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| Titel |
The calcareous nannofossil Prinsiosphaera achieved rock-forming abundances in the latest Triassic of western Tethys: consequences for the δ13C of bulk carbonate |
| VerfasserIn |
N. Preto, C. Agnini, M. Rigo, M. Sprovieri, H. Westphal |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 9 ; Nr. 10, no. 9 (2013-09-23), S.6053-6068 |
| Datensatznummer |
250085335
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| Publikation (Nr.) |
 copernicus.org/bg-10-6053-2013.pdf |
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| Zusammenfassung |
| The onset of pelagic biomineralization was a milestone in the history of the
long-term inorganic carbon cycle: as soon as calcareous nannofossils became
major limestone producers, the pH and supersaturation state of the global
ocean were stabilized (the so-called mid-Mesozoic revolution). But although
it is known that calcareous nannofossils were abundant already by the end of
the Triassic, no estimates exist on their contribution to hemipelagic
carbonate sedimentation. With this work, we estimate the volume proportion of
Prinsiosphaera, the dominant late Triassic calcareous nannofossil,
in hemipelagic and pelagic carbonates of western Tethys. The investigated
Upper Triassic lime mudstones are composed essentially of microspar and tests
of calcareous nannofossils, plus minor bioclasts. Prinsiosphaera had
become a significant component of lime mudstones since the late Norian, and
was contributing up to ca. 60% of the carbonate by the late Rhaetian in
periplatform environments with hemipelagic sedimentation. The increasing
proportion of Prinsiosphaera in upper Rhaetian hemipelagic lime
mudstones is paralleled by an increase of the δ13C of bulk
carbonate. We interpreted this isotopic trend as related to the diagenesis of
microspar, which incorporated respired organic carbon with a low
δ13C when it formed during shallow burial. As the proportion of
nannofossil tests increased, the contribution of microspar with low
δ13C diminished, determining the isotopic trend. We suggest that a
similar diagenetic effect may be observed in many Mesozoic limestones with a
significant, but not yet dominant, proportion of calcareous plankton. |
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