Abundances of organic carbon, sulfur, and reactive iron in sediments of 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 empirical 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 quality of organic matter. All three limitations are evident in our sample pools. The results suggest that C/S-ratios in recent and fossil marine sediments rich in organic matter may be unsuitable as paleoenvironmental indicators.

Supplement to: Emeis, Kay-Christian; Morse, John W (1993): Zur Systematik der Kohlenstoff-Schwefel-Eisen-Verhältnisse in Auftriebssedimenten. Geologische Rundschau, 82(4), 604-618