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Impact de la tansition climatique Eocène - Oligocène sur les écosystèmes continentaux : Etude du bassin de Rennes

Abstract : The study of past climate changes on the terrestrial realm provides clues to understand the mechanisms,chronology, and timing of ecosystems response to climate disturbances. The Eocene-Oligocene Transition(EOT) of the Eocene-Oligocene boundary (EOb) is well suited for this type of study because it records the last climatic transition between the greenhouse and icehouse modes via a misunderstood interval: thedoubthouse period. This climatic transition was studied through the analysis of organic-rich lacustrine sediments. After an astro-calibrated age model was set up, we reconstructed the evolution of vegetation by using molecular biomarkers specific of plant groups and of local climate (temperature and hydrological conditions) by using molecular and isotopic proxies. The climate record exhibits a marked cooling and drying at the EOT. The evolution of vegetation did not show any abrupt change but exhibited pronounced and rhythmic changes in phase with excentricity during an interval that started 1750 ka before the EOb and lasted until 300 ka after. This interval named Environmental Transition Interval (ETI) was warmer and wetter, and coincides with the doubthouse period. The start of the ETI is concomitant with changes in the recording of orbital parameters. The good expression of solar cycles in the sediments from that period attests to the setting or strengthening of ocean-atmosphere couplings linked to the establishment of the Antarctic icesheet. This work partly solves the uncertainties that prevailed on the doubthouse period.
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Julie Ghirardi. Impact de la tansition climatique Eocène - Oligocène sur les écosystèmes continentaux : Etude du bassin de Rennes. Sciences de la Terre. Université d'Orléans, 2016. Français. ⟨NNT : 2016ORLE2093⟩. ⟨tel-02441344⟩

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