The present study evaluated the influence of halomorphic, hydromorphic, and sulfate reduction conditions on sand fraction mineralogy and on the geochemistry of three mangrove soils from the Iriri River estuary. Three representative soil profiles selected from a transect had their geochemical conditions characterized and their effects on the mineralogy of the soils were described. The mineralogical analyses (XRD and EDS) and the physicochemical (Eh and pH) conditions found indicate the occurrence of pyritization in the investigated area. The mineralogical soil assembly is composed of both allochthonous (kaolinite, mica, and smectite) and autochthonous clays (mica, smectite, and pyrite). Based on the XRD and EDS data, it is speculated the possibility of glauconite formation in these soils. The halomorphic and hydromorphic conditions determine the Eh and pH values. Under such environment Fe2+ and SO are found free the soil solution with a tendency to stabilize as pyrite (FeS2), thus favorinf the pyritization process.
mineralogy stability; sulfidic soils; pyrite; glauconite
