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| Titel |
New stratigraphic and isotopic record of the Toarcian Oceanic Anoxic Event from Hungary |
| VerfasserIn |
Tamás Müller, Gregory Price, David Bajnai, Anita Nyerges, József Pálfy  , Zoltán May |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250132823
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| Publikation (Nr.) |
 EGU/EGU2016-13365.pdf |
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| Zusammenfassung |
| In the Early Toarcian (∼183 Ma) major global environmental changes took place in the
ocean-atmosphere system, including the widely discussed Toarcian Oceanic Anoxic Event
(T-OAE). This phenomenon is characterized by strong perturbation of the carbon-cycle and
other geochemical systems. A peculiar negative carbon-isotope excursion (CIE) is a hallmark
of the event, reflecting the injection of large amount of isotopically light carbon into
the ocean-atmosphere system, possible due to dissociation of gas-hydrate from
shelf areas. This observed negative CIE and a subsequent broad positive anomaly
could be also key signals for chemostratigraphical correlation. In our study we
obtained new, high-resolution organic carbon isotope data from the Réka Valley
section of the Mecsek Mts. in southern Hungary. The Mecsek Basin was located
at the European margin where a thick Lower Jurassic succession of siliciclastic
hemipelagic sediments is interrupted by 13 m of organic-rich black shales in the
Lower Toarcian. The δ13Corg data from the Réka Valley section is characterized
by very negative values (averaging -32 ), with apparently cyclic fluctuation. The
shape of the δ13Corg shows that a continuous and complete record can be found
in the Réka Valley and also suggests mixed features between the carbon isotope
record of the NW European and Tethyan regions. We have also carried out high
resolution handheld XRF analyzes to study cyclostratigraphic signals in the section. The
distribution of four elements Ti, Ca, Si and Al were used in our studies beside the
δ13Corg data. The duration for the negative shift at Réka Valley, calculated from XRF
signals, is either 550–750 kyr, 200–275 kyr or 116–158 kyr, based on 100 kyr
short eccentricity, 36.6 kyr obliquity or 21.1 kyr precession signals, respectively.
Several previous studies concluded that the most probable astronomical forcing
factor during the CIE of the Toarcian OAE is obliquity. Therefore, we assume a
duration around 200–275 kyr for the CIE at the Réka Valley based on obliquity
controlled astronomical forcing. The section was previously biostratigraphically
poorly constrained, our new data on calcareous nannoplankton help improve the
dating. Biozones NJ5b, NJ6 and NJ7 are spanning the negative CIE, NJ6 covers the
interval where δ13Corg values are the most negative. The new high resolution isotope
data allow reliable chemostratigraphic correlation of the Réka Valley with other
European Toarcian successions (e.g. Peniche, Yorkshire, Dotternhausen and Valdorbia). |
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