Content and Composition of Rare Earth Elements in Ferromanganese Formations from the East Siberian Sea as an Indicator of Recent Sedimentation and Diagenesis Conditions

The distribution of rare earth elements (REEs) in different morphotypes (ferruginous and ferromanganese crusts, discoid nodules, biomorphoses) of ferromanganese formations (FMFs) of the East Siberian Sea has been studied for the first time. The FMFs were formed during (sub)oxic diagenesis at different distances from the land and, accordingly, from the main sources of sedimentary material. Seaward, with an increase in the oxidation of sediments, primarily because of reducing sedimentation rates, FMFs, against a rising manganese content in them (Mn from 0.09 to 12.34%, Mn/Fe ratio from 0.01 to 1.15), show a decrease in the total REE content (Sigma REE from 166.90 to 96.86 mg kg(-1)), depletion in cerium (Ce-an from 0.90 to 0.71), and enrichment with middle REEs. Due to the rapid growth of FMFs, which should be faster than sedimentation rates, reactive REE species do not have time to accumulate; therefore, REE total content in FMFs is everywhere lower than in sediments.