Papers by Nefeli Kafousia
This thesis concerns the study of the Lower Jurassic and particularly the Toarcian where an ocean... more 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 ...
Submitted by Sarafidou Maria ([email protected]) on 2016-04-18T12:42:20Z No. of bitstreams: 1 521_Agi... more Submitted by Sarafidou Maria ([email protected]) on 2016-04-18T12:42:20Z No. of bitstreams: 1 521_Agiadi et al 2014 poster.pdf: 57872499 bytes, checksum: 45b87bc51227452113dff32e8b7e7491 (MD5)
Paleoceanography and Paleoclimatology, 2019
The Messinian Salinity Crisis (MSC; 5.97–5.33 Ma) is an enigmatic episode of paleoceanographic ch... more 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 ch...
Basin Research, 2016
This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry,... more This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry, borehole data and seismic profiles) of the Messinian-Zanclean deposits on Zakynthos Island (Ionian Sea) focuses on the sedimentary succession recording the pre-evaporitic phase of the Messinian salinity crisis (MSC) through the reestablishment of the marine conditions in a transitional area between the eastern and the western Mediterranean. Two intervals are distinguished through the palaeoenvironmental reconstruction of the pre-evaporitic Messinian in Kalamaki: (a) 6.45-6.122 Ma and (b) 6.122-5.97 Ma. Both the planktonic foraminifer and the fish assemblages indicate a cooling phase punctuated by hypersalinity episodes at around 6.05 Ma. Two evaporite units are recognized and associated with the tectonic evolution of the Kalamaki-Argassi area. The Primary Lower Gypsum (PLG) unit was deposited during the first MSC stage (5.971-5.60 Ma) in late-Messinian marginal basins within the pre-Apulian foreland basin and in the wedge-top (<300 m) developed over the Ionian zone. During the second MSC stage (5.60-5.55 Ma), the PLG evaporites were deeply eroded in the forebulge-backbulge and the wedge-top areas, and supplied the foreland basin's depocentre with gypsum turbidites assigned to the Resedimented Lower Gypsum (RLG) unit. In this study, we propose a simple model for the Neogene-Pliocene continental foreland-directed migration of the Hellenide thrusting, which explains the palaeogeography of the Zakynthos basin. The diapiric movements of the Ionian Triassic evaporites regulated the configuration and the overall subsidence of the foreland basin and, therefore, the MSC expression in this area.
International Journal of Earth Sciences, 2016
biostratigraphic and geographic distribution of 32 taxa is significantly expanded into the Torton... more 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.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
The Early Jurassic was characterized by a global disturbance of the carbon cycle known as the Toa... more 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), CaCO 3 , δ 13 C carb , δ 18 O carb and δ 13 C org. 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.
Geological Magazine, 2011
The Early Toarcian (Early Jurassic, c. 183 Ma) was characterized by an Oceanic Anoxic Event (T-OA... more 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, δ13Ccarb, 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 ocean-margin basin, which formed in mid-Triassic times along the northeast passive margin of Apulia. In two sections through the Kastelli Pelites, ...
Bulletin of the Geological Society of Greece
The Early Toarcian Oceanic Anoxic Event (ca 183 Ma) coincides with high palaeotemperatures, regio... more The Early Toarcian Oceanic Anoxic Event (ca 183 Ma) coincides with high palaeotemperatures, regional anoxia to euxinia, marine transgression, mass extinction and high rates of organic-carbon burial in a global context. Most of the detailed studies of this event have investigated deposits formed in the epicontinental seas of northern Europe, although coeval organic-rich shales are known locally in the Tethyan region. However, the global or regional character of this event is still under debate. In this study we present, for the first time, a high-resolution geochemical record of the Early Toarcian Oceanic Anoxic event in pelagic sediments (Kastelli Pelites) formed in a long-lived Mesozoic deep-sea basin, corresponding to the western passive margin of the Pindos Ocean of western Greece. Our data record both the positive excursion in total organic carbon (TOC) and the characteristic negative excursion in δ13Ccarb. The δ13Ccarb values are very stable in the bottom of the section (~2‰), ...
This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry,... more This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry, borehole data and seismic profiles) of the Messinian–Zanclean deposits on Zakynthos Island (Ionian Sea) focuses on the sedimentary succession recording the pre-evaporitic phase of the Messinian salinity crisis (MSC) through the re-establishment of the marine conditions in a transitional area between the eastern and the western Mediterranean. Two intervals are distinguished through the palaeoenvironmental reconstruction of the pre-evaporitic Messinian in Kalamaki: (a) 6.45–6.122 Ma and (b) 6.122–5.97 Ma. Both the planktonic foraminifer and the fish assemblages indicate a cooling phase punctuated by hypersalinity episodes at around 6.05 Ma. Two evaporite units are recognized and associated with the tectonic evolution of the Kalamaki–Argassi area. The Primary Lower Gypsum (PLG) unit was deposited during the first MSC stage (5.971–5.60 Ma) in late-Messinian marginal basins within the pre-Ap...
