Biostratigraphy, sedimentology, stable isotopes and organic matter of the Jurassic sediments from Western Greece

This thesis concerns the study of the Lower Jurassic and particularly the Toarcian where an oceanic anoxic event has been recorded at about 183 Ma ago. The Toarcian Oceanic Anoxic Event (Τ-OAE) has been studied here in five different sections from western Greece. Three of these sections are located in the Ionian Zone and two in the Pindos Zone. The aim of this study is to recognize the Toarcian sediments of these two Zones and to investigate if the Τ-OAE has been recorded in each one of these. Moreover where it has been recorded, further research has been conducted in order to extract more information about the palaeoenvironment. The Τ-OAE coincides with marine anoxia to euxinia, high palaeotemperatures, high CO₂, sea transgression and mass extinctions. In order to recognize this event it is essential to find a positive excursion in total organic carbon (TOC) and a negative and/or positive excursion in carbon isotopes. The geochemical characteristics that have been studied here are the TOC δ¹³Ccarb, δ¹³Corg δ¹⁸Ocarb, δ³⁴SCAS, δ¹⁸OCAS and pyrite framboids. The first three, are those that confirm the presence of the Τ-OAE, while the rest of these can provide information about the palaeoenvironment. Analyzing the first three in all the sections, leaves no doubt that the Τ-OAE has been recorded in the Ionian and the Pindos Zone. Thus, a detailed look at all the biogeochemical characteristics makes clear that the Τ-ΟΑΕ has not been recorded in the same way in any of the sections. The percentage of TOC in the Ionian Zone is much more higher than in the Pindos Zone. This confirms the greater depth of the latter, which is consistent with the oceanic character of this Zone. In all the sections apart from Petousi (a section from Ionian Zone) a positive excursion in TOC and a negative in both carbon isotopes (carbonates and organic matter) were recorded. In Petousi section, apart from the negative carbon isotope excursion, there is also a positive excursion. The study of the pyrite framboids in a section from the Ionian Zone (Toka section) reveal a euxinic environment similar to that of the Black Sea. On the other hand, the Pindos Zone lacks pyrite framboids. This, in combination with the study of δ³⁴SCAs of the same section (Kastelli section), reveals an anoxic but not euxinic environment. In conclusion, this thesis confirms that the Toarcian Oceanic Anoxic Event is a global eventwith the regional character.Η παρούσα διδακτορική διατριβή αφορά στη μελέτη του Κατωτέρου Ιουρασικού με έμφαση στο Τοάρσιο (περίπου 183 Ma) όπου έχει καταγράφει ένα ωκεάνιο ανοξικό γεγονός. Το Ωκεάνιο Ανοξικό Γεγονός του Τοάρσιου (Τ-ΟΑΕ), μελετήθηκε λεπτομερώς σε πέντε τομές της Δυτικής Ελλάδας από την Ιόνια Ζώνη και τη Ζώνη της Πίνδου. Το Τ-ΟΑΕ έχει συσχετιστεί με θαλάσσια ανοξία, υψηλές παλαιοθερμοκρασίες, υψηλά επίπεδα CΟ₂, αλλαγές στη στάθμη της θάλασσας και μαζικές εξαφανίσεις ειδών. Στην παρούσα μελέτη αναλύθηκαν τα βιογεωχημικά χαρακτηριστικά του, δηλαδή η βιοστρωματογραφία, τα σταθερά ισότοπα του άνθρακα, του οξυγόνου και του θείου, ο ολικός οργανικός άνθρακας (TOC) και τα συσσωματώματα σιδηροπυρίτη των ιζημάτων. Τα βασικά χαρακτηριστικά του Τ-ΟΑΕ είναι η αύξηση του TOC και η αρνητική ή/και θετική μεταβολή στα ισότοπα του άνθρακα, τα υπόλοιπα βιογεωχημικά στοιχεία που μελετήθηκαν μας δίνουν πληροφορίες για το παλαιοπεριβάλλον. Από τα αποτελέσματα των βιοστρωματογραφικών αναλύσεων, έγινε δυνατός ο ακριβής προσδιορισμός της ηλικίας συγκεκριμένων οριζόντων σχηματισμών του Κατωτέρου Ιουρασικού. Ενώ από τη μελέτη των βασικών χαρακτηριστικών του Τ-ΟΑΕ έγινε σαφές ότι αυτό έχει καταγράφει και στις δυο Ζώνες. Σε όλες τις μελετηθείσες τομές έχουν καταγράφει κατά το Τοάρσιο η αύξηση στο ποσοστό του ολικού οργανικού άνθρακα και χαρακτηριστικές μεταβολές στα ισότοπα του άνθρακα. Επίσης προέκυψε ότι οι μεταβολές των ισοτόπων του άνθρακα είναι αρνητικές σε όλες τις τομές, εκτός από μια τομή της Ιόνιας Ζώνης (τομή Πετούσι) στην οποία έχει καταγραφεί τόσο αρνητική όσο και θετική μεταβολή στα ισότοπα του άνθρακα. Από τη συνολική έρευνα διαπιστώθηκε επίσης το πόσο σημαντική είναι η λεπτομερής δειγματοληψία για τη μελέτη αυτών των γεγονότων. Μέσα από τη λεπτομέρεια, φαίνεται ότι ενώ το Τ-ΟΑΕ έχει καταγραφεί σε όλες τις τομές, δεν έχει καταγραφεί με τον ίδιο τρόπο. Στην Ιόνια Ζώνη, η συγκέντρωση του TOC είναι σαφώς μεγαλύτερη της αντίστοιχης της Πίνδου. Αυτό είναι συμβατό με το μεγαλύτερο βάθος της ωκεάνιας λεκάνης Πίνδου. Η μελέτη των συσσωματωμάτων σιδηροπυρίτη σε τομή της Ιόνιας Ζώνης φανερώνει περιβάλλον ευξεινικό, παρόμοιο με αυτό της Μαύρης Θάλασσας. Ενώ στην Ζώνη της Πίνδου μέσω της μελέτης του δ³⁴SCAS και των συσσωματωμάτων σιδηροπυρίτη φαίνεται ότι το περιβάλλον ήταν ανοξικό άλλα όχι ευξεινικό. Όλα τα στοιχεία της παρούσας διδακτορικής διατριβής συνηγορούν υπέρ της άποψης ότι το Ωκεάνιο Ανοξικό Γεγονός του Τοάρσιου ήταν ένα γεγονός παγκόσμιας εμβέλειας με τοπικό χαρακτήρα

