Mechanism of organo-nickel co-enrichment in marine black shale

Organic matter and metal elements are commonly co-enriched in marine black shales. However, the element types vary among different shales and the relevant mechanisms of organo-metal co-enrichment are still unclear. The super-enrichment of organic matter and nickel in the ore bed of Early Cambrian marine black shale of southern China provides an ideal opportunity to investigate this mechanism. Herein, to clarify the coenrichment mechanism of organic matter and , the laminated structure of this ore bed was characterized and the geochemical and mineralogical proxies of different laminae were analyzed. The results indicated that there are four types of laminae in this ore bed, namely, siliceous laminae, calcareous laminae, clay minerals laminae, and organic-rich laminae. Clay minerals laminae and organic-rich laminae were deposited under anoxic environments, while siliceous laminae were deposited under strong oxidizing to anoxic environments. Neither organic matter nor are distributed homogeneously in the ore bed; organic matter is mainly concentrated in organic-rich laminae, while is largely enriched in clay minerals laminae. Clay minerals and organic matter have strong adsorption capacity for , and the adsorption capacity of clay minerals (such as illite) for is stronger than that of organic matter. Hydrothermal events and terrestrial input are key factors affecting the paleoenvironment and laminated structure during the deposition of the ore bed. Although organic matter and are co-enriched in the ore bed, their enrichment stages and conditions vary according to the geochemical differences among laminae.