RARE-EARTH ELEMENTS OF PACIFIC PELAGIC SEDIMENTS

The chemical compositions of 140 deep-sea sediment samples collected in the Pacific were examined. The characteristic features of the abundances of REEs in the sediment samples, including pelagic red clay, calcareous ooze, and blue mud, are demonstrated especially by a variety of Ce anomalies in the shale-normalized REE pattern. Cerium abundances in blue mud samples showed little anomaly. Calcareous ooze showed a general negative Ce anomaly. The spatial distribution of the Ce anomaly in red clay appears to depend on the latitude: the red clay samples from the lower latitudes show a negative Ce anomaly, while those from the high latitudes show a positive anomaly. The positive Ce anomaly in red clay is considered to be caused by preferential scavenging of Ce from sea water to sediment. The pelagic sediments in the equatorial Pacific which show a large negative Ce anomaly have high REEs and P content and are depleted in light REEs in the shale-normalized REE pattern. The results of microscopic observation and separation by grain size indicate that a large negative Ce anomaly was incorporated with the phosphate phase in the pelagic sediment. This implies that the deep-sea sediment is rich in fish bone debris which are composed of biogenic calcium phosphate. Fish bone debris readily accumulates REE with a large negative Ce anomaly. Low sedimentation rate and high biological activity in the Central Equatorial Pacific results in a high content offish bone debris in the sediment, which cause a large negative Ce anomaly. © 1990.