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Environmental influences on major bioevents in the Ediacaran, in the Ordovician and at the Permian-Triassic boundary

By Tonggang Zhang

Abstract

De multiples analyses géochimiques (isotopes du carbone et du soufre, spéciation du fer, contenu en carbone et soufre dans le sédiment et éléments traces) ont été effectuées pour étudier les influences environnementales sur la diversification de la faune d'Édiacara (~570 Ma), à l'Ordovicien inférieur et moyen (~470 Ma), aux extinctions de masse de l'Ordovicen (~445 Ma) et de la limite Permien-Trias (~251 Ma). Les enregistrements haute-résolution de o13 Cet de o13 C org d'une section provenant de Honghuayuan (Sud de la Chine) ont montré une élévation de +8%o du o13 C dans le Floian de l'Ordovicien. Cela implique une hausse du taux d'enfouissement de la matière organique pendant la première partie de l'Ordovicien récent qui aurait pu contribuer au refroidissement climatique et déclencher cet évènement. Les deux valeurs positives du o13Corg correspondent aux deux pulses de l'extinction de masse de l'Ordovicien. Cela implique des changements dans le cycle biogéochimique du carbone qui sont associés à ['extinction de masse de l'Ordovicien. Les valeurs élevées de o34S de la pyrite, le bref passage à des valeurs négatives du o34S de 20%o, associés à un ralentissement de la glaciation traduiraient des conditions anoxiques dans l'océan profond pendant la période hirnantienne. Ces conditions anoxiques pourraient avoir pris part à l'extinction de masse à la fin de l'Ordovicien dans le Sud de la Chine et probablement ailleurs. La spéciation des isotopes du Fe et du S, les données de pyrite provenant de la formation de Sheepbed (Canada) et de Doushantuo (Chine) ont suggéré que J'oxygénation progressive des eaux de fond pourrait avoir permis l'apparition burtale des animaux au début de l'Édiacarien et avoir déclenché leur diversification.. Les données isotopiques de C et S, à la limite Pr-T de Nhi Tao (Vietnam), exposent un appauvrissement en 34S, des valeurs négatives du o13 C des carbonates, et une variation positive significative entre les horizons pyriteux (proxy : [S]py et o34Spy) et o13 C de carbonate (10-20 cm). Ces données isotopiques suggèrent que la remontée des eaux profondes anoxiques pourrait avoir servie comme mécanisme de déclenchement pour l'extinction de masse du Permien. \ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : diversification, extinction de masse, isotope du carbone, isotope du soufre, spéciation du Fe, procédé de refroidissement, oxique, anoxiqu

Topics: Impact environnemental, Biodiversité, Faune, Extinction (Biologie), Isotope du carbone, Ordovicien (Période géologique), Permien (Période géologique)
Year: 2010
OAI identifier: oai:www.archipel.uqam.ca:3555

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