Connectivity controls on the late Miocene eastern Mediterranean fish fauna

International audienceEnvironmental change significantly affects the production of fish resources and their dependent societies. The paleontological record offers unique insight into the effects of long-term paleoenvironmental variability on the fish species’ distributions and abundances. In the present study, we investigate the late Miocene (7.5–6.5 Ma) fish assemblages of the Potamida section in western Crete (eastern Mediterranean). The determined fish taxa are examined in a paleobiogeographic context, with regard to their geographic and stratigraphic distribution from the early Miocene (~13 Ma) through today. In addition, present-day ecological data are used to reconstruct the paleoenvironmental conditions in the study area. Planktonic foraminifer biostratigraphy significantly improves the earlier dating of the studied sequence. The late Miocene fish fauna of Potamida includes 35 taxa (seven in open nomenclature) from 13 teleost families. The eastern Mediterranean biostratigraphic and geographic distribution of 32 taxa is significantly expanded into the Tortonian, whereas 13 species are recorded for the first time from the Messinian. Four stages are distinguished in the area’s paleoenvironmental evolution. (1) The Potamida area was an open marine environment with depths exceeding 150 m between ~7.5–7.45 Ma. (2) Between 7.45–7.36 Ma, the results suggest depths between 300–400 m. (3) The depositional depth increases between 7.36–7.28 Ma to 400–550 m. (4) Later on, approximately between 6.8–6.6 Ma, the depth is again estimated around 100–150 m

Large sea surface temperature, salinity, and productivity-preservation changes preceding the onset of the Messinian Salinity Crisis in the eastern Mediterranean Sea

International audienceThe Messinian Salinity Crisis (MSC; 5.97-5.33 Ma) is an enigmatic episode of paleoceanographic change, when kilometer-thick evaporite units were deposited in the Mediterranean basin. Here, we use geochemical (biomarker, isotope) data to reconstruct sea surface temperature, salinity, and productivity-preservation changes in the Mediterranean basin just before the MSC. The proxy data indicate that the Mediterranean Sea was significantly saltier and colder between 6.415 Ma and 6.151 Ma, than between 6.151 and 5.971 Ma. Salinity decrease at 6.151 Ma seems to be a relatively fast event just preceding the inception of a warming phase that lasted almost uninterrupted until the MSC onset. The water exchange with the Paratethys could have caused, along with the African rivers, an increased freshwater supply, resulting in normal marine Mediterranean waters between 6.151-5.971 Ma, despite the severe restriction of marine connections with the Atlantic at that time. SST changes determined a sharp drop in productivity and/or preservation of organic matter, marked by deposition of calcareous marls. Productivity and preservation were relatively high and constant until 6.01 Ma. Afterward, increased influx of terrestrial organic matter and probably enhanced water column stratification prevailed. Around 5.971 Ma, modifications in aquatic vs. terrestrially-derived biomarkers indicate changes in organic matter influx at the MSC onset

