Pré-caracterização microestrutural de microfósseis calcários aplicados como proxies paleoambientais e paleoecológicas no início do Daniano

Abstract

This thesis addresses the importance of geochemical pre-characterization, based on microstructural analysis of Danian calcareous microfossils. Based on the hypothesis that more assertive paleotemperature estimates can be reconstructed with microstructural analysis of fossils, this thesis allowed to make new paleoenvironmental and paleoclimatic contributions for the Danian in the South Atlantic Ocean. The study carried out with samples from Ocean Drilling Program (ODP) Site 1262, Walvis Ridge, revealed that stable oxygen isotope (δ 18O) records from benthic foraminifera were diagenetically altered by growth of authigenic carbonates. This process was observed at stratigraphic levels that recorded reduced bottom water oxygenation, such as during the Dan-C2 and Chron C29n events. The ocean surface at this location was also affected, as observed in the internal structures of planktonic foraminifera. Changes in the ecosystem, associated with increases in temperature, appear to have been environment for calcareous dinocysts. Isotopic measurements of these calcareous spheres reflect original environmental signatures. In a shallow marine context, in the Neuquén Basin, Argentina, the Cretaceous (K-Pg) boundary is very well delimited and characterized. The excellent preservation of early Danian ostracod assemblage was confirmed by different geochemical pre characterization techniques, such as SEM-EDS (scanning electron microscopy coupled energy dispersive spectroscopy), µXRD (micro x-ray diffraction) and µRAMAN (Raman spectroscopy). Records of organic matter, such as kerogen, were identified in ostracod valves, suggesting excelent preservation. The excellent results allowed us to infer paleecological preferences of four Danian species, contributing to the scarce isotopic database recorded for this Fossil Group over this time interval. Clear disperion patterns of carbon (δ 13C) and oxygen isotope values revealed evident intraspecific differences between ornate and smooth species.