Geochemical Evidence for the Formation of Soils by Interaction Between Guano and Volcanic Rocks, Rata Island, Fernando de Noronha (Pernambuco)

Abstract

The phosphatic soils found in the northern part of the Rata island, in the Fernando de Noronha Archipelago, wereformed by reaction of bird guano with weathered mafi c rocks of the Quixaba Formation. Phosphate minerals identifi edinclude crandallite as a major constituent. The unique guano signature preserved in soil is characterized by high levelsof Cu, Pb, Zn, As, U, and Sr. On the other hand, the inheritance of the geochemical signature of the nepheline-basalts isdemonstrated by the anomalous concentrations of Ba, Nb, Ta, Cr, Hf, V and Zr in soils, and by the remarkable similaritybetween REE patterns in rock and soils.

Keywords

• Phosphatic soils
• Guano
• Fernando de Noronha
• Rata island
• Crandallite