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| Titel |
Carbon cycle perturbations recorded by δ13C of bulk organic matter: the Carnian Pluvial Event in the Dolomites, northern Italy |
| VerfasserIn |
Nereo Preto, Anna Breda, Jacopo Dal Corso, Manuel Rigo, Guido Roghi, Christoph Spötl |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106886
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| Publikation (Nr.) |
 EGU/EGU2015-6565.pdf |
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| Zusammenfassung |
| A period of increased rainfall occurred in the Carnian (Late Triassic), known as Carnian
Pluvial Event (CPE), which is evidenced by major lithological changes in continental
and marine successions at tropical latitudes. Increased continental weathering and
erosion led to the supply of large amounts of siliciclastics into the marginal basins
of the Tethys. Seawater anoxia is also observed locally in semi-restricted basins.
Simultaneously, microbial factories on high-relief carbonate platforms were replaced by
metazoan factories, forming low-relief carbonate ramps and mixed low-gradient
shelves.
This environmental change has been shown to be closely associated with a negative
carbon isotope excursion. A negative δ13C shift is recorded by bulk organic matter in the
Milieres section (central Dolomites) and parallels a coeval excursion in carbon-isotope
records of higher plant and marine algal biomarker, thus testifying a global change in the
isotopic composition of carbon dioxide in the atmosphere and of dissolved inorganic carbon
(DIC) in the ocean. This isotopic excursion was identified in organic carbon records
throughout the western Tethys, but so far could not be reproduced convincingly using carbon
isotope records from carbonate.
A long carbon isotope record was produced from bulk organic matter of the early to late
Carnian Milieres - Dibona section in the Dolomites, northern Italy. Carbon isotope
analyses of carbonate (limestone and dolomite) were also obtained. This new carbon
isotope record illustrates the structure of this complex carbon cycle perturbation
related to the CPE. But while sharp carbon isotope oscillations are evident in the
bulk organic carbon record, there is no evidence of a similar pattern in carbonate
record. It can be shown that the carbon isotope record of carbonates is influenced by
fractionation and diagenetic processes that completely obliterated the original δ13C
signal.
We conclude that the Carnian carbonates of the Dolomites do not record the δ13C
of marine DIC. We suggest that the identification of the Carnian carbon isotope
excursion in carbonate records may only be possible if the isotopic analyses are
coupled with petrographic screening that prove a minimal diagenetic overprint. |
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