Ocean circulation in the Toarcian (Early Jurassic), a key control on deoxygenation and carbon burial on the European Shelf

The Toarcian Oceanic Anoxic Event (T-OAE, ∼183 My) was a long-lasting episode of ocean deoxygenation during the Early Jurassic. The event is related to a period of global warming and characterized by major perturbations to the hydrological and carbon cycles with high rates of organic matter burial in shelf seas. Ocean circulation during the Toarcian and its influence on marine biogeochemical cycles are still not fully understood. Here,we assess the spatial extent of anoxia in the NW Tethys Ocean during the T-OAE, the relationship with ocean circulation and the impact on organic carbon burial, using new and existing sedimentary records from the European Epicontinental Shelf (EES) in combination with general circulation model results. We demonstrate that bottom waters on the southwestern part of the shelf were mainly oxic during the T-OAE, while those in the northeastern basins were mostly anoxic or even sulfidic. Results for two ocean-atmosphere models (FOAM and MITgcm) suggest the presence of a strong clockwise gyre over the EES, which brought oxygenated equatorial waters from the Tethys Ocean to the southern shelf. The northward limb of the gyre was significantly weakened due to the rough bathymetry of the northern shelf, making this relative small region highly sensitive to local ocean stratification. These sluggish ocean dynamics promoted bottom water anoxia and enhanced burial of organic carbon in the northeastern basins, which accounted for 3–5% of the total carbon extracted from the ocean-atmosphere system as recorded by the positive carbon isotope shift

Oceanic response to Pliensbachian and Toarcian magmatic events: Implications from an organic-rich basinal succession in the NW Tethys

The Bächental bituminous marls (Bächentaler Bitumenmergel) belonging to the Sachrang Member of the Lower Jurassic Middle Allgäu Formation were investigated using a multidisciplinary approach to determine environmental controls on the formation of organic-rich deposits in a semi-restricted basin of the NW Tethys during the Early Jurassic. The marls are subdivided into three units on the basis of mineralogical composition, source-rock parameters, redox conditions, salinity variations, and diagenetic processes. Redox proxies (e.g., pristane/phytane ratio; aryl isoprenoids; bioturbation; ternary plot of iron, total organic carbon, and sulphur) indicate varying suboxic to euxinic conditions during deposition of the Bächental section. Redox variations were mainly controlled by sea-level fluctuations with the tectonically complex bathymetry of the Bächental basin determining watermass exchange with the Tethys Ocean. Accordingly, strongest anoxia and highest total organic carbon content (up to 13%) occur in the middle part of the profile (upper tenuicostatum and lower falciferum zones), coincident with an increase in surface-water productivity during a period of relative sea-level lowstand that induced salinity stratification in a stagnant basin setting. This level corresponds to the time interval of the lower Toarcian oceanic anoxic event (T-OAE). However, the absence of the widely observed lower Toarcian negative carbon isotope excursion in the study section questions its unrestricted use as a global chemostratigraphic marker. Stratigraphic correlation of the thermally immature Bächental bituminous marls with the Posidonia Shale of SW Germany on the basis of C27/C29 sterane ratio profiles and ammonite data suggests that deposition of organic matter-rich sediments in isolated basins in the Alpine realm commenced earlier (late Pliensbachian margaritatus Zone) than in regionally proximal epicontinental seas (early Toarcian tenuicostatum Zone). The late Pliensbachian onset of reducing conditions in the Bächental basin coincided with an influx of volcaniclastic detritus that was possibly connected to complex rifting processes of the Alpine Tethys and with a globally observed eruption-induced extinction event. The level of maximum organic matter accumulation in the Bächental basin corresponds to the main eruptive phase of the Karoo-Ferrar large igneous province (LIP), confirming its massive impact on global climate and oceanic conditions during the Early Jurassic. The Bächental marl succession is thus a record of the complex interaction of global (i.e., LIP) and local (e.g., redox and salinity variations, basin morphology) factors that caused reducing conditions and organic matter enrichment in the Bächental basin. These developments resulted in highly inhomogeneous environmental conditions in semi-restricted basins of the NW Tethyan domain during late Pliensbachian and early Toarcian time

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

A global event with a regional character: The Early Toarcian Oceanic Anoxic Event in the Pindos Ocean (northern Peloponnese, Greece)

