Application of the apatite oxygen paleobarometer (AOP) across the Neoproterozoic-Cambrian transition

•Samarium3+ substitution into the apatite lattice correlates with oxygen availability.•Deposits of apatite occur globally at the Neoproterozoic-Cambrian transition.•Diverse organisms were apatite-fossilized during the “Cambrian Explosion of Life.”•Fluorescence spectra of fossilizing apatite record local oxygen concentrations.•Such apatite documents an increase of low O2-concentrations at the onset of Cambrian. Fluorescence signatures of samarium3+ substituted into apatite for calcium2+ have been shown experimentally to correlate with oxygen availability, such substituted apatite being a principal diagenetic mineral emplaced in shallow-water environments during the Neoproterozoic-Cambrian global phosphogenic event coeval with the “Cambrian Explosion of Life.” The occurrence of Sm3+-substituted apatite, encrusting, infilling and permineralizing components of shallow water microbial communities suggested that quantification of these fluorescence signatures might provide a widely applicable mineral-based paleobarometer by which to measure oxygen concentrations in the environment in which such apatite precipitated. To test this hypothesis, fluorescence spectroscopic analyses have been carried out on the Sm3+-substituted apatite of photic-zone microscopic fossils and fossil-associated ooids of near-shore facies of the Ediacaran Doushantuo (South China) and Early Cambrian Chulaktau (South Kazakhstan) Formations, and of the open ocean apatite-biomineralized phytoplanktonic “scale fossils” (Characodictyon) of the mid-Neoproterozoic (Tonian) Fifteenmile Group (Yukon Canada). Results obtained – quantified by the newly devised apatite oxygen paleobarometer metric – indicate a low (