Τμήμα Γεωλογίας (ΔΔ)

Permanent URI for this collection

Browse

Recent Submissions

Now showing 1 - 5 of 165
  • Thumbnail Image
    Item
    Open Access
    Marine geoarchaeological survey in the Vathy bay of Astypalea island, south Aegean sea
    (2024) Νότη, Αλεξάνδρα; Noti, Alexandra
    Coastal restricted basins serve as invaluable repositories of information concerning global sea level changes and regional climate shifts, offering crucial insights into paleogeographic, paleoenvironmental and paleoclimatic conditions. This study employs a multi-faceted approach, integrating geophysical, visual, sedimentological, and geochemical data, to meticulously reconstruct the paleogeography, paleoenvironment, and paleoclimate of Vathy bay, in the South Aegean Sea. Examining a submerged archaeological site near cape Elliniko, the study utilizes dense radiocarbon analyses, providing accurate dating of ancient constructions and human activities. The research delineates three major environmental stages during the Holocene, identified as seismic facies (SF1-3) and lithological units (LU I-III). These stages highlight the basin's gradual transition from isolated to shallow marine conditions over the last 9.1 thousand years. Notably, the study pinpoints the onset of marine influence around 7.3 thousand years ago, coinciding with a global mean sea level of approximately -8 meters. Analysis further reveals arid periods between 7.3–6 and 4.1 thousand years ago, leading to Sr-rich carbonate precipitation in the basin and a general trend of aridification. Conversely, wetter conditions prevailed during the intervals of 9.1–7.3 and 6–5.4 thousand years ago. Additionally, geochemical proxies, particularly ASTC1 records, provide high-resolution climate reconstructions for the last 8.7 thousand years, aligning with aridity cycles identified in various Northern Hemisphere records. These findings demonstrate a correlation between mid-Holocene aridity events and the southern migration of the Intertropical Convergence Zone (ITCZ), followed by a retreat of monsoonal rains by the end of the African Humid Period (AHP). Short-term fluctuations in Ti/Al and Zr/Si ratios indicate transient cycles of enhanced terrigenous supply, correlating with Holocene "Rapid Climate Change" events (RCCs). Importantly, the study's spectral analysis identifies cyclical patterns of dry/cold climatic conditions with periodicities at 2500, 1200, and 525 years, corresponding with Hallstatt and Bond cycles, reflecting drier conditions and heightened dust input. The marine geoarchaeological research unveils submerged ancient structures, including linear constructions, conical rubble structures, and submerged walls, indicating potential harbor installations and navigational landmarks. These findings underline the intricate relationship between sea level changes, climate variability, sedimentation, and human activities, emphasizing the interconnectedness of climate systems across different regions and time scales. This study not only sheds light on the complex Holocene climate dynamics in the Eastern Mediterranean but also elucidates early human interactions with the coastal environment, providing crucial historical context for the region.
  • Thumbnail Image
    Item
    Embargo
    Taxonomy, biodiversity and evolution of fossil chelonians from the Late Miocene Locality of Höwenegg (South Germany)
    (2023-10-17) Παππά, Ιρένα; Irena Pappa
    The influence of climate fluctuations and geotectonic shifts during the Late Cenozoic era in the Western Palearctic region underscores the significance of ectothermic reptiles, such as chelonians, in serving as indicators of environmental changes. Chelonians are renowned for their exceptional fossil record, as they provide a valuable perspective on the climatic and environmental changes and which have played a significant role in shaping their evolution and diversity in Europe, particularly from the Tertiary period to the present day. The study of European chelonians has made substantial contributions to our comprehension of chelonians diversity throughout history, marked by numerous research initiatives and doctoral theses. Nevertheless, unanswered queries concerning fossil chelonians in Northern and Central Europe persist, as well as a pronounced disparity between the number of existing and extinct chelonian species, both within Europe and on a global scale as well. Specifically, it is evident that climate change has affected the reptilian fauna in Europe and has left its mark on the chelonian populations, even though the exact magnitude of this impact remains uncertain. There is an observable reduction in the diversity of freshwater turtle species, along with a transition from pleurodiran to cryptodiran turtles, suggesting that cryptodires possessed superior adaptations to colder conditions. Numerous chelonians, including tortoises and freshwater turtles, were impacted by climatic fluctuations that occurred in the Western Palearctic during the Neogene period. As a result, some of these species went extinct, such as Chelydropsis, while others experienced a reduction in their diversity. Höwenegg stands out as a remarkable fossil site, yielding a wide range of fossils, including vertebrates and invertebrates. The Höwenegg is