RESUMOOs solos fosfáticos encontrados na porção norte da ilha Rata, no Arquipélago de Fernando de Noronha, foram formados pela reação do guano de aves marinhas com as rochas máfi cas intemperizadas da Formação Quixaba. Os minerais fosfáticos determinados no solo incluem a crandalita como o constituinte mais importante. A assinatura do guano preservada no solo é caracterizada por altos teores de Cu, Pb, Zn, As, U, e Sr. Por outro lado, a herança da assinatura geoquímica dos nefelina basaltos é demonstrada pelas concentrações anômalas de Ba, Nb, Ta, Cr, Hf, V e Zr nos solos e pela notável similaridade entre os padrões de ETR na rocha e nos solos.Palavras-chave: Solos fosfáticos; Guano; Fernando de Noronha; Ilha Rata; Crandalita. ABSTRACTThe phosphatic soils found in the northern part of the Rata island, in the Fernando de Noronha Archipelago, were formed by reaction of bird guano with weathered mafi c rocks of the Quixaba Formation. Phosphate minerals identifi ed include crandallite as a major constituent. The unique guano signature preserved in soil is characterized by high levels of Cu, Pb, Zn, As, U, and Sr. On the other hand, the inheritance of the geochemical signature of the nepheline-basalts is demonstrated by the anomalous concentrations of Ba, Nb, Ta, Cr, Hf, V and Zr in soils, and by the remarkable similarity between REE patterns in rock and soils.

A 72 cm long core was collected from Lagoa da Viração (LV), a small pond in the Fernando de Noronha island, northern Brazil. Sediments from the lower section of the core (20—72 cm depth) contain essentially mineral matter, while in the upper section (0—20 cm depth) mineral matter is mixed with organic matter. Lithogenic conservative elements — Si, Al, Fe, Ti, Co, Cr, Cu, Ba, Ga, Hf, Nb, Ni, Y, V, Zn, Zr and REE — exhibit remarkably constant values throughout the core, with concentrations similar to those of the bedrock. The vertical distribution of soluble elements — Ca, Mg, Na, K, P, Mn and Sr — is also homogeneous, but these elements are systematically depleted in relation to the bedrock. LOI, TOC, Br, Se, Hg and Pb, although showing nearly constant values in the lower section of the core, are significantly enriched in the upper section. The concentration profiles of Br and Se suggest that they may be accounted for by natural processes, related to the slight affinity of these elements for organic matter. On the other hand, the elevated levels of Hg and Pb in recent sediments may be explained by their long-range atmospheric transport and deposition. Furthermore, the isotopic composition of Pb clearly indicates that anthropogenic sources contributed to the Pb burden in the uppermost pond sediments.