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| Titel |
Early-middle Eocene transition in calcareous nannofossil assemblages at IODP Site U1410 (Southeast Newfoundland Ridge, NW Atlantic) |
| VerfasserIn |
Carlotta Cappelli, Claudia Agnini, Yuhji Yamamoto |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141010
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| Publikation (Nr.) |
 EGU/EGU2017-4470.pdf |
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| Zusammenfassung |
| The early-middle Eocene interval documents the shift from the warmest greenhouse
conditions occurred during the Early Eocene Climatic Optimum (EECO, 52-50 Ma) to the
beginning of the cooling phase which led to the Oligocene icehouse regime. This important
transition is well expressed as a reversal in the global oxygen and carbonate isotope trends
(Zachos et al., 2001). Moreover, this interval was a time of remarkable transformation in the
marine biosphere. Communities of calcareous nannoplankton, marine calcifying
algae at the base of the oceans food chain, experienced transient and permanent
profound changes. Calcareous nannofossil are regarded as remarkable tools both in
biostratigraphy and paleoecology, with several taxa that show different responses to changes
in physical parameters of surface waters. Here, we aim to document calcareous
nannoplankton assemblage changes across the early-middle Eocene transition, in
order to upset the biostratigraphic framework and to increase comprehension of
how phytoplankton communities responded to paleoenvironmental changes at that
time.
The sedimentary successions recovered at IODP Site U1410 (Exp. 342; 41˚ 19.6987′N;
49˚ 10.1995′W, Norris et al., 2012) on the Southeast Newfoundland Ridge (NW Atlantic)
offer an expanded record of the early-middle Eocene interval that is marked by
an increase in accumulation rate related to sedimentation of clay-rich nannofossil
oozes. Quantitative analysis of calcareous nannofossil assemblages was conducted,
encompassing calcareous nannofossil Zones NP12 –NP15 or CNE4-CNE10 (Martini, 1971;
Agnini et al., 2014). The study interval records the appearance and proliferation
of Noelaerhabdaceae family (i.e, Reticulofenestra/Dictyococcites group), which
can be considered one of the most significant shifts in the assemblage structure
of the Paleogene. This change was probably favored by modifications in surface
water chemistry. The middle Eocene clay-rich sediments contain well preserved
nannofossils, making this Site suitable for a comprehensive taxonomic revision of
Nannotetrina and Chiasmolithus. Biohorizons related to species belonging to these two
genera are used to mark middle Eocene biozone boundary, a better characterization
of their taxonomy would thus improve their reliability as biostratigraphic tools.
Furthermore, during the early middle Eocene a new evolutionary lineage, which
includes S. kempii - S. perpendicularis- S. furcatholitoides morph. A - S. cuniculus - S.
furcatholitoides morph. B occurred among sphenoliths. This plexus is characterized by
progressive morphological changes which, if correctly identify, will allow for a very
detailed subdivision of this interval. Even more interestingly, we would assess if there
is any relationship between this evolutionary trend and the surrounding abiotic
conditions.
Agnini, C., Fornaciari, E., Raffi, I., Catanzariti, R., Pälike, H., Backman, J., and Rio, D.,
Newslett. Stratigr., 47, 131–181 (2014).
Martini E., in: Farinacci, A. (Ed.), Proceedings 2nd International Conference Planktonic
Microfossils Roma: Rome (Ed. Tecnosci.) 2, 739-785 (1971).
Norris R.D., Wilson P.A., Blum P. and the IODP Expedition 342 Scientists, Proceedings
of the Integrated Ocean Drilling Program, 342, 1-148 (2012).
Zachos J., Pagani M., Sloan L., Thomas E., Billups K., Science, 292, 686-693 (2001). |
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