The transfer of rare earth elements during early diagenesis in REY-rich sediments: An example from the Central Indian Ocean Basin

• The REY-rich sediments in the CIOB consist of phillipsite-bearing pelagic clay. • The REY in these sediments were captured by bioapatite and micronodule from seawater. • Driven by weak early diagenesis , the REY released to porewater from the micronodules. • The REY in porewater were also captured by the bioapatite. Rare earth element and ytterbium (REY)-rich deep-sea sediments are recently discovered potential undersea rare earth element (REE) resources. Here, we present the results of the mineralogical and geochemical characterization of REY-rich sediments collected from the Central Indian Ocean Basin (CIOB). These data were used to provide a jigsaw puzzle for the investigation of REY transfer during early diagenesis and to discuss the formation mechanism of REY-rich sediments. The research results show that the REY-rich sediments distributed in the CIOB mainly consist of phillipsite-bearing pelagic clay and pelagic clay, and are characterized by enrichments in middle REEs (MREEs) and heavy REEs (HREEs), negative Ce anomalies and positive Y anomalies. The REY in these sediments are mainly captured dirtcely from overlying seawater by bioapatite and micronodules at the water-sediment interface. After burial, driven by the redox reaction between organic matter and an oxidizer (free O 2 and Mn and Fe oxides), the REY-rich sediments experienced weak early diagenesis, and the REY released from hydrogenetic micronodules were captured by the bioapatite.