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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 42 (1972)No. 2. (June), Pages 434-440

Petrology and Origin of Some Phosphorites from the South African Continental Margin

Robin J. Parker, William G. Siesser

ABSTRACT

Phosphorites (phosphatized limestones) are areally widespread on the South African continental margin. These rocks have packstone or wackestone textures and are typically composed of microfossils (chiefly planktonic foraminifers), with lesser amounts of macrofossil fragments and terrigenous grains set in a collophane/micrite matrix. The average P2O5 content of these rocks is about fifteen percent. Some varieties are exceedingly ferruginous, owing to the intimately mixed goethite in their matrices.

The faunal and textural characteristics of these phosphorites are strikingly similar to those of certain unphosphatized Miocene limestones dredged from the same area. Mineralogical and geochemical evidence indicates that the lime mud matrix of some of these limestones was replaced by francolite. Phosphatization was accomplished under submarine conditions by permeating, phosphate-rich solutions.


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