Piritas framboidais associadas ao biofilme em sedimentos de manguezal de Coroa Grande, Baía de Sepetiba, RJ.

Abstract

Biofilm formed over inter-tidal mangrove sediments are formed under slightlyacid pH (6.2); salinity range from 15.3 to 25 and mostly anoxic conditions (Eh= -235 mV),although occasional; oxic conditions (Eh= +192 mV) may occur. X-ray analysis showedthe presence of halite, caolinite, quartz, mica, vermiculite and smectite. Neutronactivation analysis showed an enrichment of metals (e.g. Fe) in the biofilm compared tosurrounding sediments. MEV, EDX and EMAX analysis of the biofilm identified bacteriaand diatoms (Auliscus coelatus Bail, Actinopthycus undulatus, Biddulphia sp., Cocconeisscutellum, Cyclotella stylorum Bright, Fragilaria sp., Melosira nummuloides, Naviculalanceolata,Thalassionema sp., Thalassiosira sp.) as major living constituents. Organicmatter, feldspar crystals, mica and quartz grains, showing different degrees ofweathering, as well as iron sulfide microcrystals and framboidal pyrites were alsoisolated from the biofilm. An interaction between microorganism and framboidal pyritesand clays were observed, forming fine mineral films and microcrystals, suggesting bothcontrolled and induced biomineralization.