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Réponses du système Terre aux perturbations géologiques du cycle du carbone. Isotopes du carbone, modelisation et apport des isotopes du bore.

Abstract : Studying geological carbon cycle disruption helps to further understand modern carbon cycle and to better apprehend the consequences of the current increase in atmospheric CO2. Specifically, geological crisis highlight the reaction ability of the environment to stressful situation. We used a multi‐proxy approach to study the Triassic‐Jurassic (TJ) boundary events. This transition period is characterized by a succession of two carbon isotopes negative excursions (CINEs) in sections from Tethyan realm. Through GEOCLIM modeling, we show that the Central Atlantic Magmatic Province (CAMP) likely generated the carbonate production crisis observed during the first CINE provided that emplacement is modeled as a succession of intense short‐lived pulses (<400y) as suggested by recent studies. If emitted mantellic carbon is isotopically light (<‐20‰), CAMP emplacement also generated the first CINE. We investigated British and Austrian sections through carbon and nitrogen isotopes for local consequences of global TJ transition events (CAMP emplacement and sea level variations). We showed that the biological pump is perturbated by eutrophication and blooms of prokaryotic organisms. A supplementary tool is provided by boron isotopic composition (δ11B) of carbonates that record seawater pH. However, inter‐laboratory discrepancies prevent this tool from being broadly used. Here, we present a recently developed injection device for boron isotopes analysis on MC‐ICP‐ MS and use it for studying boron isotopes on Middle Jurassic limestones during a time of carbonate production perturbation. Nevertheless, we remain speculative in our interpretation for carbonate δ11B values record both seawater pH and δ11B values. As a consequence, we initiated the reconstruction of Phanerozoic seawater δ11B values by measuring δ11B values in marine halites. The reconstructed values exhibit clear variations through time that are related to geodynamic parameters. This study underlines the necessity for multi‐proxy approach to bring new light on atmospheric pCO2 and seawater chemical composition.
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https://tel.archives-ouvertes.fr/tel-00655630
Contributor : Guillaume Paris <>
Submitted on : Saturday, December 31, 2011 - 7:56:46 PM
Last modification on : Friday, May 3, 2019 - 12:54:02 PM
Long-term archiving on: : Sunday, April 1, 2012 - 2:21:38 AM

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  • HAL Id : tel-00655630, version 1

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Guillaume Paris. Réponses du système Terre aux perturbations géologiques du cycle du carbone. Isotopes du carbone, modelisation et apport des isotopes du bore.. Géochimie. Institut de physique du globe de paris - IPGP, 2009. Français. ⟨tel-00655630⟩

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