Composição do sedimento das praias entre o Pontal do Peba e Pontal do Coruripe - Alagoas, com ênfase nos componentes biogênicos

• Autor(a) principal: Vieira, Laysa Raisa de Souza
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFS
• Texto Completo: https://ri.ufs.br/handle/riufs/5411
• topic: Geociências; Geologia; Composição de sedimentos; Areia; Praias (Alagoas); Areia de praia; Grãos bioclásticos; Beach sands; Sediment composition; Bioclastic grains; CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS

A beach is an accumulation on the shore of unconsolidated sediment and its composition and texture are directly related to the available source of material and the coastal processes that modify the sediments during long periods. Coastal and shallow marine sediments are usually of heterogeneous nature, composed of variable mixtures of siliciclastic and bioclastic particles. Surface samples collected in the beach face from eighteen stations along south Alagoas coast were analyzed concerning textural and compositional characteristics. Mean grain size and sorting were obtained through dry mechanical sieving, with processing of the samples using the SYSGRAN package. Three hundred grains were identified for each grain size class coarser than 0.125 mm. Compositional analysis was carried out with the identification of 300 grains for each grain size class coarser than 0.125 mm. Grain size distribution ranged from medium sand to very fine sand with predominance of the latter, mostly moderately sorted. Coarser sands were found in Pontal do Peba and in the narrow beaches of Miaí de Cima and Barreiras. The sedimentation in the studied beaches showed predominance of siliciclastic grains, mainly quartz. The highest concentrations of bioclastic grains are near the Ponta do Peba bank and the north of this point the proportion of bioclasts gradually decreases. The main biogenic components are molluscs shells and fragments of red algae and Halimeda. Echinoderms spines and fragments, bryozoans and foraminifera tests also contribute significantly to the beach deposit. The sediment distribution pattern suggests that in addition to the grains originated from the hinterland, the continental shelf constitutes an important sediment source for the beaches.