located 2.5 km south of the town of Immendingen and consists of the most northern volcano complex of the Southwest German Hegau Volcanic area. Excavations at this site occurred over several decades, from 1950 to 2013, although they became intermittent over the years. Among the notable fossils unearthed at Höwenegg are chelonians, encompassing both tortoises and freshwater turtles. Most of these specimens were found in suboptimal preservation states, often due to taphonomic changes. The primary goal of this doctoral thesis was to enhance our understanding of Neogene turtle diversity in Germany and Central Europe through the analysis of fossil material from the Höwenegg region. More specifically, the main objectives of the doctoral thesis were: to conduct a detailed paleontological study of the skeletal material of chelonians from the fossiliferous area; the estimation of the number of taxa resulting from the material of both tortoises and aquatic turtles and their identification; the determination of any new extinct terrestrial or aquatic taxoon of chelonians derived from the material under study; the contribution of the study of the material to the general knowledge of the classification and evolution of the Neogene chelonian fauna in Germany; the assessment of the biodiversity of the site. Hence, a thorough analysis of the chelonian specimens was conducted. The material underwent comprehensive macroscopic examination, and a systematic classification approach was employed to categorize and describe the different taxa present in the material. Subsequently, for certain taxa, a phylogenetic analysis was undertaken to precisely determine their phylogenetic position and their links with other taxa. Based on the findings, it became evident that there was a minimum of four distinct taxa, comprising one tortoise and three freshwater turtles. Phylogenetic analyses were employed on the tortoise material to determine if it was either a large Testudinini or a small Geochelonini member. Additionally, for the freshwater genus Chelydropsis, the analysis aimed to ascertain whether it represented another member of Chelydropsis murchisoni, which was prevalent in Germany during this period, or if it was a distinct species. The phylogenetic analyses revealed that the terrestrial taxon seems to align with the large Testudinins. In most of the generated phylogenetic trees, it occupied an intermediate position within the Testudinini. However, it does not seem to be a member of the Testudo genus, which is characterised by tortoises with a hinge. Furthermore, the taxon was closely associated with Chersine hermanni, forming an exclusive clade with it. Comparative analysis was carried out with other terrestrial chelonians, encompassing both geochelonins and members of the testudinins group. Based on all the results, there is a tentative suggestion that this taxon may represent a new species closely related to the hermanni group, though this inference is made with some reservations due to the relatively low statistical support in the phylogenetic analyses. Regarding the Chelydropsis, it included the best-preserved and most complete specimen in the material, a nearly fully intact skeleton. Furthermore, the analysis and comparisons with other Chelydropsis species revealed that this taxon appears to be a distinct species, distinct from Chelydropsis murchisoni, and exhibits certain similarities with earlier Chelydropsis species, such as Chelydropsis decheni or Chelydropsis aubasi. Based on our analyses, the conclusions suggest that this taxon likely consists of a new species. Additionally, two other freshwater taxa were identified within the material. The first taxon belonged to Geoemydidae, based on the analysis of certain shell fragments. The second freshwater taxon was categorised as a member of Trionychinae. The study identified a total of four different taxa in the studied locality, including three freshwater turtles and one tortoise. To assess the site's biodiversity, a comparative analysis was conducted by examining Late Miocene fossil-rich sites, primarily in Germany, and expanding the study to a broader European context as well. Data from the Paleobiology Database were utilized, with a specific focus on the Tortonian, which encompasses MN9. Comparisons with other localities indicate that Höwenegg stands out as a site with notably high biodiversity, not only on a national scale but also within a broader European context. This study underscores the need for a comprehensive reevaluation of the chelonian material from previously examined sites. Many species names used in these sites have become obsolete, and there have been inaccuracies in past taxonomic assignments. Historically, smaller aquatic turtles were commonly classified as emydids, while larger terrestrial ones were often categorized as “Cheirogaster” or Geochelone. A similar situation occurred in Höwenegg, where part of the terrestrial material had been attributed to geochelonin (Cheirogaster back then member of geochelonins) and the pond turtle material was attributed to emydids. However, this research has revealed that the large terrestrial taxon is actually a member of the testudinins not geochelonins, while the pond turtle is attributed to Geoemydids, and not to Emydids.
