Valdir do Amaral Vaz Manso

Detrital carbonate sedimentation of the Rocas Atoll, South Atlantic

Located 266 km offshore Brazilian coast, Rocas Reef complex is the only atoll in the South Atlantic. Two scientific expeditions carried out detailed sedimentological studies of the complex. Sand texture was dominant in the sedimentary environment, although other textures such as gravel, sandy gravel and gravelly sand, were also observed. Mean size ranged from fine sand to coarse sand (-1.23 to 2.34o), with an average value of 0.69o (sand fraction), which from a geological perspective represents a high-energy environment. The values of mean size varied in the different geomorphologic compartments, a response to variable hydrodynamics on the reef. Sorting ranged from very well sorted to poorly sorted, with a mean value of 0.97o (moderately sorted). The values of mean size and sorting are directly proportional (i.e. the larger the grain size, the better the sorting), a fact that might be controlled by the decreasing of organism diversity that contributes to the sedimentary environment as the mean size of the particles increase. Skewness parameter was used to correlate positive values to depositional environments. The Kurtosis parameter showed little relevance in this study. The sedimentary particles analyzed are exclusively composed of biogenic grains. In total eleven major groups were described, coralline algae being the most unusual.

Oceanographic parameters in continental margin of the State of Ceará (northeastern Brazil) deduced from C and O isotopes in foraminifers

Specimens of Recent foraminifera of Amphistegina radiata, Peneroplis planatus and Globigerinoides ruber, from fifty samples of surface sediments of the continental margin of the State of Ceará, Brazil, have been analyzed for carbon and oxygen isotopes to investigate oceanographic parameters and determine the values of delta18O of the oceanic water. From a comparison between values of delta18O obtained for ocean water using the linear equations by (Craig and Gordon 1965) and the one by Wolff et al. (1998), it became evident that the former yielded a more reliable value (0.2 per thousand SMOW) than the latter. Lower values of delta18O for the ocean water in this continental margin resulted from continental water influence. Values of 18O (-0.3 per thousand to -1.5 per thousand PDB for benthic foraminifera and -0.6 per thousand to -2.4 per thousand PDB for planktic foraminifera), attest to a variation of temperatures of oceanic water masses, in average, between 20 to 22 degrees C in deep water and 24 to 27 degrees C, in surface water. Values of delta13C from +3.2% to -0.2 per thousand PDB (benthic foraminifera) reflect a variation in the apparent oxygen utilization (AOU) in the continental margin and indicate that the environments of bacteriological decomposition of organic matter are not continuous along the investigated area.

Tropical Sandy Beaches of Pernambuco State

Pernambuco state is located in the Northeast region of Brazil and has a 187 km long coastline containing a range of coastal environments including beaches, estuaries, reefs and headlands all with varying degrees of preservation and occupation. The coast of which 156 km (83 %), is sandy beaches, can be divided into three physiographic sectors. Sand deposits are limited to a narrow strip of the Holocene beach area, deposited between the low-water line and the Holocene terraces. They are predominately quartz, with some beaches containing heavy minerals. The shoreface and the inner shelf has a highly complex underwater topography owing to the presence of beachrock, coral and algae reefs structures at several different depths, as well as paleochannels and other features. The coast has three well defined zonation in terms of wave energy: (1) Goiana to Paulista city, has a high wave convergence zone offshore with a high dissipation/diffraction rates across the inner shelf due to its wide reefs and shallow shelf resulting in low waves at the shore; (2) Paulista to Cabo city, an intermediate wave convergence zone marked by few divergence zones at low tide; (3) Ipojuca to Sao Jose da Coroa Grande city there are fewer convergence zones but the inner shelf has numerous discontinuous reefs inducing refraction and diffraction patterns. This pattern is controls the shoreline morphology and beach morphodynamic behavior. Based on this the beaches can be divided into three sectors: with the reef protected northern beaches are tide-modified; the exposed southern beaches are wave-dominated; and the middle sector beaches where the beachrock reefs controls the relation between wave and tide are geomorphologically controlled.

PROCESSOS EROSIVOS COSTEIROS DA PRAIA DE BOA VIAGEM

Resumen pt: Em todo o mundo, as zonas costeiras sofrem com as atividades antropogenicas, impondo-lhes severos impactos e, em alguns casos, extrapolando os limites de...

Índices de vulnerabilidade à erosão das praias da Ilha de Itamaracá, litoral norte de Pernambuco, Brasil

As praias do Forte Orange, Pilar e Jaguaribe estao localizadas a 50 km ao norte da cidade do Recife, no municipio da Ilha de Itamaraca. Nas ultimas decadas apresentou um rapido crescimento urbano, ligado principalmente as atividades turisticas da orla. As construcoes irregulares e empreendimentos turisticos na zona da pos-praia diminui a capacidade de transporte dos sedimentos, e sua deposicao no sistema praial interferindo na morfodinâmica do ambiente e, assim, promove a instalacao da erosao marinha. O estudo teve como objetivo identificar e avaliar atraves de indices quantitativos e qualitativos o grau de vulnerabilidade a erosao costeira. Para isto foi levado em consideracao as atividades humanas e as caracteristicas naturais da praia. A metodologia foi realizada a partir do mapeamento de toda a orla. Identificou-se cada setor, por celulas e os indices do grau de vulnerabilidade foram definidos como: alto, medio e baixo. No setor 1 (Sul) observou-se um grau moderado de vulnerabilidade a erosao, este apresentou uma pos-praia desenvolvida com certa tendencia a progradacao. O setor 2 (Centro) recebeu um alto grau de vulnerabilidade, onde parte da pos-praia foi totalmente ocupada, apresentou estruturas rigidas de protecao a costa. O setor 3 (Norte) recebeu tambem alto grau de vulnerabilidade, este setor apresentou boa parte da pos-praia ocupada com construcoes inadequadas e um pequeno trecho deste ambiente desenvolvido, com tendencia a progradacao. A identificacao de setores por meio do grau de vulnerabilidade mostrou ser uma importante ferramenta de analise e fornece subsidios a politica publicas e ao gerenciamento costeiro.

The coastal zone of the state of Pernambuco: environmental, sedimentary, textural and compositional description of São José da Cora Grande beach

understand the impacts of this demographic pressure upon the beaches. For that matter, the evaluation of the variation in the texture of the beach sediments along the coast can provide important information about the main processes that act in sandy beaches. São José da Coroa Grande is located on the coat of Pernambuco 123 km from Recife, the State capital. There are serious erosion problems that are associated to the occupation of the backshore. This study aims at identifying the environmental and sedimentary characteristics of the beaches in São José da Coroa Grande, evaluating the granulometric features of the medium foreshore correlating them to the inclination of the beach face. For a better analysis, the geo-environmental description of the beach aided to infer morphodynamic stages along the beach. The results show predominance of quartz sand with dominance of thin sand. Most grains are moderately selected with asymmetry between very negative to approximately symmetric. Regarding the kurtosis of the sediments, there was a Revista Brasileira de Geografia Física V. 08 N. 05 (2015) 1303-1320.