Goldschmidt2021 abstracts
Geochimica Et Cosmochimica Acta, 2006
Two new records of seawater sulfate-sulfur isotopes derived from carbonate associated sulfate sug... more Two new records of seawater sulfate-sulfur isotopes derived from carbonate associated sulfate suggest that other isotopic records found in sediments from the European epicontinental sea (EES) during the Toarcian may represent principally local scale rather than global changes. The first of these, from belemnites from the Yorkshire coast in the UK (within the EES), describe a rapid change from +16.5& to +22.2& d 34 S VCDT between the semicelatum and exaratum ammonite subzones. Radiometric dating shows that the entire Toarcian represents around 5 myr and individual subzones (if equal in length) can be calculated to be around 400,000 years in duration. Hence, it is conservatively estimated that this 6& isotopic change occurred in 1.5 myr or less. This is considerably shorter than the modern residence time of sulfate in the oceans (20 myr) and requires either; that the concentration of oceanic sulfate in the Toarcian was much lower than its modern value, or; that the European epicontinental sea became isolated from the worlds oceans at this time. A second record from southern Tibet from sediments deposited on the margin of Tethys, whilst having less exact dating and a degree of scatter, shows no such consistent change and records an average value of around +18& d 34 S VCDT . The Tibetan data therefore favours the hypothesis that the EES developed a chemistry significantly different from that of the worlds oceans during the Toarcian. If correct, this suggests that carbon (and other) isotope data from Toarcian sediments from the EES only records regional variation and calls into question previous models of extensive synchronous global carbon burial, as well as the need for large scale methane release at this time.
Here we present two records of marine SO4-O isotopes derived from carbonate associated sulfate (C... more Here we present two records of marine SO4-O isotopes derived from carbonate associated sulfate (CAS) across the Toarcian anoxic event, one from a Tethyan open ocean margin (Tibet) and the other from within the European Epicontinental Sea (EES, Yorkshire, UK). Limestones from Tibet record average SO4-δ18O of+ 13.1±1.3‰ across the interval with no systematic change. Belemnites from Yorkshire however record considerably heavier values which change in a systematic way. These start at~+ 15‰ in the uppermost Pliensbachian ...
This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry,... more This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry, borehole data and seismic profiles) of the Messinian–Zanclean deposits on Zakynthos Island (Ionian Sea) focuses on the sedimentary succession recording the pre-evaporitic phase of the Messinian salinity crisis (MSC) through the re-establishment of the marine conditions in a transitional area between the eastern and the western Mediterranean. Two intervals are distinguished through the palaeoenvironmental reconstruction of the pre-evaporitic Messinian in Kalamaki: (a) 6.45–6.122 Ma and (b) 6.122–5.97 Ma. Both the planktonic foraminifer and the fish assemblages indicate a cooling phase punctuated by hypersalinity episodes at around 6.05 Ma. Two evaporite units are recognized and associated with the tectonic evolution of the Kalamaki–Argassi area. The Primary Lower Gypsum (PLG) unit was deposited during the first MSC stage (5.971–5.60 Ma) in late-Messinian marginal basins within the pre-Apulian foreland basin and in the wedge-top (<300 m) developed over the Ionian zone. During the second MSC stage (5.60–5.55 Ma), the PLG evaporites were deeply eroded in the forebulge–backbulge and the wedge-top areas, and supplied the foreland basin's depocentre with gypsum turbidites assigned to the Resedimented Lower Gypsum (RLG) unit. In this study, we propose a simple model for the Neogene–Pliocene continental foreland-directed migration of the Hellenide thrusting, which explains the palaeogeography of the Zakynthos basin. The diapiric movements of the Ionian Triassic evaporites regulated the configuration and the overall subsidence of the foreland basin and, therefore, the MSC expression in this area.
Geological Magazine, 2011
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
A global perturbation in the carbon cycle has been recorded in the Early Toarcian (~ 183 Ma) and ... more A global perturbation in the carbon cycle has been recorded in the Early Toarcian (~ 183 Ma) and is marked by enhanced organic-carbon burial and mass extinction. It is also associated with high palaeotemperatures, both positive and negative excursions in carbon-isotope ratios, and the development of anoxic to euxinic conditions in marine environments: together these phenomena have been designated as constituting an Oceanic Anoxic Event. Here we provide a high-resolution, multiproxy biostratigraphic and chemostratigraphic study from a section that belongs to the central Ionian Zone in Greece. Calcareous nannofossil distribution, as well as the TOC, δ 13 C carb and δ 13 C org , have all been determined. The nannofossil zones NJT 5b, NJT 6 and NJT 7 have been recognized in the section. In the NJT 5b zone a small positive excursion in TOC and negative excursion in δ 13 C carb is recorded, tentatively assigned to the Pliensbachian/Toarcian boundary. In the NJT 6 zone, the main negative carbon-isotope excursion characteristic of this interval is developed, associated with a relative increase in TOC. The difference in this section, compared with sections from the Pindos Zone but in common with sections elsewhere, is the record of a positive excursion in the NJT 7 zone in both organic and carbonate carbon isotopes. This study offers new biostratigraphic and geochemical data for the Ionian Zone, and further illustrates the impact of Toarcian Oceanic Anoxic Event in the Tethyan region.
Geochimica et Cosmochimica Acta Supplement, Jun 1, 2009
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Papers by Nefeli Kafousia