  • Thumbnail Image
    Item
    Open Access
    Ανάπτυξη μεθοδολογιών εκτίμησης της επικινδυνότητας κατολισθήσεων από ισχυρούς σεισμούς : εφαρμογή στο νησί της Λευκάδας
    (2023-12-08) Σέρβου, Αικατερίνη; Servou, Aikaterini
    Στην παρούσα διατριβή γίνεται προσπάθεια ανάπτυξης μεθοδολογιών αποτίμησης της επιδεκτικότητας (susceptibility) και της επικινδυνότητας (hazard) καταπτώσεων βράχων που έχουν κύριο έναυσμα εκδήλωσης τον σεισμό, με εφαρμογή το νησί της Λευκάδας. Δίνεται ιδιαίτερη έμφαση στα πρανή της δυτικής παράκτιας ζώνης του νησιού, όπου οι ασβεστολιθικές βραχομάζες (ενότητες Παντοκράτορα, Βίγλας και Παξών) λόγω τεκτονισμού, παρουσιάζουν ένα ευρύ πλαίσιο τεχνικογεωλογικής συμπεριφοράς. Στο πλαίσιο της παρούσας εργασίας πραγματοποιήθηκε τεχνικογεωλογική διάκριση όλων των γεωλογικών ενοτήτων του νησιού, ενώ η έρευνα εστιάστηκε στις τρεις συγκεκριμένες περιοχές – ενότητες, που καλύπτουν το σύνολο των πρανών της δυτικής παράκτιας ζώνης. Σχεδιάστηκε και δημιουργήθηκε ψηφιακή Βάση Δεδομένων από 137 περιπτώσεις – συμβάντα καταπτώσεων βράχων που λεπτομερώς καταγράφηκαν επιτόπου αμέσως μετά από το σεισμό του 2015 στα πρανή της δυτικής παράκτιας ζώνης, τα οποία στη συνέχεια συμπληρώθηκαν με περιπτώσεις – συμβάντα από παλαιότερους σεισμούς χρησιμοποιώντας διάφορες πηγές πληροφόρησης. Η εκτίμηση της επιδεκτικότητας έγινε μέσω των μεταβολών της έντασης (κινητικής ενέργειας) της κατάπτωσης συγκεκριμένου βραχοτεμάχους για την κάθε περιοχή – ενότητα με θεωρητικές προσεγγίσεις – προσομοιώσεις και χρήση του λογισμικού Rocfall (Rocscience Inc.) το οποίο αποτελεί ένα από τα πλέον ευρέως χρησιμοποιούμενα λογισμικά προσομοίωσης καταπτώσεων, σε 66 επιλεγμένες διαδοχικές διατομές. Τα δεδομένα εισόδου των προσομοιώσεων προήλθαν από επεξεργασία των στοιχείων της ψηφιακής Βάσης Δεδομένων και από αντίστροφες αναλύσεις των καταγεγραμμένων πραγματικών συμβάντων, με εφαρμογή ειδικού υπολογιστικού κώδικα (ana-rock). Δοκιμάστηκαν δύο κύρια επιμέρους σενάρια από πλευράς σεισμών για την εκτίμηση της έντασης, με την είσοδο της εδαφικής ταχύτητας σαν αρχική στις προσομοιώσεις και συγκεκριμένα (α) σε κανονικές συνθήκες (ασεισμικές με αρχική ταχύτητα μηδέν) και (β) επιλέγοντας τους δύο πιο πρόσφατους ισχυρούς σεισμούς (2003 και 2015) που εκδηλώθηκαν στο νησί (με τις αντίστοιχες εδαφικές ταχύτητες σαν αρχικές). Από την εφαρμογή δεν παρατηρήθηκαν σημαντικές διαφοροποιήσεις στην ένταση (<15%). Προτάθηκε και εκτιμήθηκε επίσης η «κανονικοποιημένη» ένταση (normalized intensity) που εκφράζει από κοινού την επιδεκτικότητα και το μέγεθος – έκταση (σφοδρότητα) του φαινομένου σαν ένα ποιοτικό μέτρο ομογενοποίησης της κινητικής ενέργειας που εμφανίζεται στις επιμέρους ενότητες. Τόσο ή ένταση όσο και η «κανονικοποιημένη» ένταση αποδόθηκαν σε χάρτες κατάλληλης κλίμακας. Για την αποτίμηση της επικινδυνότητας αξιοποιήθηκαν στοιχεία επανενεργοποίησης - επανεκδήλωσης κατολισθήσεων με τη μορφή καταπτώσεων βράχων, που εντοπίστηκαν σε 131 καταγεγραμμένα περιστατικά της Βάσης Δεδομένων από σεισμούς 100ετίας και έγινε εκτίμηση της περιόδου επαναφοράς και της αντίστοιχης ετήσιας πιθανότητας επαναφοράς αυτών των καταπτώσεων. Ο συνδυασμός της «κανονικοποιημένης» έντασης και της πιθανότητας επαναφοράς οδήγησε σε αδρή εκτίμηση της επικινδυνότητας καταπτώσεων βράχων και την τελική απόδοσή της σε χάρτη κατάλληλης κλίμακας.
  • Thumbnail Image
    Item
    Embargo
    Taxonomic, taphonomical and geochemical study of the Late Pleistocene faunal bone assemblages from Melitzia Cave, Mani peninsula, Greece
    (2023-09-28) Τζώρτζη, Μαριάνθη; Tzortzi, Marianthi
