NATURE AND ORIGIN OF MIXED APATITE-GLAUCONITE PELLETS FROM THE CONTINENTAL-SHELF OFF SOUTH-AFRICA

A close regional relationship between glauconite and apatite in the surficial shelf sediments off South Africa is paralleled by an intimate association of these minerals within authigenic pellets contained in the sediment. This mixed-mineral assemblage originated by contemporaneous alteration of finely divided particles of calcium carbonate (micrite) and intermixed illite clays in the bottom sediment to form carbonate apatite and glauconite, respectively. The pellets formed when the partially lithified bottom sediment was disaggregated during a regression. The outer margins of many of these mixed-mineral pellets have been rounded and glauconitized during the reworking process. This model adequately explains the often-reported, well-rounded and superior-sorted nature of glauconite, as well as the common association of these lag deposits with unconformities in the stratigraphic rock record. It also accounts for the many varied geochemical, mineralogical and morphological features exhibited by these pellets. © 1979.