Apatite-glauconite associations off Peru and Chile: palaeo-oceanographic implications

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Abstract
Authigenic apatite and glauconite occur within organic-rich diatomaceous sediment from the coastal upwelling zone off Peru and Chile. Both minerals are found as unconsolidated pellets and within indurated phosphate nodules. Uranium disequilibrium dating has shown that the apatite may range from present-day to +100,000 yr (Quaternary) in age. Episodes of phosphorite formation appear to be related to major climatic variations. The occurrence and progressive alteration of glauconite within some of these phosphate nodules also appears to be related to large scale oceanographic phenomena which fluctuated during the Quaternary. A lateral shifting or contraction of the oxygen minimum zone and locus of maximum upwelling in response to climate variations best explains the data.