Publicação
Magnetic records of acidification events at the cretaceous-paleogene (KPg) and paleocene-eocene thermal maximum (PETM) boundaries
| Resumo: | The KPg mass extinction (~66 Ma) and the PETM (~56 Ma) are both abrupt and global climate events in Earth’s history. The KPg mass extinction is commonly attributed to the Chicxulub impact, but in the last decades it has been linked to the Deccan volcanism. The abrupt warming during the PETM is attributed to methane release from seafloor sediments as consequence of the ocean warming due to the North Atlantic Igneous Province (NAIP) volcanic activity. The mechanisms by which these magmatic events led to global climate changes are still poor constrained. A recent approach combining rock magnetic techniques and mineralogical data provided interesting benchmarks to identify period of iron oxides dissolution linked to environmental acidification. Here, magnetic techniques such as magnetic susceptibility and isothermal remanent magnetization are applied to two marine sections encompassing the KPg (Zumaia, Spain) and PETM (Egypt, GSSP) transitions, in order to provide new insights to identify period of severe environmental changes in the geological record and their link to magmatic activity. The magnetic results obtained for both sections, Zumaia and Dababiya, correlate with biostratigraphic, mineralogical and geochemical data from previous studies at different sections worldwide, demonstrating not only the reliability of the data as well as the global dimension of both events. The data obtained for Zumaia supports an important climate event preceding the KPg boundary. Volcanic markers like magnetite dissolution previously identified in Bidart and Gubbio are confirmed here in the case of the Zumaia section. Magnetite depletion also corroborates the presence of akaganéite and Mercury at Zumaia to support the volcanic theory. On a global scale, these markers correlate with global warming, an increase in atmospheric CO2, environmental acidification via acid rains and presence of high stress opportunistic planctik foraminifera blooms. This climate perturbation also corresponds to the age of the main Deccan eruptions, recently dated by U-P method on zircon, reinforcing the link with the Deccan traps. In contrary to the KPg transition, the PETM at Dababiya is characterized by an increase in magnetite content, which is interpreted as the dissolution of carbonate and relative enrichment in detrital materials (clays). In addition, high concentration of goethite is observed along the section, specially above the PETM, where an increase in biological productivity is observed (Khozyem et al., 2015). In the PETM interval goetite decreases considerably. Goethite content at Dababiya is interpreted as the diagenetic oxidation of pirite and thus an indicator of anoxia during PETM. The increase in magnetite and decrease in goethite at the PETM also correlates with higher ratios of V/Cr, indicative of anoxic conditions (Khozyem et al., 2015). The high magnetite/low goetite interval at Dababiya also correlates with the Carbon Isotope Excursion (CIE) minimum that characterizes the PETM and with a calcite and foraminifera disappearance, supporting an ocean acidification starting below the PE boundary. Mercury enrichments in the same interval, together with negative excursions of 187Os/188Os, supports the role of volcanism (NAIP) to initiate the concomitant warming and sea level rise that mark the PETM. Comparasion of the magnetic properties of the KPg and PETM highlight different climate processes: dissolution of detrital magnetite onland in the case of KPg point environmental acidification by acid rains, whereas ocean acidification due to methane release and subsequent carbonate dissolution characterized the PETM. These findings provide new clues to identify climate and environmental acidification in the geological record and improve our understanding of future anthropogenic climate changes. |
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| Autores principais: | Andrade, Mariana do Amaral Frazão Queiroz de |
| Assunto: | Extinção em Massa do Cretácico-Paleogénico Pico Térmico do Paleocénico-Eocénico Magnetismo Ambiental Alterações Paleoclimáticas Acidificação Teses de mestrado - 2018 |
| Ano: | 2018 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | The KPg mass extinction (~66 Ma) and the PETM (~56 Ma) are both abrupt and global climate events in Earth’s history. The KPg mass extinction is commonly attributed to the Chicxulub impact, but in the last decades it has been linked to the Deccan volcanism. The abrupt warming during the PETM is attributed to methane release from seafloor sediments as consequence of the ocean warming due to the North Atlantic Igneous Province (NAIP) volcanic activity. The mechanisms by which these magmatic events led to global climate changes are still poor constrained. A recent approach combining rock magnetic techniques and mineralogical data provided interesting benchmarks to identify period of iron oxides dissolution linked to environmental acidification. Here, magnetic techniques such as magnetic susceptibility and isothermal remanent magnetization are applied to two marine sections encompassing the KPg (Zumaia, Spain) and PETM (Egypt, GSSP) transitions, in order to provide new insights to identify period of severe environmental changes in the geological record and their link to magmatic activity. The magnetic results obtained for both sections, Zumaia and Dababiya, correlate with biostratigraphic, mineralogical and geochemical data from previous studies at different sections worldwide, demonstrating not only the reliability of the data as well as the global dimension of both events. The data obtained for Zumaia supports an important climate event preceding the KPg boundary. Volcanic markers like magnetite dissolution previously identified in Bidart and Gubbio are confirmed here in the case of the Zumaia section. Magnetite depletion also corroborates the presence of akaganéite and Mercury at Zumaia to support the volcanic theory. On a global scale, these markers correlate with global warming, an increase in atmospheric CO2, environmental acidification via acid rains and presence of high stress opportunistic planctik foraminifera blooms. This climate perturbation also corresponds to the age of the main Deccan eruptions, recently dated by U-P method on zircon, reinforcing the link with the Deccan traps. In contrary to the KPg transition, the PETM at Dababiya is characterized by an increase in magnetite content, which is interpreted as the dissolution of carbonate and relative enrichment in detrital materials (clays). In addition, high concentration of goethite is observed along the section, specially above the PETM, where an increase in biological productivity is observed (Khozyem et al., 2015). In the PETM interval goetite decreases considerably. Goethite content at Dababiya is interpreted as the diagenetic oxidation of pirite and thus an indicator of anoxia during PETM. The increase in magnetite and decrease in goethite at the PETM also correlates with higher ratios of V/Cr, indicative of anoxic conditions (Khozyem et al., 2015). The high magnetite/low goetite interval at Dababiya also correlates with the Carbon Isotope Excursion (CIE) minimum that characterizes the PETM and with a calcite and foraminifera disappearance, supporting an ocean acidification starting below the PE boundary. Mercury enrichments in the same interval, together with negative excursions of 187Os/188Os, supports the role of volcanism (NAIP) to initiate the concomitant warming and sea level rise that mark the PETM. Comparasion of the magnetic properties of the KPg and PETM highlight different climate processes: dissolution of detrital magnetite onland in the case of KPg point environmental acidification by acid rains, whereas ocean acidification due to methane release and subsequent carbonate dissolution characterized the PETM. These findings provide new clues to identify climate and environmental acidification in the geological record and improve our understanding of future anthropogenic climate changes. |
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