SYSTEMATICS OF CARBON-SULFUR-IRON RATIOS IN UPWELLING SEDIMENTS

Abundances of organic carbon, sulfur, and reactive iron in sediments o f three upwelling environments (Peru, Oman and Benguela) suggest that organic carbon/reduced sulfur ratios (C/S-ratios) in this category of marine sediments deviate considerably from previously established empi rical ratios in normal marine sediments. To clarify the discrepancies, we investigated those components of the diagenetic system that limit the formation of pyrite: sulfate concentrations and reduction rates in pore waters, availability of reactive iron, and the quantity and qual ity of organic matter. All three limitations are evident in our sample pools. The results suggest that C/S-ratios in recent and fossil marin e sediments rich in organic matter may be unsuitable as paleoenvironme ntal indicators.