Abstract
In July 2009, samples from the sediment-water interface were collected on the Cabo Frio - RJ inner shelf, in front of the Pero Beach, in order to characterize environmentally this area through the study of benthic foraminifera. The study area lies between the latitudes 22oS and 23oS, and the longitudes 41oW and 42oW and presents water depths ranging from 10m to 30 m. In the laboratory the samples were washed, dried in an oven, splitted and taxonomically classified. Thirty-seven samples were analyzed and almost all specimens were identified in species. The samples with higher abundance, richness and diversity were found in deeper regions far away from the coast, containing more than 5000 individuals. Three abundant samples were found in the south entrance, near the Ponta do Pero. The presence of abundant broken specimens was observed, indicating the current dynamics in the region. Overall the species Poroeponides lateralis and Eponides repandus, typical from the shelf, and Bulimina marginata, typical species of proximal environments, appeared as dominant (present with a percentage of 10% or more). Quinqueloculina agglutinans and Textularia agglutinans were considered principal species in seven samples (present with a percentage of 5% or more). The presence of Buccella peruviana characterizes the influence of the currents from the south of Brazil in the Cabo Frio shelf. Ten barren samples were found, most of them located in shallower regions. Although the samples are located in the inner shelf and at low depth, 30% of the samples had high abundance and diversity, probably by the upwelling effects which occur in the region. Three biofacies were identified. Two of them were characterized by changes from a proximal environment to a shelf environment and, in one of these two, the abundance of Buccella peruviana was observed. The other biofacies presented broken specimens in abundance.
Highlights
Foraminíferos são microorganismos pertencentes ao Reino Protoctista, Filo Granuloreticulosa, Classe Foraminifera, possuem 16 ordens e vivem sobretudo em ambientes marinhos (Sen Gupta, 1999)
Foi observada a contagem mínima de 300 espécimes de foraminíferos bentônicos por amostra
Quase todos os espécimes triados foram identificados em espécies utilizando trabalhos como Loeblich & Tappan (1988), Cushman (1931), Boltovskoy et al (1980) e o catálogo Ellis & Messina (1940 et seq.), além de artigos específicos
Summary
Foraminíferos são microorganismos pertencentes ao Reino Protoctista, Filo Granuloreticulosa, Classe Foraminifera, possuem 16 ordens e vivem sobretudo em ambientes marinhos (Sen Gupta, 1999). Possuem carapaça ou teca de formas variadas, de constituição calcária (composta por carbonato de cálcio), aglutinante (aglutinada por partículas do sedimento em que vivem) ou, mais raramente, orgânica ou silicosa (Vilela, 2011). Com a morte do organismo, sua carapaça fica preservada no sedimento. A determinação de paleoambientes pode ser bem detalhada com o estudo desses microfósseis (Boltovskoy, 1965; Murray, 2006). Tais organismos e suas tecas encontradas nos sedimentos indicam com precisão características como profundidade, salinidade, temperatura, níveis de oxigênio, características do substrato e energia do meio em que viveram, o que permite a reconstituição ambiental e paleoambiental da área estudada. A biofácies é definida como uma associação de organismos, encontrados em rochas sedimentares, representando um ambiente deposicional particular. Não leva em conta o caráter litológico dos sedimentos fossilíferos e seu uso pode ou não ser restrito a uma unidade litoestratigráfica (Emery & Myers, 1996)
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