IDENTIFICATION OF NEWLY GENERATED IRON PHASES IN RECENT ANOXIC SEDIMENTS - FE-57 MOSSBAUER AND MICRORAMAN SPECTROSCOPIC STUDIES

Both biota (primarily bacteria) and conditions of low natural redox po tential and pH involved in surface sediments from the Seine estuary (i n Northern France) are responsible for the reduction of sedimentary ox idized forms of iron into iron(II). Such processes generate insoluble inorganic compounds. Iron-57 Mossbauer spectroscopy has been used to c haracterize newly generated iron(II) carbonates [solid solution FexCa1 -xCO3 and 'green rusts', (FeFeII)-Fe-III(CO3)(OH)] in these recent ano xic sediments. It is also demonstrated that sedimentary iron reduction s occurring in these sediments play an important role in the biogeoche mical cycles of sulfur. Thus, using X-ray diffraction, pyrite was dete cted in sulfide-rich sediments (1.5-1.8 wt.%). Furthermore, laser Rama n microprobe spectroscopy has helped us to establish the existence of small quantities of pyrite and amorphous iron sulfide(s), scarcely det ectable by conventional macroanalysis techniques, and to visualize/dis criminate them on the anoxic sediment surface.