Sulfur species in oceanic phosphorites

The sulfur species were investigated by chemical methods in the recent, Pliocene-Pleistocene, and Miocene phosphorites from the inner and outer Namibian shelf; in the Late Quaternary phosphorites from the Peru-Chile shelf, and in the Miocene phosphorites from selected submarine rises of the Sea of Japan. The following concentrations of the sulfur species were determined: 0.25-1.147% of sulfate S, 0.012-1.473% of pyritic S, 0.005-0.141% of organic S, and <0.0001-0.04% of elemental S. Sulfate sulfur commonly predominates over other species, but pyritic sulfur is more abundant in some samples. The sulfate to pyritic sulfur ratio in the shelf phosphorites varies from 0.36 to 18, and it increases up to 37-52 in the phosphorites from submarine rises. The major part of the sulfate sulfur is incorporated into apatite of phosphorites, Samples enriched in organic matter contain more pyritic sulfur, but no correlation between organic matter and pyritic sulfur, nor between organic matter and organic sulfur, is observed. The relative amount of non-pyritic Fc(II) in the phosphorites from reducing environments decreases with the process of phosphate lithification owing to the continued reduction processes.