DEPOSITIONAL ENVIRONMENT AND ORIGIN OF BURIED POLLYMETALLIC NODULES: AN INTERPRETATION OF PISTON CORE WPC1101 FROM CC ZONE OF EASTERN PACIFIC

The Piston Core WPC1101 was taken from the Clarion-Clipperton Fracture Zone, Equatorial Pacific in 2011. Polymetallic nodules have been discovered both on the top and in the sediment sequence 3.4-3.5 m deep. This paper summarized the results of sedimentology, magneto-stratigraphy, clay mineralogy and element geochemistry for interpretation of its depositional environment. The main component of the core consists of siliceous clay; the values of M/I show that the volcanic and hydrothermal activities occurred on the ocean floor were stronger in late Oligocene than in Pliocene. From the bottom to the top, the content of biogenetic SiO₂ increases, while Al₂O₃, which represents terrigenous components, remains relatively constant in content. Contents of P₂O₅, CaO, Cu, Co, Ni are diluted attributing to the increment of biogenetic SiO₂. The buried polymetallic nodules are developed together with a depositional hiatus, when the primary productivity was high. Processes which favor the enrichment of transitional metals in buried nodules cause the depletion of REE³⁺ in nodules and the enrichment of REE³⁺ in associated sediments. In contrast, Ce appears to be enriched in nodules, but not involved in diagenetic reactions.