    The present thesis focuses on reconstructing the ecological dynamics of the Upper Pleistocene in Greece. The study concentrates on analysing macrofaunal remains from Melitzia Cave in Mani Peninsula. Greece's geographical significance as a potential crossroads between Africa and Eurasia, coupled with favourable climatic conditions during glacial periods, contributed to its habitation by hominins. The research aims to dissect the ecological context of the time by examining the macrofaunal assemblage from Melitzia Cave, utilizing diverse techniques. The sediment deposits within the cave, organized into seven stratigraphic units, span a timespan from 45,500±947.5 BP to 10,915±235 BP. This chronological sequence offers a valuable opportunity to explore shifts in environmental conditions and the intricate interactions between humans and the surrounding ecosystem. While the Palaeolithic period in Greece remains relatively understudied compared to later historical phases, the rich archaeological record of the Mani Peninsula, characterised by numerous cave sites and hominid presence, makes it an ideal research location. Melitzia Cave, situated on Oitylo Bay, provides evidence of hominin occupation during specific time intervals. This research aims to thoroughly categorise, analyse taphonomy, and reconstruct paleoenvironments. The research methodology employs systematic palaeontology for species identification and taphonomical analysis to understand bone modifications and accumulation processes. Additionally, stable isotope analysis of tooth enamel is employed to infer dietary habits and mobility patterns. By integrating these methodologies, we seek to paint a comprehensive picture of the ecological context, the human-environment interactions, and the preservation conditions that prevailed during the Upper Pleistocene in Greece. The identified dominant species, including red deer (Cervus elaphus), fallow deer (Dama dama), alpine ibex (Capra ibex), and partridge (Alectoris graeca), suggest adaptability to temperate and rocky habitats. The presence of larger carnivore species in the lowermost units (I, II, and III), along with the absence of human traces and the reverse trend in the uppermost units, potentially reflects the intricate interplay between humans and carnivores, both sharing the same ecological niche. Evidence of human presence is evident across the uppermost units of Melitzia Cave through recovered lithic artifacts. The cave was utilized for various activities, exhibiting varying intensities over time. Units VIa and VIb showcase a denser concentration of lithics, and faunal remains compared to lower units. The assemblage predominantly consists of artiodactyls, typical of butchery sites. Although not monospecific, all artiodactyls are present in varying concentrations among units. This diversity aligns with kill-butchering sites observed during the Middle Palaeolithic in Europe. The avifauna is well-represented, reflecting a trend towards hunting smaller, swifter game during the Upper Palaeolithic. Skeletal remains in the cave exhibit signs of human-induced bone modifications, with minimal evidence of carnivore damage. The data suggests that human predation played a primal role in shaping the assemblage, primarily involving meat and marrow extraction. However, due to the scarcity of skeletal remains in some units, identifying the responsible agent (human or non-human predator) poses challenges. Human-induced bone modifications become more conspicuous in Unit V, characterised by abundant percussion marks. Unit VI showcases extensive human contribution through remains dominated by ungulates, displaying butchery marks, burning traces, and percussion marks. Larger artiodactyls, mainly C. elaphus, dominate this unit. The presence of skeletal elements with low food utility suggests a hunting stand or primary butchery location, with high-utility parts possibly transported elsewhere. The reconstruction of palaeoenvironmental and palaeoclimatic conditions around the cave during the Last Glacial Maximum, using stable isotope analysis on teeth of the three most abundant ruminant taxa, confirms the presence of a refugium. The study indicates prevailing arid conditions and open canopy vegetation, mirroring modern conditions. Seasonal shifts in δ18O values point to fluctuations in humidity and aridity, with stable