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he provenance of Early Cretaceous sandstones dredged on the northern margin of the Demerara Plateau, offshore French Guiana and Suriname, reveals the sediment routing system that prevailed through the Equatorial Atlantic rifting. Fission-track analysis and U-Pb dating of 310 and 111 detrital zircons, respectively, have been performed. Microfacies analysis and inherited cooling ages suggest that the sandstones were deposited in shallow marine environments during the Early Cretaceous, before the Late Albian drowning of the marginal plateau. Most of the U-Pb zircon crystallisation ages are comprised between 700 and 600 Ma and attributed to the Pan-African-Brasiliano orogeny. Statistical and chronological evidences suggest that the zircon fission-track cooling ages were inherited from source material. Triassic peak ages (>50% of the population) are attributed to the early phase of Central Atlantic rifting. One sample records a cooling phase at ca. 170 Ma, presumably following volcanic hotspot activity and the opening of the Central Atlantic Ocean. Two other samples record the rapid exhumation of the French Guiana transform margin during the Equatorial Atlantic rifting (127 ± 11 and 106 ± 8 Ma). We propose a source-to-sink model in which the Pan-African-Brasiliano basement of the margin was eroded as a result of flexural uplift along the French Guiana margin, and the detrital material funnelled in the Cacipore graben sustained the Early Cretaceous syn-rift sedimentation on the marginal plateau.

Detailed geochemical and mineralogical insights into some of the richest rare earth elements and yttrium (REY)-containing bioapatites from ocean-floor sediments have been provided by combining laser ablation inductively coupled plasma diffraction analysis, and Ce L3-edge high energy-resolution X-ray absorption near edge structure (HR-XANES) spectroscopy. Bioapatites at 1.94 and 4.70 m below the seafloor (mbsf) of the Clarion-Clipperton Zone (CCZ) of the Pacific Ocean have 26,600 (RSD = 15.7%, n = 20) and 30,300 (RSD = 14.6%, n = 10) mg/kg (mg/kg) total REY, respectively, and bioapatites at 2.28 and 6.95 mbsf of the Peru Basin have 15,500 (RSD = 15.6%, n = 20) and 15,700 (RSD = 17.8%, n = 29) mg/kg total REY, respectively. All bioapatite specimens have a variety of isomorphic substitutions in all atomic positions of the crystallographic structure. The average crystallochemical formula of bioapatites at 6.95 mbsf of the Peru Basin is [(PO4)2.71(SiO4)0.04(CO3,SO4)0.25][Ca4.57Na0.29Y0.04][F0.87Cl0.21]. All other substituents are below 0.04 atoms per formula unit. HR-XANES provides the first direct evidence for trivalent Ce in sediment apatites. The strong negative geochemical anomaly of Ce in fossil bioapatites is well explained by the occurrence of four valent Ce-MnO2 and CeO2 within the sediment and in seafloor ferromanganese nodules.