Dating rare earth element enrichment in deep-sea sediments using U-Pb geochronology of bioapatite

Deep-sea sediments rich in rare earth elements and yttrium (REY) are promising mineral resources that are believed to be associated with the burial of fish debris. However, the nature of the REY enrichment is poorly understood, in part due to a lack of robust age constraints. We report bioapatite U-Pb ages from an Ocean Drilling Program (Leg 199, Hole 1218A) core and a REY-rich sedimentary core from the Pacific Ocean, which yielded U-Pb ages rang -ing from 22.8 to 18.2 Ma and 6.5 to 2.2 Ma, respectively. The U-Pb fish teeth ages from the 1218A core are consistent with biostratigraphic constraints, shed light on the application of the U-Pb bioapatite chronometer, and yield an absolute time scale for stratigraphy, especially for sequences deposited below the calcite compensation depth (CCD), where there is an ab-sence of fossil carbonate. The successful measurement of U-Pb ages from REY-enriched fish teeth in the REY-rich sediment core suggests the mineralization occurred no later than the Miocene in the western Pacific Ocean. Uranium is positively correlated with REY, suggesting that the U and REY were incorporated into the fish teeth lattice simultaneously, making the bioapatite U-Pb chronometer suitable for constraining the timing of REY mineralization. When combined with published data, our study suggests that the Miocene REY accumula-tion event in the western Pacific Ocean was influenced by high P2O5 and MnO2 contents cor-related with oxic bottom water.