cretaceous limestones in both areas contain abundant small chert nodules, whereas in the upper Cretaceous nodules are larger, but less abundant. Siliceous concretions represent an early diagenetic event with a strong influence from the underlying rocks. Soft sediment deformation: Different types of soft-sediment deformations were recognized, that took place synsedimentary or just after sedimentation. The different types are related with the intense of tectonic activity, the rotation of the blocks internal to the basin or due to diapiric intrusions that deformed the sedimentary basin floor. Porosity: Porosity measurements for both areas from lower and upper Cretaceous limestones showed the average diameter of mesopores. Geochemical analysis: The obtained data showed that TOC (0.02-3.45%) indicate to good oil potential and a type II/III kerogen with the ability to produce liquid and gaseous hydrocarbons for Kastos Island and TOC (0.01-0.72%) with fair oil potential and type IV kerogen for Araxos peninsula. The results based on the Odd to even predominance, was indicated an anoxic deposition environment.