ABSTRACT

The account is concerned with the diagenetic processes resulting in the phosphatization of a series of calcarenites on the island of Remire, Amirantes. The field relationships, together with details of petrography, mineralogy, and chemistry are discussed.

At least four modes of emplacement are involved: (1) as derived phosphate pebbles, with or without carbonates, but with textural evidence of an origin as carbonate sediments; (2) as a primary phosphate sediment, lacking direct evidence of a carbonate origin; (3) as a primary phosphate cement, lining voids within a calcarenite; (4) as a result of in-place phosphatization of a calcarenite. Processes three and four dominate throughout the island. The mechanisms by which these come about are considered. Textural features indicate certain peculiarities in the behavior of the phosphate depositing media. A possible explanation for these is offered.

The origin of the phosphates is tentatively linked with the history of the island, suggesting that they are the remnant of sediments deposited during a period of higher sea level.