Minerais pesados e morfodinâmica das praias da planície deltaica do Rio Doce

• Ano de defesa: 2022
• Autor(a) principal: Castro, Lucas Bermudes de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Espírito Santo; BR; Mestrado em Oceanografia Ambiental; Centro de Ciências Humanas e Naturais; UFES; Programa de Pós-Graduação em Oceanografia Ambiental
• Palavras-chave em Português: Processos morfodinâmicos; Minerais pesados; Planície deltaica; subject.br-rjbn; Ciências Ambientais
• Link de acesso: http://repositorio.ufes.br/handle/10/16625

In this study, the morphodynamic and sedimentary processes responsible for the distribution and selection of heavy minerals on the beaches of a wave-dominated delta are investigated. The evolution of the deltaic plain of the Doce River is associated with high volumes of river input, long-term geological fluctuations in sea level, and variations in long- and short-term oceanographic processes. The results indicate that the proximity to the river mouth and the redistribution of sediment along the coast by longitudinal currents are responsible for a gradation of the morphological parameters of the beach between the southern and northern ends of the plain, as well as in the textural parameters of the sediments. As for the assemblages of heavy minerals, the establishment of a relationship between morphodynamics and the deposition of mineral species is less evident, but conditioned by the predominant direction of the longshore drift from the mouth. Thus, the less dense and more unstable minerals, such as amphiboles, follow the direction resulting from the longitudinal current and are associated with dissipative beaches, with low slopes and composed of fine sands, to the north of the Doce River. On the other hand, the enrichment by denser and ultrastable minerals, such as monazites, zircon and opaque minerals rich in iron, were more commonly associated with beaches to the south of the mouth, with coarse sands and a sloping beach face. The analysis of the concentration of heavy minerals in different granulometric intervals allowed us to conclude that, in general, the minerals tend to follow the “law of hydraulic equivalence” proposed by Rubey (1933), given by the density and size of the grain. However, in addition to the sediment texture, the beach morphology and the wave spreading pattern, hydrodynamic processes of the beach, interfere in the selection of heavy minerals on the beach face, suggesting the occurrence of other processes acting in the distribution and selection of heavy minerals, among them, selective drag and selection by shear.