Large sea surface temperature, salinity, and productivity-preservation changes preceding the onset of the Messinian Salinity Crisis in the eastern Mediterranean Sea

International audienceThe Messinian Salinity Crisis (MSC; 5.97-5.33 Ma) is an enigmatic episode of paleoceanographic change, when kilometer-thick evaporite units were deposited in the Mediterranean basin. Here, we use geochemical (biomarker, isotope) data to reconstruct sea surface temperature, salinity, and productivity-preservation changes in the Mediterranean basin just before the MSC. The proxy data indicate that the Mediterranean Sea was significantly saltier and colder between 6.415 Ma and 6.151 Ma, than between 6.151 and 5.971 Ma. Salinity decrease at 6.151 Ma seems to be a relatively fast event just preceding the inception of a warming phase that lasted almost uninterrupted until the MSC onset. The water exchange with the Paratethys could have caused, along with the African rivers, an increased freshwater supply, resulting in normal marine Mediterranean waters between 6.151-5.971 Ma, despite the severe restriction of marine connections with the Atlantic at that time. SST changes determined a sharp drop in productivity and/or preservation of organic matter, marked by deposition of calcareous marls. Productivity and preservation were relatively high and constant until 6.01 Ma. Afterward, increased influx of terrestrial organic matter and probably enhanced water column stratification prevailed. Around 5.971 Ma, modifications in aquatic vs. terrestrially-derived biomarkers indicate changes in organic matter influx at the MSC onset

Connectivity controls on the late Miocene eastern Mediterranean fish fauna

Summarization: Environmental change significantly affects the production of fish resources and their dependent societies. The paleontological record offers unique insight into the effects of long-term paleoenvironmental variability on the fish species’ distributions and abundances. In the present study, we investigate the late Miocene (7.5–6.5 Ma) fish assemblages of the Potamida section in western Crete (eastern Mediterranean). The determined fish taxa are examined in a paleobiogeographic context, with regard to their geographic and stratigraphic distribution from the early Miocene (~13 Ma) through today. In addition, present-day ecological data are used to reconstruct the paleoenvironmental conditions in the study area. Planktonic foraminifer biostratigraphy significantly improves the earlier dating of the studied sequence. The late Miocene fish fauna of Potamida includes 35 taxa (seven in open nomenclature) from 13 teleost families. The eastern Mediterranean biostratigraphic and geographic distribution of 32 taxa is significantly expanded into the Tortonian, whereas 13 species are recorded for the first time from the Messinian. Four stages are distinguished in the area’s paleoenvironmental evolution. (1) The Potamida area was an open marine environment with depths exceeding 150 m between ~7.5–7.45 Ma. (2) Between 7.45–7.36 Ma, the results suggest depths between 300–400 m. (3) The depositional depth increases between 7.36–7.28 Ma to 400–550 m. (4) Later on, approximately between 6.8–6.6 Ma, the depth is again estimated around 100–150 m.Presented on: International Journal of Earth Science

Large sea surface temperature, salinity, and productivity-preservation changes preceding the onset of the Messinian salinity crisis in the Eastern Mediterranean Sea

Summarization: The Messinian Salinity Crisis (MSC; 5.97–5.33 Ma) is an enigmatic episode of paleoceanographic change, when kilometer-thick evaporite units were deposited in the Mediterranean basin. Here we use geochemical (biomarker and isotope) data to reconstruct sea surface temperature, salinity, and productivity-preservation changes in the Mediterranean basin just before the MSC. The proxy data indicate that the Mediterranean Sea was significantly saltier and colder between 6.415 and 6.151 Ma, than between 6.151 and 5.971 Ma. Salinity decrease at 6.151 Ma seems to be a relatively fast event just preceding the inception of a warming phase that lasted almost uninterrupted until the MSC onset. The water exchange with the Paratethys could have caused, along with the African rivers, an increased freshwater supply, resulting in normal marine Mediterranean waters between 6.151 and 5.971 Ma, despite the severe restriction of marine connections with the Atlantic at that time. Sea surface temperature changes determined a sharp drop in productivity and/or preservation of organic matter, marked by deposition of calcareous marls. Productivity and preservation were relatively high and constant until 6.01 Ma. Afterward, increased influx of terrestrial organic matter and probably enhanced water column stratification prevailed. Around 5.971 Ma, modifications in aquatic versus terrestrially derived biomarkers indicate changes in organic matter influx at the MSC onset.Παρουσιάστηκε στο: Paleoceanography and Paleoclimatolog