Dynamics of calcareous nannoplankton during the Neogene: climatic and oceanographic implications
Variations in the composition of calcareous nannofossil assemblages of several Neogene series (from the North Atlantic and the Antarctic Ocean, Indian sector) were studied. Particular interest has been given to the quantification of data and high stratigraphic resolution. The analysis of the recordi...
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| Other Authors: | , , , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | French |
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HAL CCSD
1991
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| Subjects: | |
| Online Access: | https://theses.hal.science/tel-02307706 https://theses.hal.science/tel-02307706/document https://theses.hal.science/tel-02307706/file/These_L_Beaufort_1991_UCBL.pdf |
| Summary: | Variations in the composition of calcareous nannofossil assemblages of several Neogene series (from the North Atlantic and the Antarctic Ocean, Indian sector) were studied. Particular interest has been given to the quantification of data and high stratigraphic resolution. The analysis of the recordings obtained (due in particular to the mathematical treatment of the signals) made it possible to show the great sensitivity of the calcareous nannoplankton to the climatic variations:- the renewal of nannoplankton takes place during the last deglaciation (in the North Atlantic) by closely following the climatic changes.- all Miocene series studied contain periodic signals of frequencies identical to those of Milankovitch. It has been possible to study the modulation of eccentricity cycles and to see at what times they are particularly powerful.- many changes in nannoplankton composition observed in these Miocene series are directly correlated with paleoceanographic or palaeoclimatic events as evidenced by stable isotope studies of oxygen or calcium carbonate content in sediments.- the longest record (from 25 to 8.5 Ma) allows to trace the movements of the Antarctic polar front in the Miocene in a very detailed way (a sample every 18 000 years). Five major Miocene cooling phases could be identified. Les variations de composition des assemblages de nannofossiles calcaires de plusieurs séries néogènes (de l’Atlantique Nord et de l’océan Antarctique, secteur indien) ont été étudiés. Un intérêt particulier a été apporté à la quantification des données et à la haute résolution stratigraphique. L’analyse des enregistrements obtenus (grâce en particulier au traitement mathématique des signaux) a permis de montrer la grande sensibilité du nannoplancton calcaire aux variations climatiques :- le renouvellement du nannoplancton s’effectue durant la dernière déglaciation (dans l’Atlantique Nord) en suivant de façon proche les changements climatiques.- toutes les séries du Miocène étudiées contiennent des signaux périodiques de ... |
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