Examinando por Materia "REE"

Mostrando 1 - 1 de 1
  • No hay miniatura disponible
    Publicación
    Tierras raras durante el Campaniano-Maastrichtiano en el Valle Medio del Magdalena
    (Universidad EAFIT, 2025) Arbeláez Gallo, Emilio José; Betancur Guerra, Simón; Cárdenas Rozo, Andrés Leonardo
    This work determines the geological processes that enabled REE enrichment in the La Renta Formation and the base of the Umir Formation in the MMV. A high-resolution stratigraphic section was measured at the La Renta Formation neostratotype (Aguablanca Creek, Lebrija, Santander), complemented with petrography, XRD, XRF, and ICP-MS analyses. Results indicate that REE enrichment in the La Renta Formation occurs in phosphorites genetically related to storms (tempestites) in a mid-ramp environment under the influence of upwelling currents, where oceanic-diagenetic capture of REE by carbonate fluorapatite (CFA) resulted in HREE enrichment (La/Yb_N≈0.64). Ce/Ce* (0.46) and Y/Ho (58.3) ratios suggest that the primary source was a metallogenically enriched ocean due to Late Cretaceous submarine magmatism. On the other hand, in the Umir Formation, enrichment occurs in a basal conglomerate with total concentrations of ΣREE+Y≈700 ppm, enriched in HREE (La/Yb_N≈0.64) and displaying the diagnostic mineral sequence: glauconite-fluorapatite-pyrite-dolomite, produced by sulfur-oxidizing bacteria. This finding reflects a second phosphogenic event in an environment distinct from the La Renta Formation, with more reducing conditions and greater terrigenous influence (Y/Ho=46.9, Eu/Eu*=1.08), which was subsequently eroded and accumulated in lenses over the Campanian–Maastrichtian unconformity. Consequently, REE contents in the La Renta Formation and the base of the Umir Formation result from prior oceanic enrichment controlled by distinct paleoenvironmental processes specific to each formation's depositional environment.