climate seasonality observed throughout the Melitzia Cave sedimentary sequence. Slightly increased aridity is noted during the Younger Dryas. The strontium isotope ratios of enamel in three ruminant taxa suggest a local origin, with potential movement between similar areas. The higher strontium ratios of Taygetos mountain in the northeast indicate limited migration southeast. Geochemical analysis of bones from the cave indicates modifications in apatite structure. Discrepancies in mineral composition and crystallinity index (CI) are observed across units, with lower units showing higher CI values. FTIR spectra reveal variations in characteristic bands, including a band at 1087 cm-1 linked to fluoride ions and diagenesis. Bands at 1020 cm-1 and 1030 cm-1 correspond to nonstoichiometric and stoichiometric apatite, respectively, with the latter dominating in older samples. Lower units' samples display higher diagenetic modification, supported by CI values and FTIR characteristics. In summary, the multidisciplinary investigation of the macrofaunal remains in Melitzia Cave not only enhances our understanding of past ecosystems but also illuminates the intricate interaction between humans and their environment during the Upper Pleistocene. Consistent habitation patterns in this region imply that the relatively stable local environment supported prolonged human presence. This study underscores the importance of the Mani Peninsula and its caves as fertile grounds for exploring the complexities of prehistoric human existence and their ecological contexts as well.
  • Thumbnail Image
    Item
    Open Access
    Petrographical and geochemical features of the mesozoic bituminous formations of Parnassos-Ghiona Zone, Greece
    (2023-10-03) Δαμουλιάνου, Μαρία Έλλη; Damoulianou, Maria Elli
    The scientific interest regarding the hydrocarbon generation potential in Greece is generally focused on the formations of the Ionian Unit in the western areas of the country, where oil-seepages are well known. In contrast, Parnassos-Ghiona geotectonic Unit (PGU), Central Mainland Greece, has mainly been studied for the presence of bauxite ores. However, so-called bituminous limestone strata overlying the three bauxite strata are described in the up-to-date literature, as well as other Upper Cretaceous organic-rich strata including local coal lenses and thin shale layers, occur on top of the b3 bauxite horizon across PGU. In the present study, a series of outcrop and underground sites, as well as lab-core sections, representing all three bauxite strata hosted within PGU and their underlying/overlying formations, have been studied by means of organic petrology and geochemistry, including both Rock-Eval and GC-MS analysis, mineralogy and inorganic geochemistry, as well as microfacies analysis for the case of the carbonate strata. The aim of this study is to interpret the palaeoenvironmental setting during the deposition of the studied formations; the aspects of the palaeoenvironmental evaluation include the determination of the conditions favouring the organic matter accumulation subsequently to the b2 and b3 bauxite formations, as well as the determination of the palaeoenvironmental trend of PGU since the deposition of the Upper Cretaceous b3 strata towards the occurrence of the Paleogene dubmarine fan deposits. In addition, part of the main scope of the present study has been the assessment of the hydrocarbon generation potential of the studied PGU strata. Beginning from the older b1 ore body, the study of the outcrop sections of interest revealed that the bauxite-mud deposition during Middle-Upper Jurassic (Callovian-Oxfordian) was promptly followed by flooding of the karstic cavities at the studied sites, evolving into a shallow-marine depositional setting, corresponding to the D1 and D2 platform stages (see Carras, 1995), depending on the site, of the Distomon limestone strata. The restricted platform interior later evolved into