The Early Toarcian (Early Jurassic, c. 183 Ma) was characterized by an Oceanic Anoxic Event (T-OAE), primarily identified by the presence of globally distributed approximately coeval black organic-rich shales. This event corresponded with relatively high marine temperatures, mass extinction, and both positive and negative carbon-isotope excursions. Because most studies of the T-OAE have taken place in northern European and Tethyan palaeogeographic domains, there is considerable controversy as to the regional or global character of this event. Here, we present the first high-resolution integrated chemostratigraphic (carbonate, organic carbon, δ13 C carb, δ13Corg) and biostratigraphic (calcareous nannofossil) records from the Kastelli Pelites cropping out in the Pindos Zone, western Greece. During the Mesozoic, the Pindos Zone was a deep-sea oceanmargin basin, which formed in mid-Triassic times along the northeast passive margin of Apulia. In two sections through the Kastelli Pelites, the chemostratigraphic and biostratigraphic (nannofossil) signatures of the most organic-rich facies are identified as correlative with the Lower Toarcian, tenuicostatum/polymorphum-falciferum/serpentinum/levisoni ammonite zones, indicating that these sediments record the T-OAE. Both sections also display the characteristic negative carbon-isotope excursion in organic matter and carbonate. This occurrence reinforces the global significance of the Early Toarcian Oceanic Anoxic Event. © 2010 Cambridge University Press

A global event with a regional character: the Early Toarcian Oceanic Anoxic Event in the Pindos Ocean (northern Peloponnese, Greece)

The Early Toarcian (Early Jurassic, c. 183 Ma) was characterized by an Oceanic Anoxic Event (T-OAE), primarily identified by the presence of globally distributed approximately coeval black organic-rich shales. This event corresponded with relatively high marine temperatures, mass extinction, and both positive and negative carbon-isotope excursions. Because most studies of the T-OAE have taken place in northern European and Tethyan palaeogeographic domains, there is considerable controversy as to the regional or global character of this event. Here, we present the first high-resolution integrated chemostratigraphic (carbonate, organic carbon, δ13 C carb, δ13Corg) and biostratigraphic (calcareous nannofossil) records from the Kastelli Pelites cropping out in the Pindos Zone, western Greece. During the Mesozoic, the Pindos Zone was a deep-sea oceanmargin basin, which formed in mid-Triassic times along the northeast passive margin of Apulia. In two sections through the Kastelli Pelites, the chemostratigraphic and biostratigraphic (nannofossil) signatures of the most organic-rich facies are identified as correlative with the Lower Toarcian, tenuicostatum/polymorphum-falciferum/serpentinum/levisoni ammonite zones, indicating that these sediments record the T-OAE. Both sections also display the characteristic negative carbon-isotope excursion in organic matter and carbonate. This occurrence reinforces the global significance of the Early Toarcian Oceanic Anoxic Event. © 2010 Cambridge University Press

Menopause Effect on Blood Fe and Cu Isotope Compositions

International audienc

The Toarcian Oceanic Anoxic Event in the Ionian Zone, Greece

The Early Jurassic was characterized by a global disturbance of the carbon cycle known as the Toarcian Oceanic Anoxic Event (T-OAE). This event is recorded worldwide by a negative excursion in marine and terrestrial carbon-isotope ratios, typically interrupting an overarching positive trend attributed to large-scale burial of marine organic matter under oxygen-depleted conditions. The negative excursion is attributed to introduction of isotopically light carbon into the ocean-atmosphere system. Three sections from the Ionian Zone in Greece have been analysed in terms of biostratigraphy, Total Organic Carbon (TOC), CaCO3, δ13Ccarb, δ18Ocarb and δ13Corg. On the basis of bio- and chemostratigraphy, the age of Pliensbachian-Toarcian formations from the Ionian Zone in Greece has been refined and the geochemical signature of the T-OAE recognized. All sections illustrate the characteristic negative excursion in carbon isotopes from both carbonates and organic matter and, in only one locality, a positive excursion has also been recorded. The recognition of the T-OAE in this part of the Tethyan continental margin offers additional information on the global impact and amplitude of this important Jurassic palaeoceanographic event. © 2013