Composition of phosphate containing sediments and phosphatic grains from the Namibian shelf

Recent phosphatic grains from diatomaceous oozes, as well as Pliocene grains from phosphatic sands of the Namibian shelf were studied by a scanning electron microscopy coupled with microprobe analysis. Lithification of the grains occurred together with changes in their composition and structure resulting from progressive phosphatization of biogenic material and partial crystallization of phosphatic matter, which is presented by three predominant forms: colloform, globular, and microcrystalline. Recent grains and associated nodules are authigenic. Their structure and composition related to Pliocene redeposited grains, which might be generated under similar conditions.