a deeper part of the rimmed platform exterior model, which was established during the Upper Jurassic (Upper Kimmeridgian - Upper Tithonian), as suggested by the pelagic wackstones/ packstone collected at the AG site. The study of the aforementioned “Distomon” limestone strata following the b1 horizon formation do not support the accumulation and preservation of OM during these times. The study of the Upper Jurassic (Kimmeridgian-Tithonian) b2 bauxite strata, at one outcrop section at the western part of the PGU extent (DES6), revealed that the main bauxite paragenesis consists of boehmite and goethite and less of haematite, whereas the transitional bauxite-shale stage is dominated by the presence of chamosite. A thin organic-rich bauxite-shale layer on the top of the b2 horizon is mainly characterized by type IV bituminite and solid-bitumen content and displays a T max value falling within the oil-generation window. Hence, the HC generation from strata deposited right after the b2 ore body formation is not excluded. The sections of interest overlying the Upper Cretaceous (Cenomanian-Turonian) b3 horizon revealed the establishment of different depositional settings, depending on the studied site, including prompt deepening towards a shallow-marine platform interior setting (FZ7-9), during which adequate accumulation and/or preservation of organic matter was in cases favored right after the bauxite-mud deposition, shallow-marine basins with limited water circulation, as well as proximal to the sea paralic mires controlled by high-energy/tidal and oxidizing conditions. The study of the coal lenses revealed the establishment of two different coal-forming modes of organic matter depositional settings, including paralic mires on the top of the lateritic mud deposition, and paralic mires developed upon the Lower Cretaceous limestone bedrock. The low/very low grade humic coal lenses at the Vagoneto and Gouves sites formed by accumulation of mostly herbaceous plants, being characterized by elevated amounts of detrovitrinite and inertinite, and variable amounts of liptinites usually in the form of sporinite and alginite. Accordingly, the Rock-Eval data indicate the occurrence of all kerogen types, with the Types III and IV generally prevailing. The overall coal-petrographic data indicate intense oxidation in the palaeo-mires, possibly related to the dry warm Turonian climate and/or the influence of brackish waters. Τhe thermal maturity of the coal lenses , based on both vitrinite reflectance and Rock-Eval data, indicates Medium Rank Bituminous coals or, in terms of hydrocarbon generation, the early oil window stage. The uppermost Upper Cretaceous (Senonian) limestone strata was deposited under the conditions of shallow-marine platform interior setting (FZ7-9), during which adequate accumulation and/or preservation of organic matter was not favored. During the Upper Cretaceous, the palaeoenvironmental evolution of the PGU reached the FZ6 of the platform margin within the stratigraphic extent of the studied strata, followed by two alterations of carbonate platform settings and flysch-forming environments (reporting the onset of the orogenetic status within PGU during the transition of Maastrichtian and Paleogene), as recorded on the alteration of submarine fan deposits and pelagic limestones, before the final occurrence of the Paleogene sub-marine fan deposits. The Paleogene submarine fan deposits, represented by one site comprising a few-meter-thick sequence of alternating sandstone and marl strata, displayed a small amount of both indigenous and migrated solid hydrocarbons (corresponding to a maximum of 0.5 wt.-% TOC), suggesting a possible migration of hydrocarbons from the Cretaceous organic-rich formations. However, the reservoir features along with the theory of in-situ hydrocarbon generation in this sedimentary sequence belonging to the PGU Paleogene submarine fan deposits needs to be further investigated.