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| Titel |
The Middle Jurassic Watznaueria (coccolith-type algae) diversification impact on carbon cycle and bulk carbonate composition |
| VerfasserIn |
Baptiste Suchéras-Marx, Abel Guihou, Fabienne Giraud, Emanuela Mattioli, Christophe Lécuyer, Bernard Pittet |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250045813
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| Zusammenfassung |
| Today, coccolithophores are one of the major carbonate producers in the ocean and therefore
play an important role in modern carbon cycle. These green-brown algae produce
micrometric carbonate platelets called coccoliths, abundantly documented in the fossil
record. However, their influence on the carbon cycle back in time is still elusive. During the
Early Bajocian (Middle Jurassic, ~-170 Ma) the coccolith-type nannofossil genus
Watznaueria underwent significant diversification, rapidly becoming the major pelagic
carbonate producers and so for 80 Ma. This diversification is synchronous with a
δ13C positive excursion recorded in the bulk carbonate from different localities in
Europe suggesting a strong reorganization of the carbon cycle. This work tests
the hypothesis of a causal link between the diversification of Watznaueria and the
positive δ13C excursion. We have chosen as support for our test the Early Bajocian
section of Cabo Mondego (Portugal), a carbonate-rich outcrop that is the GSSP of the
Aalenian/Bajocian boundary. By coupling quantification of absolute abundance of coccoliths,
biometrical analysis and isotope geochemistry, we show that the global pelagic
carbonate production increased by 15% during the Early Bajocian. Conversely, we
calculated the δ13C values of the four main carbonate producers – i.e. coccoliths s.l,
Watznaueria spp., Schizosphaerella (incertae sedis) and unidentified carbonate – by
least square regression of a simple mass balance calculation. Our results suggest
that both the diversification of Watznaueriagnd the increase in pelagic carbonate
production cannot account for the positivegδ13C excursion recorded in bulk carbonate. |
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