Investigações sobre processos morfodinâmicos foram realizadas em praias da costa setentrional da Ilha de Fernando de Noronha, visando-se averiguar variações nos per s praiais ao longo do tempo, distinguindo-se os setores mais vulneráveis aos agentes que promovem mobilidades praiais. A análise qualitativa destes per s, no período de agosto de 2000 a abril de 2001, mostra claramente uma tendência erosiva com perda signi cativa de material sedimentar na maioria de suas praias. As praias apresentaram diferentes coe cientes de variação do volume sedimentar, sendo suas possíveis causas atribuídas às particularidades geomorfológicas desses diferentes setores, as quais promovem menor atuação dos agentes hidrodinâmicos locais. Os envelopes praiais são bioclásticos, com granulometria areia na a média com seleção moderada a boa, e predominância de assimetria muito negativa. Nestes envelopes estudados a variabilidade morfológica mostrou-se eventualmente acentuada, porém, guardando signi cativa semelhança na forma de suas curvas granulométricas. Os resultados indicam uma possível transferência de material detrítico praial de NE para SE sendo, neste sentido, factível uma irreversível perda parcial deste material por dispersão na plataforma.

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The aim of this research was to reconstruct vegetation changes (with climate inferences) that occurred during the Holocene in the Fernando de Noronha Island, Pernambuco State, northeastern Brazil. The research approach included the use of geochemical (mineralogy, elemental), carbon isotopes (δ 13 C, 14 C) and pollen analyses in soil organic matter (SOM) and sediments collected in Lagoa da Viração and Manguezal do Sueste. The carbon isotopes data of SOM indicated that there was no significant vegetation changes during the last 7400 BP, suggesting that the climate was not the determinant factor for the vegetation dynamics. The pollen analysis of the sediment of a core collected in the Lagoa da Viração showed the absence of Quaternary material in the period between 720 BP and 90 BP. The mineralogical analysis of deeper layer showed the presence of diopside indicating this material was developed "in situ". Only in the shallow part of the core were found pollen of similar plant species of the modern vegetation. The geochemistry and isotope results, in association with the sediment type and pollen analyses of sediment samples of Manguezal do Sueste, indicated variations in the vegetation and in its location since the middle Holocene. Such variations can be associated with climatic events and sea level oscillations and also with anthropogenic events considering the last five hundred years.

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Continental shelf sediments from the state of Ceará, northeastern Brazil, have been studied to investigate meteoric diagenesis of marine sediments of previously defined ancient coastal lines. Major elements for 131 samples of carbonate sediments and C and O isotopes for 51 carapace samples of benthonic foraminifers of the Amphistegina radiata and Peneroplis planatus species were analyzed. Geochemical signatures of δ 13 C, δ 18 O, SiO 2 (stoichiometrically calculated as quartz %), Sr and Mn, and XRD document the impact of meteoric diagenesis on relict sediments from current depths of 25-30 m, 45 m, and 80 m. Morphologies of the marine shelf at these depths, interpreted from previous bathymetric profiles, correspond to holocenic marine terraces. Despite a recent sedimentary cover, it was possible to confirm that these terraces possess relict detrital, biogenic, and continental material, that resulted from erosional reworking of ancient coastlines during the Flandrian transgression.