Atol das Rocas, Atlântico Sul Equatorial: considerações sobre a classificação do recife biogênico

Abstract

The Rocas Atoll is considered the only atoll in the Equatorial South Atlantic and one of the lowest in the world. Due to not have corals as major bioconstructors and have morphological differences from the Caribbean and Indo-Pacific reefs their classification as Atoll as may be considered controversial during the twentieth century. Field analysis and Aerial photographs were taken to investigate the characteristics of the biogenic reef and discuss the classification as Atoll. The results show that there are a number of characteristics that confirm the classification in the category of Atoll and similar to other reefs of same morphology as ellipsoid form, development in volcanic mountains, sand cays and greater width of the ring reef on the leeward. Differentiated features include ring reef consisting predominantly of calcareous algae, foraminifera and vermetid gastropods; lagoon with a maximum depth of 6m and restricted to a small portion of the reef, the presence of calcarenite on one of the islands and the probably presence of reef residues (called “rocas”) derived from eustatic fluctuations in the Neogene.