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

2011 ◽  
Vol 148 (4) ◽  
pp. 619-631 ◽  
Author(s):  
N. KAFOUSIA ◽  
V. KARAKITSIOS ◽  
H. C. JENKYNS ◽  
E. MATTIOLI
Keyword(s):  
Carbon Isotope ◽  
Passive Margin ◽  
Oceanic Anoxic Event ◽  
Northern European ◽  
Carbon Isotope Excursion ◽  
Anoxic Event ◽  
Considerable Controversy ◽  
Regional Character ◽  
Globally Distributed ◽  
Ammonite Zones

AbstractThe 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, 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.

scholarly journals PRELIMINARY DATA FROM THE FIRST RECORD OF THE EARLY TOARCIAN OCEANIC ANOXIC EVENT IN THE SEDIMENTS OF THE PINDOS ZONE (GREECE)

2017 ◽  
Vol 43 (2) ◽  
pp. 627 ◽  
Author(s):  
Kafousia N. Kafousia N. ◽  
V. Karakitsios ◽  
H.C. Jenkyns
Keyword(s):  
Organic Carbon ◽  
Carbon Isotope ◽  
First Record ◽  
Passive Margin ◽  
Oceanic Anoxic Event ◽  
Carbonate Carbon ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Anoxic Event ◽  
Regional Character

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‰), whereas higher in the section the values drop down to ~ -5‰. Following this negative excursion, the carbonate carbon-isotope ratios return to background values. The TOC excursion is modest, rising from a background of 0.05% to ~ 2% and then returning to a background of 0.04%. Because both relative enrichment in TOC and the negative carbon-isotope excursion that characterize the Toarcian OAE are recorded in some of the deepest marine sediments of the Tethyan region, the global significance of the event is reinforced.

Carbon-isotope and microfaunal stratigraphy bounding the Lower Aptian Oceanic Anoxic Event 1a in northeastern Tunisia

2013 ◽  
Vol 39 ◽  
pp. 133-148 ◽  
Author(s):  
Abdallah Elkhazri ◽  
Hassen Abdallah ◽  
Saloua Razgallah ◽  
Michel Moullade ◽  
Wolfgang Kuhnt
Keyword(s):  
Carbon Isotope ◽  
Oceanic Anoxic Event ◽  
Lower Aptian ◽  
Anoxic Event ◽  
Northeastern Tunisia

The chemostratigraphy and environmental significance of the Marlstone and Junction Bed (Beacon Limestone, Toarcian, Lower Jurassic, Dorset, UK)

2021 ◽  
pp. 1-15
Author(s):  
Hugh C. Jenkyns ◽  
Sophie Macfarlane
Keyword(s):  
Carbon Isotope ◽  
Oxygen Isotopes ◽  
Lower Jurassic ◽  
Carbon And Oxygen Isotopes ◽  
Oceanic Anoxic Event ◽  
Nodular Limestone ◽  
Anoxic Event ◽  
Reference Curves ◽  
High Degree ◽  
Organic Rich Sediment

Abstract Two fallen blocks of the Marlstone and stratigraphically overlying Junction Bed sampled on the beach below Doghouse Cliff in Dorset, UK (Wessex Basin) have been examined for carbon and oxygen isotopes of bulk carbonate as well as for strontium, carbon and oxygen isotopes and Mg:Ca ratios in the contained belemnites. The sequence, which contains most of the Toarcian zones and subzones within a metre or less of grey to yellow to pink, red and brown fossil-rich nodular limestone, is extremely condensed and lithologically similar to pelagic red limestones of the Tethyan Jurassic that are locally mineralized with Fe-Mn oxyhydroxides (e.g., Rosso Ammonitico). Strontium-isotope ratios of the contained belemnites are compatible with existing reference curves and both blocks show a rise to more radiogenic values post-dating the Pliensbachian–Toarcian boundary. The high degree of correlation between the relatively negative carbon and oxygen isotopes of the bulk carbonate is compatible with significant diagenetic overprint, and contrasts with higher carbon-isotope values in coeval condensed coccolith-rich limestones elsewhere. Evidence for the characteristic signature of the Toarcian Oceanic Anoxic Event, as represented by organic-rich sediment, is absent, possibly owing to a stratigraphic gap. Both blocks exhibit abrupt carbon-isotope shifts to lower values, one of which could represent the limbs of an incompletely recorded negative excursion associated with the Toarcian Oceanic Anoxic Event. That the Toarcian Oceanic Anoxic Event was also a significant hyperthermal is illustrated in both blocks by a drop in oxygen-isotope values and rise in Mg:Ca ratios of belemnites close to the base of the Junction Bed in the lowest part of the serpentinum zone.

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