Chemical composition of concretions and host bottom sediments from the Kara Sea

During study of distribution of 57 chemical elements in flattened, pellet-shaped, and pipe-like iron-manganese concretions of the Kara Sea it has been found that F2O3 and MnO2 contents in them are 52.5% and 5.30%; 18.3% and 24.2%; 13.0% and 0.44%, respectively. The pellet-shaped concretions are enriched in non-ferrous metals and minor elements (especially in As, Co, Mo, and Sb) to the highest degree relative to bottom sediments, the flattened concretions are enriched to a lesser degree, and the pipe-like ones are enriched to the least degree. Relative enrichment in the medium elements and the negative cerium anomaly are observed in distribution of the rare earth elements, which is also revealed in host sediments to a lesser degree. Low content of ore and rare elements in iron-manganese concretions of the Kara Sea relative to oceanic concretions is related mostly to high sedimentation rates and short exposition period of the concretions on the sea floor.