A predominantly ferruginous condition in the Ediacaran deep ocean: Geochemistry of black shales in the Ediacaran Doushantuo Formation, South China

The enrichment factors (EFs) of most redox sensitive trace elements in the sediments of both sections are low (≤1), while EF-Mo shows moderately enriched (∼3-60), which is similar to the modern Cariaco Basin. Because of paleogeographic restriction or persistent ocean stratification, the trace elements renewal would be mostly obstructed in the isolated deep water, and their inventory could become depleted, which cause the low EFs of most trace elements in sediments. However, for the non-euxinic deep ocean, a “particulate shuttle” would transport Mo from shallow water to deep water through adsorption-desorption on the Mn-Fe-oxyhydroxides, which maintained moderate Mo enrichment in seawater and related sediments.