Geochimica et Cosmochimica Acta   2015 年 150 卷

2015.02.01

To improve our understanding of ocean chemistry and biogeochemical cycling following the termination of large-scale Paleoproterozoic iron formation (IF) deposition (~1.85 billion years ago [Ga]), we conducted a Fe-S-C-Mo geochemical study of the ~1.65Ga Chuanlinggou Formation, Yanshan Basin, North China. Despite the cessation of IF deposition, our results suggest the presence of anoxic but non-euxinic (ferruginous) conditions persisted below the surface mixed layer for the deepest portion of the continental rifting basin and that this pattern is apparently independent of the local organic carbon content. However, our paired S-isotope data of carbonate-associated sulfate and pyrite suggest presence of sulfate in pore fluids, which is not consistent with insufficient sulfate for bacterial sulfate reduction in the water column. Despite evidence for deposition under anoxic conditions, sedimentary molybdenum (Mo) concentrations are mostly not enriched relative to average continental crust. This relationship is consistent with the notion that sulfide-dominated conditions in the water column and/or the sediments are required for Mo enrichment and validates past assertions that Mo enrichment patterns in ancient shales track both the local presence and global distribution of euxinia specifically. In addition, we identified extensive diagenetic carbonate precipitation in the upper Chuanlinggou Formation with only moderately negative ??