The Behavior of Rare Earth Elements during Green Clay Authigenesis on the Congo Continental Shelf

Clay mineral authigenesis at continental margins plays an important role in global marine element cycles. However, despite being increasingly used as tracers for both modern and past oceanographic conditions, the behavior of rare earth elements (REEs) their isotopes during clay still remains poorly known. In this study, we report on a detailed geochemical investigation glauconite from West African shelf, near mouth Congo River. Elemental, neodymium, hafnium isotope analyses were conducted acid leachate separated clay-size fractions pellets, order to investigate REE formation authigenic clays. Our data indicate that kaolinite dissolution subsequent Fe-bearing act net source REEs seawater. We show enhanced glauconitization, inferred increasing Fe K contents, is accompanied by significant decoupling toward markedly LREE-enriched shale-normalized patterns neoformed separates. Using Nd Hf SEM observations, rule out any seawater influence argue shift primarily reflects progressively overwhelming presence insoluble nanocrystals detrital LREE-rich phosphates, which are known occur close association with tropical soils. Due marked insolubility surface environments, such can be preserved subsequently incorporated into aggregates green clays forming peloids. Most strikingly, combined loss (due dissolution) entrapment inherited LREE-bearing accessory phases minerals) preferential release dissolved fraction characterized seawater-like distribution patterns. These findings reinforce emerging view possibly play major cycling.