GEOCHEMISTRY OF RARE-EARTH ELEMENTS IN 2-COLOR CORE SEDIMENTS FROM THE KOREA DEEP-OCEAN STUDY (KODOS)-90 SITE, NE EQUATORIAL PACIFIC

Major factors controlling the variation of rare earth element (REE) co ntents in deep-sea sediments were identified using box-core sediments from the Korea Deep Ocean Study (KODOS)-90 site in the western part be tween the Clarion-Clipperton fracture zones, northeast equatorial Paci fic. Four of ten core columns can be divided into two layers by a shar p color boundary; an upper pale brown layer (Unit A) and a lower dark brown layer (Unit B). Trivalent REEs (3 + REEs) as well as micronodule s, smectite, smectite aggregate, and fish remains (spicules and spines ) are highly enriched in Unit B compared to Unit A. 3 + REEs in micron odule, smectite, and smectite aggregate are not significantly concentr ated compared to those in bulk Unit B sediments. 3 + REE contents in c oarse-grained fish remains (>25 mu m), which is likely biogenic apatit e, are about seven and two times higher, respectively, than the conten ts in Units A and B. Contents of fish remains in bulk Unit B sediments , however, are too low to explain the enrichment of 3 + REEs in Unit B . Based on the results of phosphorus speciation and linear relationshi ps in two pair diagrams (La contents vs. total inorganic phosphorus an d 1/(Ce/Ce) vs, total inorganic phosphorous), it can be inferred that 3 + REEs are dominantly enriched in apatite in fine sediments (<25 mu m) with strong negative Ce anomaly and convex-type distribution patte rn of REEs normalized with NASC. It is suggested that apatite grains, supplied abundantly from surface water during the time of Unit B forma tion with high paleo-productivity, had incorporated and concentrated 3 + REEs.